Sample records for activated silica gel

1. Laser based on dye-activated silica gel

SciTech Connect

Altshuler, G.B.; Bakhanov, V.A.; Dulneva, E.G.; Erofeev, A.V.; Mazurin, O.V.; Roskova, G.P.; Tsekhomskaya, T.S.

1987-06-01

Silica gel activated by a dye is used as a new laser medium. The lasin characteristics of rhodamine 6G in silica gel are reported. An important characteristic of the dye laser is its long service life, which is determined by the photostability of the dye in silic gel.(AIP)

2. Optical activation of Si nanowires using Er-doped, sol-gel derived silica

SciTech Connect

Suh, Kiseok; Shin, Jung H.; Park, Oun-Ho; Bae, Byeong-Soo; Lee, Jung-Chul; Choi, Heon-Jin

2005-01-31

Optical activation of Si nanowires (Si-NWs) using sol-gel derived Er-doped silica is investigated. Si-NWs of about 100 nm diameter were grown on Si substrates by the vapor-liquid-solid method using Au catalysts and H{sub 2} diluted SiCl{sub 4}. Afterwards, Er-doped silica sol-gel solution was spin-coated, and annealed at 950 deg. C in flowing N{sub 2}/O{sub 2} environment. Such Er-doped silica/Si-NWs nanocomposite is found to combine the advantages of crystalline Si and silica to simultaneously achieve both high carrier-mediated excitation efficiency and high Er{sup 3+} luminescence efficiency while at the same time providing high areal density of Er{sup 3+} and easy current injection, indicating the possibility of developing sol-gel activated Si-NWs as a material platform for Si-based photonics.

3. Viscoelasticity of silica gels

SciTech Connect

Scherer, G.W.

1995-12-01

The response of silica gels to mechanical loads depends on the properties of the solid phase and the permeability of the network. Understanding this behavior is essential for modeling of stresses developed during drying or heating of gels. The permeability and the mechanical properties are readily determined from a simple beam-bending experiment, by measuring the load relaxation that occurs at constant deflection. Load decay results from movement of the liquid within the network; in addition, there may be viscoelastic relaxation of the network itself. Silica gel is viscoelastic in chemically aggressive media, but in inert liquids (such as ethanol or acetone) it is elastic. Experiments show that the viscoelastic relaxation time decreases as the concentration and pH of the water in the pore liquid increase. During drying, the permeability decreases and the viscosity increases, both exhibiting a power-law dependence on density of the gel network.

4. Enzyme encapsulation in silica gel prepared by polylysine and its catalytic activity

Kawachi, Yuki; Kugimiya, Shin-ichi; Nakamura, Hitomi; Kato, Katsuya

2014-09-01

Enzymes used in industrial applications are often immobilized onto different types of supports because they are sensitive to pH, temperature, and various other environmental conditions. However, many of the current immobilization approaches face problems such as the requirement of tedious multi-step procedures, loss of enzyme activity during immobilization, and poor reusability. In this study, we chose poly-L-lysine (Ki) as a catalyst for silica mineralization and attempted a one-step “leave to stand” synthesis method under mild conditions, so as to simultaneously maintain both high enzymatic activity and reusability. To examine the effect of Kx on the enzymatic reaction of lipase, we performed hydrolysis of 2-octylacetate without adding a silica precursor. Results indicate that Kx hardly exerts adverse influence on the enzymatic activity of lipase. The lipase encapsulated in the silica gel prepared by leave to stand (Gelstand) retained 70% of the activity compared to the free solution, which is two times higher than that obtained by mixing (Gelmix). However, the Km value was found to be similar to that of free enzymes. These results suggest that the leave to stand is a suitable procedure for immobilization, without any decrease in the mass transfer of substrate. The Gel-stand sample retained 100% activity even after the 5th cycle, and retained above 95% of its activity after 4 h of heat treatment at 65 °C. Using phenyltriethoxysilane as a silica precursor, tertiary structural stability of enzyme was obtained, and its Kcat value was improved when compared to a free solution.

5. Sol-gel derived silica/siloxane composite materials: The effect of loading level and catalyst activity on silica domain formation

SciTech Connect

Black, E.P.; Ulibarri, T.A.; Beaucage, G.; Schaefer, D.W.; Assink, R.A.; Bergstrom, D.F.; Giwa-Agbomeirele, P.A.; Burns, G.T.

1993-11-01

Currently, the production of in situ reinforcement in polymeric systems by sol-gel methods is undergoing rapid development. However, understanding of synthesis/structure/property relationships is still lacking. In order to produce sol-gel derived composite materials with sufficient mechanical properties for commercial applications, this deficit of information must be addressed. We have completed a detailed investigation of in situ silica growth in polydimethylsiloxane (PDMS)/tetraethylorthosilicate (TEOS) systems. Factors which affect the domain growth, such as catalyst activity and silica loading, have been examined by solid state {sup 29}Si NMR, SEM, mechanical testing and small angle neutron scattering.

6. Cerium-activated sol-gel silica glasses for radiation dosimetry in harsh environment

El Hamzaoui, Hicham; Capoen, Bruno; Helou, Nissrine Al; Bouwmans, Géraud; Ouerdane, Youcef; Boukenter, Aziz; Girard, Sylvain; Marcandella, Claude; Duhamel, Olivier; Chadeyron, Geneviève; Mahiou, Rachid; Bouazaoui, Mohamed

2016-04-01

Cerium-doped silica glass has been prepared for ionizing radiation dosimetry applications, using the sol-gel route and densification under different atmospheres. In comparison with the glass densified under air atmosphere, the one obtained after sintering the xerogel under helium gas presents improved optical properties, with an enhancement of the photoluminescence quantum yield up to 33%, which is attributed to a higher Ce3+ ions concentration. Such a glassy rod has been jacketed in a quartz tube and then drawn at high temperature to a cane, which has been used as active material in a fibered remote x-ray radiation dosimeter. The sample exhibited a reversible linear radioluminescence intensity response versus the dose rate up to 30 Gy s-1. These results confirm the potentialities of this material for in vivo or high rate dose remote dosimetry measurements.

7. Building, characterising and catalytic activity testing of Co-C-protected amino acid complexes covalently grafted onto chloropropylated silica gel

Varga, G.; Timár, Z.; Csendes, Z.; Bajnóczi, É. G.; Carlson, S.; Canton, S. E.; Bagi, L.; Sipos, P.; Pálinkó, I.

2015-06-01

Co-C-protected amino acid (C-protected L-histidine, L-tyrosine, L-cysteine and L-cystine) complexes were covalently grafted onto chloropropylated silica gel, and the materials thus obtained were structurally characterised by mid/far IR and X-ray absorption spectroscopies. The superoxide dismutase-like activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that covalent grafting and the preparation of the anchored complexes were successful in most cases. The coordinating groups varied upon changing the conditions of the syntheses. All materials displayed catalytic activity, although catalytic activities differed widely.

8. Metal-silica sol-gel materials

NASA Technical Reports Server (NTRS)

Stiegman, Albert E. (Inventor)

2002-01-01

The present invention relates to a single phase metal-silica sol-gel glass formed by the co-condensation of a transition metal with silicon atoms where the metal atoms are uniformly distributed within the sol-gel glass as individual metal centers. Any transition metal may be used in the sol-gel glasses. The present invention also relates to sensor materials where the sensor material is formed using the single phase metal-silica sol-gel glasses. The sensor materials may be in the form of a thin film or may be attached to an optical fiber. The present invention also relates to a method of sensing chemicals using the chemical sensors by monitoring the chromatic change of the metal-silica sol-gel glass when the chemical binds to the sensor. The present invention also relates to oxidation catalysts where a metal-silica sol-gel glass catalyzes the reaction. The present invention also relates to a method of performing oxidation reactions using the metal-silica sol-gel glasses. The present invention also relates to organopolymer metal-silica sol-gel composites where the pores of the metal-silica sol-gel glasses are filled with an organic polymer polymerized by the sol-gel glass.

9. Sol-gel derived mesoporous cobalt silica catalyst: Synthesis, characterization and its activity in the oxidation of phenol

Andas, Jeyashelly; Adam, Farook; Rahman, Ismail Ab.

2014-10-01

Highly mesoporous cobalt silica rice husk catalysts with (5-15 wt.%) Co2+ loading were prepared via a simple sol-gel technique at room temperature. The successful insertion of cobalt ions into silica matrix was evidenced from FT-IR, NMR, XPS and AAS analyses. Preservation of the mesoporosity nature of silica upon incorporating Co2+ was confirmed from the N2-sorption studies. The topography and morphology viewed by TEM analysis differs as the cobalt concentration varies from 5 to 15 wt.%. Parallel pore channels and spherical nanoparticles of 9.44 nm were achieved for cobalt silica catalysts with 10 and 15 wt.% respectively. Cobalt catalysts were active in the liquid-phase oxidation of phenol with H2O2 as an oxygen source. The performances of the catalysts were greatly influenced by various parameters such as reaction temperature, catalyst amount, molar ratio of substrate to oxidant, nature of solvent, metal loading and homogeneous precursor salt. Water served as the best reaction medium for this oxidation system. The regeneration studies confirmed cobalt catalyst could be reused for five cycles without experiencing large loss in the conversion. Both leaching and reusability studies testified that the catalysts were truly heterogeneous.

10. Moisture Transport in Silica Gel Particle Beds: I. Theoretical Study

SciTech Connect

Pesaran, A. A.; Mills, A. F.

1986-08-01

Diffusion mechanisms of moisture within silica gel particles are investigated. It is found that for microporous silica gel surface diffusion is the dominant mechanism of moisture transport, while for macroporous silica gel both Knudsen and surface diffusion are important.

11. Cell response to silica gels with varying mechanical properties

Lefebvre, Molly Ann

Sol-gel encapsulation has a variety of applications in biotechnology and medicine: creating biosensors, biocatalysts, and bioartificial organs. However, encapsulated cell viability is a major challenge. Consequently, interactions between cells and their 3D microenvironment were studied through rheological, metabolic activity, and extraction studies to aid in the development of new gel protocols. The cells were encapsulated in variations of three silica sol-gels with varying stiffness. It was hypothesized that the cell viability and the amount of extracted cells would depend on gel stiffness. For two gels, there was no apparent correlation between the gel stiffness and the cell viability and extracted cell quantity. These gels did strongly depend on the varying gel ingredient, polyethylene glycol. The third gel appeared to follow the hypothesized correlation, but it was not statistically significant. Finally, one gel had a significantly longer period of cell viability and higher quantity of extracted cells than the other gels.

12. Electron donor properties of claus catalysts--1. Influence of NaOH on the catalytic activity of silica gel

SciTech Connect

Dudzik, Z.; George, Z.M.

1980-05-01

ESR spectroscopy showed that SO/sub 2/ adsorbed on silica gel impregnated with NaOH formed the SO/sub 2//sup -/ anion radical. With increasing NaOH concentration, the SO/sub 2/ adsorption and the activity for the reaction of H/sub 2/S with SO/sub 2/ (Claus reaction) went through a maximum at 1.0-1.4% NaOH. The SO/sub 2/ anion radical apparently formed by electron transfer from the catalyst surface and was a reaction intermediate which reacted rapidly with H/sub 2/S. The NaOH catalyst had similar stability and activity as commercial alumina catalyst in five-day tests under Claus conditions.

13. Procedure to prepare transparent silica gels

NASA Technical Reports Server (NTRS)

Barber, Patrick G. (Inventor); Simpson, Norman R. (Inventor)

1987-01-01

This invention relates to the production of silica gels and in particular to a process for the preparation of silica gels which can be used as a crystal growth medium that simulates the convectionless environment of space to produce structurally perfect crystals. Modern utilizations of substances in electronics, such as radio transmitters and high frequency microphones, often require single crystals with controlled purity and structural perfection. The near convectionless environment of silica gel suppresses nucleation, thereby reducing the competitive nature of crystal growth. This competition limits the size and perfection of the crystal; and it is obviously desirable to suppress nucleation until, ideally, only one crystal grows in a predetermined location. A silica gel is not a completely convectionless environment like outer space, but is the closest known environment to that of outer space that can be created on Earth.

14. Silica Gel for Enhanced Activity and Hypochlorite Protection of Cyanuric Acid Hydrolase in Recombinant Escherichia coli

PubMed Central

2015-01-01

ABSTRACT Chlorinated isocyanuric acids are widely used water disinfectants that generate hypochlorite, but with repeated application, they build up cyanuric acid (CYA) that must be removed to maintain disinfection. 3-Aminopropyltriethoxysilane (APTES)-treated Escherichia coli cells expressing cyanuric acid hydrolase (CAH) from Moorella thermoacetica exhibited significantly high CYA degradation rates and provided protection against enzyme inactivation by hypochlorite (chlorine). APTES coating or encapsulation of cells had two benefits: (i) overcoming diffusion limitations imposed by the cell wall and (ii) protecting against hypochlorite inactivation of CAH activity. Cells encapsulated in APTES gels degraded CYA three times faster than nonfunctionalized tetraethoxysilane (TEOS) gels, and cells coated with APTES degraded CYA at a rate of 29 µmol/min per mg of CAH protein, similar to the rate with purified enzyme. UV spectroscopy, fluorescence spectroscopy, and scanning electron microscopy showed that the higher rates were due to APTES increasing membrane permeability and enhancing cyanuric acid diffusion into the cytoplasm to reach the CAH enzyme. Purified CAH enzyme was shown to be rapidly inactivated by hypochlorite. APTES aggregates surrounding cells protected via the amine groups reacting with hypochlorite as shown by pH changes, zeta potential measurements, and infrared spectroscopy. APTES-encapsulated E. coli cells expressing CAH degraded cyanuric acid at high rates in the presence of 1 to 10 ppm hypochlorite, showing effectiveness under swimming pool conditions. In contrast, CAH activity in TEOS gels or free cells was completely inactivated by hypochlorite. These studies show that commercially available silica materials can selectively enhance, protect, and immobilize whole-cell biocatalysts for specialized applications. PMID:26530383

15. Apparent and partial specific adsorption of 1,10-phenanthroline on mixtures of Ca-montmorillonite, activated carbon, and silica gel.

PubMed

Ferreiro, Eladio A; de Bussetti, Silvia G

2005-12-01

16. Preparation of novel silica-coated alginate gel beads for efficient encapsulation of yeast alcohol dehydrogenase.

PubMed

Xu, Song-Wei; Lu, Yang; Li, Jian; Zhang, Yu-Fei; Jiang, Zhong-Yi

2007-01-01

17. Growth of hydroxyapatite nanoparticles on silica gels.

PubMed

Rivera-Muñoz, E M; Huirache-Acuña, R; Velázquez, R; Alonso-Núñez, G; Eguía-Eguía, S

2011-06-01

Synthetic, hydroxyapatite nanoparticles were grown on the surface of silica gels. The synthesis of those nanoparticles was obtained by immersing silica gels in a simulated body fluid (SBF) at 37 degrees C. The SBF was replaced every week to keep constant the Ca and P ion concentration and subsequent growth of hydroxyapatite was evaluated after 1-6 weeks of total soaking time in SBF. Hydroxyapatite nanoparticles were observed by scanning electron microscopy (SEM) on the surface of silica gel samples and confirmed by energy dispersive X-ray spectroscopy (EDS), Fourier Transform Infra Red Spectroscopy (FTIR) and powder X-ray Diffractometry (XRD) analysis. These particles show a regular shape and uniform size every week, keeping within the nanoscale always. Both the size and morphology of hydroxyapatite nanoparticles obtained are the result of the use of different chemical additives in the synthesis of silica gels, since they affect the liquid-to-solid interface, and the growth could correspond to a diffusion limited aggregation (DLA) process. A more detailed analysis, with higher magnifications, showed that hydroxyapatite nanoparticles are not solid spheres, showing a branched texture and their size depends on the scale and resolution of the measure instrument. PMID:21770224

18. "Gray Areas": Silica gels, amorphous silica and cryptocrystalline silica on fault surfaces

Rowe, C. D.; Kirkpatrick, J. D.; White, J. C.; Faber, C.; Caine, J. S.

2012-12-01

Silica gels, in the form of their solid-phase equivalents, are widely found in brittle fault zones and are commonly associated with mineral deposits. High- to moderate-velocity rotary friction experiments have produced silica gels on sliding surfaces coeval with dramatic slip weakening. In light of the latter, silica gel formation has been proposed as a potential mechanism of slip weakening during earthquakes in the shallow crust. However, low velocity sliding experiments have also produced significant amounts of amorphous material distributed throughout slipping layers, and dramatic weakening is not observed. Comparison of the products of laboratory experiments to geological examples is complicated by the diagenesis and lithification of silica gels. They may form hydrous and amorphous solids, hydrous crystalline solids, or dehydrate to quartz. In addition, the abundance and style of occurrence of these products in faults suggest that there are multiple origins for silica gels in faults. We review the mechanisms by which silica gels may form in fault zones and describe the solidification, crystallization and dehydration evolution of the silica. Analytical transmission electron microscope (TEM) observations of slip-surface silica deposits from the Corona Fault, San Francisco, the Dixie Valley Fault, Nevada, and the Olive Fault, Namibia typify the nano- to micro-structural evolution of the fault surface silica layers. We suggest criteria for identifying these materials in natural fault rocks. Some of these gels may form by comminution and hydrolization of silica-rich wall rocks, as has been observed in high-velocity experiments (Corona Fault). Others may form by depressurization and boiling of aqueous fluids, probably during fault valving (Olive Fault). Silica saturated hydrothermal fluids released during faulting may contribute in some cases (Dixie Valley Fault). Regardless of the mechanism of gel formation, the dramatic rheological weakening observed in friction

19. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

PubMed

Das, R K; Das, M

2015-09-01

The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy.

20. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

PubMed

Das, R K; Das, M

2015-09-01

The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy. PMID:25600993

1. Soluble polymers in sol-gel silica

Beaudry, Christopher Laurent

In the last few years, the inherent versatility of sol-gel processing has led to a significant research effort on inorganic/organic materials. One method of incorporating an organic phase into sol-gel silica is dissolving an organic polymer in a tetraethylorthosilicate (TEOS) solution, followed by in situ polymerization of silica in the presence of organic polymer. The first part of the study involved the development of a two-step (acid-base) synthesis procedure to allow systematic control of acidity in TEOS solutions. With this procedure, it was possible to increase the pH of the TEOS solution while correlating the acidity and properties. The properties were the gelation time, syneresis rate, drying behavior, and xerogel pore structure, as determined by nitrogen sorption. Furthermore, controlling the acidity was shown to control the silica xerogel pore structure. In the second part of the study, the two-step procedure was used to synthesize silica/poly(ethylene glycol) (PEG), and silica/poly(vinyl acetate) (PVAc) composite materials. The content of organic polymer and the molecular weight were varied. The gelation time, the syneresis rate, the drying behavior, and the pore structure were determined for compositions with 10% PEG (M.W. 2,000), 5, 10, and 15% PEG (M.W. 3,400), and 10 and 25% PVAc (M.W. 83,000). Other compositions and molecular weights of PEG lead to sedimentation. In the PEG compositions, the tendency to phase separate was correlated with the effects of the processing variables on the segregation strength and polymerization rate. The PVAc compositions did not show any visible phase separation during processing, giving the composite xerogels an appearance similar to pure silica. The property differences between gels with PEG and gels with PVAc show the relative strength of the interactions with silica. Both polymers exhibit hydrogen bonding between the phases. In the case of PEG, hydrogen bonding between the ether oxygens of the polymer and silanol

2. Influence of the preservation period in silica-gel on the predatory activity of the isolates of Duddingtonia flagrans on infective larvae of cyathostomins (Nematoda: Cyathostominae).

PubMed

Braga, Fabio Ribeiro; Araújo, Jackson Victor; Araujo, Juliana Milani; Tavela, Alexandre de Oliveira; Ferreira, Sebastião Rodrigo; Freitas Soares, Filippe E; Benjamin, Laércio dos Anjos; Frassy, Luiza Neme

2011-08-01

The continued maintenance of nematophagous fungi predatory activity under laboratory conditions is one of the basic requirements for a successful biological control. The purpose of this study was to evaluate the influence of time on the preservation of the fungus Duddingtonia flagrans (AC001 and CG722) stored in silica-gel for 7 years and their subsequent predatory activity on cyathostomin L(3) larvae in 2% water-agar medium (2% WA). Samples of the isolates AC001 and CG722, originating from vials containing grains of silica-gel sterilized and stored for 7 years, were used. After obtaining fungal conidia, the predation test was conducted over 7 days on the surface of 9.0 cm Petri dishes filled with 2% WA. In the treated groups each Petri dish contained 500 cyathostomin L(3) and conidia of fungal isolates in 2% WA. In the control group (without fungi) the plates contained 500 L(3) in 2% WA. The experimental results showed that isolated AC001 and CG722 were efficient in preying on cyathostomin L(3) (p<0.01) compared to control (without fungus). However, no difference was observed (p>0.01) in the predatory activity of the fungal isolates tested. Comparing the groups, there was a significant reductions of cyathostomin L(3) (p<0.01) of 88.6% and 78.4% on average recovered from the groups treated with the isolates AC001 and CG722, respectively, after 7 days. The results of this test showed that the fungus D. flagrans (AC001 and CG722) stored in silica-gel for at least 7 years maintained its predatory activity on cyathostomin L(3). PMID:21627962

3. Absorption of isoflurane by silica gel.

PubMed

Lumb, A B; Landon, M J

1991-07-01

We have studied the capacity of the drying agent silica gel (SG) to absorb isoflurane from gas samples. When dry, SG was able to absorb 31 times its own volume of isoflurane vapour, which could be recovered almost completely from the SG by displacement with water vapour. However, we were unable to demonstrate any significant absorption of isoflurane by wet SG. Care must be taken, therefore, when using SG as a drying agent in the sampling line of an analyser during research involving volatile anaesthetic agents. PMID:1650238

4. Silica scintillating materials prepared by sol-gel methods

SciTech Connect

Werst, D.W.; Sauer, M.C. Jr.; Cromack, K.R.; Lin, Y.; Tartakovsky, E.A.; Trifunac, A.D.

1993-12-31

Silica was investigated as a rad-hard alternative to organic polymer hosts for organic scintillators. Silica sol-gels were prepared by hydrolysis of tetramethoxysilane in alcohol solutions. organic dyes were incorporated into the gels by dissolving in methanol at the sol stage of gel formation. The silica sol-gel matrix is very rad-hard. The radiation stability of silica scintillators prepared by this method is dye-limited. Transient radioluminescence was measured following excitation with 30 ps pulses of 20 MeV electrons.

5. Sol-gel encapsulation of binary Zn(II) compounds in silica nanoparticles. Structure-activity correlations in hybrid materials targeting Zn(II) antibacterial use.

PubMed

Halevas, E; Nday, C M; Kaprara, E; Psycharis, V; Raptopoulou, C P; Jackson, G E; Litsardakis, G; Salifoglou, A

2015-10-01

In the emerging issue of enhanced multi-resistant properties in infectious pathogens, new nanomaterials with optimally efficient antibacterial activity and lower toxicity than other species attract considerable research interest. In an effort to develop such efficient antibacterials, we a) synthesized acid-catalyzed silica-gel matrices, b) evaluated the suitability of these matrices as potential carrier materials for controlled release of ZnSO4 and a new Zn(II) binary complex with a suitably designed well-defined Schiff base, and c) investigated structural and textural properties of the nanomaterials. Physicochemical characterization of the (empty-loaded) silica-nanoparticles led to an optimized material configuration linked to the delivery of the encapsulated antibacterial zinc load. Entrapment and drug release studies showed the competence of hybrid nanoparticles with respect to the a) zinc loading capacity, b) congruence with zinc physicochemical attributes, and c) release profile of their zinc load. The material antimicrobial properties were demonstrated against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus cereus) and negative (Escherichia coli, Pseudomonas aeruginosa, Xanthomonas campestris) bacteria using modified agar diffusion methods. ZnSO4 showed less extensive antimicrobial behavior compared to Zn(II)-Schiff, implying that the Zn(II)-bound ligand enhances zinc antimicrobial properties. All zinc-loaded nanoparticles were less antimicrobially active than zinc compounds alone, as encapsulation controls their release, thereby attenuating their antimicrobial activity. To this end, as the amount of loaded zinc increases, the antimicrobial behavior of the nano-agent improves. Collectively, for the first time, sol-gel zinc-loaded silica-nanoparticles were shown to exhibit well-defined antimicrobial activity, justifying due attention to further development of antibacterial nanotechnology.

6. Transparent poly(vinyl acetate)-silica gels by a sol-gel process

Wojcik, Anna B.; Klein, Lisa C.

1993-12-01

Rod shaped silica-poly(vinyl acetate) (PVAc) gels have been prepared by a sol gel process. In situ polymerization of tetraethoxysilane (TEOS) was accomplished in the presence of low molecular weight PVAc by dissolving various amounts of PVAc in a mixture of TEOS, ethanol, water and hydrochloric acid (HCl). Gelation of this mixture was carried out between room temperature and slightly above. Silica-PVAc rods recovered from cylindrical molds were homogeneous and transparent. Gels with weight percents of PVAc ranging from 2% to 50% were prepared. Silica-PVAc gels have higher flexure strengths, less brittle character and improved water durability in comparison with pure sol- gel silica.

7. Maintenance of Bacterial Cultures on Anhydrous Silica Gel

ERIC Educational Resources Information Center

Lennox, John E.

1977-01-01

Suspensions of 20 different cultures were grown on appropriate media, then pipetted into sterile anhydrous silica gel. Silica gel cultures after incubation and refrigerated storage were tested for viability. Results showed little mutation, low replication, low contamination, minimal expenses, and survival up to two years. (CS)

8. Adsorption Characteristics of Silica Gels Treated with Fluorinated Silylation Agents

PubMed

Monde; Nakayama; Yano; Yoko; Konakahara

1997-01-01

Branched-chain polyfluorosilane (monochlorodimethyl[4,4-bis(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl)-bonded silica gels were prepared. The surface properties of the silica gels modified with various organic silanes were evaluated by the adsorption density of polar and nonpolar gases calculated from adsorption isotherms of nitrogen, carbon dioxide, and normal butane gases. The polyfluorocarbon-bonded silica gel surface was found to be both hydrophobic and oleophobic in nature, whereas the hydrocarbon-bonded silica gel surface was characterized only as hydrophobic. The trifunctional fluorinated silane provides the silica gel surface with a more hydrophilic nature than the monofunctional silane because of the formation of a denser polymeric coating layer with a larger number of silanols. PMID:9056313

9. Adsorption Characteristics of Silica Gels Treated with Fluorinated Silylation Agents

PubMed

Monde; Nakayama; Yano; Yoko; Konakahara

1997-01-01

Branched-chain polyfluorosilane (monochlorodimethyl[4,4-bis(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl)-bonded silica gels were prepared. The surface properties of the silica gels modified with various organic silanes were evaluated by the adsorption density of polar and nonpolar gases calculated from adsorption isotherms of nitrogen, carbon dioxide, and normal butane gases. The polyfluorocarbon-bonded silica gel surface was found to be both hydrophobic and oleophobic in nature, whereas the hydrocarbon-bonded silica gel surface was characterized only as hydrophobic. The trifunctional fluorinated silane provides the silica gel surface with a more hydrophilic nature than the monofunctional silane because of the formation of a denser polymeric coating layer with a larger number of silanols.

10. Synthesis, structure, and mechanical properties of silica nanocomposite polyrotaxane gels.

PubMed

Kato, Kazuaki; Matsui, Daisuke; Mayumi, Koichi; Ito, Kohzo

2015-01-01

A significantly soft and tough nanocomposite gel was realized by a novel network formed using cyclodextrin-based polyrotaxanes. Covalent bond formation between the cyclic components of polyrotaxanes and the surface of silica nanoparticles (15 nm diameter) resulted in an infinite network structure without direct bonds between the main chain polymer and the silica. Small-angle X-ray scattering revealed that the homogeneous distribution of silica nanoparticles in solution was maintained in the gel state. Such homogeneous nanocomposite gels were obtained with at least 30 wt % silica content, and the Young's modulus increased with silica content. Gelation did not occur without silica. This suggests that the silica nanoparticles behave as cross-linkers. Viscoelastic measurements of the nanocomposite gels showed no stress relaxation regardless of the silica content for <20% compression strain, indicating an infinite stable network without physical cross-links that have finite lifetime. On the other hand, the infinite network exhibited an abnormally low Young's modulus, ~1 kPa, which is not explainable by traditional rubber theory. In addition, the composite gels were tough enough to completely maintain the network structure under 80% compression strain. These toughness and softness properties are attributable to both the characteristic sliding of polymer chains through the immobilized cyclodextrins on the silica nanoparticle and the entropic contribution of the cyclic components to the elasticity of the gels. PMID:26664642

11. Synthesis, structure, and mechanical properties of silica nanocomposite polyrotaxane gels

PubMed Central

Matsui, Daisuke; Mayumi, Koichi

2015-01-01

Summary A significantly soft and tough nanocomposite gel was realized by a novel network formed using cyclodextrin-based polyrotaxanes. Covalent bond formation between the cyclic components of polyrotaxanes and the surface of silica nanoparticles (15 nm diameter) resulted in an infinite network structure without direct bonds between the main chain polymer and the silica. Small-angle X-ray scattering revealed that the homogeneous distribution of silica nanoparticles in solution was maintained in the gel state. Such homogeneous nanocomposite gels were obtained with at least 30 wt % silica content, and the Young’s modulus increased with silica content. Gelation did not occur without silica. This suggests that the silica nanoparticles behave as cross-linkers. Viscoelastic measurements of the nanocomposite gels showed no stress relaxation regardless of the silica content for <20% compression strain, indicating an infinite stable network without physical cross-links that have finite lifetime. On the other hand, the infinite network exhibited an abnormally low Young’s modulus, ~1 kPa, which is not explainable by traditional rubber theory. In addition, the composite gels were tough enough to completely maintain the network structure under 80% compression strain. These toughness and softness properties are attributable to both the characteristic sliding of polymer chains through the immobilized cyclodextrins on the silica nanoparticle and the entropic contribution of the cyclic components to the elasticity of the gels. PMID:26664642

12. Phase behavior and rheological characterization of silica nanoparticle gel

Metin, Cigdem O.; Rankin, Kelli M.; Nguyen, Quoc P.

2014-01-01

Preferential injection into high permeability thief zones or fractures can result in early breakthrough at production wells and large unswept areas of high oil saturation, which impact the economic life of a well. A variety of conformance control techniques, including polymer and silica gel treatments, have been designed to block flow through the swept zones. Over a certain range of salinities, silica nanoparticle suspensions form a gel in bulk phase behavior tests. These gels have potential for in situ flow diversion, but in situ flow tests are required to determine their applicability. To determine the appropriate scope of the in situ tests, it is necessary to obtain an accurate description of nanoparticle phase behavior and gel rheology. In this paper, the equilibrium phase behavior of silica nanoparticle solutions in the presence of sodium chloride (NaCl) is presented with four phase regions classified as a function of salinity and nanoparticle concentration. Once the gelation window was clearly defined, rheology experiments of silica nanoparticle gels were also carried out. Gelation time decreases exponentially as a function of silica concentration, salinity, and temperature. Following a power law behavior, the storage modulus, G', increases with particle concentration. Steady shear measurements show that silica nanoparticle gels exhibit non-Newtonian, shear thinning behavior. This comprehensive study of the silica nanoparticle gels has provided a clear path forward for in situ tests to determine the gel's applicability for conformance control operations.

13. Platinum/Tin Oxide/Silica Gel Catalyst Oxidizes CO

NASA Technical Reports Server (NTRS)

Upchurch, Billy T.; Davis, Patricia P.; Schryer, David R.; Miller, Irvin M.; Brown, David; Van Norman, John D.; Brown, Kenneth G.

1991-01-01

Heterogeneous catalyst of platinum, tin oxide, and silica gel combines small concentrations of laser dissociation products, CO and O2, to form CO22 during long times at ambient temperature. Developed as means to prevent accumulation of these products in sealed CO2 lasers. Effective at ambient operating temperatures and installs directly in laser envelope. Formulated to have very high surface area and to chemisorb controlled quantities of moisture: chemisorbed water contained within and upon its structure, makes it highly active and very longlived so only small quantity needed for long times.

14. Covalent immobilization of glucose oxidase onto new modified acrylonitrile copolymer/silica gel hybrid supports.

PubMed

Godjevargova, Tzonka; Nenkova, Ruska; Dimova, Nedyalka

2005-08-12

New polymer/silica gel hybrid supports were prepared by coating high surface area of silica gel with modified acrylonitrile copolymer. The concentrations of the modifying agent (NaOH) and the modified polymer were varied. GOD was covalently immobilized on these hybrid supports and the relative activity and the amount of bound protein were determined. The highest relative activity and sufficient amount of bound protein of the immobilized GOD were achieved in 10% NaOH and 2% solution of modified acrylonitrile copolymer. The influence of glutaraldehyde concentration and the storage time on enzyme efficiency were examined. Glutaraldehyde concentration of 0.5% is optimal for the immobilized GOD. It was shown that the covalently bound enzyme (using 0.5% glutaraldehyde) had higher relative activity than the activity of the adsorbed enzyme. Covalently immobilized GOD with 0.5% glutaraldehyde was more stable for four months in comparison with the one immobilized on pure silica gel, hybrid support with 10% glutaraldehyde and the free enzyme. The effect of the pore size on the enzyme efficiency was studied on four types of silica gel with different pore size. Silica with large pores (CPC-Silica carrier, 375 A) presented higher relative activity than those with smaller pore size (Silica gel with 4, 40 and 100 A). The amount of bound protein was also reduced with decreasing the pore size. The effect of particle size was studied and it was found out that the smaller the particle size was, the greater the activity and the amount of immobilized enzyme were. The obtained results proved that these new polymer/silica gel hybrid supports were suitable for GOD immobilization. PMID:16080168

15. Adsorption Kinetics at Silica Gel/Ionic Liquid Solution Interface.

PubMed

Flieger, Jolanta; Tatarczak-Michalewska, Małgorzata; Groszek, Anna; Blicharska, Eliza; Kocjan, Ryszard

2015-12-10

A series of imidazolium and pyridinium ionic liquids with different anions (Cl(-), Br(-), BF₄(-), PF₆(-)) has been evaluated for their adsorption activity on silica gel. Quantification of the ionic liquids has been performed by the use of RP-HPLC with organic-aqueous eluents containing an acidic buffer and a chaotropic salt. Pseudo-second order kinetic models were applied to the experimental data in order to investigate the kinetics of the adsorption process. The experimental data showed good fitting with this model, confirmed by considerably high correlation coefficients. The adsorption kinetic parameters were determined and analyzed. The relative error between the calculated and experimental amount of ionic liquid adsorbed at equilibrium was within 7%. The effect of various factors such as initial ionic liquid concentration, temperature, kind of solvent, kind of ionic liquid anion and cation on adsorption efficiency were all examined in a lab-scale study. Consequently, silica gel showed better adsorptive characteristics for imidazolium-based ionic liquids with chaotropic anions from aqueous solutions in comparison to pyridinium ionic liquids. The adsorption was found to decrease with the addition of organic solvents (methanol, acetonitrile) but it was not sensitive to the change of temperature in the range of 5-40 °C.

16. Stable and responsive fluorescent carbon nanotube silica gels

SciTech Connect

Dattelbaum, Andrew M; Gupta, Gautam; Doorn, Stephen K; Duque, Juan G

2010-05-03

Here we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous suspension of surfactant-wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes. The vapor phase silica process is performed at room temperature and is simple, reproducible, relatively quick, and requires no dilution of SWNT dispersions. However, exposure of aqueous SWNT suspensions to TMOS vapors resulted in an acidification of the suspension prior to gelation that caused a decrease in the emission signal from sodium dodecylsulfate (SDS) wrapped SWNT. We also show that although the SWNT are encapsulated in silica the emission signal from the encapsulated SWNT may be attenuated by exposing the nanocomposites to small aromatic molecules known to mitigate SWNT emission. These results demonstrate a new route for the preparation of highly luminescent SWNT/silica composite materials that are potentially useful for future sensing applications.

17. Time and frequency dependent rheology of reactive silica gels.

PubMed

Wang, Miao; Winter, H Henning; Auernhammer, Günter K

2014-01-01

In a mixture of sodium silicate and low concentrated sulfuric acid, nano-sized silica particles grow and may aggregate to a system spanning gel network. We studied the influence of the finite solubility of silica at high pH on the mechanical properties of the gel with classical and piezo-rheometers. Direct preparation of the gel sample in the rheometer cell avoided any pre-shear of the gel structure during the filling of the rheometer. The storage modulus of the gel grew logarithmically with time with two distinct growth laws. The system passes the gel point very quickly but still shows relaxation at low frequency, typically below 6 rad/s. We attribute this as a sign of structural rearrangements due to the finite solubility of silica at high pH. The reaction equilibrium between bond formation and dissolution maintains a relatively large bond dissolution rate, which leads to a finite life time of the bonds and behavior similar to physical gels. This interpretation is also compatible with the logarithmic time dependence of the storage modulus. The frequency dependence was more pronounced for lower water concentrations, higher temperatures and shorter reaction times. With two relaxation models (the modified Cole-Cole model and the empirical Baumgaertel-Schausberger-Winter model) we deduced characteristic times from the experimental data. Both models approximately described the data and resulted in similar relaxation times.

18. The Influence of Microgravity on Silica Sol-Gel Formation

NASA Technical Reports Server (NTRS)

Sibille, L.; Smith, D. D.; Cronise, R.; Hunt, A. J.; Wolfe, D. B.; Snow, L. A.; Oldenberg, S.; Halas, N.; Rose, M. Franklin (Technical Monitor)

2000-01-01

We discuss space-flight experiments involving the growth of silica particles and gels. The effect of microgravity on the growth of silica particles via the sol-gel route is profound. In four different recipes spanning a large range of the parameter space that typically produces silica nanoparticles in unit-gravity, low-density gel structures were instead formed in microgravity. The particles that did form were generally smaller and more polydisperse than those grown on the ground. These observations suggest that microgravity reduces the particle growth rate, allowing unincorporated species to form aggregates and ultimately gel. Hence microgravity favors the formation of more rarefied structures, providing a bias towards diffusion-limited cluster-cluster aggregation. These results further suggest that in unit gravity, fluid flows and sedimentation can significantly perturb sol-gel substructures prior to gelation and these deleterious perturbations may be "frozen" into the resulting microstructure. Hence, sol-gel pores may be expected to be smaller, more uniform, and less rough when formed in microgravity.

19. Structure of chemical vapor deposition titania/silica gel

SciTech Connect

Leboda, R.; Gun'ko, V.M.; Marciniak, M.; Malygin, A.A.; Malkin, A.A.; Grzegorczyk, W.; Trznadel, B.J.; Pakhlov, E.M.; Voronin, E.F.

1999-10-01

The structure of porous silica gel/titania synthesized using chemical vapor deposition (CVD) of titania via repeated reactions of TiCl{sub 4} with the surface and subsequent hydrolysis of residual Ti-Cl bonds at different temperatures was investigated by means of low-temperature nitrogen adsorption-desorption, X-ray diffraction (XRD), IR spectroscopy, and theoretical methods. A globular model of porous solids with corpuscular structure was applied to estimate the porosity parameters of titania/silica gel adsorbents. The utilization of this model is useful, for example, to predict conditions for synthesis of titania/silica with a specified structure. Analysis of pore parameters and fractal dimension suggests that the porosity and fractality of samples decrease with increasing amount of TiO{sub 2} covering the silica gel surface in a nonuniform layer, which represents small particles embedded in pores and larger particles formed at the outer surface of silica globules. Theoretical simulation shows that the Si-O-Ti linkages between the cover and the substrate can be easily hydrolyzed, which is in agreement with the IR data corresponding to the absence of a band at 950 cm {sup {minus}1} (characteristic of Si-O-Ti bridges) independent of the concentration of CVD-titania.

20. Surface properties of mesoporous carbon-silica gel adsorbents

SciTech Connect

Leboda, R.; Turov, V.V.; Charmas, B.; Skubiszewska-Zieba, J.; Gun'ko, V.M.

2000-03-01

Carbon/silica (carbosil) samples prepared utilizing mesoporous silica gel (Si-60) modified by methylene chloride pyrolysis were studied by nitrogen adsorption, quasi-isothermal thermogravimetry, p-nitrophenol adsorption from aqueous solution, and {sup 1}H NMR methods. The structural characteristics and other properties of carbosils depend markedly on the synthetic conditions and the amount of carbon deposited. The changes in the pore size distribution with increasing carbon concentration suggest grafting of carbon mainly in pores, leading to diminution of the mesopore radii. However, heating pure silica gel at the pyrolysis temperature of 550 C leads to an increase in the pore radii. The quasi-isothermal thermogravimetry and {sup 1}H NMR spectroscopy methods used to investigate the water layers on carbosils showed a significant capability of carbosils to adsorb water despite a relatively large content of the hydrophobic carbon deposit, which represents a nonuniform layer incompletely covering the oxide surface.

1. A silica gel based method for extracting insect surface hydrocarbons.

PubMed

Choe, Dong-Hwan; Ramírez, Santiago R; Tsutsui, Neil D

2012-02-01

Here, we describe a novel method for the extraction of insect cuticular hydrocarbons using silica gel, herein referred to as "silica-rubbing". This method permits the selective sampling of external hydrocarbons from insect cuticle surfaces for subsequent analysis using gas chromatography-mass spectrometry (GC-MS). The cuticular hydrocarbons are first adsorbed to silica gel particles by rubbing the cuticle of insect specimens with the materials, and then are subsequently eluted using organic solvents. We compared the cuticular hydrocarbon profiles that resulted from extractions using silica-rubbing and solvent-soaking methods in four ant and one bee species: Linepithema humile, Azteca instabilis, Camponotus floridanus, Pogonomyrmex barbatus (Hymenoptera: Formicidae), and Euglossa dilemma (Hymenoptera: Apidae). We also compared the hydrocarbon profiles of Euglossa dilemma obtained via silica-rubbing and solid phase microextraction (SPME). Comparison of hydrocarbon profiles obtained by different extraction methods indicates that silica rubbing selectively extracts the hydrocarbons that are present on the surface of the cuticular wax layer, without extracting hydrocarbons from internal glands and tissues. Due to its surface specificity, efficiency, and low cost, this new method may be useful for studying the biology of insect cuticular hydrocarbons.

2. Spectroscopic and biocatalytic properties of a chlorophyll-containing extract in silica gel

Lipke, Agnieszka; Trytek, Mariusz; Fiedurek, Jan; Majdan, Marek; Janik, Ewa

2013-11-01

UV-Vis absorption and fluorescence spectra of chlorophyll a (in the form of spinach extract) in acetone solution and in silica gel showed a predominance of pigment dimers in its overall concentration and an evident transformation of chlorophyll a to pheophytin with time. The dimerization constant of chlorophyll a in acetone was log Kdim = 2.14, whereas the constants for chlorophyll a and pheophytin a in alcogel were log Kdim = 4.70 and log Kdim = 5.22, respectively. Biocatalytic experiments indicated the possibility of using the pigment embedded in silica gel, i.e. mainly its dimeric form, for biotransformation of α-pinene to pinocarveyl hydroperoxide, trans-pinocarveol, pinocarvone and myrtenal. The advantage of a heterogeneous biocatalytic system (composed of a solvent and silica gel) over a homogeneous system (single phase of chloroform) is the possibility of reusing the biocatalyst with about 10% preservation of its activity.

3. Luminescence properties of Cr-doped silica sol gel glasses

Strek, Wieslaw; Lukowiak, Edward; Deren, Przemyslaw J.; Maruszewski, K.; Trabjerg, Ib; Koepke, Czeslaw; Malashkevich, G. E.; Gaishun, Vladimir E.

1997-11-01

The emission of Cr-doped silica glass obtained by the sol- gel method is characterized by an orange broad band with a maximum at 610 nm. Its nature is examined by the absorption, excited state absorption, emission, excitation and lifetime measurements over a wide range of temperature and for different concentration of Cr ions. Our measurement show that in spite of fact that the absorption properties of Cr- doped silica sol-gel glass are predominantly associated with Cr4+ centers, the observed in visible range emission can be assigned neither to Cr3+ nor to Cr4+ ions. The discussion of the nature of observed emission was carried out for all possible valencies of the Cr ions. In conclusion is suggested that it may be ascribed to the transitions on the monovalent Cr1+ ion. The reducing agents occurring during the sol-gel process and leading to lowering the Cr valency are discussed.

4. 40 CFR 721.9680 - Alkaline titania silica gel (generic name).

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkaline titania silica gel (generic... Specific Chemical Substances § 721.9680 Alkaline titania silica gel (generic name). (a) Chemical substance... alkaline titania silica gel (PMN P-95-529) is subject to reporting under this section for the...

5. 40 CFR 721.9680 - Alkaline titania silica gel (generic name).

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkaline titania silica gel (generic... Specific Chemical Substances § 721.9680 Alkaline titania silica gel (generic name). (a) Chemical substance... alkaline titania silica gel (PMN P-95-529) is subject to reporting under this section for the...

6. 40 CFR 721.9680 - Alkaline titania silica gel (generic name).

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkaline titania silica gel (generic... Specific Chemical Substances § 721.9680 Alkaline titania silica gel (generic name). (a) Chemical substance... alkaline titania silica gel (PMN P-95-529) is subject to reporting under this section for the...

7. 40 CFR 721.9680 - Alkaline titania silica gel (generic name).

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkaline titania silica gel (generic... Specific Chemical Substances § 721.9680 Alkaline titania silica gel (generic name). (a) Chemical substance... alkaline titania silica gel (PMN P-95-529) is subject to reporting under this section for the...

8. 40 CFR 721.9680 - Alkaline titania silica gel (generic name).

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkaline titania silica gel (generic... Specific Chemical Substances § 721.9680 Alkaline titania silica gel (generic name). (a) Chemical substance... alkaline titania silica gel (PMN P-95-529) is subject to reporting under this section for the...

9. Diffusion of dissolved ions from wet silica sol-gel monoliths: implications for biological encapsulation.

PubMed

Dickson, David J; Lassetter, Bethany; Glassy, Benjamin; Page, Catherine J; Yokochi, Alexandre F T; Ely, Roger L

2013-02-01

Divalent nickel (Ni(2+)), Cu(II)EDTA, methyl orange, and dichromate were used to investigate diffusion from hydrated silica sol-gel monoliths. The objective was to examine diffusion of compounds on a size regime relevant to supporting biological components encapsulated within silica gel prepared in a biologically compatible process space with no post-gelation treatments. With an initial sample set, gels prepared from tetraethoxysilane were explored in a factorial design with Ni(2+) as the tracer, varying water content during hydrolysis, acid catalyst present during hydrolysis, and the final concentration of silica. A second sample set explored diffusion of all four tracers in gels prepared with aqueous silica precursors and a variety of organically modified siloxanes. Excluding six outliers which displayed significant syneresis, the mean diffusion constant (D(gel)) across the entire process space of sample set 1 was 2.42×10(-10) m(2) s(-1); approximately 24% of the diffusion coefficient of Ni(2+) in unconfined aqueous solution. In sample set 2, the tracer size and not gel hydrophobicity was the primary determinant of changes in diffusion rates. A strong linear inverse correlation was found between tracer size and the magnitude of D(gel). Based on correlation with the tracers used in this investigation, the characteristic 1-h diffusion distance for carbonate species relevant to supporting active phototrophic organisms was approximately 1.5mm. These results support the notion that silica sol-gel formulations may be optimized for a given biological entity of interest with manageable impact to the diffusion of small ions and molecules.

10. Accelerated subcritical drying of large alkoxide silica gels

Wang, Shiho; Kirkbir, Fikret; Chaudhuri, S. R.; Sarkar, Arnab

1992-12-01

Fracture during drying has been the key hurdle in fabrication of large monolithic silica glass from alkoxide gels. Although existing literature suggests pore enlargement, aging, chemical additives, supercritical drying and freeze drying as helpful in avoiding fracture during drying, successful accelerated sub-critical drying of large silica monoliths from alkoxide gels has not yet been reported. In the present approach, acid catalyzed sols of TEOS, ethanol and water (pH equals 2) were cast as cylindrical rods in plastic molds of 8.0 and 10.0 cm diameter with volumes of 2000 cc and 3000 cc respectively. The resultant gels were aged for about 7 days and dried in a specially designed chamber under sub-critical conditions of the pore field. We have obtained monolithic dry gels in drying times of 3 - 7 days for sizes of 2000 - 3000 cc. The dry gels have narrow unimodal pore size distributions, with average pore radius of about 20 angstroms as measured by BET. Although capillary stress during drying increases with reduction of pore size, it was found that in this approach it is easier to dry gels of smaller pore size.

11. Photoacoustic spectra of malachite green adsorbed on silica gel surface

Sikorska, Anna; Zachara, Stanislaw

1992-11-01

Photoacoustic spectra of malachite green adsorbed on silica gel were investigated at high dye concentrations. The measurements were carried out for two markedly differing layer thicknesses of dyed silica. The ratio of maxima of two characteristic dye bands at (lambda) equals 620 nm and (lambda) equals 425 nm was chosen as an indicator of concentration dependent changes in the shapes of the photoacoustic spectra investigated. The comparison of experimental data with the theoretical model implies that the changes observed in the shape of the spectrum result first of all from the mechanism of the signal generation in inhomogeneous medium.

12. Asymmetric bioreduction of acetophenones by Baker's yeast and its cell-free extract encapsulated in sol-gel silica materials

Kato, Katsuya; Nakamura, Hitomi; Nakanishi, Kazuma

2014-02-01

Baker's yeast (BY) encapsulated in silica materials was synthesized using a yeast cell suspension and its cell-free extract during a sol-gel reaction of tetramethoxysilane with nitric acid as a catalyst. The synthesized samples were fully characterized using various methods, such as scanning electron microscopy, nitrogen adsorption-desorption, Fourier transform infrared spectroscopy, thermogravimetry, and differential thermal analysis. The BY cells were easily encapsulated inside silica-gel networks, and the ratio of the cells in the silica gel was approximately 75 wt%, which indicated that a large volume of BY was trapped with a small amount of silica. The enzyme activity (asymmetric reduction of prochiral ketones) of BY and its cell-free extract encapsulated in silica gel was investigated in detail. The activities and enantioselectivities of free and encapsulated BY were similar to those of acetophenone and its fluorine derivatives, which indicated that the conformation structure of BY enzymes inside silica-gel networks did not change. In addition, the encapsulated BY exhibited considerably better solvent (methanol) stability and recyclability compared to free BY solution. We expect that the development of BY encapsulated in sol-gel silica materials will significantly impact the industrial-scale advancement of high-efficiency and low-cost biocatalysts for the synthesis of valuable chiral alcohols.

13. Spherulitic crystallization of holmium tartrates in silica gels

Want, Basharat

2011-09-01

Spherulites of holmium tartrate trihydrate and holmium nitro-tartrate monohydrate have been grown in silica gel medium by making holmium nitrate to react with tartaric acid at high supersaturations. The mechanism of spherulitic growth of holmium tartrates is discussed. The spherulitic crystallization is shown to be due to heterogeneous nucleation. In the early stages of growth an amorphous spherical mass gets nucleated inside the gel. Crystal fibers diverge radially from the surface of the spherical mass giving rise to a spherical polycrystalline holmium tartrate. Thermal stability of the two types of spherulites grown in the silica gel shows that the holmium tartrate trihydrate is more stable than holmium nitro-tartrate monohydrate. The surface morphology and internal structure of the spherulites of holmium tartrates have been studied by using scanning electron microscopy. The results on growth kinetics are given by studying the variation of radius of spherulites as a function of time. A non-linear time-size relations under several conditions of growth have been observed, which suggests a non-uniform solute concentration at the crystal surface.

14. The sol-gel entrapment of noble metals in hybrid silicas: a molecular insight

PubMed Central

2013-01-01

Background Why are metal nanoparticles sol-gel entrapped in ORMOSIL so active and stable? In other words, why ORMOSIL-entrapped metal nanoparticles are more active and selective than many heterogenized counterparts, including silica-entrapped noble metals? Results Unveiling specific interactions between MNPs and the molecular structure of ORMOSIL, this work investigates subtle structural aspects through DRIFT spectroscopy. Conclusions The results point to interactions between entrapped Pd and Pt nanocrystallites with the organosilica sol-gel cages similar to those taking place in enzymes. PMID:24079552

15. Applications of Geothermally-Produced Colloidal Silica in Reservoir Management - Smart Gels

DOE Data Explorer

Hunt, Jonathan

2013-01-31

In enhanced geothermal systems (EGS) the reservoir permeability is often enhanced or created using hydraulic fracturing. In hydraulic fracturing, high fluid pressures are applied to confined zones in the subsurface usually using packers to fracture the host rock. This enhances rock permeability and therefore conductive heat transfer to the circulating geothermal fluid (e.g. water or supercritical carbon dioxide). The ultimate goal is to increase or improve the thermal energy production from the subsurface by either optimal designs of injection and production wells or by altering the fracture permeability to create different zones of circulation that can be exploited in geothermal heat extraction. Moreover, hydraulic fracturing can lead to the creation of undesirable short-circuits or fast flow-paths between the injection and extraction wells leading to a short thermal residence time, low heat recovery, and thus a short-life of the EGS. A potential remedy to these problems is to deploy a cementing (blocking, diverting) agent to minimize short-cuts and/or create new circulation cells for heat extraction. A potential diverting agent is the colloidal silica by-product that can be co-produced from geothermal fluids. Silica gels are abundant in various surface and subsurface applications, yet they have not been evaluated for EGS applications. In this study we are investigating the benefits of silica gel deployment on thermal response of an EGS, either by blocking short-circuiting undesirable pathways as a result of diverting the geofluid to other fractures; or creating, within fractures, new circulation cells for harvesting heat through newly active surface area contact. A significant advantage of colloidal silica is that it can be co-produced from geothermal fluids using an inexpensive membrane-based separation technology that was developed previously using DOE-GTP funding. This co-produced silica has properties that potentially make it useful as a fluid diversion agent

16. Active gel physics

Prost, J.; Jülicher, F.; Joanny, J.-F.

2015-02-01

The mechanical behaviour of cells is largely controlled by a structure that is fundamentally out of thermodynamic equilibrium: a network of crosslinked filaments subjected to the action of energy-transducing molecular motors. The study of this kind of active system was absent from conventional physics and there was a need for both new theories and new experiments. The field that has emerged in recent years to fill this gap is underpinned by a theory that takes into account the transduction of chemical energy on the molecular scale. This formalism has advanced our understanding of living systems, but it has also had an impact on research in physics per se. Here, we describe this developing field, its relevance to biology, the novelty it conveys to other areas of physics and some of the challenges in store for the future of active gel physics.

17. Phase equilibria and thermodynamic modeling of ethane and propane hydrates in porous silica gels.

PubMed

Seo, Yongwon; Lee, Seungmin; Cha, Inuk; Lee, Ju Dong; Lee, Huen

2009-04-23

In the present study, we examined the active role of porous silica gels when used as natural gas storage and transportation media. We adopted the dispersed water in silica gel pores to substantially enhance active surface for contacting and encaging gas molecules. We measured the three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria of C(2)H(6) and C(3)H(8) hydrates in 6.0, 15.0, 30.0, and 100.0 nm silica gel pores to investigate the effect of geometrical constraints on gas hydrate phase equilibria. At specified temperatures, the hydrate stability region is shifted to a higher pressure region depending on pore size when compared with those of bulk hydrates. Through application of the Gibbs-Thomson relationship to the experimental data, we determined the values for the C(2)H(6) hydrate-water and C(3)H(8) hydrate-water interfacial tensions to be 39 +/- 2 and 45 +/- 1 mJ/m(2), respectively. By using these values, the calculation values were in good agreement with the experimental ones. The overall results given in this study could also be quite useful in various fields, such as exploitation of natural gas hydrate in marine sediments and sequestration of carbon dioxide into the deep ocean.

18. Preparation of Nanowire Silica Inside Self-Assembled Sodium Bis(2-ethylhexyl) Sulfosuccinate (AOT) Gels.

PubMed

Lai, Wei-Chi; Hong, Li-Tzuen

2016-09-22

In conventional sol-gel methods, gel formation occurs due to aggregation of particles into irregular shapes of larger size. In this study, we conducted hydrolysis-condensation reactions of tetraethyl orthosilicate (TEOS) within water-laden channels inside the space created by self-assembled AOT molecules to prepare regular and nanosized silica in self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) gels. The AOT gels were obtained by adding small amounts of water to organic solvents containing high concentrations of AOT. Adding silica significantly influenced the rheological properties and microstructures of these AOT/silica gels. Rheological studies showed that the storage modulus G' and loss modulus G″ of the AOT gel systems became very close and even crossed, indicating that the gel is "weak"; however, for the AOT/silica gel systems, the rheological data demonstrated that G' is greater than G″ at all frequencies, indicative of a real gel with a G' of approximately 10(5) pa. Small-angle X-ray scattering (SAXS) results showed that the gels initially had a hexagonal close-packed cylindrical structure with long-range order and transitioned to nonclose-packed cylindrical structures without long-range order as the silica formed. The cylinder is expected to comprise stacks of silica molecules surrounded by AOT molecules, and the radius of the cylinder is close to the sum of the length of one AOT molecule and half the size of one silica molecule. The rheological and SAXS data show that silica in the AOT/silica systems grew in the axial direction due to the confinement of these cylindrical structures, leading to nanowire silica structures. After removal of the AOT components, the nanowire silica was approximately 5-10 nm in diameter, as observed using transmission electron microscopy (TEM). PMID:27602986

19. Preparation of Nanowire Silica Inside Self-Assembled Sodium Bis(2-ethylhexyl) Sulfosuccinate (AOT) Gels.

PubMed

Lai, Wei-Chi; Hong, Li-Tzuen

2016-09-22

In conventional sol-gel methods, gel formation occurs due to aggregation of particles into irregular shapes of larger size. In this study, we conducted hydrolysis-condensation reactions of tetraethyl orthosilicate (TEOS) within water-laden channels inside the space created by self-assembled AOT molecules to prepare regular and nanosized silica in self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) gels. The AOT gels were obtained by adding small amounts of water to organic solvents containing high concentrations of AOT. Adding silica significantly influenced the rheological properties and microstructures of these AOT/silica gels. Rheological studies showed that the storage modulus G' and loss modulus G″ of the AOT gel systems became very close and even crossed, indicating that the gel is "weak"; however, for the AOT/silica gel systems, the rheological data demonstrated that G' is greater than G″ at all frequencies, indicative of a real gel with a G' of approximately 10(5) pa. Small-angle X-ray scattering (SAXS) results showed that the gels initially had a hexagonal close-packed cylindrical structure with long-range order and transitioned to nonclose-packed cylindrical structures without long-range order as the silica formed. The cylinder is expected to comprise stacks of silica molecules surrounded by AOT molecules, and the radius of the cylinder is close to the sum of the length of one AOT molecule and half the size of one silica molecule. The rheological and SAXS data show that silica in the AOT/silica systems grew in the axial direction due to the confinement of these cylindrical structures, leading to nanowire silica structures. After removal of the AOT components, the nanowire silica was approximately 5-10 nm in diameter, as observed using transmission electron microscopy (TEM).

20. Effectiveness of silica based sol-gel microencapsulation method for odorants and flavors leading to sustainable environment.

PubMed

2015-01-01

Microencapsulation has become a hot topic in chemical research. Technology mainly used for control release and protection purposes. The sol-gel micro encapsulation approach for fragrance and aroma in porous silica-based materials leads to sustainable odorant and flavored materials with novel and unique beneficial properties. Sol-gel encapsulation of silica based micro particles considered economically cheap as capital investment in manufacturing is very low and environmentally friendly. Amorphous sol-gel SiO2 is non-toxic and safe, whereas the sol-gel entrapment of delicate chemicals in its inner pores results in pronounced chemical and physical stabilization of the entrapped active agents, thereby broadening the practical utilization of chemically unstable essential oils (EOs). Reviewing progress in the fabrication of diverse odorant and flavored sol-gels, shows us how different synthetic strategies are appropriate for practical application with important health and environmental benefits.

1. Effectiveness of silica based sol-gel microencapsulation method for odorants and flavors leading to sustainable environment.

PubMed

2015-01-01

Microencapsulation has become a hot topic in chemical research. Technology mainly used for control release and protection purposes. The sol-gel micro encapsulation approach for fragrance and aroma in porous silica-based materials leads to sustainable odorant and flavored materials with novel and unique beneficial properties. Sol-gel encapsulation of silica based micro particles considered economically cheap as capital investment in manufacturing is very low and environmentally friendly. Amorphous sol-gel SiO2 is non-toxic and safe, whereas the sol-gel entrapment of delicate chemicals in its inner pores results in pronounced chemical and physical stabilization of the entrapped active agents, thereby broadening the practical utilization of chemically unstable essential oils (EOs). Reviewing progress in the fabrication of diverse odorant and flavored sol-gels, shows us how different synthetic strategies are appropriate for practical application with important health and environmental benefits. PMID:26322304

2. Effectiveness of silica based Sol-gel microencapsulation Method for odorants and flavours leading to sustainable Environment

2015-08-01

Microencapsulation has become a hot topic in chemical research. Technology mainly used for control release and protection purposes. The sol-gel micro encapsulation approach for fragrance and aroma in porous silica-based materials leads to sustainable odorant and flavored materials with novel and unique beneficial properties. Sol-gel encapsulation of silica based micro particles considered economically cheap as capital investment in manufacturing is very low and environmentally friendly. Amorphous sol-gel SiO2 is non-toxic and safe, whereas the sol-gel entrapment of delicate chemicals in its inner pores results in pronounced chemical and physical stabilization of the entrapped actives, thereby broadening the practical utilization of chemically unstable essential oils. Reviewing progress in the fabrication of diverse odorant and flavoured sol-gels, shows us how different synthetic strategies are appropriate for practical application with important health and environmental benefits.

3. Effectiveness of silica based sol-gel microencapsulation method for odorants and flavors leading to sustainable environment

PubMed Central

2015-01-01

Microencapsulation has become a hot topic in chemical research. Technology mainly used for control release and protection purposes. The sol-gel micro encapsulation approach for fragrance and aroma in porous silica-based materials leads to sustainable odorant and flavored materials with novel and unique beneficial properties. Sol-gel encapsulation of silica based micro particles considered economically cheap as capital investment in manufacturing is very low and environmentally friendly. Amorphous sol-gel SiO2 is non-toxic and safe, whereas the sol-gel entrapment of delicate chemicals in its inner pores results in pronounced chemical and physical stabilization of the entrapped active agents, thereby broadening the practical utilization of chemically unstable essential oils (EOs). Reviewing progress in the fabrication of diverse odorant and flavored sol-gels, shows us how different synthetic strategies are appropriate for practical application with important health and environmental benefits. PMID:26322304

4. Adsorption from the liquid phase on silica gels of various structural heterogeneity

SciTech Connect

Goworek, J.; Derylo-Marczewska, A.; Borowka, A.

1999-08-31

Competition of liquid components for silica gel surface was tested for binary liquid mixtures: methanol + benzene and 2-propanol + n-heptane. The adsorption isotherms were measured using silica gels for column chromatography Si-40 and Si-100 from Merck. On the basis of specific surface excess isotherms the surface layer capacities were calculated. Taking into account the properties of the bulk solutions, the influence of geometrical structure of silicas on the composition of the surface phase is discussed.

5. Sensitive spectrophotometric determination of phosphate using silica-gel collectors.

PubMed

Nagai, Masahiro; Sugiyama, Masahito; Hori, Toshitaka

2004-02-01

Phosphate, 3 - 10 nmol, in 1 dm3 of natural-water samples was quantitatively collected along with 10 micromol of Fe(III) ion onto a silica-gel collector in the pH range of 5.4 - 6.2. The amount of Fe(III) ion needed was limited to such a low level that the Pyrocatechol Violet method could be applied without removing the Fe(III) ion, providing a superior determination method for phosphate. Surface-water samples of the north basin of Lake Biwa and the Tanabe Bay in the Wakayama prefecture were selected as being representative of natural water with extremely low phosphate concentrations, and were found to have phosphate concentrations of 3.68 and 4.31 nmol dm(-3), respectively.

6. Holographic diffraction gratings recording in organically modified silica gels

Cheben, P.; Belenguer, T.; Nuñez, A.; del Monte, F.; Levy, D.

1996-11-01

The silica gel-methyl methacrylate organically modified ceramic is proposed for recording of volume holograms. Both low-spatial-frequency (54 line pairs /mm-1 ) and high-spatial-frequency (1400 line pairs /mm-1 ) holographic gratings were successfully recorded in the medium by interference of two coherent beams of 351.1-nm wavelength. High diffraction efficiencies (93%) and extremely low absorption and scattering coefficients were measured during the holographic reconstruction by a 632.8-nm He-Ne beam. The optimum UV recording exposure was \\similar 3J cm -2 . A grating refractive-index modulation amplitude of 1.1 \\times 10-4 was achieved. Virtually no changes in diffraction efficiency were observed after thermal-heating, light-curing, and long-term-aging experiments.

7. Regenerated silica gel as stationary phase on vacuum column chromatography to purify temulawak’s extracts

SciTech Connect

Cahyono, Bambang; Maduwu, Ratna Dewi; Widayat,; Suzery, Meiny

2015-12-29

Commercial silica gel only used once by many researchers and affected high cost for purification process, also less support the green chemistry program. This research focused in regeneration silica gel that used purification of temulawak’s extracts (Curcuma xanthorrhiza Roxb) by vacuum column chromatography. Sample extracts (contains 10.1195±0.5971% of curcuminoids) was purified by vacuum column chromatography (pressure: 45 kPa, column: 100mm on length and 16mm on diameter). Ethanol 96% and acetone were compared as eluent. The amount of solvent and yield of curcuminoids used as indicator purification. The silica gel was regenerated with heating in 600°C for 8 hours The silica gels were analyzed by IR spectroscopy and X-ray diffraction. Furthermore, regenerated silica gel was used as the stationary phase in vacuum column chromatography under the same conditions with the previous purification. All the purification experiments were performed in three repetitions. Based on regression equation, y=0.132x+0.0011 (r{sup 2}=0.9997) the yield of curcuminoids on purified products using ethanol as the eluent was improved 4.26% (to 14.3724±0.5749%) and by acetone was improved 3,03% (to 13.1450 ±0.6318%). The IR spectrum of both silica gel showed the same vibration profile and also there were three crystallinity peaks missing on its X-ray diffraction. Regenerated silica gel has the same performance with new silica gel in purification of temulawak’s extract: by ethanol has increased 4.08% (14.1947±0.7415%) and 2.93% (13.0447±0.4822) by acetone. In addition, all purification products showed similar TLC profiles. Purification using regenerated silica gel as the adsorbent on vacuum column chromatography has exactly same potential with the new silica gel.

8. Regenerated silica gel as stationary phase on vacuum column chromatography to purify temulawak's extracts

Cahyono, Bambang; Maduwu, Ratna Dewi; Widayat, Suzery, Meiny

2015-12-01

Commercial silica gel only used once by many researchers and affected high cost for purification process, also less support the green chemistry program. This research focused in regeneration silica gel that used purification of temulawak's extracts (Curcuma xanthorrhiza Roxb) by vacuum column chromatography. Sample extracts (contains 10.1195±0.5971% of curcuminoids) was purified by vacuum column chromatography (pressure: 45 kPa, column: 100mm on length and 16mm on diameter). Ethanol 96% and acetone were compared as eluent. The amount of solvent and yield of curcuminoids used as indicator purification. The silica gel was regenerated with heating in 600°C for 8 hours The silica gels were analyzed by IR spectroscopy and X-ray diffraction. Furthermore, regenerated silica gel was used as the stationary phase in vacuum column chromatography under the same conditions with the previous purification. All the purification experiments were performed in three repetitions. Based on regression equation, y=0.132x+0.0011 (r2=0.9997) the yield of curcuminoids on purified products using ethanol as the eluent was improved 4.26% (to 14.3724±0.5749%) and by acetone was improved 3,03% (to 13.1450 ±0.6318%). The IR spectrum of both silica gel showed the same vibration profile and also there were three crystallinity peaks missing on its X-ray diffraction. Regenerated silica gel has the same performance with new silica gel in purification of temulawak's extract: by ethanol has increased 4.08% (14.1947±0.7415%) and 2.93% (13.0447±0.4822) by acetone. In addition, all purification products showed similar TLC profiles. Purification using regenerated silica gel as the adsorbent on vacuum column chromatography has exactly same potential with the new silica gel.

9. Sol-Gel processing of silica nanoparticles and their applications.

PubMed

Singh, Lok P; Bhattacharyya, Sriman K; Kumar, Rahul; Mishra, Geetika; Sharma, Usha; Singh, Garima; Ahalawat, Saurabh

2014-11-01

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized. PMID:25466691

10. Sol-Gel Synthesis of Ordered β-Cyclodextrin-Containing Silicas

Trofymchuk, Iryna Mykolaivna; Roik, Nadiia; Belyakova, Lyudmila

2016-03-01

New approaches for β-cyclodextrin-containing silicas synthesis were demonstrated. Materials with hexagonally ordered mesoporous structure were prepared by postsynthesis grafting and by co-condensation methods. β-Cyclodextrin activated by a N, N'-carbonyldiimidazole was employed for postsynthesis treatment of 3-aminopropyl-modified MCM-41 support as well as for sol-gel synthesis with β-cyclodextrin-containing organosilane and tetraethyl orthosilicate participation in the presence of cetyltrimethylammonium bromide. The successful incorporation of cyclic oligosaccharide moieties in silica surface layer was verified by means of FT-IR spectroscopy and chemical analysis. Obtained β-cyclodextrin-containing materials were characterized by X-ray diffraction, transmission electron microscopy, and low-temperature adsorption-desorption of nitrogen. In spite of commensurable loading of β-cyclodextrin groups attained by both proposed approaches (up to 0.028 μmol · m-2), it was found that co-condensation procedure provides uniform distribution of β-cyclodextrin functionalities in silica framework, whereas postsynthesis grafting results in modification of external surface of silica surface. Adsorption of benzene from aqueous solutions onto the surface of β-cyclodextrin-containing materials prepared by co-condensation method was studied as the function of time and equilibrium concentration. Langmuir and Freundlich models were used to evaluate adsorption processes and parameters. Adsorption experiments showed that β-cyclodextrin-containing silicas could be promising for the trace amount removal of aromatics from water.

11. Radiation hardening in sol-gel derived Er{sup 3+}-doped silica glasses

SciTech Connect

Hari Babu, B. E-mail: matthieu.lancry@u-psud.fr; León Pichel, Mónica; Ollier, Nadège; El Hamzaoui, Hicham; Bigot, Laurent; Savelii, Inna; Bouazaoui, Mohamed; Poumellec, Bertrand; Lancry, Matthieu E-mail: matthieu.lancry@u-psud.fr; Ibarra, Angel

2015-09-28

The aim of the present paper is to report the effect of radiation on the Er{sup 3+}-doped sol-gel silica glasses. A possible application of these sol-gel glasses could be their use in harsh radiation environments. The sol-gel glasses are fabricated by densification of erbium salt-soaked nanoporous silica xerogels through polymeric sol-gel technique. The radiation-induced attenuation of Er{sup 3+}-doped sol-gel silica is found to increase with erbium content. Electron paramagnetic resonance studies reveal the presence of E′{sub δ} point defects. This happens in the sol-gel aluminum-silica glass after an exposure to γ-rays (kGy) and in sol-gel silica glass after an exposure to electrons (MGy). The concentration levels of these point defects are much lower in γ-ray irradiated sol-gel silica glasses. When the samples are co-doped with Al, the exposure to γ-ray radiation causes a possible reduction of the erbium valence from Er{sup 3+} to Er{sup 2+} ions. This process occurs in association with the formation of aluminum oxygen hole centers and different intrinsic point defects.

12. Performance of Silica Gel in the Role of Residual Air Drying

NASA Technical Reports Server (NTRS)

Jan, Darrell L.; Hogan, John A.; Koss, Brian; Palmer, Gary H.; Richardson, Justine; Linggi, Paul

2014-01-01

Removal of carbon dioxide (CO2) is a necessary step in air revitalization and is often accomplished with sorbent materials. Since moisture competes with CO2 in sorbent materials, it is necessary to remove the water first. This is typically accomplished in two stages: bulk removal and residual drying. Silica gel is used as the bulk drying material in the Carbon Dioxide Removal Assembly (CDRA) in operation on ISS. There has been some speculation that silica gel may also be capable of serving as the residual drying material. This paper will describe test apparatus and procedures for determining the performance of silica gel in residual air drying.

13. Interference of silica nanoparticles with the traditional Limulus amebocyte lysate gel clot assay.

PubMed

Kucki, Melanie; Cavelius, Christian; Kraegeloh, Annette

2014-04-01

Endotoxin contaminations of engineered nanomaterials can be responsible for observed biological responses, especially for misleading results in in vitro test systems, as well as in vivo studies. Therefore, endotoxin testing of nanomaterials is necessary to benchmark their influence on cells. Here, we tested the traditional Limulus amebocyte lysate gel clot assay for the detection of endotoxins in nanoparticle suspensions with a focus on possible interference of the particles with the test system. We systematically investigated the effects of nanomaterials made of, or covered by, the same material. Different types of bare or PEGylated silica nanoparticles, as well as iron oxide-silica core shell nanoparticles, were tested. Detailed inhibition/enhancement controls revealed enhanced activity in the Limulus coagulation cascade for all particles with bare silica surface. In comparison, PEGylation led to a lower degree of enhancement. These results indicate that the protein-particle interactions are the basis for the observed inhibition and enhancement effects. The enhancement activity of a particle type was positively related to the calculated particle surface area. For most silica particles tested, a dilution of the sample within the maximum valid dilution was sufficient to overcome non-valid enhancement, enabling semi-quantification of the endotoxin contamination. PMID:23884096

14. Cryoporometry and relaxometry of water in silica-gels.

PubMed

Valckenborg, R; Pel, L; Kopinga, K

2001-01-01

Both cryoporometry and relaxometry are tools to determine the pore size distribution (PSD) of a porous material with NMR. The melting point depression is described by the Gibbs-Thomson equation, yielding the PSD from cryoporometry. The enhanced relaxivity is caused by the surface of the porous material, yielding the PSD from relaxometry. The description in the classical paper of Brownstein and Tarr is only valid for one pore (size). The extended theory of McCall et al. is needed to describe a heterogeneous coupled porous system. As testing material a series of silica-gels called Nucleosil is chosen with typical pore sizes of 5, 10, 12 and 30 nm. Transverse relaxation time distributions are measured using a CPMG-sequence for every temperature of the cryoporometry measurement. These show a mono exponential behaviour, indicating a strongly coupled porous structure. Using the cryoporometry data, an attempt is made to reproduce the averaged relaxivity. Agreement is found for pores with typical pore sizes between 10 nm and 1 microm. The model is not valid for pores smaller than 10 nm. PMID:11445338

15. Copper oxide and selenide nanoparticles embedded into sol-gel-derived silica glasses doped with europium

Gurin, Valerij S.; Yumashev, Konstantin V.; Prokoshin, P. V.; Zolotovskaya, S. A.; Alexeenko, A. A.

2002-11-01

The silica sol-gel derived glasses co-doped with CuxO and CuxSe nanoparticles and Eu3+ ions have been fabricated. The analysis of luminescence spectra of a series of glasses with different composition allows us to suppose the direct energy transfer between copper oxide nanoparticle and Eu3+ ion. A luminescence signal of europium ions occurs as the result of excitation of the complex active centres (SiO2:Cu2O:Eu3+) in the absorption range of copper oxide.

16. Insecticidal efficacy of silica gel with Juniperus oxycedrus ssp. oxycedrus (Pinales: Cupressaceae) essential oil against Sitophilus oryzae (Coleoptera: Curculionidae) and Tribolium confusum (Coleoptera: Tenebrionidae).

PubMed

Athanassiou, Christos G; Kavallieratos, Nickolas C; Evergetis, Epameinondas; Katsoula, Anna-Maria; Haroutounian, Serkos A

2013-08-01

the EO. Results herein suggest that the simultaneous use of silica gel and J. oxycedrus ssp. oxycedrus EO enhances significantly its activity against S. oryzae.

17. Suitability of Silica Gel to Process INEEL Sodium Bearing Waste - Letter Report

SciTech Connect

Kirkham, Robert John; Herbst, Alan Keith

2000-09-01

The suitability of using the silica gel process for Idaho National Engineering and Environmental Laboratory (INEEL) sodium bearing waste was investigated during fiscal year 2000. The study was co-funded by the Tanks Focus Area as part of TTP No. ID-77WT-31 and the High Level Waste Program. The task also included the investigation of possible other absorbents. Scoping tests and examination of past work showed that the silica gel absorption/adsorption and drying method was the most promising; thus only silica gel was studied and not other absorbents. The documentation on the Russian silica gel process provided much of the needed information but did not provide some of the processing detail so these facts had to be inferred or gleaned from the literature.

18. Immobilization of Cross-Linked Phenylalanine Ammonia Lyase Aggregates in Microporous Silica Gel

PubMed Central

Cui, Jian Dong; Li, Lian Lian; Bian, Hong Jie

2013-01-01

A separable and highly-stable enzyme system was developed by adsorption of phenylalanine ammonia lyase (PAL) from Rhodotorula glutinis in amino-functionalized macroporous silica gel and subsequent enzyme crosslinking. This resulted in the formation of cross-linked enzyme aggregates (PAL-CLEAs) into macroporous silica gel (MSG-CLEAs). The effect of adsorptive conditions, type of aggregating agent, its concentration as well as that of cross-linking agent was studied. MSG-CLEAs production was most effective using ammonium sulfate (40%-saturation), followed by cross-linking for 1 h with 1.5% (v/v) glutaraldehyde. The resulting MSG-CLEAs extended the optimal temperature and pH range compared to free PAL and PAL-CLEAs. Moreover, MSG-CLEAs exhibited the excellent stability of the enzyme against various deactivating conditions such as temperature and denaturants, and showed higher storage stability compared to the free PAL and the conventional PAL-CLEAs. Such as, after 6 h incubation at 60°C, the MSG-CLEAs still retained more than 47% of the initial activity whereas PAL-CLEAs only retained 7% of the initial activity. Especially, the MSG-CLEAs exhibited good reusability due to its suitable size and active properties. These results indicated that PAL-CLEAs on MSG might be used as a feasible and efficient solution for improving properties of immobilized enzyme in industrial application. PMID:24260425

19. Slow Release of Permanganate from Injectable Fumed Silica Gel: Rheological Properties and Release Dynamics

Yang, S.; Zhong, L.; Oostrom, M.; Li, G.

2014-12-01

ISCO (In Situ Chemical Oxidation) has been proved to be a useful remediation technology in destroying most prevalent aqueous organic contaminants. For permanganate (MnO4-) in particular, the chemistry of degradative oxidation is well established for cleaning up groundwater containing trichloroethene (TCE) and tetrachloroethene (PCE). However the long-term effectiveness of the application of this oxidant has been questioned due to the observed post remediation rebound of contaminant concentrations. To improve the efficiency of ISCO using MnO4-under specific site conditions, the technology of emplacing slow-releasing permanganate in an aquifer has been studied. We have developed an injectable slow-release permanganate slurry/gel (ISRPG) by mixing KMnO4 with fumed silica in water. Ideally, the slurry/gel forms would release low concentration of MnO4- by diffusion to maintain a desired concentration level of the agent within the chemically active zone. We have investigated the properties and tested the application of this ISRPG in laboratory studies. Rheological study indicated ISRPG has high viscosity and shear thinning property. The viscosity of silica gel could be lowered by mechanical mixing thus making it easy for subsurface injection. Batch tests revealed that MnO4- was diffused from ISRPG and the gel did not disperse but maintained its initial shape. In column experiments we showed that permanganate release covered 6 times more effluent pore volumes when ISRPG was injected compared to MnO4- solution injection. We also observed TCE degradation by released MnO4-, and the remedial performance occurred over a much longer timeframe with ISRPG compared to MnO4- solution injection. In 2-D flow cell tests we demonstrated that water flows around the injected gel, carrying MnO4- diffused out from the gel and forming a downstream oxidant plume, while the gel was stationary. ISRPG slowly released low concentrations of permanganate to maintain a predetermined level of the

20. Sol-gel silica films embedding NIR- emitting Yb-quinolinolate complexes

SciTech Connect

Figus, Cristiana Quochi, Francesco Piana, Giacomo; Saba, Michele; Mura, Andrea; Bongiovanni, Giovanni; Artizzu, Flavia; Mercuri, Maria Laura; Serpe, Angela; Deplano, Paola

2014-10-21

Sol-gel silica thin films embedding an ytterbium quinolinolato complex (YbClQ{sub 4}) have been obtained using different alkoxides. Homogeneous, crack- and defect-free thin films of optical quality have been successfully deposited on glass substrate by dip-coating. The silica thin films have been characterized by time-resolved photoluminescence. The luminescence properties of the YbClQ{sub 4} are preserved in silica films prepared through an optimized sol-gel approach. The excited state lifetime of the lanthanide is comparable to those observed in bulk and longer than the corresponding ones in solution.

1. An Experimental Study of the Liesegang Phenomenon and Crystal Growth in Silica Gels.

ERIC Educational Resources Information Center

Sharbaugh, Amandus H., III; Sharbaugh, Amandus H., Jr.

1989-01-01

Reports on a 30-year-old longitudinal study of reactions in gels. Described are reactions and crystal growth in silica gels and diffusion studies of the Liesegang ring formation. Color photographs showing the reactions and graphs upon the diffusions are presented. (YP)

2. Preconcentration and Determination of Mefenamic Acid in Pharmaceutical and Biological Fluid Samples by Polymer-grafted Silica Gel Solid-phase Extraction Following High Performance Liquid Chromatography

PubMed Central

2015-01-01

Mefenamic acid is a nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-infammatory and antipyretic actions. It is used to relieve mild to moderate pains. Solid-phase extraction of mefenamic acid by a polymer grafted to silica gel is reported. Poly allyl glycidyl ether/iminodiacetic acid-co-N, N-dimethylacrylamide was synthesized and grafted to silica gel and was used as an adsorbent for extraction of trace mefenamic acid in pharmaceutical and biological samples. Different factors affecting the extraction method were investigated and optimum conditions were obtained. The optimum pH value for sorption of mefenamic acid was 4.0. The sorption capacity of grafted adsorbent was 7.0 mg/g. The best eluent solvent was found to be trifluoroacetic acid-acetic acid in methanol with a recovery of 99.6%. The equilibrium adsorption data of mefenamic acid by grafted silica gel was analyzed by Langmuir model. The conformation of obtained data to Langmuir isotherm model reveals the homogeneous binding sites of grafted silica gel surface. Kinetic study of the mefenamic acid sorption by grafted silica gel indicates the good accessibility of the active sites in the grafted polymer. The sorption rate of the investigated mefenamic acid on the grafted silica gel was less than 5 min. This novel synthesized adsorbent can be successfully applied for the extraction of trace mefenamic acid in human plasma, urine and pharmaceutical samples. PMID:26330865

3. Formation of bimodal porous silica-titania monoliths by sol-gel route

2011-10-01

Silica-titania monoliths with micrometer-scale macroporous and nanometer-scale mesoporous structure and high titania contents are prepared by sol-gel process and phase separation. Titanium alkoxide precursor was not effective in the preparation of high titania content composites because of strong decrease in phase separation tendency. Bimodal porous gels with high titania content were obtained by using inorganic salt precursors such as titanium sulfate and titanium chloride. Various characterization techniques, including SEM, XRD, Hg porosimetry and N2 adsorption have been carried out to investigate the formation process and physical-chemical properties of silica-titania monoliths. The characterization results show that the silica-titania monoliths possess a bimodal porous structure with well-dispersed titania inside silica network. The addition of titania in silica improves the thermal stability of both macroporous and mesoporous structures.

4. [Preparation and chromatographic performance of a eugenol-bonded silica gel stationary phase for high performance liquid chromatography].

PubMed

Xu, Lili; Zhong, Minghua; Chen, Xiaojing

2015-05-01

A eugenol-bonded silica gel stationary phase (EGSP) for high performance liquid chromatography ( HPLC) has been synthesized by the solid-liquid successive reaction method. The preparation process included two steps: firstly, γ-glycidoxypropyltrimethoxy-silane (KH-560) was covalently attached to the surface of spherical silica gel. Then the bonded silica gel continued to react with eugenol ligand, which was a plant active component, and obtained EGSP. The structure of EGSP was characterized by elemental analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. Using naphthalene as a probe, the column efficiency was tested under the mobile phase of acetonitrile-water (35:65, v/v) at a flow rate of 0.8 mL/min. The chromatographic properties and the retention mechanism of EGSP were evaluated by using neutral, basic and acidic analytes as solute probes. Meanwhile, the comparative study with C18 column and phenyl column was also carried out under the same chromatographic conditions. The result showed that the eugenol ligand was successfully bonded to the surface of silica gel with a 0.28 mmol/g of bonded amount, and the theoretical plate number of EGSP column was about 24 707 N/m. The EGSP appeared to be a kind of excellent reversed-phase stationary phase with suitable hydrophobicity and various synergistic sites. The eugenol ligand bonded on silica gel could first provide π-π interaction sites for different analytes because of its benzene ring and alkenyl. In addition, the methoxy groups of eugenol were responsible for dipole-dipole and hydrogen-bonding interactions between the ligand and solutes in the effective separation process. Comparing with traditional C18 column and phenyl column, EGSP has an advantage in the fast separation of polar compounds under simple experimental conditions. PMID:26387202

5. [Preparation and chromatographic performance of a eugenol-bonded silica gel stationary phase for high performance liquid chromatography].

PubMed

Xu, Lili; Zhong, Minghua; Chen, Xiaojing

2015-05-01

A eugenol-bonded silica gel stationary phase (EGSP) for high performance liquid chromatography ( HPLC) has been synthesized by the solid-liquid successive reaction method. The preparation process included two steps: firstly, γ-glycidoxypropyltrimethoxy-silane (KH-560) was covalently attached to the surface of spherical silica gel. Then the bonded silica gel continued to react with eugenol ligand, which was a plant active component, and obtained EGSP. The structure of EGSP was characterized by elemental analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. Using naphthalene as a probe, the column efficiency was tested under the mobile phase of acetonitrile-water (35:65, v/v) at a flow rate of 0.8 mL/min. The chromatographic properties and the retention mechanism of EGSP were evaluated by using neutral, basic and acidic analytes as solute probes. Meanwhile, the comparative study with C18 column and phenyl column was also carried out under the same chromatographic conditions. The result showed that the eugenol ligand was successfully bonded to the surface of silica gel with a 0.28 mmol/g of bonded amount, and the theoretical plate number of EGSP column was about 24 707 N/m. The EGSP appeared to be a kind of excellent reversed-phase stationary phase with suitable hydrophobicity and various synergistic sites. The eugenol ligand bonded on silica gel could first provide π-π interaction sites for different analytes because of its benzene ring and alkenyl. In addition, the methoxy groups of eugenol were responsible for dipole-dipole and hydrogen-bonding interactions between the ligand and solutes in the effective separation process. Comparing with traditional C18 column and phenyl column, EGSP has an advantage in the fast separation of polar compounds under simple experimental conditions.

6. A silica sol-gel design strategy for nanostructured metallic materials.

PubMed

Warren, Scott C; Perkins, Matthew R; Adams, Ashley M; Kamperman, Marleen; Burns, Andrew A; Arora, Hitesh; Herz, Erik; Suteewong, Teeraporn; Sai, Hiroaki; Li, Zihui; Werner, Jörg; Song, Juho; Werner-Zwanziger, Ulrike; Zwanziger, Josef W; Grätzel, Michael; DiSalvo, Francis J; Wiesner, Ulrich

2012-03-18

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate. This approach allows a wide range of biological functionalities and metals--including noble metals--to be combined into a library of sol-gel materials with a high degree of control over composition and structure. We demonstrate that the sol-gel process based on these precursors is compatible with block-copolymer self-assembly, colloidal crystal templating and the Stöber process. As a result of the exceptionally high metal content, these materials can be thermally processed to make porous nanocomposites with metallic percolation networks that have an electrical conductivity of over 1,000 S cm(-1). This improves the electrical conductivity of porous silica sol-gel nanocomposites by three orders of magnitude over existing approaches, opening applications to high-current-density devices.

7. Interfacial behavior of silicone oils interacting with nanosilica and silica gels.

PubMed

Gun'ko, V M; Turov, V V; Krupska, T V; Ruban, A N; Kazanets, A I; Leboda, R; Skubiszewska-Zięba, J

2013-03-15

The interfacial behavior of silicone oils Oxane 1000 and Oxane 5700 (polydimethylsiloxanes, PDMS) interacting with dried or hydrated (hydration h=0.005 or 0.1g/g) silica gels Si-60 and Si-100 or nanosilica A-400 was studied using low-temperature (1)H NMR spectroscopy over the 210-310 K range. Broadening of the melting temperature range toward both sides from the freezing point is observed for silicone oils confined in mesopores (2-15 nm in radius) of silica gel particles (0.2-0.5 mm in size) or voids (1-100 nm) between silica nanoparticles (5-10 nm in size) in their aggregates. This effect is a consequence of the phase state heterogeneity, since both liquid and solid-like fractions of adsorbed PDMS are observed over a large temperature range. The adsorbed PDMS heterogeneity depends on the pore size distribution (confined space effect), and it is lower for silica gel Si-100 possessing broader pores than Si-60. An increase in the amounts of adsorbed polymer and water diminishes the effects of confined space on PDMS because a fraction of the polymers is located in broader pores or out of pores (voids). This leads to relative decrease in interactions of PDMS with the silica surface. (1)H NMR spectra of PDMS and n-decane bound to silica gels reveal much stronger heterogenization of adsorbed PDMS (depending on the polymer length) than that of the alkane.

8. Radiation hardening of sol gel-derived silica fiber preforms through fictive temperature reduction.

PubMed

Hari Babu, B; Lancry, Matthieu; Ollier, Nadege; El Hamzaoui, Hicham; Bouazaoui, Mohamed; Poumellec, Bertrand

2016-09-20

The impact of fictive temperature (Tf) on the evolution of point defects and optical attenuation in non-doped and Er3+-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of erbium salt-soaked nanoporous silica xerogels through the polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by FTIR, UV-vis-NIR absorption spectroscopy, electron paramagnetic resonance, and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV-vis range. Furthermore, it was found that γ-radiation "hardness" is higher in Er3+-doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction.

9. Solidification of Acidic, High Nitrate Nuclear Wastes by Grouting or Absorption on Silica Gel

SciTech Connect

A. K. Herbst; S. V. Raman; R. J. Kirkham

2004-01-01

The use of grout and silica gel were explored for the solidification of four types of acidic, high nitrate radioactive wastes. Two methods of grouting were tested: direct grouting and pre-neutralization. Two methods of absorption on silica gel were also tested: direct absorption and rotary spray drying. The waste simulant acidity varied between 1 N and 12 N. The waste simulant was neutralized by pre-blending calcium hydroxide with Portland cement and blast furnace slag powders prior to mixing with the simulant for grout solidification. Liquid sodium hydroxide was used to partially neutralize the simulant to a pH above 2 and then it was absorbed for silica gel solidification. Formulations for each of these methods are presented along with waste form characteristics and properties. Compositional variation maps for grout formulations are presented which help determine the optimum "recipe" for a particular waste stream. These maps provide a method to determine the proportions of waste, calcium hydroxide, Portland cement, and blast furnace slag that provide a waste form that meets the disposal acceptance criteria. The maps guide researchers in selecting areas to study and provide an operational envelop that produces acceptable waste forms. The grouts both solidify and stabilize the wastes, while absorption on silica gel produces a solid waste that will not pass standard leaching procedures (TCLP) if required. Silica gel wastes can be made to pass most leach tests if heated to 600ºC.

10. Radiation hardening of sol gel-derived silica fiber preforms through fictive temperature reduction.

PubMed

Hari Babu, B; Lancry, Matthieu; Ollier, Nadege; El Hamzaoui, Hicham; Bouazaoui, Mohamed; Poumellec, Bertrand

2016-09-20

The impact of fictive temperature (Tf) on the evolution of point defects and optical attenuation in non-doped and Er3+-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by the densification of erbium salt-soaked nanoporous silica xerogels through the polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by FTIR, UV-vis-NIR absorption spectroscopy, electron paramagnetic resonance, and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV-vis range. Furthermore, it was found that γ-radiation "hardness" is higher in Er3+-doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction. PMID:27661569

11. Relationship between sol-gel conditions and enzyme stability: a case study with β-galactosidase/silica biocatalyst for whey hydrolysis.

PubMed

Escobar, Sindy; Bernal, Claudia; Mesa, Monica

2015-01-01

The sol-gel process has been very useful for preparing active and stable biocatalysts, with the possibility of being reused. Especially those based on silica are well known. However, the study of the enzyme behavior during this process is not well understood until now and more, if the surfactant is involved in the synthesis mixture. This work is devoted to the encapsulation of β-galactosidase from Bacillus circulans in silica by sol-gel process, assisted by non-ionic Triton X-100 surfactant. The correlation between enzyme activity results for the β-galactosidase in three different environments (soluble in buffered aqueous reference solution, in the silica sol, and entrapment on the silica matrix) explains the enzyme behavior under stress conditions offered by the silica sol composition and gelation conditions. A stable β-galactosidase/silica biocatalyst is obtained using sodium silicate, which is a cheap source of silica, in the presence of non-ionic Triton X-100, which avoids the enzyme deactivation, even at 40 °C. The obtained biocatalyst is used in the whey hydrolysis for obtaining high value products from this waste. The preservation of the enzyme stability, which is one of the most important challenges on the enzyme immobilization through the silica sol-gel, is achieved in this study.

12. Relationship between sol-gel conditions and enzyme stability: a case study with β-galactosidase/silica biocatalyst for whey hydrolysis.

PubMed

Escobar, Sindy; Bernal, Claudia; Mesa, Monica

2015-01-01

The sol-gel process has been very useful for preparing active and stable biocatalysts, with the possibility of being reused. Especially those based on silica are well known. However, the study of the enzyme behavior during this process is not well understood until now and more, if the surfactant is involved in the synthesis mixture. This work is devoted to the encapsulation of β-galactosidase from Bacillus circulans in silica by sol-gel process, assisted by non-ionic Triton X-100 surfactant. The correlation between enzyme activity results for the β-galactosidase in three different environments (soluble in buffered aqueous reference solution, in the silica sol, and entrapment on the silica matrix) explains the enzyme behavior under stress conditions offered by the silica sol composition and gelation conditions. A stable β-galactosidase/silica biocatalyst is obtained using sodium silicate, which is a cheap source of silica, in the presence of non-ionic Triton X-100, which avoids the enzyme deactivation, even at 40 °C. The obtained biocatalyst is used in the whey hydrolysis for obtaining high value products from this waste. The preservation of the enzyme stability, which is one of the most important challenges on the enzyme immobilization through the silica sol-gel, is achieved in this study. PMID:26313518

13. Evaluation of an ambient air sampling system for tritium (as tritiated water vapor) using silica gel adsorbent columns

SciTech Connect

Patton, G.W.; Cooper, A.T.; Tinker, M.R.

1995-08-01

Ambient air samples for tritium analysis (as the tritiated water vapor [HTO] content of atmospheric moisture) are collected for the Hanford Site Surface Environmental Surveillance Project (SESP) using the solid adsorbent silica gel. The silica gel has a moisture sensitive indicator which allows for visual observation of moisture movement through a column. Despite using an established method, some silica gel columns showed a complete change in the color indicator for summertime samples suggesting that breakthrough had occurred; thus a series of tests was conducted on the sampling system in an environmental chamber. The purpose of this study was to determine the maximum practical sampling volume and overall collection efficiency for water vapor collected on silica gel columns. Another purpose was to demonstrate the use of an impinger-based system to load water vapor onto silica gel columns to provide realistic analytical spikes and blanks for the Hanford Site SESP. Breakthrough volumes (V{sub b}) were measured and the chromatographic efficiency (expressed as the number of theoretical plates [N]) was calculated for a range of environmental conditions. Tests involved visual observations of the change in the silica gels color indicator as a moist air stream was drawn through the column, measurement of the amount of a tritium tracer retained and then recovered from the silica gel, and gravimetric analysis for silica gel columns exposed in the environmental chamber.

14. Heat of immersion of silica gel in normal alkanes and alcohols

SciTech Connect

Dubinin, M.M.; Isirikyan, A.A.; Nikolaev, K.M.; Polyakov, N.S.; Tatarinova, L.I.

1986-12-20

In order to differentiate phenomena on a smooth surface from those related to surface curvature, they must, strictly speaking, study these phenomena separately on completely nonporous and porous adsorbents of the same chemical nature. However, it is virtually impossible to obtain a completely nonporous adsorbent with a sufficiently developed surface. Thus, a permissible compromise for solving this problem lies in the selection of a porous adsorbent such that, on one hand, the effect of surface curvature is excluded due to wide pores and, on the other hand, reliable quantitative data for the properties of this surface with virtually zero curvature are obtained due to the development of the surface. For these purposes, they used a modification of their previous method and obtained silica gel (SG) with a developed surface s = 218 m/sup 2//g and broad pores D/sub max/ = 20 nm. They found that mesoporous silica gel with 20 nm pore diameter may be taken as a practical model of nonporous amorphous silica, according to the liquid immersion heats. The heats of wetting of the hydrated amorphous silica surface by normal aliphatic alcohols and hydrocarbons are independent of the number of carbon atoms in the molecules and are 220 and 65 mJ/m/sup 2/, respectively. The interphase (liquid-solid) surface layer or normal alcohol molecules on silica gel is a Langmuir palisade with the OH alcohol groups directed toward the silica surface.

15. Porous Silica Sol-Gel Glasses Containing Reactive V2O5 Groups

NASA Technical Reports Server (NTRS)

Stiegman, Albert E.

1995-01-01

Porous silica sol-gel glasses into which reactive vanadium oxide functional groups incorporated exhibit number of unique characteristics. Because they bind molecules of some species both reversibly and selectively, useful as chemical sensors or indicators or as scrubbers to remove toxic or hazardous contaminants. Materials also oxidize methane gas photochemically: suggests they're useful as catalysts for conversion of methane to alcohol and for oxidation of hydrocarbons in general. By incorporating various amounts of other metals into silica sol-gel glasses, possible to synthesize new materials with broad range of new characteristics.

16. Shape dependence of nonlinear optical behaviors of nanostructured silver and their silica gel glass composites

SciTech Connect

Zheng Chan; Du Yuhong; Feng Miao; Zhan Hongbing

2008-10-06

Nanostructured Ag in shapes of nanoplate, nanowire, and nanoparticle, as well as their silica gel glass composites have been prepared and characterized. Nonlinear optical (NLO) properties were measured at 532 and 1064 nm using open aperture z-scan technique and studied from the view of shape effect. NLO behaviors of the nanostructured Ag are found to be shape dependent in suspensions at both the investigated wavelengths, although they originate differently. Comparing to the mother suspensions, the Ag/silica gel glass nanocomposites present rather dissimilar NLO behaviors, which is quite interesting for further studies.

17. Study of Lanthanide Complexes with BTFA in Silica Gels by Photoacoustic Spectroscopy

Liu, R. Y.; Zhang, H. X.; Yang, Y. T.; Zhang, S. Y.; Liu, X. J.

2016-06-01

In this work, lanthanide β -diketonate complexes Ln(btfa){}3 \\cdot 2H2O (Ln^{3+}: Eu^{3+}, Sm^{3+ }, and Tb^{3+}; btfa: 4,4,4-trifluoro-l-phenyl-1,3-butanedione) were incorporated into silica gels by a sol-gel method. Photoacoustic (PA) spectra of these complex-doped silica samples were measured and studied. The PA intensity of the β -diketonate ligand is nearly the same for lanthanide complexes in wet gels. After heat treatment at 150°C, however, the PA intensity of the ligand increases for Eu^{3+}, Sm^{3+}, and Tb^{3+} complexes in silica gels, respectively. Different PA intensities of the samples are interpreted by comparison with their luminescence spectra. The luminescence result is consistent with the PA spectra. The result indicates that lanthanide β -diketonate complexes cannot be formed in silica gels without a suitable heat treatment. Moreover, the relaxation process model is proposed based on the PA and luminescence results.

18. Controlling the porosity of microporous silica by sol-gel processing using an organic template approach

SciTech Connect

Lu, Y.; Cao, G.Z.; Kale, R.P.; Delattre, L.; Lopez, G.P.; Brinker, C.J. |

1996-12-31

The authors use an organic template approach to prepare microporous silica with controlled pore size and narrow pore size distributions. This was accomplished by fabricating relatively dense hybrid silica matrices incorporating organic template ligands by sol-gel synthesis and then removing the organic ligands to create a microporous silica network. Comparison of computer simulation results and experimental data indicated that using this fugitive template approach, pore volume can be controlled by the amount of organic template added to the system, and pore size can be controlled by the size of the organic ligands.

19. Extraction of antibiotic zwittermicin A from Bacillus thuringiensis by macroporous resin and silica gel column chromatography.

PubMed

Hao, Zaibin; Yan, Li; Liu, Jianguo; Song, Fuping; Zhang, Jie; Li, Xia

2015-01-01

To establish a production process capable of providing refined zwittermicin A (ZwA) on a large scale, the macroporous resin and silica gel column chromatography were used to separate and purify the antibiotic ZwA from the fermentation broth of Bacillus thuringiensis HD-1. The result of high-performance liquid chromatography-mass spectrometry after purification suggests that the samples of ZwA were of high purity, 89%, and the average yield was 20 mg L(-1). Erwinia herbicola LS005, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis were used to assess the toxicity of ZwA. The antibiotic had strong antibacterial activity against E. herbicola LS005 and a color reaction with ninhydrin. PMID:25099664

20. Two-dimensional (2D) infrared (IR) correlation spectroscopy for dynamic absorption behavior of oleic acid (OA) onto silica gel

Genkawa, Takuma; Kanematsu, Wataru; Shinzawa, Hideyuki

2014-07-01

Dynamic absorption behavior of oleic acid (OA) onto silica gel was probed by infrared (IR) spectroscopy. Once OA is injected into silica gel placed on a horizontal attenuated total reflectance prism, the silica gel starts to absorb the OA molecules due to the molecular-level interaction based on hydrogen bonding between the COOH of OA and the OH of silica gel. The substantial level of variation of spectral feature is readily observed during the absorption of OA onto silica gel. 2D correlation analysis of the time-dependent IR spectra reveals fine details of absorption dynamics of OA molecules depending on the molecular structure. The predominant absorption of the monomers occurs at the onset of the absorption, and it is then quickly followed by the decrease in the dimers. In other words, the dissociation of the liquid crystals occurs via the disuniting of the tightly packed OA dimers.

1. Thin-film silica sol-gels doped with ion responsive fluorescent lipid bilayers

SciTech Connect

Sasaki, D.Y.; Shea, L.E.; Sinclair, M.B.

1999-01-12

A metal ion sensitive, fluorescent lipid-b i layer material (5oA PSIDA/DSPC) was successfully immobilized in a silica matrix using a tetramethoxysilane (TMOS) sol-gel procedure. The sol-gel immobilization method was quantitative in the entrapment of seif-assembled Iipid-bilayers and yielded thin films for facile configuration to optical fiber piatforms. The silica matrix was compatible with the solvent sensitive lipid bilayers and provided physical stabilization as well as biological protection. Immobilization in the silica sol-gel produced an added benefit of improving the bilayer's metal ion sensitivity by up to two orders of magnitude. This enhanced performance was attributed to a preconcentrator effect from the anionic surface of the silica matrix. Thin gels (193 micron thickness) were coupled to a bifurcated fiber optic bundle to produce a metal ion sensor probe. Response times of 10 - 15 minutes to 0.1 M CUCIZ were realized with complete regeneration of the sensor using an ethylenediarninetetraacetic acid (EDTA) solution.

2. Investigation of the processes of impregnation and drying of granular silica gel

Fedorov, A. V.; Zhilin, A. A.; Korobeinikov, Yu. G.

2011-09-01

The process of capillary impregnation and drying of silica gel grains in the acousto-convective drier of the ITPM of the Siberian branch of the Russian Academy of Sciences has been investigated experimentally. Two methods for humidifying a material with developed surface and internal structures have been considered. A comparison of these methods has been made and the influence of the impregnation rate on the geometry of silica gel grains has been analyzed. Silica gel grains were dried by three methods: microwave, convective, and acousto-convective. The dependence of the drying rate and the quality of the dried material on the chosen drying method has been shown. To describe the moisture extraction, we propose a mathematical model based on a two-dimensional diffusion equation written in the cylindrical system of coordinates. The moisture distribution in cylindrical samples consisting of silica gel grains has been obtained numerically for various values of the initial moisture content with the use of certain diffusion coefficients and the dependence of the moisture transfer coefficient on the frequency of acousto-convective action.

3. Synthesis and Evaluation of Molecularly Imprinted Silica Gel for 2-Hydroxybenzoic Acid in Aqueous Solution

PubMed Central

2013-01-01

A molecularly imprinted silica gel sorbent for selective removal of 2-Hydroxybenzoic acid (2-HA) was prepared by a surface imprinting technique with a sol-gel process. The 2-HA molecularly imprinted silica gel (2-HA-MISG) sorbent was evaluated by various parameters, including the influence of pH, static, kinetic adsorption and selectivity experiments. The optimum adsorption capacity to the 2-HA appeared to be around pH 2 by the polymer. Morevoer, the imprinted sorbent displayed fast uptake kinetics, obtained within 20 min. The adsorption capacity of the 2-HA-MISG (76.2 mg g−1) was higher than that of the non-imprinted silica gel (NISG) (42.58 mg g−1). This indicates that the 2-HA-MISG offers a higher affinity for 2-HA than the NISG. The polymer displays good selectivity and exhibits good reusability. Experimental results show the potential of molecularly imprinted silica sorbent for selective removal of 2-HA. PMID:23493059

4. Studies of the separation performance of silanized silica gel for simulated distillation.

PubMed

Boczkaj, Grzegorz; Momotko, Malwina; Przyjazny, Andrzej; Kamiński, Marian

2016-02-01

We present the results of investigations of the chromatographic (sorptive) properties of silanized silica gel as a stationary phase for gas chromatography used for simulated distillation. Commercially available silanized sorbent (particle diameter range 63-200 μm, average pore size 60 Å) was sieved to obtain the 80-100 mesh fraction (180-150 μm). The obtained results revealed that silanized silica gel allows the complete separation of a mixture of n- and iso-alkanes in the C1 -C7 range. Such a separation is achieved with a temperature program starting with an initial temperature of 50˚C, which is advantageous because the gas chromatograph oven does not have to be cooled below room temperature. The use of temperature programming with a final temperature of 300˚C ensures separation and elution of all mixture components from C1 to n-C28 in one run. This study confirms the applicability of silanized silica gel as a stationary phase for the investigation of distillation temperature distribution of gasoline and diesel fuel based on the simulated distillation procedure according to ASTM D2887. The deviations of individual points of distillation curve obtained using ASTM D2887 and columns packed with silanized silica gel were within the reproducibility range of the standard procedure. PMID:26634792

5. EFFECTS OF TEMPERATURE ON TRICHLOROETHYLENE DESORPTION FROM SILICA GEL AND NATURAL SEDIMENTS. 1. ISOTHERMS. (R822626)

EPA Science Inventory

Aqueous phase isotherms were calculated from vapor phase desorption isotherms
measured at 15, 30, and 60 C for
trichloroethylene on a silica gel, an aquifer sediment, a soil, a sand fraction,
and a clay and silt fraction, all at...

6. EFFECTS OF TEMPERATURE ON TRICHLOROETHYLENE DESORPTION FROM SILICA GEL AND NATURAL SEDIMENTS. 2. KINETICS. (R822626)

EPA Science Inventory

Isothermal desorption rates were measured at 15, 30, and 60 src="/ncer/pubs/images/deg.gif">C for trichloroethylene (TCE) on a silica gel,
an aquifer sediment, a soil, a sand fraction, and a clay and silt fraction, all
at 100% relative humidity. Temperature-st...

7. Chemically-Tailored Surfaces of Silica Gel and Alumina Examined Using Color

ERIC Educational Resources Information Center

Taralp, Alpay; Buyukbayram, Gulen; Armagan, Onsel; Yalcin, Ender

2004-01-01

Color is used for studying the chemically-tailored surfaces of silica gel and alumina. When this technique of using color was applied by the students, they were able to grasp the principles of surface engineering and acquire an appreciation of its merits and at the same time they were able to learn the fundamentals of aldehyde chemistry,…

8. A polyvinyl alcohol-coated silica gel stationary phase for hydrophilic interaction chromatography.

PubMed

Ji, Shunli; Zheng, Yang; Zhang, Feifang; Liang, Xinmiao; Yang, Bingcheng

2015-09-21

Multiple layers of polyvinyl alcohol (PVA) coating are generated onto silica gel by thermal immobilization to form a stationary phase applied for hydrophilic interaction liquid chromatography (HILIC). It offers an easy way to manipulate the thickness of PVA coating and the obtained stationary phase demonstrated high efficiency and high chemical stability. PMID:26280030

9. Studies of the separation performance of silanized silica gel for simulated distillation.

PubMed

Boczkaj, Grzegorz; Momotko, Malwina; Przyjazny, Andrzej; Kamiński, Marian

2016-02-01

We present the results of investigations of the chromatographic (sorptive) properties of silanized silica gel as a stationary phase for gas chromatography used for simulated distillation. Commercially available silanized sorbent (particle diameter range 63-200 μm, average pore size 60 Å) was sieved to obtain the 80-100 mesh fraction (180-150 μm). The obtained results revealed that silanized silica gel allows the complete separation of a mixture of n- and iso-alkanes in the C1 -C7 range. Such a separation is achieved with a temperature program starting with an initial temperature of 50˚C, which is advantageous because the gas chromatograph oven does not have to be cooled below room temperature. The use of temperature programming with a final temperature of 300˚C ensures separation and elution of all mixture components from C1 to n-C28 in one run. This study confirms the applicability of silanized silica gel as a stationary phase for the investigation of distillation temperature distribution of gasoline and diesel fuel based on the simulated distillation procedure according to ASTM D2887. The deviations of individual points of distillation curve obtained using ASTM D2887 and columns packed with silanized silica gel were within the reproducibility range of the standard procedure.

10. BINARY DESORPTION ISOTHERMS OF TCE AND PCE FROM SILICA GEL AND NATURAL SOLIDS. (R822626)

EPA Science Inventory

Binary solute desorption isotherms of trichloroethylene (TCE) and tetrachloroethylene (PCE) at 100% relative humidity from silica gel and two well-characterized natural solids were investigated. Results indicated that the ideal adsorbed solution theory (IAST) was able to descr...

11. The evaluation of physical properties and in vitro cell behavior of PHB/PCL/sol-gel derived silica hybrid scaffolds and PHB/PCL/fumed silica composite scaffolds.

PubMed

Ding, Yaping; Yao, Qingqing; Li, Wei; Schubert, Dirk W; Boccaccini, Aldo R; Roether, Judith A

2015-12-01

PHB/PCL/sol-gel derived silica hybrid scaffolds (P5S1S) and PHB/PCL/fumed silica composite scaffolds (P5S1N) with a 5:1 organic/inorganic ratio were fabricated through a combination of electrospinning and sol-gel methods and dispersion electrospinning, respectively. In contrast to the silica nanoparticle aggregates appearing on the fiber surface of P5S1N, smooth and uniform fibers were obtained for P5S1S. The fiber diameter distribution, tensile strength, thermal gravimetric analysis (TGA), and cellular behavior of both types of scaffolds were characterized and studied. The tensile strength results and TGA indicated that the interfacial interaction between the organic and the inorganic phase was enhanced in P5S1S over the nanocomposite scaffolds, and cells exhibited significantly higher alkaline phosphate activity (ALP) for P5S1S, which makes P5S1S hybrid scaffolds candidate materials for bone tissue engineering applications. PMID:26364089

12. Wet powder processing of sol-gel derived mesoporous silica-hydroxyapatite hybrid powders.

PubMed

Andersson, Jenny; Johannessen, Espen; Areva, Sami; Järn, Mikael; Lindén, Mika

2006-08-01

This paper describes a method by which a porous silica coating layer can be obtained on different apatite particles through a simple sol-gel synthesis route. Sol-gel derived powders of hydroxyapatite (HAP) and beta tricalciumphosphate (beta-TCP) were coated with a mesoporous silica using C16TAB (hexadecyltrimethylammonium bromide) as a template in order to induce mesophase formation. Further calcination of the material removes the template from the mesophase and leaves a highly ordered hexagonal arranged mesoporous silica structure with a core of HAP/beta-TCP. The phase purity of the SiO2/apatite composites has been thoroughly investigated by the means of FT-IR, XRD, and solid state 31P MAS NMR. The phase purity of these materials is shown to be dependent on the solubility properties of the used apatites. The hybrid materials are suitable as a multifunctional biomaterial where osteoconductive properties can be combined with drug delivery.

13. Moisture sensor based on evanescent wave light scattering by porous sol-gel silica coating

DOEpatents

Tao, Shiquan; Singh, Jagdish P.; Winstead, Christopher B.

2006-05-02

An optical fiber moisture sensor that can be used to sense moisture present in gas phase in a wide range of concentrations is provided, as well techniques for making the same. The present invention includes a method that utilizes the light scattering phenomenon which occurs in a porous sol-gel silica by coating an optical fiber core with such silica. Thus, a porous sol-gel silica polymer coated on an optical fiber core forms the transducer of an optical fiber moisture sensor according to an embodiment. The resulting optical fiber sensor of the present invention can be used in various applications, including to sense moisture content in indoor/outdoor air, soil, concrete, and low/high temperature gas streams.

14. Silica gel as a particulate carrier of poorly water-soluble substances in aquatic toxicity testing.

PubMed

Breitholtz, Magnus; Ricklund, Niklas; Bengtsson, Bengt-Erik; Persson, N Johan

2007-05-31

Aquatic toxicity tests were originally developed for water-soluble substances. However, many substances are hydrophobic and thus poorly water-soluble, resulting in at least two major implications. Firstly, toxicity may not be reached within the range of water solubility of the tested compound(s), which may result in the formation of solids or droplets of the tested substance and consequently an uneven exposure. Secondly, because of multi-phase distribution of the tested substance it may be complicated to keep exposure concentrations constant. To overcome such problems, we have introduced silica gel as a particulate carrier in a toxicity test with the benthic copepod Nitocra spinipes. The main objective of the current study was to evaluate whether a controlled exposure could be achieved with the help of silica gel for testing single poorly water-soluble substances. A secondary objective was to evaluate whether an equilibrium mass balance model could predict internal concentrations that were consistent with the toxicity data and measured internal concentrations of two model hydrophobic substances, i.e., the polybrominated diphenyl ethers BDE-47 and BDE-99. Larval N. spinipes were exposed for 6 days to BDE-47 and BDE-99, respectively, in the silica gel test system and, for comparative reasons, in a similar and more traditional semi-static water test system. Via single initial amounts of the model substances administered on the silica gel, effects on both larval development and mortality resulted in higher and more concentration-related toxicity than in the water test system. We conclude that the silica gel test system enables a more controlled exposure of poorly water-soluble substances than the traditional water test system since the concentration-response relationship becomes distinct and there is no carrier solvent present during testing. Also, the single amount of added substance given in the silica gel test system limits the artefacts (e.g., increased chemical

15. Suspensions, gels, and composite electrolytes based on fumed silica: Rheology and microstructure

Raghavan, Srinivasa Ramamurthy

The goals of this thesis are to understand and predict the microstructure at-rest and under shear for a novel class of colloidal dispersions formed by dispersing fumed silica particles in polymeric liquids. Microstructures are probed using rheology, and are correlated with the prevailing colloidal interactions. The interactions of hydrophilic fumed silica (having Si-OH surface groups) are shown to be controlled by the H-bonding ability of the liquid. In weakly H-bonding liquids, the silica forms gels (networks) by inter-particle H-bonding. In contrast, strongly H-bonding liquids form a solvation layer on each silica unit, thus resulting in a kinetically-stabilized, low-viscosity suspension. The interactions of hydrophobic silicas having n-alkyl surface chains are governed by the compatibility between surface chains and solvent. In non-polar alkanes, these silicas show pronounced dependence on temperature and alkane chain length. In polar media, the silicas form gels---here, the mismatch in chemical nature between chains and solvent causes the surfaces to become "sticky". A unique correlation is obtained between the elastic modulus (G') of the fumed silica network and bulk parameters characterizing the above mismatch. Fumed silica gels undergo complex microstructural changes when subjected to shear. Following moderate extents of oscillatory shear, the microstructure is irreversibly degraded to a significant extent, whereas the microstructure reverts to its near-equilibrium state following large extents of shear. These anomalous results are postulated to arise due to shear-induced changes in the floc structure. Fumed silica suspensions exhibit shear-thickening under steady shear and strain-thickening under oscillatory shear. For the first time, an equivalence between the two phenomena is shown, on the basis of a "modified Cox-Merz rule". Both shear and strain-thickening are postulated to occur due to the formation of temporary clusters under high deformations

16. Self-Pumping Active Gel

Wu, Kun-Ta; Hishamunda, Jean Bernard; Fraden, Seth; Dogic, Zvonimir

Isotropic active gels are the network which is consist of cross-linked building blocks and the structure of which changes randomly and isotropically with time. Dogic et. al. show that pairs of anti-parallel microtubules form extensile bundles, which merge, extend, and buckle. In an unconfined system, the dynamics of these bundles causes spontaneous turbulent-like flow driven by motion of microscopic molecular motors. We found that confining these active gels in a millimeter sized toroids causes a transition into a new dynamical state characterized by circulation currents persisting for hours until ATP is depleted. We show how toroid dimensions impact the properties of self-organized circular currents, how directions of circulation can be designed by engineering ratchet-shaped boundaries, and how circulations of connected toroids can be either synchronized or antisynchronized. Furthermore, we demonstrate that the flow rate in the circulation is independent of curvature and length of flow path. The flow rate persists for centimeters without decay, disregarding conventional pipe flow resistance. Such findings pave the path to self-pumping pipe transport and performing physical work with biological system.

17. Shock compression of silica gel as the analog experiments of hydrous comet and meteorite

Arasuna, Akane; Okuno, Masayuki; Mizukami, Tomoyuki; Chen, Liliang; Mashimo, Tsutomu; Arai, Shoji; Okudera, Hiroki

2013-04-01

The studies for structural changes of hydrous silica materials by shock compression are important to obtain the information for compression behaviors of comet and meteorite made of silicate material, ice and hydroxyl on the impact event. In this study, TEOS-derived synthetic silica gels for the analog material of hydrous amorphous silica minerals were compressed under shock pressures of 11, 13, 17, 21, 27, and 31 GPa using a single-stage propellant gun. All recovered samples have been investigated by XRD measurements, Raman and IR spectroscopies, in order to elucidate the shock compression behavior of silica gel. Pressure variation of first sharp diffraction peak (FSDP) positions of samples was estimated from measured XRD patterns. FSDP position of as-prepared sample was smaller than silica glass. It indicates that medium range structure of silica gel, i.e. ring structure of SiO4 tetrahedra, is smaller than that of silica glass. FSDP positions showed negative shift with increasing pressure and approached that of silica glass at 31 GPa. It suggests that medium range structure of silica gel approached to silica glass by shock compression. Raman spectrum of as-prepared sample showed an intense D1 band at 480 cm-1 and a broad band at around 450 cm-1. The former is attributed to the oxygen-breathing mode of the four-membered ring of SiO4 tetrahedra and the latter to the symmetrical Si-O-Si stretching mode. The presence of strong D1 band of as-prepared sample indicates that the sample might contain considerable amount of four-membered rings in the structure. Shocked sample showed that the broad band around 450 cm-1 became prominent above 21 GPa, whereas D1 band became much less intense. These indicate that medium range structure of shocked sample above 21 GPa approached to that of silica glass. Furthermore, IR spectrum of shocked silica gel at 21 GPa indicates that the center part of sample showed development of vitrification as compared with the extremity part of the

18. SILICA GEL BEHAVIOR UNDER DIFFERENT EGS CHEMICAL AND THERMAL CONDITIONS: AN EXPERIMENTAL STUDY

SciTech Connect

Hunt, J D; Ezzedine, S M; Bourcier, W; Roberts, S

2012-01-19

Fractures and fracture networks are the principal pathways for migration of water and contaminants in groundwater systems, fluids in enhanced geothermal systems (EGS), oil and gas in petroleum reservoirs, carbon dioxide leakage from geological carbon sequestration, and radioactive and toxic industrial wastes from underground storage repositories. When dealing with EGS fracture networks, there are several major issues to consider, e.g., the minimization of hydraulic short circuits and losses of injected geothermal fluid to the surrounding formation, which in turn maximize heat extraction and economic production. Gel deployments to direct and control fluid flow have been extensively and successfully used in the oil industry for enhanced oil recovery. However, to the best of our knowledge, gels have not been applied to EGS to enhance heat extraction. In-situ gelling systems can either be organic or inorganic. Organic polymer gels are generally not thermostable to the typical temperatures of EGS systems. Inorganic gels, such as colloidal silica gels, however, may be ideal blocking agents for EGS systems if suitable gelation times can be achieved. In the current study, we explore colloidal silica gelation times and rheology as a function of SiO{sub 2} concentration, pH, salt concentration, and temperature, with preliminary results in the two-phase field above 100 C. Results at 25 C show that it may be possible to choose formulations that will gel in a reasonable and predictable amount of time at the temperatures of EGS systems.

19. NiO-silica based nanostructured materials obtained by microemulsion assisted sol-gel procedure

SciTech Connect

Mihaly, M.; Comanescu, A.F.; Rogozea, A.E.; Vasile, E.; Meghea, A.

2011-10-15

Graphical abstract: TEM micrograph of NiO/SiO{sub 2} nanoparticles. Highlights: {yields} Microemulsion assisted sol-gel procedure for NiO silica nanomaterials synthesis. {yields} Controlling the size and shape of nanoparticles and avoiding their aggregation. {yields} Narrow band-gap semiconductors (energies <3 eV) absorbing VIS or near-UV light biologically and chemically inert semiconductors entrapping/coating in silica network. {yields} Low cost as the microemulsion is firstly used in water metallic cation extraction. -- Abstract: NiO-silica based materials have been synthesized by microemulsion assisted sol-gel procedure. The versatility of these soft nanotechnology techniques has been exploited in order to obtain different types of nanostructures, such as NiO nanoparticles, NiO silica coated nanoparticles and NiO embedded in silica matrix. These materials have been characterized by adequate structural and morphology techniques: DLS, HR-TEM/SAED, BET, AFM. Optical and semiconducting properties (band-gap values) of the synthesized materials have been quantified by means of VIS-NIR diffuse reflectance spectra, thus demonstrating their applicative potential in various electron transfer phenomena such as photocatalysis, electrochromic thin films, solid oxide fuel cells.

20. Evolution of microstructure in mixed niobia-hybrid silica thin films from sol-gel precursors.

PubMed

Besselink, Rogier; Stawski, Tomasz M; Castricum, Hessel L; ten Elshof, Johan E

2013-08-15

The evolution of structure in sol-gel derived mixed bridged silsesquioxane-niobium alkoxide sols and drying thin films was monitored in situ by small-angle X-ray scattering. Since sol-gel condensation of metal alkoxides proceeds much faster than that of silicon alkoxides, the incorporation of d-block metal dopants into silica typically leads to formation of densely packed nano-sized metal oxide clusters that we refer as metal oxide building blocks in a silica-based matrix. SAXS was used to study the process of niobia building block formation while drying the sol as a thin film at 40-80°C. The SAXS curves of mixed niobia-hybrid silica sols were dominated by the electron density contrast between sol particles and surrounding solvent. As the solvent evaporated and the sol particles approached each other, a correlation peak emerged. Since TEM microscopy revealed the absence of mesopores, the correlation peak was caused by a heterogeneous system of electron-rich regions and electron poor regions. The regions were assigned to small clusters that are rich in niobium and which are dispersed in a matrix that mainly consisted of hybrid silica. The correlation peak was associated with the typical distances between the electron dense clusters and corresponded with distances in real space of 1-3 nm. A relationship between the prehydrolysis time of the silica precursor and the size of the niobia building blocks was observed. When 1,2-bis(triethoxysilyl)ethane was first hydrolyzed for 30 min before adding niobium penta-ethoxide, the niobia building blocks reached a radius of 0.4 nm. Simultaneous hydrolysis of the two precursors resulted in somewhat larger average building block radii of 0.5-0.6 nm. This study shows that acid-catalyzed sol-gel polymerization of mixed hybrid silica niobium alkoxides can be rationalized and optimized by monitoring the structural evolution using time-resolved SAXS.

1. Ternary Phase-Separation Investigation of Sol-Gel Derived Silica from Ethyl Silicate 40

PubMed Central

Wang, Shengnan; Wang, David K.; Smart, Simon; Diniz da Costa, João C.

2015-01-01

A ternary phase-separation investigation of the ethyl silicate 40 (ES40) sol-gel process was conducted using ethanol and water as the solvent and hydrolysing agent, respectively. This oligomeric silica precursor underwent various degrees of phase separation behaviour in solution during the sol-gel reactions as a function of temperature and H2O/Si ratios. The solution composition within the immiscible region of the ES40 phase-separated system shows that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. A mesoporous structure was obtained at low temperature due to weak drying forces from slow solvent evaporation on one hand and formation of unreacted ES40 cages in the other, which reduced network shrinkage and produced larger pores. This was attributed to the concentration of the reactive sites around the phase-separated interface, which enhanced the condensation and crosslinking. Contrary to dense silica structures obtained from sol-gel reactions in the miscible region, higher microporosity was produced via a phase-separated sol-gel system by using high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, which coupled with stiffening of the network, made it more resistant to compression and densification. PMID:26411484

2. Two substrate-confined sol-gel coassembled ordered macroporous silica structures with an open surface.

PubMed

Guo, Wenhua; Wang, Ming; Xia, Wei; Dai, Lihua

2013-05-21

A sol-gel cooperative assembly method was demonstrated for the fabrication of inverse opal films with an open surface. In this method, a sol-gel silicate precursor was cooperatively assembled into the interstitial spaces of microspheres at the same time when polystyrene templates formed in between two desired substrates. Silica inverse opals with a three-dimensional ordered macroporous (3DOM) structure were obtained after selective removing the colloidal templates by calcination. The open surfaces with a high degree of interconnected porosity and extremely uniform pore size were characterized by scanning electron microscope (SEM). Optical transmission spectra reveals the existence of considerable deep band gaps of up to 70% and steep band edges of up to 6%/nm in the [111] directions of the 3DOM silica samples. A little shrinkage confirmed by transmission spectra is not larger than 3%, in consistent with the results measured by SEM, which revealing the sufficient and compact infiltration into the interstitial spaces by our confined sol-gel coassembly method. With different incidence angles, the positions of pseudogaps can be easily tuned in the wide range from 720 nm to 887 nm, agreed well with the calculated values by the Bragg law. All the results prove that the sol-gel coassembly method with two substrates confinement is a simple, low cost, convenient and versatile method for the fabrication of silica inverse opals without overlayers in large domains. PMID:23614663

3. Ternary Phase-Separation Investigation of Sol-Gel Derived Silica from Ethyl Silicate 40

Wang, Shengnan; Wang, David K.; Smart, Simon; Diniz da Costa, João C.

2015-09-01

A ternary phase-separation investigation of the ethyl silicate 40 (ES40) sol-gel process was conducted using ethanol and water as the solvent and hydrolysing agent, respectively. This oligomeric silica precursor underwent various degrees of phase separation behaviour in solution during the sol-gel reactions as a function of temperature and H2O/Si ratios. The solution composition within the immiscible region of the ES40 phase-separated system shows that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. A mesoporous structure was obtained at low temperature due to weak drying forces from slow solvent evaporation on one hand and formation of unreacted ES40 cages in the other, which reduced network shrinkage and produced larger pores. This was attributed to the concentration of the reactive sites around the phase-separated interface, which enhanced the condensation and crosslinking. Contrary to dense silica structures obtained from sol-gel reactions in the miscible region, higher microporosity was produced via a phase-separated sol-gel system by using high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, which coupled with stiffening of the network, made it more resistant to compression and densification.

4. Ternary Phase-Separation Investigation of Sol-Gel Derived Silica from Ethyl Silicate 40.

PubMed

Wang, Shengnan; Wang, David K; Smart, Simon; da Costa, João C Diniz

2015-01-01

A ternary phase-separation investigation of the ethyl silicate 40 (ES40) sol-gel process was conducted using ethanol and water as the solvent and hydrolysing agent, respectively. This oligomeric silica precursor underwent various degrees of phase separation behaviour in solution during the sol-gel reactions as a function of temperature and H2O/Si ratios. The solution composition within the immiscible region of the ES40 phase-separated system shows that the hydrolysis and condensation reactions decreased with decreasing reaction temperature. A mesoporous structure was obtained at low temperature due to weak drying forces from slow solvent evaporation on one hand and formation of unreacted ES40 cages in the other, which reduced network shrinkage and produced larger pores. This was attributed to the concentration of the reactive sites around the phase-separated interface, which enhanced the condensation and crosslinking. Contrary to dense silica structures obtained from sol-gel reactions in the miscible region, higher microporosity was produced via a phase-separated sol-gel system by using high H2O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, which coupled with stiffening of the network, made it more resistant to compression and densification. PMID:26411484

5. Catalyst-free synthesis of sodium amide nanoparticles encapsulated in silica gel

Ogilvie, Alexander D.; Makepeace, Joshua W.; Hore, Katie; Ramirez-Cuesta, Anibal J.; Apperley, David C.; Mitchels, John M.; Edwards, Peter P.; Sartbaeva, Asel

2013-12-01

Crystalline sodium amide nanoparticles encapsulated in an amorphous silica framework were formed by ammoniation of a precursor material, silica gel loaded with metallic sodium, under mild conditions and without catalysis. This ammoniation was performed in situ on TOSCA beamline at ISIS, RAL, using anhydrous gaseous ammonia. The resulting material exhibits no pyrophoricity and much reduced air- and moisture-sensitivity compared to the bulk amide. The nanoparticles formed will offer a greatly increased surface area for chemical reactions where amide is currently used as an important ingredient for industrial applications. We anticipate that this method of sodium amide production will have a diversity of applications.

6. Probing the interplay between factors determining reaction rates on silica gel using termolecular systems.

PubMed

Kirkpatrick, Iain; Worrall, David R; Williams, Siân L; Buck, Craig J T; Meseguer, Rafael G

2012-10-01

In this study we have compared energy and electron transfer reactions in termolecular systems using a nanosecond diffuse reflectance laser flash photolysis technique. We have previously investigated these processes on silica gel surfaces for bimolecular systems and electron transfer in termolecular systems. The latter systems involved electron transfer between three arene molecules with azulene acting as a molecular shuttle. In this study we present an alternative electron transfer system using trans β-carotene as an electron donor in order to effectively immobilise all species except the shuttle, providing the first unambiguous evidence for radical ion mobility. In the energy transfer system we use naphthalene, a structural isomer of azulene, as the shuttle, facilitating energy transfer from a selectively excited benzophenone sensitiser to 9-cyanoanthracene. Bimolecular rate constants for all of these processes have been measured and new insights into the factors determining the rates of these reactions on silica gel have been obtained.

7. Tailoring the oxidation state of cobalt through halide functionality in sol-gel silica

PubMed Central

Olguin, Gianni; Yacou, Christelle; Smart, Simon; Diniz da Costa, João C.

2013-01-01

The functionality or oxidation state of cobalt within a silica matrix can be tailored through the use of cationic surfactants and their halide counter ions during the sol-gel synthesis. Simply by adding surfactant we could significantly increase the amount of cobalt existing as Co3O4 within the silica from 44% to 77%, without varying the cobalt precursor concentration. However, once the surfactant to cobalt ratio exceeded 1, further addition resulted in an inhibitory mechanism whereby the altered pyrolysis of the surfactant decreased Co3O4 production. These findings have significant implications for the production of cobalt/silica composites where maximizing the functional Co3O4 phase remains the goal for a broad range of catalytic, sensing and materials applications. PMID:24022785

8. Recent developments in silica sol-gel anti-reflection (AR) coatings

SciTech Connect

Sermon, P.A.; Vong, M.S.W.; Bazin, N.; Badheka, R.; Spriggs, D.

1995-12-31

Silica sol-gel anti-reflective (AR) coatings have been investigated with particular reference to their laser induced damage threshold (LIDT) when subjected to irradiation from a Nd pulse laser at 1,064nm. Coatings (whose thickness was optimized for minimum reflection at 1,064nm) were deposited by spinning silica sols (average particle size 15nm) produced formed by the base (ammonium hydroxide) catalyzed hydrolysis/condensation of TEOS in ethanol. Addition of polyethylene glycols (PEGs) increased the size of the colloidal silica particles and also induced some particle aggregation in the sol, unlike a similar chain length diol. Increases in the LIDT of the coatings possibly depend upon the impurity levels, the wettability of the substrate and the presence of PEG. LIDT improvements may be obtained by control of substrate and coating surface wettability, hydrophilicity and surface chemistry.

9. Drug entrapment in silica microspheres through a single step sol-gel process and in vitro release behavior.

PubMed

Yilmaz, Elvan; Bengisu, Murat

2006-04-01

A single step sol-gel process was used to precipitate silica microspheres containing ibuprofen or naproxen for controlled drug delivery applications. The drug release behavior from these systems was analyzed in vitro. Pure ibuprofen and naproxen exhibited linear release with time, while sol-gel silica entrapped drugs were released with a logarithmic time dependence starting with an initial burst effect followed by a gradual decrease. Microscopic analysis combined with gravimety and infrared spectroscopy indicated that some of the drug is entrapped as large crystals attached to silica microspheres while the rest is encapsulated inside the microspheres. Drug-loaded silica microspheres with no open porosity and with a narrow particle size distribution were obtained. Both erosion of the microspheres and diffusion through them contributed to drug release. Sol-gel precipitation of silica microspheres is a promising method for drug entrapment and controlled release.

10. Possible silica gel in the Olive Fault, Naukluft Nappe Complex, Namibia: A geologic record of dynamic weakening in faults during continental orogenesis

Faber, C.; Rowe, C. D.; Miller, J. A.; Backeberg, N.; Sylvester, F.

2009-12-01

The apparently low frictional strength of faults during earthquake slip is not sufficiently well explained. Dynamic weakening has been observed in recent laboratory experiments at seismic slip rates, even if materials are strong at slow slip rates. Di Toro et al. (2004) performed experiments on crystalline rocks at slip rates of 1m/s and observed frictional strength drops to near zero. Examination of the slip surface revealed an amorophous silica had formed during fast slip and interpreted this as a solidified silica gel. If similar silica gel forms during earthquakes, and solidifies to amorphous silica, it would be expected to slowly crystallize over time. Ujiie et al (2007) reported a microcrystalline silica fault vein from the Shimanto Complex (Japan) which contains colloidal microspheres of silica, consistent with its origin as a silica gel. This vein may have been created during seismic slip, although other explanations are possible. No other natural examples of this potentially important coseismic weakening mechanism have been reported. To investigate whether silica gel actually forms during seismic slip, it will be necessary to discover and fully characterize additional natural examples. The Naukluft Nappe Complex in central Namibia is a foreland thrust stack at the distal southern margin of the Pan-African Damara Orogen (active at ~ 550Ma). A fault vein of microcrystalline silica has been found in an intra-nappe thrust fault . The vein occurs as a mostly continuous, planar, 0.1-1.0cm-thick fault vein within dolomite breccias of the Olive Fault. There are no other veins of silica associated with the fault. The hanging wall and footwall are dolomite and calcareous shales, respectively. The layer is petrographically similar to the microcrystalline silica described by Ujiie et al. (2007). The silica layer is purple-blue to white in color cathodoluminescence, in contrast to the bright turquoise typical of quartz. Although X-ray diffraction spectra show only

11. Augmentation of Cooling Output by Silica Gel-Water Adsorption Cycle Utilizing the Waste Heat of GHP

The GHP (Gas engine Heat Pump) system is expected to have high energy-efficiency in utilizing the waste heat exhausted from a gas engine. In summer season, a silica gel-water adsorption cooling unit driven by the exhaust heat is considered as a cooling system for saving energy. In this work, an attempt was made to improve the COP of a silica gel-water adsorption cooling system by enhancing heat and mass transfer in the silica gel adsorption layer. A unit cell was introduced as a simplified model of adsorber for analyzing the phenomena of heat and mass transfer in the adsorbent. This cell was composed of a single tube with a silica gel layer bonded on its external surface. Optimization of heat and mass transfer characteristics for the unit cell was carried out by experimental and analytical approach.

12. Controllable synthesis of hollow mesoporous silica particles by a facile one-pot sol-gel method.

PubMed

Song, Jing-Chuan; Xue, Fei-Fei; Lu, Zhong-Yuan; Sun, Zhao-Yan

2015-07-01

A simple and facile one-pot sol-gel method is proposed for the fabrication of hollow mesoporous silica particles. Both the particle size and the shell thickness can be well controlled by moderately tuning some experimental parameters.

13. Development of novel biocompatible hybrid nanocomposites based on polyurethane-silica prepared by sol gel process.

PubMed

Rashti, Ali; Yahyaei, Hossein; Firoozi, Saman; Ramezani, Sara; Rahiminejad, Ali; Karimi, Roya; Farzaneh, Khadijeh; Mohseni, Mohsen; Ghanbari, Hossein

2016-12-01

Due to high biocompatibility, polyurethane has found many applications, particularly in development of biomedical devices. A new nanocomposite based on thermoset polyurethane and silica nanoparticles was synthesized using sol-gel method. Sol-gel process was fulfilled in two acidic and basic conditions by using tetraethylorthosilicate (TEOS) and trimethoxyisocyanatesilane as precursors. The hybrid films characterized for mechanical and surface properties using tensile strength, contact angle, ATR-FTIR and scanning electron microscopy. Biocompatibility and cytotoxicity of the hybrids were assessed using standard MTT, LDH and TUNEL assays. The results revealed that incorporation of silica nanoparticles was significantly improved tensile strength and mechanical properties of the hybrids. Based on the contact angle results, silica nanoparticles increased hydrophilicity of the hybrids. Biocompatibility by using human lung epithelial cell line (MRC-5) demonstrated that the hybrids were significantly less cytotoxic compared to pristine polymer as tested by MTT and LDH assays. TUNEL assay revealed no signs of apoptosis in all tested samples. The results of this study demonstrated that incorporation of silica nanoparticles into polyurethane lead to the enhancement of biocompatibility, indicating that these hybrids could potentially be used in biomedical field in particular as a new coating for medical implants. PMID:27612823

14. Preparation and complex characterization of silica holmium sol-gel monoliths.

PubMed

Cacaina, D; Areva, S; Laaksonen, H; Simon, S; Ylänen, H

2011-01-01

Amorphous, sol-gel derived SiO(2) are known to biocompatible and bioresorbable materials. Biodegradable and inert materials containing radioactive isotopes have potential application as delivery vehicles of the beta radiation to the cancer tumors inside the body. Incorporation of holmium in the sol-gel derived SiO(2) could lead to the formation of a biodegradable material which could be used as carrier biomaterial for the radiation of radioactive holmium to the various cancer sites. The homogeneity of the prepared sol-gel silica holmium monoliths was investigated by Back Scattered Electron Imaging of Scanning Electron Microscope equipped with Energy Dispersive X-ray Analysis, X-ray Induced Photoelectron Spectroscopy and Nuclear Magnetic Resonance Spectroscopy. The biodegradation of the monoliths was investigated in Simulated Body Fluid and TRIS (Trizma pre-set Crystals) solution. The results show that by suitable tailoring of the sol-gel processing parameters holmium can be homogeneously incorporated in the silica matrix with a controlled biodegradation rate.

15. Synthesis of silica nanoparticles from Vietnamese rice husk by sol–gel method

PubMed Central

2013-01-01

Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol–gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles. PMID:23388152

16. Thickness controlled sol-gel silica films for plasmonic bio-sensing devices

SciTech Connect

Figus, Cristiana Quochi, Francesco Artizzu, Flavia Saba, Michele Marongiu, Daniela Mura, Andrea; Bongiovanni, Giovanni; Floris, Francesco; Marabelli, Franco; Patrini, Maddalena; Fornasari, Lucia; Pellacani, Paola; Valsesia, Andrea

2014-10-21

Plasmonics has recently received considerable interest due to its potentiality in many fields as well as in nanobio-technology applications. In this regard, various strategies are required for modifying the surfaces of plasmonic nanostructures and to control their optical properties in view of interesting application such as bio-sensing, We report a simple method for depositing silica layers of controlled thickness on planar plasmonic structures. Tetraethoxysilane (TEOS) was used as silica precursor. The control of the silica layer thickness was obtained by optimizing the sol-gel method and dip-coating technique, in particular by properly tuning different parameters such as pH, solvent concentration, and withdrawal speed. The resulting films were characterized via atomic force microscopy (AFM), Fourier-transform (FT) spectroscopy, and spectroscopic ellipsometry (SE). Furthermore, by performing the analysis of surface plasmon resonances before and after the coating of the nanostructures, it was observed that the position of the resonance structures could be properly shifted by finely controlling the silica layer thickness. The effect of silica coating was assessed also in view of sensing applications, due to important advantages, such as surface protection of the plasmonic structure.

17. Synthesis of palladium-doped silica nanofibers by sol-gel reaction and electrospinning process

SciTech Connect

San, Thiam Hui; Daud, Wan Ramli Wan; Kadhum, Abdul Amir Hassan; Mohamad, Abu Bakar; Kamarudin, Siti Kartom; Shyuan, Loh Kee; Majlan, Edy Herianto

2012-06-29

Nanofiber is drawing great attention nowadays with their high surface area per volume and flexibility in surface functionalities that make them favorable as a proton exchange membrane in fuel cell application. In this study, incorporation of palladium nanoparticles in silica nanofibers was prepared by combination of a tetraorthosilane (TEOS) sol-gel reaction with electrospinning process. This method can prevent the nanoparticles from aggregation by direct mixing of palladium nanoparticles in silica sol. The as-produced electrospun fibers were thermally treated to remove poly(vinyl pyrrolidone) (PVP) and condensation of silanol in silica framework. PVP is chosen as fiber shaping agent because of its insulting and capping properties for various metal nanoparticles. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the silica fibers and Pd nanoparticles on the fibers. Spun fibers with average diameter ranged from 100nm to 400nm were obtained at optimum operating condition and distribution of Pd nanoparticles on silica fibers was investigated.

18. Direct electrochemistry of lactate dehydrogenase immobilized on silica sol-gel modified gold electrode and its application.

PubMed

Di, Junwei; Cheng, Jiongjia; Xu, Quan; Zheng, Huie; Zhuang, Jingyue; Sun, Yongbo; Wang, Keyu; Mo, Xiangyin; Bi, Shuping

2007-12-15

The direct electrochemistry of lactate dehydrogenase (LDH) immobilized in silica sol-gel film on gold electrode was investigated, and an obvious cathodic peak at about -200 mV (versus SCE) was found for the first time. The LDH-modified electrode showed a surface controlled irreversible electrode process involving a one electron transfer reaction with the charge-transfer coefficient (alpha) of 0.79 and the apparent heterogeneous electron transfer rate constant (K(s)) of 3.2 s(-1). The activated voltammetric response and decreased charge-transfer resistance of Ru(NH(3))(6)(2+/3+) on the LDH-modified electrode provided further evidence. The surface morphologies of silica sol-gel and the LDH embedded in silica sol-gel film were characterized by SEM. A potential application of the LDH-modified electrode as a biosensor for determination of lactic acid was also investigated. The calibration range of lactic acid was from 2.0 x 10(-6) to 3.0 x 10(-5) mol L(-1) and the detection limit was 8.0 x 10(-7) mol L(-1) at a signal-to-noise ratio of 3. Finally, the effect of environmental pollutant resorcinol on the direct electrochemical behavior of LDH was studied. The experimental results of voltammetry indicated that the conformation of LDH molecule was altered by the interaction between LDH and resorcinol. The modified electrode can be applied as a biomarker to study the pollution effect in the environment.

19. The controlled release of drugs from emulsified, sol gel processed silica microspheres.

PubMed

Radin, Shula; Chen, Tiffany; Ducheyne, Paul

2009-02-01

Controlled release silica sol gels are room temperature processed, porous, resorbable materials with generally good compatibility. Many molecules including drugs, proteins and growth factors can be released from sol gels and the quantity and duration of the release can vary widely. Processing parameters render these release properties exquisitely versatile. The synthesis of controlled release sol gels typically includes acid catalyzed hydrolysis to form a sol with the molecules included. This is then followed by casting, aging and drying. Additional steps such as grinding and sieving are required to produce sol gel granules of a desirable size. In this study, we focus on the synthesis of sol gel microspheres by using a novel process with only two steps. The novelty is related to acid-base catalysis of the sol prior to emulsification. Sol gel microspheres containing either vancomycin (antibiotic) or bupivacaine (analgesic) were successfully synthesized using this method. Both drugs showed controlled, load dependent and time dependent release from the microspheres. The in vitro release properties of sol gel microspheres were remarkably different from those of sol gel granules produced by grinding and sieving. In contrast to a fast, short-term release from granules, the release from microspheres was slower and of longer duration. In addition, the degradation rate of microspheres was significantly slower than that of the granules. Using various mathematical models, the data reveal that the release from sol gel powder is governed by two distinct phases of release. In addition, the release from emulsified microspheres is delayed, a finding that can be attributed to differences in surface properties of the particles produced by emulsification and those produced by casting and grinding. The presented results represent an excellent data set for designing and implementing preclinical studies.

20. Water repellent porous silica films by sol-gel dip coating method.

PubMed

Rao, A Venkateswara; Gurav, Annaso B; Latthe, Sanjay S; Vhatkar, Rajiv S; Imai, Hiroaki; Kappenstein, Charles; Wagh, P B; Gupta, Satish C

2010-12-01

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes. In the present research work, water repellent porous silica films are prepared on glass substrate at room temperature by sol-gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), water (H(2)O) constant at 1:12.90:4.74, respectively, with 2M NH(4)OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22. A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact angle as high as 164° and water sliding angle as low as 4° was obtained for silica film prepared from M=0.22. The surface morphological studies of the prepared silica film showed the porous structure with pore sizes typically ranging from 200nm to 1.3μm. The superhydrophobic silica films prepared from M=0.22 retained their superhydrophobicity up to a temperature of 285°C and above this temperature the films became superhydrophilic. The porous and water repellent silica films are prepared by proper alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water contact angle measurements.

1. Infrared spectroscopy analysis of the local atomic structure in silica prepared by sol-gel

Martínez, J. R.; Ruiz, F.; Vorobiev, Y. V.; Pérez-Robles, F.; González-Hernández, J.

1998-11-01

Infrared spectroscopy has been used to analyze the structural changes in samples prepared by the sol-gel method. Silica gels were prepared from alcoholic solutions of tetraethylorthosilicate (TEOS) with different H2O/TEOS molar ratios. The IR spectra of these gels, in the Si-O bond stretching region, shows that their structure strongly depends on the H2O/TEOS ratio. The relative change in intensity of the Si-O stretching modes, in samples prepared using different H2O/TEOS ratios, are interpreted in terms of different degrees of structural disorder. According to our infrared absorption data, a decrease in the H2O/TEOS ratio from about 7, the SiO2 structure evolves from a three-dimensional network toward a chainlike structure.

2. Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

Nikolova, D.; Krstić, J.; Spasov, L.; Simeonov, D.; Lončarević, D.; Stefanov, Pl.; Jovanović, D.

2011-12-01

The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

3. Photoinduced acceleration of the effluent rate of developing solvents in azobenzene-tethered silica gel.

PubMed

Fujiwara, Masahiro; Akiyama, Minako; Hata, Momoko; Shiokawa, Kumi; Nomura, Ryoki

2008-08-01

The switching of a molecular length of azobenzene between its trans and cis forms by photoirradiation originates various photoresponsive systems in the molecular level and/or nanolevel. Recently, we and another group separately reported that some azobenzene-modified mesoporous silicas remarkably promote the release of molecules from the inside of the mesopore to the outside, when the lights, both UV and visible lights, were irradiated simultaneously. In these cases, the release rates of molecules were enhanced by the impeller-like effect of molecular motion of azobenzene moiety attributed to the continuous photoisomerization between the trans and cis isomers. This paper presents that azobenzene-substituent-tethered amorphous silica gel could promote the development of solvents in chromatography systems by photoirradiation. In column chromatography system where azobenzene-tethered silica gel was packed, the irradiation of both UV and visible lights increased the effluent rate of the developing solvents. The single irradiation of UV light scarcely enhanced the rate, while the visible light irradiation longer than 400 nm in wavelength also accelerated the development of the solvent moderately. The same kinds of phenomena were observed when this photopromoted chromatography system was applied to thin layer chromatography (TLC). Hydrocarbon developing solvents in the regions, where UV and visible lights were irradiated, moved up the TLC plate higher than those without photoirradiation. When the pyrene solution in the developing solvent was utilized in the chromatography systems, the similar photoacceleration of pyrene development was observed at the same level as the developing solvents.

4. Laser Surface Treatment of Silica Sol-gel Coating to Produce Nanocrystalline Structure

Razavi, R. Shoja; Gordani, Gh.; Hojjati, A.

2011-12-01

In this study two methods of laser and furnace sintering are used to prepare nanocrystalline structure of silica sol-gel coating on glass substrate. In laser sintering method, an Nd:YAG pulsed laser with a laser pulse energy of 1 J used to sinter the silica sol-gel coating. To evaluate the surface morphology and microstructural analysis, XRD and SEM were used. The optical properties of coatings were examined by UV/VIS spectroscopy. The results indicated that the laser sintered coating was denser than the furnace sintered coating. No porosity and cracks were detected on the surface of laser sintered coating. Using Scherer mathematical equation, it was shown that the grain size of laser sintered coating is well within nano size range. The uniformity of nanocrystalline structure clearly improved the reflection of incident beam from the laser sintered coating. This was mainly due to increase in grain boundary regions which in turn can cause some the wavelength of the incident beam to be transmitted from silica coatings.

5. Development of vapor deposited silica sol-gel particles for use as a bioactive materials system.

PubMed

Snyder, Katherine L; Holmes, Hallie R; VanWagner, Michael J; Hartman, Natalie J; Rajachar, Rupak M

2013-06-01

Silica-based sol-gel and bioglass materials are used in a variety of biomedical applications including the surface modification of orthopedic implants and tissue engineering scaffolds. In this work, a simple system for vapor depositing silica sol-gel nano- and micro-particles onto substrates using nebulizer technology has been developed and characterized. Particle morphology, size distribution, and degradation can easily be controlled through key formulation and manufacturing parameters including water:alkoxide molar ratio, pH, deposition time, and substrate character. These particles can be used as a means to rapidly modify substrate surface properties, including surface hydrophobicity (contact angle changes >15°) and roughness (RMS roughness changes of up to 300 nm), creating unique surface topography. Ions (calcium and phosphate) were successfully incorporated into particles, and induced apatitie-like mineral formation upon exposure to simulated body fluid Preosteoblasts (MC3T3) cultured with these particles showed up to twice the adhesivity within 48 h when compared to controls, potentially indicating an increase in cell proliferation, with the effect likely due to both the modified substrate properties as well as the release of silica ions. This novel method has the potential to be used with implants and tissue engineering materials to influence cell behavior including attachment, proliferation, and differentiation via cell-material interactions to promote osteogenesis.

6. Nanorods of Various Oxides and Hierarchically Structured Mesoporous Silica by Sol-Gel Electrophoresis

SciTech Connect

Limmer, Steven J.; Hubler, Timothy L.; Cao, Guozhong

2003-01-02

In this paper, we report the template-based growth of nanorods of oxides and hierarchically structured mesoporous silica, formed by means of a combination of sol-gel processing and elecrophoretic deposition. Both single metal oxides (TiO2) and complex oxides (Pb(Zr0.52Ti0.48)O3) have been grown by this method. This method has also been applied to the growth of nanorods of mesoporous silica having an ordered pore structure, where the pores are aligned parallel to the long axis of the nanorod. Uniformly sized nanorods of about 125-200 nm in diameter and 10 um in length were grown over large areas with near unidirectional alignment. Appropriate sol preparation yielded the desired stoichiometric chemical composition and crystal structure of the oxide nanorods, with a heat treatment (500-700 C for 15-30 min) for crystallization, densification and any necessary pyrolysis.

7. Shock-wave compression of silica gel as a model material for comets

Arasuna, Akane; Okuno, Masayuki; Chen, Liliang; Mashimo, Tsutomu; Okudera, Hiroki; Mizukami, Tomoyuki; Arai, Shoji

2016-07-01

A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth's surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si-OH) that led to the formation of a new Si-O-Si network structure containing larger rings (e.g., six-membered ring of SiO4 tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.

8. Thick silica gel coatings on methylsilsesquioxane monoliths using anisotropic phase separation.

PubMed

Kanamori, Kazuyoshi; Nakanishi, Kazuki; Hanada, Teiichi

2006-11-01

Silica gel coatings on methyltrimethoxysilane (MTMS)-derived monoliths have been studied using wetting transition. Wetting transition is observed in a small confined space, where a coating solution phase-separates into a well-coarsened dimension, making all the phase-separating polymerizing silica phase dynamically flow onto the existing surface of a mold. Bulk coating experiments have shown reductions of both macropore volume and diameter due to the coated layer. Comparing HPLC efficiencies of the coated monolith with those of the non-coated MTMS monolith revealed that the retention factors drastically increased in both normal- and reversed-phase modes. This is attributed to the existence of considerable amounts of accessible micropores left inside the coated layer, where analyte molecules travel and adsorb for a considerable period of time.

9. High-temperature adsorption of n-octane, benzene, and chloroform onto silica gel surface

SciTech Connect

Bilinski, B.

2000-05-01

The adsorption properties of silica gel surface for compounds differing in types of intermolecular interactions were studied under conditions in which the same silica was investigated by means of a gas phase titration method, i.e., at high temperature and low surface coverage. Adsorption isotherms of n-octane, benzene, and chloroform were determined at 373, 363, and 353 K. Based on these isotherms the isosteric heat of adsorption was calculated. Moreover, the adsorption energy distribution function and the derivative of film pressure with respect to the adsorbed amount were computed from the isotherms determined at 373 K. The obtained results were compared to those determined by gas phase titration. It was stated that on the dependencies of film pressure derivative some linear sections appeared that corresponded to the inflection points on gas phase titration curves. The results are discussed in terms of both the type and the strength of surface-molecule interactions.

10. Dynamics of Proteins Encapsulated in Silica Sol-gel Glasses Studied with IR Vibrational Echo Spectroscopy

PubMed Central

Massari, Aaron M.; Finkelstein, Ilya J.; Fayer, Michael D.

2008-01-01

Spectrally-resolved infrared stimulated vibrational echo spectroscopy is used to measure the fast dynamics of heme-bound CO in carbonmonoxy-myoglobin (MbCO) and hemoglobin (HbCO) embedded in silica sol-gel glasses. On the time scale of ~100 fs to several ps, the vibrational dephasing of the heme-bound CO is measurably slower for both MbCO and HbCO relative to aqueous protein solutions. The fast structural dynamics of MbCO, as sensed by the heme-bound CO, are influenced more by the sol-gel environment than those of HbCO. Longer time scale structural dynamics (tens of ps), as measured by the extent of spectral diffusion, are the same for both proteins encapsulated in sol-gel glasses compared to aqueous solutions. A comparison of the sol-gel experimental results to viscosity dependent vibrational echo data taken on various mixtures of water and fructose shows that the sol-gel encapsulated MbCO exhibits dynamics that are the equivalent to the protein in a solution that is nearly 20 times more viscous than bulk water. In contrast, the HbCO dephasing in the sol-gel reflects only a 2-fold increase in viscosity. Attempts to alter the encapsulating pore size by varying the molar ratio of silane precursor to water (R-value) used to prepare the sol-gel glasses were found to have no effect on the fast or steady-state spectroscopic results. The vibrational echo data are discussed in the context of solvent confinement and protein-pore wall interactions to provide insights into the influence of a confined environment on the fast structural dynamics experienced by a biomolecule. PMID:16551107

11. Effects of temperature on trichloroethylene desorption from silica gel and natural sediments. 1. Isotherms

SciTech Connect

Werth, C.J.; Reinhard, M.

1997-03-01

Aqueous phase isotherms were calculated from vapor phase desorption isotherms measured at 15, 30, and 60{degree}C for trichloroethylene on a silica gel, an aquifer sediment, a soil, a sand fraction, and a clay and silt fraction, all at 100% relative humidity. Isosteric heats of adsorption (Q{sub st}(q)) were calculated as a function of the sorbed concentration, q, and examined with respect to the following mechanisms: adsorption on water wet mineral surfaces, sorption in amorphous organic matter (AOM), and adsorption in hydrophobic micropores. Silica gel, sand fraction, and clay and silt fraction 60{degree}C isotherms are characterized by a Freundlich region and a region at very low concentrations where isotherm points deviate from log-log linear behavior. The latter is designated the non-Freundlich region. For the silica gel, values of Q{sub st}(q) (9.5-45 kJ/mol) in both regions are consistent with adsorption in hydrophobic micropores. For the natural solids, values of Q{sub st}(q) in the Freundlich regions are less than or equal to zero and are consistent with sorption on water wet mineral surfaces and in AOM. In the non-Freundlich regions, diverging different temperature isotherms with decreasing q and Q{sub st}(q) value of 34 kJ/mol for the clay and silt fraction suggest that adsorption is occurring in hydrophobic micropores. The General Adsorption Isotherm is used to capture this adsorption heterogeneity. 57 refs., 5 figs., 2 tabs.

12. Acrylate-silica polymer nanocomposites obtained by sol-gel reactions. Structure, properties and scaffold preparation

Rodriguez Hernandez, Jose Carlos

The manuscript deals with the development and characterization of hybrid materials based on poly(hydroxyethyl acrylate) (hereafter PHEA) reinforced by the inclusion of an amorphous silica phase. Both phases were simultaneously synthesized: the organic phase underwent a free radical polymerization reaction induced by the small addition of a thermal initiator (benzoyl peroxide); besides, silica (SiO2) was polymerized by an acid catalyzed sol-gel reaction of the silicon alkoxide tetraethoxysilane (hereafter TEOS). The sol-gel reaction conditions where silicon dioxide is formed influence the final silica structure: degree of condensation, linear versus branched intermediate species, average size, and so on. Some of the key parameters to control SiO2 topology on sol-gel derived composites include the catalyst nature used to increase the alkoxide reactivity (as well as its amount, pH), the available water to hydrolyze the silica precursor (referred to the stoichiometric amount needed to fully hydrolyze one molecule of TEOS) and ratio between the organic and inorganic phases on the final hybrid. The former (catalyst) and the second (water) conditions were fixed so as to synthesize materials with silica average sizes around tens of nanometres (nanocomposites); the latter, the relative ratio between organic and inorganic phases, was systematically changed. Besides, it is introduced a methodology to prepare a new kind of scaffolds made by nanocomposites whose pore morphology consists of a cylindrical channel mesh, which are perpendicular between themselves. The procedure is based on the well-known method of intermediate templates, this time prepared by a stack of woven fabrics which are first pressed and afterwards sintered. After the filling of the holes left inside the template by the monomeric solution and subsequent thermal polymerization, templates are removed by the selective solvent of the material it is made up. A suitable template preparation is found to be crucial

13. Rapid separation of polychlorinated biphenyls from DDT and its analogues on silica gel

USGS Publications Warehouse

Snyder, Diane; Reinert, Robert E.

1971-01-01

Polychlorinated biphenyls (PCB's), which are used in industry worldwide (i), have been found as residues in numerous wildlife species (2-7). Because of the similarity in chemical characteristics, PCB compounds interfere with gas liquid chromatographic (GLC) analysis of certain chlorinated hydrocarbon insecticides (8). In the present study, we sought a rapid microanalytical procedure for separation of PCB's from DDT and its analogues before analysis with GLC. A small silica gel column was found to be suitable for removing two of the Aroclor series of PCB's (1254 and 1260) from DDT and its analogues.

14. Experiments on Hemoglobin in Single Crystals and Silica Gels Distinguish among Allosteric Models

PubMed Central

Henry, Eric R.; Mozzarelli, Andrea; Viappiani, Cristiano; Abbruzzetti, Stefania; Bettati, Stefano; Ronda, Luca; Bruno, Stefano; Eaton, William A.

2015-01-01

Trapping quaternary structures of hemoglobin in single crystals or by encapsulation in silica gels has provided a demanding set of data to test statistical mechanical models of allostery. In this work, we compare the results of those experiments with predictions of the four major allosteric models for hemoglobin: the quaternary two-state model of Monod, Wyman, and Changeux; the tertiary two-state model of Henry et al., which is the simplest extension of the Monod-Wyman-Changeux model to include pre-equilibria of tertiary as well as quaternary conformations; the structure-based model of Szabo and Karplus; and the modification of the latter model by Lee and Karplus. We show that only the tertiary two-state model can provide a near quantitative explanation of the single-crystal and gel experimental results. PMID:26038112

15. Durable superhydrophobic and antireflective surfaces by trimethylsilanized silica nanoparticles-based sol-gel processing.

PubMed

Manca, Michele; Cannavale, Alessandro; De Marco, Luisa; Aricò, Antonino S; Cingolani, Roberto; Gigli, Giuseppe

2009-06-01

We present a robust and cost-effective coating method to fabricate long-term durable superhydrophobic andsimultaneouslyantireflective surfaces by a double-layer coating comprising trimethylsiloxane (TMS) surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol-gel process. A dense and homogeneous organosilica gel layer was first coated onto a glass substrate, and then, a trimethylsilanized nanospheres-based superhydrophobic layer was deposited onto it. After thermal curing, the two layers turned into a monolithic film, and the hydrophobic nanoparticles were permanently fixed to the glass substrate. Such treated surfaces showed a tremendous water repellency (contact angle = 168 degrees ) and stable self-cleaning effect during 2000 h of outdoor exposure. Besides this, nanotextured topology generated by the self-assembled nanoparticles-based top layer produced a fair antireflection effect consisting of more than a 3% increase in optical transmittance. PMID:19466786

16. Improvement of arbovirus HA antigens by treatment with a colloidal silica gel and sonication.

PubMed

Traavik, T

1977-01-01

A remarkable increase in HA titers for weakly haemagglutinating Norwegian arbovirus strains, Uukuniemi and Runde viruses, was achieved by including treatment with the colloidal silica gel Aerosil in the antigen preparation scheme. By combining this procedure with sonication, the titers of sucrose-aceton extracted, infected suckling mouse brains could be increased several hundred times. Good antigens also were obtained from virus grown in BHK21/c 13 cell cultures and concentrated by polyethylene glycol 6000/NaCl. Rubella virus HA antigen and HBsAg were adsorbed to the gel, and excluded from a preparation by treatment with Aerosil. This indicates a limitation to the universal use of the method, presumably related to the particle size.

17. Durable superhydrophobic and antireflective surfaces by trimethylsilanized silica nanoparticles-based sol-gel processing.

PubMed

Manca, Michele; Cannavale, Alessandro; De Marco, Luisa; Aricò, Antonino S; Cingolani, Roberto; Gigli, Giuseppe

2009-06-01

We present a robust and cost-effective coating method to fabricate long-term durable superhydrophobic andsimultaneouslyantireflective surfaces by a double-layer coating comprising trimethylsiloxane (TMS) surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol-gel process. A dense and homogeneous organosilica gel layer was first coated onto a glass substrate, and then, a trimethylsilanized nanospheres-based superhydrophobic layer was deposited onto it. After thermal curing, the two layers turned into a monolithic film, and the hydrophobic nanoparticles were permanently fixed to the glass substrate. Such treated surfaces showed a tremendous water repellency (contact angle = 168 degrees ) and stable self-cleaning effect during 2000 h of outdoor exposure. Besides this, nanotextured topology generated by the self-assembled nanoparticles-based top layer produced a fair antireflection effect consisting of more than a 3% increase in optical transmittance.

18. Analysis of Lipid Phase Behavior and Protein Conformational Changes in Nanolipoprotein Particles upon Entrapment in Sol–Gel-Derived Silica

PubMed Central

2015-01-01

The entrapment of nanolipoprotein particles (NLPs) and liposomes in transparent, nanoporous silica gel derived from the precursor tetramethylorthosilicate was investigated. NLPs are discoidal patches of lipid bilayer that are belted by amphiphilic scaffold proteins and have an average thickness of 5 nm. The NLPs in this work had a diameter of roughly 15 nm and utilized membrane scaffold protein (MSP), a genetically altered variant of apolipoprotein A-I. Liposomes have previously been examined inside of silica sol–gels and have been shown to exhibit instability. This is attributed to their size (∼150 nm) and altered structure and constrained lipid dynamics upon entrapment within the nanometer-scale pores (5–50 nm) of the silica gel. By contrast, the dimensional match of NLPs with the intrinsic pore sizes of silica gel opens the possibility for their entrapment without disruption. Here we demonstrate that NLPs are more compatible with the nanometer-scale size of the porous environment by analysis of lipid phase behavior via fluorescence anisotropy and analysis of scaffold protein secondary structure via circular dichroism spectroscopy. Our results showed that the lipid phase behavior of NLPs entrapped inside of silica gel display closer resemblance to its solution behavior, more so than liposomes, and that the MSP in the NLPs maintain the high degree of α-helix secondary structure associated with functional protein–lipid interactions after entrapment. We also examined the effects of residual methanol on lipid phase behavior and the size of NLPs and found that it exerts different influences in solution and in silica gel; unlike in free solution, silica entrapment may be inhibiting NLP size increase and/or aggregation. These findings set precedence for a bioinorganic hybrid nanomaterial that could incorporate functional integral membrane proteins. PMID:25062385

19. Silica/quercetin sol-gel hybrids as antioxidant dental implant materials

Catauro, Michelina; Papale, Ferdinando; Bollino, Flavia; Piccolella, Simona; Marciano, Sabina; Nocera, Paola; Pacifico, Severina

2015-06-01

The development of biomaterials with intrinsic antioxidant properties could represent a valuable strategy for preventing the onset of peri-implant diseases. In this context, quercetin, a naturally occurring flavonoid, has been entrapped at different weight percentages in a silica-based inorganic material by a sol-gel route. The establishment of hydrogen bond interactions between the flavonol and the solid matrix was ascertained by Fourier transform infrared spectroscopy. This technique also evidenced changes in the stretching frequencies of the quercetin dienonic moiety, suggesting that the formation of a secondary product occurs. Scanning electron microscopy was applied to detect the morphology of the synthesized materials. Their bioactivity was shown by the formation of a hydroxyapatite layer on sample surface soaked in a fluid that simulates the composition of human blood plasma. When the potential release of flavonol was determined by liquid chromatography coupled with ultraviolet and electrospray ionization tandem mass spectrometry techniques, the eluates displayed a retention time that was 0.5 min less than quercetin. Collision-activated dissociation mass spectrometry and untraviolet-visible spectroscopy were in accordance with the release of a quercetin derivative. The antiradical properties of the investigated systems were evaluated by DPPH and ABTS methods, whereas the 2,7-dichlorofluorescein diacetate assay highlighted their ability to inhibit the H2O2-induced intracellular production of reactive oxygen species in NIH-3T3 mouse fibroblast cells. Data obtained, along with data gathered from the MTT cytotoxicity test, revealed that the materials that entrapped the highest amount of quercetin showed notable antioxidant effectiveness.

20. Microwave material characterization of alkali-silica reaction (ASR) gel in cementitious materials

Hashemi, Ashkan

Since alkali-silica reaction (ASR) was recognized as a durability challenge in cement-based materials over 70 years ago, numerous methods have been utilized to prevent, detect, and mitigate this issue. However, quantifying the amount of produced ASR byproducts (i.e., ASR gel) in-service is still of great interest in the infrastructure industry. The overarching objective of this dissertation is to bring a new understanding to the fundamentals of ASR formation from a microwave dielectric property characterization point-of-view, and more importantly, to investigate the potential for devising a microwave nondestructive testing approach for ASR gel detection and evaluation. To this end, a comprehensive dielectric mixing model was developed with the potential for predicting the effective dielectric constant of mortar samples with and without the presence of ASR gel. To provide pertinent inputs to the model, critical factors on the influence of ASR gel formation on dielectric and reflection properties of several mortar samples were investigated at R, S, and X-band. Effects of humidity, alkali content, and long-term curing conditions on ASR-prone mortars were also investigated. Additionally, dielectric properties of chemically different synthetic ASR gel were also determined. All of these, collectively, served as critical inputs to the mixing model. The resulting developed dielectric mixing model has the potential to be further utilized to quantify the amount of produced ASR gel in cement-based materials. This methodology, once becomes more mature, will bring new insight to the ASR reaction, allowing for advancements in design, detection and mitigation of ASR, and eventually has the potential to become a method-of-choice for in-situ infrastructure health-monitoring of existing structures.

1. Generation of a mesoporous silica MSU shell onto solid core silica nanoparticles using a simple two-step sol-gel process.

PubMed

Allouche, Joachim; Dupin, Jean-Charles; Gonbeau, Danielle

2011-07-14

Silica core-shell nanoparticles with a MSU shell have been synthesized using several non-ionic poly(ethylene oxide) based surfactants via a two step sol-gel method. The materials exhibit a typical worm-hole pore structure and tunable pore diameters between 2.4 nm and 5.8 nm.

2. Bedded jaspers of the Ordovician Løkken ophiolite, Norway: seafloor deposition and diagenetic maturation of hydrothermal plume-derived silica-iron gels

USGS Publications Warehouse

Grenne, Tor; Slack, John F.

2003-01-01

The jaspers are interpreted to record colloidal fallout from one or more hydrothermal plumes, followed by maturation (ageing) of an Si-Fe-oxyhydroxide gel, on and beneath the Ordovician sea floor. Small hematitic filaments in the jaspers reflect bacteria-catalysed oxidation of Fe2+ within the plume. The larger tubular filaments resulted from either microbial activity or inorganic self-organized mineral growth of Fe-oxyhydroxide within the Si-Fe-oxyhydroxide gel after deposition on the sea floor, prior to more advanced maturation of the gel as represented by the spheroidal and botryoidal silica-hematite textures. Bleaching and hematite±epidote growth are interpreted to reflect heat and fluids generated during deposition of basaltic sheet flows on top of the gels.

3. Experimental comparison of adsorption characteristics of silica gel and zeolite in moist air

Xin, F.; Yuan, Z. X.; Wang, W. C.; Du, C. X.

2016-05-01

In this work, the macro adsorption characteristic of water vapor by the allochroic silica gel and the zeolite 5A and ZSM-5 were investigated experimentally. BET analysis method presented the difference of the porosity, the micro pore volume, and the specific surface area of the material. The dynamic and the equilibrium characteristics of the sample were measured thermo-gravimetrically in the moist air. In general, the ZSM-5 zeolite showed an inferior feature of the adsorption speed and the equilibrium concentration to the others. By comparison to the result of SAPO-34 zeolite in the open literature, the 5A zeolite showed some superiorities of the adsorption. The equilibrium concentration of the ZSM-5 zeolite was higher than that of the SAPO-34 calcined in the nitrogen, whereas it was lower than that calcined in the air. The adsorption isotherm was correlated and the relation of the isotherm to the microstructure of the material was discussed. With more mesopore volume involved, the zeolite presented an S-shaped isotherm in contrast to the exponential isotherm of the silica gel. In addition, the significance of the S-shaped isotherm for the application in adsorption heat pump has also been addressed.

4. Encapsulation of protein molecules in transparent porous silica matrices via an aqueous colloidal sol-gel process

SciTech Connect

Liu, D.M.; Chen, I.W.

1999-12-10

Encapsulation of several biologically important proteins, cytochrome c, catalase, myoglobin, and hemoglobin, into transparent porous silica matrices by an aqueous colloidal sol-gel process that requires no alcohol is reported. Optical characterization indicates a successful retention of protein conformation after encapsulation. The conformation retention is strongly correlated to both the rate of gelation and the subsequent drying speed. Using hemoglobin as a model protein, a higher colloidal solid concentration and a lower synthesis pH were found, both causing faster gelation, resulting in a better retention of conformation. Hemoglobin encapsulated in a thin film, which dries faster, also showed a better retention than in the bulk. This is attributed to the fact that when a protein is isolated, and especially when it is confined to a space close to its own dimensions, conformational changes are sterically hindered, hence the structural stability. Enzymatic activity of bovine liver catalase was also monitored and showed a remarkable improvement when encapsulated using the aqueous colloidal process, compared to using the conventional alkoxide-based process. Thus, the aqueous colloidal sol-gel process offers a promising alternative to the conventional sol-gel process for encapsulating biomolecules into transparent, porous matrices.

5. Silica decorated on porous activated carbon nanofiber composites for high-performance supercapacitors

Kim, So Yeun; Kim, Bo-Hye

2016-10-01

A hybrid of silica decorated on porous activated carbon nanofibers (ACNFs) is fabricated in the form of a web via electrospinning and an activation process as an electrode material for electrochemical capacitors in an organic electrolyte. The introduction of PhSiH3 (PS) into the polyacrylonitrile (PAN) solution induces a porous ACNF structure containing silica nanoparticles (NPs) via the spontaneous sol-gel process of PS by steam in the subsequent physical activation process. These inorganic-organic hybrid composites of porous ACNF containing silica NPs show superior specific capacitance and energy density in electrochemical tests, along with good rate capability and excellent cycle life in an organic electrolyte, which is attributed to the combination of ACNF's high surface area and silica's hydrophilicity. The electrochemical performance decreases with increasing PS concentration, and this trend is consistent with the specific surface area results, which reveal the rapid formation of a double layer.

6. Diglycolamic acid modified silica gel for the separation of hazardous trivalent metal ions from aqueous solution.

PubMed

Suneesh, A S; Syamala, K V; Venkatesan, K A; Antony, M P; Vasudeva Rao, P R

2015-01-15

The surface of the silica gel was modified with diglycolamic acid moieties and the product (Si-DGAH) was characterized by elemental analysis, TG-DTA, (1)H and (29)Si NMR and scanning electron microscopy (SEM). The adsorption behavior of hazardous americium (III) and europium (III) in Si-DGAH was studied from aqueous nitric acid medium to examine the feasibility using the modified silica for the separation of Am(III) and Eu(III) from aqueous wastes. In this context, the effect of various parameters such as the duration of equilibration, and concentrations of europium, nitric acid, sodium nitrate and diethylenetriaminepentaacetic acid (DTPA) in aqueous phase, on the distribution coefficient (K(d)) of Am(III) and Eu(III) was investigated. The distribution coefficient of ∼10(3) mL/g (>99.9% extraction) was obtained for both Am(III) and Eu(III) at pH 3, and the K(d) values decreased with increase in the concentration of nitric acid. Rapid kinetics of extraction in the initial stages of equilibration, followed by the establishment of equilibrium occurred within 30 min. The extraction data were fitted into Langmuir adsorption model and the apparent europium extraction capacity was determined. Europium loading capacity of the sorbent was determined at various feed pH by column method. The study indicated the possibility of using diglycolamic acid-modified silica for the separation of Eu(III) and Am(III) from aqueous wastes. PMID:25454425

PubMed

Johari, Khairiraihanna; Saman, Norasikin; Mat, Hanapi

2014-01-01

8. Incorporation of mesoporous silica particles in gelatine gels: effect of particle type and surface modification on physical properties.

PubMed

Pérez-Esteve, Édgar; Oliver, Laura; García, Laura; Nieuwland, Maaike; de Jongh, Harmen H J; Martínez-Máñez, Ramón; Barat, José Manuel

2014-06-17

The aim of this work was to investigate the impact of mesoporous silica particles (MSPs) on the physicochemical properties of filled protein gels. We have studied the effect of the addition of different mesoporous silica particles, either bare or functionalized with amines or carboxylates, on the physical properties of gelatine gels (5% w/v). Textural properties of the filled gels were investigated by uniaxial compression, while optical properties were investigated by turbidity. The MSPs were characterized with the objective of correlating particle features with their impact on the corresponding filled-gel properties. The addition of MSPs (both with and without functionalization) increased the stiffness of the gelatine gels. Furthermore, functionalized MSPs showed a remarkable increase in the strength of the gels and a slight reduction in the brittleness of the gels, in contrast with nonfunctionalized MSPs which showed no effect on these two properties. The turbidity of the gels was also affected by the addition of all tested MSPs, showing that the particles that formed smaller aggregates resulted in a higher contribution to turbidity. MSPs are promising candidates for the development of functional food containing smart delivery systems, also being able to modulate the functionality of protein gels.

9. Analyzing the adsorption of blood plasma components by means of fullerene-containing silica gels and NMR spectroscopy in solids

Melenevskaya, E. Yu.; Mokeev, M. V.; Nasonova, K. V.; Podosenova, N. G.; Sharonova, L. V.; Gribanov, A. V.

2012-10-01

The results from studying the adsorption of blood plasma components (e.g., protein, triglycerides, cholesterol, and lipoproteins of low and high density) using silica gels modified with fullerene molecules (in the form of C60 or the hydroxylated form of C60(OH) x ) and subjected to hydration (or, alternatively, dehydration) are presented. The conditions for preparing adsorbents that allow us to control the adsorption capacity of silica gel and the selectivity of adsorption toward the components of blood plasma, are revealed. The nature and strength of the interactions of the introduced components (fullerene molecules and water) with functional groups on the silica surface are studied by means of solid state NMR spectroscopy (NMR-SS). Conclusions regarding the nature of the centers that control adsorption are drawn on the basis of NMR-SS spectra in combination with direct measurements of adsorption. The interaction of the oxygen of the hydroxyl group of silica gel with fullerene, leading to the formation of electron-donor complexes of C60-H, C60-OH, or C60-OSi type, is demonstrated by the observed changes in the NMR-SS spectra of silica gels in the presence of fullerene.

10. Characterizing tunable dynamics in an active gel

Henkin, Gil; Decamp, Stephen; Chen, Daniel; Dogic, Zvonimir

2014-03-01

We experimentally investigate dynamics of an active gel of bundled microtubules that is driven to far-from-equilibrium steady states by clusters of kinesin molecular motors. Upon the addition of ATP, the coordinated action of thousands of molecular motors drives this gel to an active, percolating state that persists for hours and is only limited by the stability of constituent proteins and the availability of the chemical fuel ATP. We extensively characterize how enhanced transport in emergent macroscopic flows depends on relevant molecular parameters, including ATP, motor, and depletant concentrations, microtubule concentration and length, as well as structure of the motor clusters. Our results show that the properties and dynamics of this active isotropic gel are highly tunable, suggesting that this is an ideal system for studying the behavior of active materials.

11. Adsorption of dichlorodifluoromethane, chlorodifluoromethane, chloropentafluoroethane, 1,1-difluoroethane, and 1,1,1,2-tetrafluoroethane on silica gel

SciTech Connect

Frere, M.; Berlier, K.; Bougard, J.; Jadot, R. . Service de Thermodynamique)

1994-10-01

The CFC's (chlorofluorocarbons) are used as working refrigerants fluids. The most commonly used are R12, R22, and R502 (48.8% R22 and 51.2% R115). Recent concerns of the effects of CFC's on the ozone layer require the development of efficient recovery methods. One technique is to adsorb the fluids onto a porous medium such as silica gel. Thermodynamic data on the adsorption of dichlorodifluoromethane (R12), chlorodifluoromethane (R22), chloropentafluoroethane (R115), 1,1-difluoroethane (R152a), and 1,1,1,2-tetrafluoroethane (R134a) on silica gel are required for the design of recovery units. The results are presented here.

12. Synthesis of molecularly imprinted polymer with 7-chloroethyl-theophylline-immobilized silica gel as template and its molecular recognition function

Zhang, Yuhui; Tong, Aijun; Li, Longdi

2004-01-01

By reaction of 7-chloroethyl-theophylline with aminopropylsilanized silica gel we synthesized a 7-chloroethyl-theophylline-immobilized silica gel as template molecule and prepared a molecularly imprinted polymer (MIP-Si), which had special recognition sites to 7-chloroethyl-theophylline. A conventional molecularly imprinted polymer (MIP) using 7-chloroethyl-theophylline as template was also prepared for comparison. Binding abilities to 7-chloroethyl-theophylline and its structural analogs revealed that the MIP-Si shows much higher binding speed and much more binding capacity than the MIP does.

13. Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions.

PubMed

Murphy, Ryan P; Hong, Kunlun; Wagner, Norman J

2016-08-23

Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions. PMID:27466883

14. SERI Desiccant Cooling Test Facility. Status report. Preliminary data on the performance of a rotary parallel-passage silica-gel dehumidifier

SciTech Connect

Schultz, K.J.

1986-04-01

This report describes the SERI Desiccant Cooling Test Facility. The facility can test bench-scale rotary dehumidifiers over a wide range of controlled conditions. We constructed and installed in the test loop a prototype parallel-passage rotary dehumidifier that has spirally wound polyester tape coated with silica gel. The initial tests gave satisfactory results indicating that approximately 90% of the silica gel was active and the overall Lewis number of the wheel was near unity. The facility has several minor difficulties including an inability to control humidity satisfactorily and nonuniform and highly turbulent inlet velocities. To completely validate the facility requires a range of dehumidifier designs. Several choices are available including constructing a second parallel-passage dehumidifier with the passage spacing more uniform.

15. Preparation and properties of aqueous castor oil-based polyurethane-silica nanocomposite dispersions through a sol-gel process.

PubMed

Xia, Ying; Larock, Richard C

2011-09-01

Waterborne castor oil-based polyurethane-silica nanocomposites with the polymer matrix and silica nanoparticles chemically bonded have been successfully prepared through a sol-gel process. The formation of silica nanoparticles in water not only reinforces the resulting coatings, but also increases the crosslink density of the nanocomposites. The (29)Si solid state NMR spectrum indicates the formation of silica and the TEM indicates that the nanoparticles are embedded in the polymers, resembling a core-shell structure. The silica nanoparticles in the polymer matrix play an important role in improving both the mechanical properties and the thermal stabilities of the resulting nanocomposites. This work provides an effective and promising way to prepare biorenewable, high performance nanocomposite coatings.

16. Role of alkyl alcohol on viscosity of silica-based chemical gels for decontamination of highly radioactive nuclear facilities

SciTech Connect

Choi, B. S.; Yoon, S. B.; Jung, C. H.; Lee, K. W.; Moon, J. K.

2012-07-01

Silica-based chemical gel for the decontamination of nuclear facilities was prepared by using fumed silica as a viscosifier, a 0.5 M Ce (IV) solution dissolved in concentrated nitric acid as a chemical decontamination agent, and tripropylene glycol butyl ether (TPGBE) as a co-viscosifier. A new effective strategy for the preparation of the chemical gel was investigated by introducing the alkyl alcohols as organic solvents to effectively dissolve the co-viscosifier. The mixture solution of the co-viscosifier and alkyl alcohols was more effective in the control of viscosity than that of the co-viscosifier only in gel. Here, the alkyl alcohols played a key role as an effective dissolution solvent for the co-viscosifier in the preparation of the chemical gel, resulting in a reducing of the amount of the co-viscosifier and gel time compared with that of the chemical gel prepared without the alkyl alcohols. It was considered that the alkyl alcohols contributed to the effective dissolution of the co-viscosifier as well as the homogeneous mixing in the formation of the gel, while the co-viscosifier in an aqueous media of the chemical decontamination agent solution showed a lower solubility. The decontamination efficiency of the chemical gels prepared in this work using a multi-channel analyzer (MCA) showed a high decontamination efficiency of over ca. 94% and ca. 92% for Co-60 and Cs-137 contaminated on surface of the stainless steel 304, respectively. (authors)

17. Novel multifunctional titania-silica-lanthanum phosphate nanocomposite coatings through an all aqueous sol-gel process.

PubMed

Smitha, Venu Sreekala; Jyothi, Chembolli Kunhatta; Peer, Mohamed A; Pillai, Saju; Warrier, Krishna Gopakumar

2013-04-01

A novel nanocomposite coating containing titania, silica and lanthanum phosphate prepared through an all aqueous sol-gel route exhibits excellent self-cleaning ability arising from the synergistic effect of the constituents in the nanocomposite. A highly stable titania-silica-lanthanum phosphate nanocomposite sol having particle size in the range of 30-50 nm has been synthesized starting from a titanyl sulphate precursor, which was further used for the development of photocatalytically active composite coatings on glass. The coatings prepared by the dip coating technique as well as the nanocomposite powders are heat treated and characterized further for their morphology and multifunctionality. The nanocomposite containing 1.5 wt% LaPO4 has shown a surface area as high as 138 m(2) g(-1) and a methylene blue degradation efficiency of 94% in two hours of UV exposure. The composite coating has shown very good homogeneity evidenced by transparency as high as 99.5% and low wetting behaviour. The present novel approach for energy conserving, aqueous derived, self-cleaning coatings may be suitable for large scale industrial applications.

18. Experimental measurement and thermodynamic modeling of the mixed CH4 + C3H8 clathrate hydrate equilibria in silica gel pores: effects of pore size and salinity.

PubMed

Lee, Seungmin; Seo, Yongwon

2010-06-15

We measured hydrate phase equilibria for the ternary CH(4) (90%) + C(3)H(8) (10%) + water mixtures in silica gel pores with nominal diameters of 6.0, 15.0, 30.0, and 100.0 nm and for the quaternary CH(4) (90%) + C(3)H(8) (10%) + NaCl + water mixtures of two different NaCl concentrations (3 and 10 wt %) in silica gel pores with nominal diameters of 6.0, 15.0, and 30.0 nm. The CH(4) (90%) + C(3)H(8) (10%) hydrate-water interfacial tension (sigma(HW)) of 42 +/- 3 mJ/m(2) was obtained through the Gibbs-Thomson equation for dissociation within cylindrical pores. With this value, the experimental results were in good agreement with the calculated ones based on the van der Waals and Platteeuw model. A correction term for the capillary effect and a Pitzer model for electrolyte solutions were adopted to calculate the activity of water in the aqueous electrolyte solutions within silica gel pores. At a specified temperature, three-phase H-L(W)-V equilibrium curves of pore hydrates were shifted to higher-pressure regions depending on pore sizes and NaCl concentrations. From the cage-dependent (13)C NMR chemical shifts of enclathrated guest molecules, the mixed CH(4) (90%) + C(3)H(8) (10%) gas hydrate was confirmed to be structure II.

19. Hydrogen generation systems and methods utilizing sodium silicide and sodium silica gel materials

SciTech Connect

Wallace, Andrew P.; Melack, John M.; Lefenfeld, Michael

2015-08-11

Systems, devices, and methods combine thermally stable reactant materials and aqueous solutions to generate hydrogen and a non-toxic liquid by-product. The reactant materials can sodium silicide or sodium silica gel. The hydrogen generation devices are used in fuels cells and other industrial applications. One system combines cooling, pumping, water storage, and other devices to sense and control reactions between reactant materials and aqueous solutions to generate hydrogen. Springs and other pressurization mechanisms pressurize and deliver an aqueous solution to the reaction. A check valve and other pressure regulation mechanisms regulate the pressure of the aqueous solution delivered to the reactant fuel material in the reactor based upon characteristics of the pressurization mechanisms and can regulate the pressure of the delivered aqueous solution as a steady decay associated with the pressurization force. The pressure regulation mechanism can also prevent hydrogen gas from deflecting the pressure regulation mechanism.

20. The enhancement of benzotriazole on epoxy functionalized silica sol-gel coating for copper protection

Peng, Shusen; Zhao, Wenjie; Li, He; Zeng, Zhixiang; Xue, Qunji; Wu, Xuedong

2013-07-01

The influence of the amount of benzotriazole (BTA) on the wetting and anticorrosion ability of the epoxy functionalized silica sol-gel (ESol) coating was studied by various complementary methods. IR results demonstrate that BTA reacted with ESol through a 1:1 addition reaction of Nsbnd H to epoxy group. The water contact angle of the ESol coating increases with an increase in the amount of BTA. SEM and adhesion tests reveal that BTA could improve the adhesion of ESol to copper surface. Moreover, the best protection was achieved when the amount of BTA equals to the molar number of epoxy group in the ESol coating according to the results of electrochemical measurements and salt spray test.

1. Thermal Characteristics of Chemical Refrigerating Apparatus using Silica-Gel/ Inorganic-Salt-Solution Pair

This report deals with chemical refrigerating apparatus using silica-gel / inorganic-salt-solution pair. Experiments are conducted by changing concentration of inorganic-salt solution and adsorbent / refrigerant pair. The following results are obtained. (1) The temperature of refrigerant in evaporator is lowered as decrease of inorganic-salt-solution concentration. (2) The available salt-concentration range as refrigerant are gained by supercooling in restricted temperature range lower than solidification temperature of solution. (3)Difference of minimum temperature among cooled refrigerants are little in low concentration region. (4)In concentration lower than about10wt%, refrigerants supercool and solidify suddenly. Accordingly these salt-solutions are not available in these region as refrigerants.

2. Study of Solar Driven Silica gel-Water based Adsorption Chiller

Habib, K.; Assadi, M. K.; Zainudin, M. H. B.

2015-09-01

In this study, a dynamic behaviour of a solar powered single stage four bed adsorption chiller has been analysed designed for Malaysian climate. Silica gel and water have been used as adsorbent-refrigerant pair. A simulation program has been developed for modeling and performance evaluation of the chiller using the meteorological data of Kuala Lumpur. The optimum cooling capacity and coefficient of performance (COP) are calculated in terms of adsorption/desorption cycle time and regeneration temperature. Results indicate that the chiller is feasible even when low temperature heat source is available. Results also show that the adsorption cycle can achieve a cooling capacity of 14 kW when the heat source temperature is about 85°C.

3. Hydrogen generation systems utilizing sodium silicide and sodium silica gel materials

SciTech Connect

Wallace, Andrew P.; Melack, John M.; Lefenfeld, Michael

2015-07-14

Systems, devices, and methods combine reactant materials and aqueous solutions to generate hydrogen. The reactant materials can sodium silicide or sodium silica gel. The hydrogen generation devices are used in fuels cells and other industrial applications. One system combines cooling, pumping, water storage, and other devices to sense and control reactions between reactant materials and aqueous solutions to generate hydrogen. Multiple inlets of varied placement geometries deliver aqueous solution to the reaction. The reactant materials and aqueous solution are churned to control the state of the reaction. The aqueous solution can be recycled and returned to the reaction. One system operates over a range of temperatures and pressures and includes a hydrogen separator, a heat removal mechanism, and state of reaction control devices. The systems, devices, and methods of generating hydrogen provide thermally stable solids, near-instant reaction with the aqueous solutions, and a non-toxic liquid by-product.

4. Performance predictions of silica-gel desiccant dehumidifiers. Technical report No. 3

SciTech Connect

Mathiprakasam, B.; Lavan, Z.

1980-01-01

The analysis of a cross-cooled desiccant dehumidifier using silica gel in the form of sheets is described. This unit is the principal component of solar powered desiccant air conditioning system. The mathematical model has first been formulated describing the dynamics of the dehumidifier. The model leads to a system of nonlinear coupled heat and mass transfer equations for the sorption processes and linear heat transfer equations for the purging processes. The model accounts for the gas film resistance and for the moisture diffusion in the desiccant. The governing equations are solved by a finite difference scheme to obtain periodic steady state solutions. The accuracy of the theoretical predictions is ascertained by comparing them with the experimental results. The performance of the dehumidifier, for a chosen set of initial conditions and dehumidifier parameters, has also been given.

5. Facile sol-gel synthesis of porous silicas using poly(propylene)imine dendrimers as templates

SciTech Connect

Larsen, Gustavo; Lotero, Edgar; Marquez, Manuel

2000-08-01

Commercially available poly(propylene)imine (DAB-Am-32 and DAB-Am-64) dendrimers were used as single-molecule templates to tailor the porosity of silicas via a nonacidic sol-gel method. X-ray diffraction on both the as-prepared (oven-dried at 373 K) and the calcined (833 K) materials revealed that modest contraction took place on template removal and that the cavities created did not achieve three-dimensional ordering under the current synthesis conditions. Transmission electron microscopy of ''Pt-stained'' samples supported this picture. A modified Horvath-Kawazoe analysis of the argon adsorption isotherms indicated that DAB-Am-64 is a much more effective template than DAB-Am-32. Pyrolysis and oxidation protocols for template removal are also presented. (c) 2000 Materials Research Society.

6. Entropy generation analysis of two-bed, silica gel-water, non-regenerative adsorption chillers

Chua, H. T.; Ng, K. C.; Malek, A.; Kashiwagi, T.; Akisawa, A.; Saha, B. B.

1998-06-01

The current thrust on the use of environmentally friendly technologies for cooling applications, inter alia, envisages the adoption of adsorption systems. Adsorption chillers are known to be inefficient' due to their low coefficient of performance. Although the basic physics of heat and mass transfer in various components of the system is well understood, there is a lacuna in the quantification of irreversibilities. In this paper, a silica gel-water, two-bed, non-regenerative chiller is analysed. It is shown that the largest cycle-averaged rate of entropy generation is in the beds and that the least is in the condenser. The entropy generation rates in the beds are further studied, showing that the maximum contribution is made during the switching phase. In general, manufacturers' effort to maximize cooling capacity is shown to correspond to maximum entropy generation in the evaporator.

7. Selective preconcentration of uranyl ion by silica gel phases modified with chelating compounds as inorganic polymeric ion exchangers.

PubMed

Mahmoud, Mohamed E; Kenawy, Ibrahim M M; Soliman, Ezzat M; Hafez, Medhat A; Akl, Magda A A; Lashein, Rabab R A

2008-03-01

Four chemically modified chelating silica gel phases (I - IV) with ion exchange groups were tested for their potential capability to selectively bind, extract and preconcentrate uranyl ions (UO(2)(2+)) from different aqueous solutions as well as ore samples. Factors affecting such determination processes were studied and optimized. These included the pH of the contact solution, the mass of the silica gel phase extractant, the stirring time during the application of a static technique and the eluent concentration for desorption of the surface-bound uranyl ion and interfering anions and cations. All these factors were evaluated on the basis of determinations of the distribution coefficient value (K(d)) and the percent recovery (R%). Percent recovery values of 91% for silica phase (II) and 93% for silica phase (IV) were identified in the optimum conditions. The proposed preconcentration method was further applied to uranium ore samples as well as granite samples. The determined percentage and ppm values are in good agreement with the standard assigned ones. The structure of the synthesized silica gel phases (I - IV) and their uranyl bound complexes were identified and characterized by means of infrared analysis, thermal analysis (TGA) and potentiometric titration.

8. Selective preconcentration of uranyl ion by silica gel phases modified with chelating compounds as inorganic polymeric ion exchangers.

PubMed

Mahmoud, Mohamed E; Kenawy, Ibrahim M M; Soliman, Ezzat M; Hafez, Medhat A; Akl, Magda A A; Lashein, Rabab R A

2008-03-01

Four chemically modified chelating silica gel phases (I - IV) with ion exchange groups were tested for their potential capability to selectively bind, extract and preconcentrate uranyl ions (UO(2)(2+)) from different aqueous solutions as well as ore samples. Factors affecting such determination processes were studied and optimized. These included the pH of the contact solution, the mass of the silica gel phase extractant, the stirring time during the application of a static technique and the eluent concentration for desorption of the surface-bound uranyl ion and interfering anions and cations. All these factors were evaluated on the basis of determinations of the distribution coefficient value (K(d)) and the percent recovery (R%). Percent recovery values of 91% for silica phase (II) and 93% for silica phase (IV) were identified in the optimum conditions. The proposed preconcentration method was further applied to uranium ore samples as well as granite samples. The determined percentage and ppm values are in good agreement with the standard assigned ones. The structure of the synthesized silica gel phases (I - IV) and their uranyl bound complexes were identified and characterized by means of infrared analysis, thermal analysis (TGA) and potentiometric titration. PMID:18332547

9. Analysis based on the diffusion model for saturation silica gel with water vapor at conservation units steam circuit TPP

Goldaev, Sergey; Khushvaktov, Alisher

2015-01-01

A quantitative analysis of the diffusion model dehumidifying air in the steam circuit of TPP, with a layer of silica gel. Showed that such an approximation, supplemented the experimental value of the coefficient of free diffusion identified by the developed method gives reliable values for the concentration of water vapor absorption over time.

10. Facile preparation of transparent and dense CdS-silica gel glass nanocomposites for optical limiting applications.

PubMed

Feng, Miao; Zhan, Hongbing

2014-04-21

To realize their practical and operable applications as a potential optical limiting (OL) material, quantum dots (QDs) need to have good processability by incorporating them into optical-quality matrices. This work reports a facile route for the room-temperature preparation of large, stable transparent monolithic CdS nanocomposites which can be easily extended to allow the introduction of acid-sensitive functional molecules/nanoparticles into a silica network by sol-gel chemistry. Our strategy involves a two-step sol-gel process (acid-catalyst hydrolysis and basic-catalyst condensation) and the co-condensation of the resulting alkoxysilane-capped CdS QDs with other alkoxysilanes, which allows the CdS QDs to become part of the silica covalent network. The degradation and agglomeration of CdS QDs were thereby effectively restrained, and large monolithic transparent CdS-silica gel glass was obtained. Using Z-scan theory and the resulting open-aperture Z-scan curves, the nonlinear extinction coefficient of the CdS-silica nanocomposite gel glass was calculated to be 1.02 × 10(-14) cm W(-1), comparable to that of the parent CdS QD dispersion, indicating their promise for OL applications.

11. Processing of CuAlMn Shape Memory Foams with Open Spherical Pores by Silica-Gel Beads Infiltration Method

Li, Hua; Yuan, Bin; Gao, Yan

2016-10-01

12. Processing of CuAlMn Shape Memory Foams with Open Spherical Pores by Silica-Gel Beads Infiltration Method

Li, Hua; Yuan, Bin; Gao, Yan

2016-08-01

13. Comparison of Nanoparticle Exposures Between Fumed and Sol-gel Nano-silica Manufacturing Facilities

PubMed Central

OH, Sewan; KIM, Boowook; KIM, Hyunwook

2014-01-01

Silica nanoparticles (SNPs) are widely used all around the world and it is necessary to evaluate appropriate risk management measures. An initial step in this process is to assess worker exposures in their current situation. The objective of this study was to compare concentrations and morphologic characteristics of fumed (FS) and sol-gel silica nanoparticles (SS) in two manufacturing facilities. The number concentration (NC) and particle size were measured by a real-time instrument. Airborne nanoparticles were subsequently analyzed using a TEM/EDS. SNPs were discharged into the air only during the packing process, which was the last manufacturing step in both the manufacturing facilities studied. In the FS packing process, the geometric mean (GM) NC in the personal samples was 57,000 particles/cm3. The geometric mean diameter (GMD) measured by the SMPS was 64 nm. Due to the high-temperature formation process, the particles exhibited a sintering coagulation. In the SS packing process that includes a manual jet mill operation, the GM NC was calculated to be 72,000 particles/cm3 with an assumption of 1,000,000 particles/cm3 when the upper limit is exceeded (5% of total measure). The particles from SS process had a spherical-shaped morphology with GMD measured by SMPS of 94 nm. PMID:24583511

14. Amorphization of quartz by friction: Implication to silica-gel lubrication of fault surfaces

Nakamura, Yu; Muto, Jun; Nagahama, Hiroyuki; Shimizu, Ichiko; Miura, Takashi; Arakawa, Ichiro

2012-11-01

To understand physico-chemical processes at real contacts (asperities) on fault surfaces, we conducted pin-on-disk friction experiments at room temperature, using single crystalline quartz disks and quartz pins. Velocity weakening from friction coefficient μ ˜ 0.6 to 0.4 was observed under apparent normal stresses of 8-19 (18 > 19), when the slip rate was increased from 0.003 to 2.6 m/s. Frictional surfaces revealed ductile deformation of wear materials. The Raman spectra of frictional tracks showed blue shifts and broadening of quartz main bands, and appearance of new peaks at 490-520 and 610 cm-1. All these features are indicative of pressure- and strain-induced amorphization of quartz. The mapping analyses of Fourier transform infrared (FT-IR) spectroscopy at room dry conditions suggest selective hydration of wear materials. It is possible that the strained Si-O-Si bridges in amorphous silica preferentially react with water to form silica-gel. In natural fault systems, amorphous materials would be produced at real fault contacts and accumulate over the fault surfaces with displacements. Subsequent hydration would lead to significant reduction of fault strength during slip.

15. Application of Hectorite-Coated Silica Gel Particles as a Packing Material for Chromatographic Resolution.

PubMed

Okada, Tomohiko; Kumasaki, Aisaku; Shimizu, Kei; Yamagishi, Akihiko; Sato, Hisako

2016-08-01

A new type of clay column particles was prepared, in which a hectorite layer (∼0.1 µm thickness) covered uniformly the surface of amorphous silica particles with an average radius of 5 µm (ref. Okada et al., The Journal of Physical Chemistry C, 116, 21864-21869 (2012)). The hectorite layer was fully ion-exchanged with Δ-[Ru(phen)3](2+) (phen = 1,10-phenanthroline) ions by being immersed in a methanol solution of Δ-[Ru(phen)3](ClO4)2 (1 mM). The modified silica gel particles thus prepared were packed into a stainless steel tube (4 mm (i.d.) × 25 cm) as a high-performance liquid chromatography column. Optical resolution was achieved when the racemic mixtures of several metal complexes or organic molecules were eluted with methanol. In the case of tris(acetylacetonato)ruthenium(III) ([Ru(acac)3]), for example, the Λ- and Δ-enantiomers gave an elution volume of 2.6 and 3.0 mL, respectively, with the separation factor of 1.2. The total elution volume (5 mL) was nearly one-tenth for the previously reported column of the same size (RU-1 (Shiseido Co., Ltd.)) packed with the spray-dried particles of synthetic hectorite (average radius 5 µm) ion-exchanged by the same Ru(II) complexes. PMID:27130880

16. Application of Hectorite-Coated Silica Gel Particles as a Packing Material for Chromatographic Resolution.

PubMed

Okada, Tomohiko; Kumasaki, Aisaku; Shimizu, Kei; Yamagishi, Akihiko; Sato, Hisako

2016-08-01

A new type of clay column particles was prepared, in which a hectorite layer (∼0.1 µm thickness) covered uniformly the surface of amorphous silica particles with an average radius of 5 µm (ref. Okada et al., The Journal of Physical Chemistry C, 116, 21864-21869 (2012)). The hectorite layer was fully ion-exchanged with Δ-[Ru(phen)3](2+) (phen = 1,10-phenanthroline) ions by being immersed in a methanol solution of Δ-[Ru(phen)3](ClO4)2 (1 mM). The modified silica gel particles thus prepared were packed into a stainless steel tube (4 mm (i.d.) × 25 cm) as a high-performance liquid chromatography column. Optical resolution was achieved when the racemic mixtures of several metal complexes or organic molecules were eluted with methanol. In the case of tris(acetylacetonato)ruthenium(III) ([Ru(acac)3]), for example, the Λ- and Δ-enantiomers gave an elution volume of 2.6 and 3.0 mL, respectively, with the separation factor of 1.2. The total elution volume (5 mL) was nearly one-tenth for the previously reported column of the same size (RU-1 (Shiseido Co., Ltd.)) packed with the spray-dried particles of synthetic hectorite (average radius 5 µm) ion-exchanged by the same Ru(II) complexes.

17. Phospholipid fatty acids as physiological indicators of Paracoccus denitrificans encapsulated in silica sol-gel hydrogels.

PubMed

Trögl, Josef; Jirková, Ivana; Kuráň, Pavel; Akhmetshina, Elmira; Brovdyová, Taťjána; Sirotkin, Alexander; Kirilina, Tatiana

2015-01-01

The phospholipid fatty acid (PLFA) content was determined in samples of Paracoccus denitrificans encapsulated in silica hydrogel films prepared from prepolymerized tetramethoxysilane (TMOS). Immediately after encapsulation the total PLFA concentration was linearly proportional to the optical density (600 nm) of the input microbial suspension (R2 = 0.99). After 7 days this relationship remained linear, but with significantly decreased slope, indicating a higher extinction of bacteria in suspensions of input concentration 108 cells/mL and higher. trans-Fatty acids, indicators of cytoplasmatic membrane disturbances, were below the detection limit. The cy/pre ratio (i.e., ratio of cyclopropylated fatty acids (cy17:0 + cy19:0) to their metabolic precursors (16:1ω7 + 18:1ω7)), an indicator of the transition of the culture to a stationary growth-phase, decreased depending on co-immobilization of nutrients in the order phosphate buffer > mineral medium > Luria Broth rich medium. The ratio, too, was logarithmically proportional to cell concentration. These results confirm the applicability of total PLFA as an indicator for the determination of living biomass and cy/pre ratio for determination of nutrient limitation of microorganisms encapsulated in sol-gel matrices. This may be of interest for monitoring of sol-gel encapsulated bacteria proposed as optical recognition elements in biosensor construction, as well as other biotechnological applications. PMID:25690547

18. Phospholipid Fatty Acids as Physiological Indicators of Paracoccus denitrificans Encapsulated in Silica Sol-Gel Hydrogels

PubMed Central

Trögl, Josef; Jirková, Ivana; Kuráň, Pavel; Akhmetshina, Elmira; Brovdyová, Tat′jána; Sirotkin, Alexander; Kirilina, Tatiana

2015-01-01

The phospholipid fatty acid (PLFA) content was determined in samples of Paracoccus denitrificans encapsulated in silica hydrogel films prepared from prepolymerized tetramethoxysilane (TMOS). Immediately after encapsulation the total PLFA concentration was linearly proportional to the optical density (600 nm) of the input microbial suspension (R2 = 0.99). After 7 days this relationship remained linear, but with significantly decreased slope, indicating a higher extinction of bacteria in suspensions of input concentration 108 cells/mL and higher. trans-Fatty acids, indicators of cytoplasmatic membrane disturbances, were below the detection limit. The cy/pre ratio (i.e., ratio of cyclopropylated fatty acids (cy17:0 + cy19:0) to their metabolic precursors (16:1ω7 + 18:1ω7)), an indicator of the transition of the culture to a stationary growth-phase, decreased depending on co-immobilization of nutrients in the order phosphate buffer > mineral medium > Luria Broth rich medium. The ratio, too, was logarithmically proportional to cell concentration. These results confirm the applicability of total PLFA as an indicator for the determination of living biomass and cy/pre ratio for determination of nutrient limitation of microorganisms encapsulated in sol-gel matrices. This may be of interest for monitoring of sol-gel encapsulated bacteria proposed as optical recognition elements in biosensor construction, as well as other biotechnological applications. PMID:25690547

19. Colloidal quantum-dot-based silica gel glass: two-photon absorption, emission, and quenching mechanism.

PubMed

Li, Jingzhou; Dong, Hongxing; Zhang, Saifeng; Ma, Yunfei; Wang, Jun; Zhang, Long

2016-09-28

Two-photon (TP) three-dimensional solid matrices have potential applications in high density optical data reading and storage, infrared-pumped visible displays, lasers, etc. Such technologies will benefit greatly from the advantageous properties of TP materials including tunable emission wavelength, photostability, and simple chemical processing. Here, this ideal TP solid is made possible by using a facile sol-gel process to engineer colloid quantum dots into silica gel glass. Characterization using an open-aperture Z-scan technique shows that the solid matrices exhibited significant TP optical properties with a TP absorption coefficient of (9.41 ± 0.39) × 10(-2) cm GW(-1) and a third-order nonlinear figure of merit of (7.30 ± 0.30) × 10(-14) esu cm. In addition, the dependence of the TP properties on high-temperature thermal treatment is studied in detail to obtain a clear insight for practical applications. The results illustrate that the sample can maintain stable TP performance below the synthesis temperature of the CdTe/CdS colloidal quantum dots. Furthermore, the mechanisms for thermal quenching of photoluminescence under different temperature regimes are clarified as a function of the composition.

20. Epoxide opening versus silica condensation during sol-gel hybrid biomaterial synthesis.

PubMed

Gabrielli, Luca; Russo, Laura; Poveda, Ana; Jones, Julian R; Nicotra, Francesco; Jiménez-Barbero, Jesús; Cipolla, Laura

2013-06-10

Hybrid organic-inorganic solids represent an important class of engineering materials, usually prepared by sol-gel processes by cross-reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3-Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid-material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2-11) was deeply investigated for the first time by solution-state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy-ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol-gel hybrid biomaterials with tuneable properties.

1. Colloidal quantum-dot-based silica gel glass: two-photon absorption, emission, and quenching mechanism.

PubMed

Li, Jingzhou; Dong, Hongxing; Zhang, Saifeng; Ma, Yunfei; Wang, Jun; Zhang, Long

2016-09-28

Two-photon (TP) three-dimensional solid matrices have potential applications in high density optical data reading and storage, infrared-pumped visible displays, lasers, etc. Such technologies will benefit greatly from the advantageous properties of TP materials including tunable emission wavelength, photostability, and simple chemical processing. Here, this ideal TP solid is made possible by using a facile sol-gel process to engineer colloid quantum dots into silica gel glass. Characterization using an open-aperture Z-scan technique shows that the solid matrices exhibited significant TP optical properties with a TP absorption coefficient of (9.41 ± 0.39) × 10(-2) cm GW(-1) and a third-order nonlinear figure of merit of (7.30 ± 0.30) × 10(-14) esu cm. In addition, the dependence of the TP properties on high-temperature thermal treatment is studied in detail to obtain a clear insight for practical applications. The results illustrate that the sample can maintain stable TP performance below the synthesis temperature of the CdTe/CdS colloidal quantum dots. Furthermore, the mechanisms for thermal quenching of photoluminescence under different temperature regimes are clarified as a function of the composition. PMID:27602563

2. Silica sol-gel encapsulated methylotrophic yeast as filling of biofilters for the removal of methanol from industrial wastewater.

PubMed

Kamanina, Olga A; Lavrova, Daria G; Arlyapov, Viacheslav A; Alferov, Valeriy A; Ponamoreva, Olga N

2016-10-01

This research suggests the use of new hybrid biomaterials based on methylotrophic yeast cells covered by an alkyl-modified silica shell as biocatalysts. The hybrid biomaterials are produced by sol-gel chemistry from silane precursors. The shell protects microbial cells from harmful effects of acidic environment. Potential use of the hybrid biomaterials based on methylotrophic yeast Ogataea polymorpha VKM Y-2559 encapsulated into alkyl-modified silica matrix for biofilters is represented for the first time. Organo-silica shells covering yeast cells effectively protect them from exposure to harmful factors, including extreme values of pH. The biofilter based on the organic silica matrix encapsulated in the methylotrophic yeast Ogataea polymorpha BKM Y-2559 has an oxidizing power of 3 times more than the capacity of the aeration tanks used at the chemical plants during methyl alcohol production. This may lead to the development of new and effective industrial wastewater treatment technologies. PMID:27542749

3. Silica sol-gel encapsulated methylotrophic yeast as filling of biofilters for the removal of methanol from industrial wastewater.

PubMed

Kamanina, Olga A; Lavrova, Daria G; Arlyapov, Viacheslav A; Alferov, Valeriy A; Ponamoreva, Olga N

2016-10-01

This research suggests the use of new hybrid biomaterials based on methylotrophic yeast cells covered by an alkyl-modified silica shell as biocatalysts. The hybrid biomaterials are produced by sol-gel chemistry from silane precursors. The shell protects microbial cells from harmful effects of acidic environment. Potential use of the hybrid biomaterials based on methylotrophic yeast Ogataea polymorpha VKM Y-2559 encapsulated into alkyl-modified silica matrix for biofilters is represented for the first time. Organo-silica shells covering yeast cells effectively protect them from exposure to harmful factors, including extreme values of pH. The biofilter based on the organic silica matrix encapsulated in the methylotrophic yeast Ogataea polymorpha BKM Y-2559 has an oxidizing power of 3 times more than the capacity of the aeration tanks used at the chemical plants during methyl alcohol production. This may lead to the development of new and effective industrial wastewater treatment technologies.

4. Specific Interactions of Neutral Side Chains of an Adsorbed Protein with the Surface of α-Quartz and Silica Gel.

PubMed

Odinokov, Alexey V; Bagaturyants, Alexander A

2015-07-16

Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of the open questions is the interaction of nonpolar side chains with siloxane cavities. Here, we use nonequilibrium molecular dynamics simulations for the detailed investigation of the binding of several hydrophobic and amphiphilic protein side chains with silica surface. These interactions were found to be a possible driving force for protein adsorption. The free energy gain was larger for the disordered surface of amorphous silica gel as compared to α-quartz, but the impact depended on the type of amino acid. The dependence was analyzed from the structural point of view. For every amino acid an enthalpy-entropy compensation behavior was observed. These results confirm a hypothesis of an essential role of hydrophobic interactions in protein unfolding and irreversible adsorption on the silica surface.

5. Er3+-activated photonic structures fabricated by sol-gel and rf-sputtering techniques

Ferrari, M.; Alombert-Goget, G.; Armellini, C.; Berneschi, S.; Bhaktha, S. N. B.; Boulard, B.; Brenci, M.; Chiappini, A.; Chiasera, A.; Duverger-Arfuso, C.; Féron, P.; Gonçalves, R. R.; Jestin, Y.; Minati, L.; Moser, E.; Nunzi Conti, G.; Pelli, S.; Rao, D. N.; Retoux, R.; Righini, G. C.; Speranza, G.

2009-05-01

The realization of photonic structures operating at visible and near infrared frequencies is a highly attractive scientific and technological challenge. Since optical fiber innovation, a huge of activity has been performed leading to interesting results, such as optical waveguides and planar lightwave circuits, microphotonic devices, optical microcavities, nanowires, plasmonic structures, and photonic crystals. These systems have opened new possibilities in the field of both basic and applied physics, in a large area covering Information Communication Technologies, Health and Biology, Structural Engineering, and Environment Monitoring Systems. Several materials and techniques are employed to successfully fabricate photonic structures. Concerning materials, Er3+-activated silica-based glasses still play an important role, although recently interesting results have been published about fluoride glass-ceramic waveguides. As far as regards the fabrication methods sol-gel route and rf sputtering have proved to be versatile and reliable techniques. In this article we will present a review of some Er3+-activated photonic structures fabricated by sol gel route and rf sputtering deposition. In the discussion on the sol-gel approach we focus our attention on the silica-hafnia binary system presenting an overview concerning fabrication protocols and structural, optical and spectroscopic assessment of SiO2-HfO2 waveguides activated by Er3+ ions. In order to put in evidence the reliability and versatility of the sol-gel route for photonics applications four different confined structures are briefly presented: amorphous waveguides, coated microspheres, monolithic waveguide laser, and core-shell nanospheres. As examples of rf sputtering technique, we will discuss Er3+-activated silica-hafnia and silica-germania waveguides, the latter system allowing fabrication of integrated optics structures by UV photo-imprinting. Finally, two examples of photonic crystal structures, one

6. Incorporating silica into cyanate ester-based network by sol-gel method: Structure and properties of subnano- and nanocomposites

Bershtein, V.; Fainleib, A.; Kirilenko, D.; Yakushev, P.; Gusakova, K.; Lavrenyuk, N.; Ryzhov, V.

2016-05-01

A series of Cyanate Ester Resins (CER)-based composites containing 0.01-10 wt. % silica, introduced by sol-gel method, was synthesized using tetraethoxysilane (TEOS) and γ-aminopropyltrimethoxysilane (APTMS), and their nanostructure and properties were characterized by means of STEM/EDXS, Far-IR spectroscopy, DMA and DSC methods. It was revealed that the most substantial positive impact on CER dynamics, thermal and mechanical properties is attained at ultra-low silica contents, e.g., at 0.1 wt. % silica where Tg and modulus increase, respectively, by 50° and 60%. In this case, silica nanoclusters are absent in the composite, and only chemically incorporated silica junctions of subnanometric size in the densely-crosslinked CER network could be implied. These composites can be designated as "polymer subnanocomposites". Contrarily, formation of silica nanoclusters and especially their aggregates of hundreds nanometers in size at silica contents of 2-10 wt. % led to the distinct negative impact on the matrix properties.

7. Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Gabrovska, M.; Krstić, J.; Tzvetkov, P.; Tenchev, K.; Shopska, M.; Vukelić, N.; Jovanović, D.

2011-12-01

Ni/SiO2 materials with identical composition (SiO2/Ni = 1.0) have been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO2 precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H2-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni2+-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni2+-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of

8. Sol-Gel-Based Titania-Silica Thin Film Overlay for Long Period Fiber Grating-Based Biosensors.

PubMed

Chiavaioli, Francesco; Biswas, Palas; Trono, Cosimo; Jana, Sunirmal; Bandyopadhyay, Somnath; Basumallick, Nandini; Giannetti, Ambra; Tombelli, Sara; Bera, Susanta; Mallick, Aparajita; Baldini, Francesco

2015-12-15

An evanescent wave optical fiber biosensor based on titania-silica-coated long period grating (LPG) is presented. The chemical overlay, which increases the refractive index (RI) sensitivity of the sensor, consists of a sol-gel-based titania-silica thin film, deposited along the sensing portion of the fiber by means of the dip-coating technique. Changing both the sol viscosity and the withdrawal speed during the dip-coating made it possible to adjust the thickness of the film overlay, which is a crucial parameter for the sensor performance. After the functionalization of the fiber surface using a methacrylic acid/methacrylate copolymer, an antibody/antigen (IgG/anti-IgG) assay was carried out to assess the performance of sol-gel based titania-silica-coated LPGs as biosensors. The analyte concentration was determined from the wavelength shift at the end of the binding process and from the initial binding rate. This is the first time that a sol-gel based titania-silica-coated LPG is proposed as an effective and feasible label-free biosensor. The specificity of the sensor was validated by performing the same model assay after spiking anti-IgG into human serum. With this structured LPG, detection limits of the order of tens of micrograms per liter (10(-11) M) are attained.

9. Gold Incorporated Mesoporous Silica Thin Film Model Surface as a Robust SERS and Catalytically Active Substrate.

PubMed

Sunil Sekhar, Anandakumari Chandrasekharan; Vinod, Chathakudath Prabhakaran

2016-01-01

Ultra-small gold nanoparticles incorporated in mesoporous silica thin films with accessible pore channels perpendicular to the substrate are prepared by a modified sol-gel method. The simple and easy spin coating technique is applied here to make homogeneous thin films. The surface characterization using FESEM shows crack-free films with a perpendicular pore arrangement. The applicability of these thin films as catalysts as well as a robust SERS active substrate for model catalysis study is tested. Compared to bare silica film our gold incorporated silica, GSM-23F gave an enhancement factor of 10³ for RhB with a laser source 633 nm. The reduction reaction of p-nitrophenol with sodium borohydride from our thin films shows a decrease in peak intensity corresponding to -NO₂ group as time proceeds, confirming the catalytic activity. Such model surfaces can potentially bridge the material gap between a real catalytic system and surface science studies. PMID:27213321

10. Corrections for measurements of tritium in subterranean vapor using silica gel.

PubMed

Whicker, Jeffrey J; Dewart, Jean M; Allen, Shannon P; Eisele, William F; McNaughton, Michael W; Green, Andrew A

2011-01-01

Hazardous contaminants buried within vadose zones can accumulate in soil gas. The concentrations and spatial extent of these contaminants are measured to evaluate potential transport to groundwater for public risk evaluation. Tritium is an important contaminant found and monitored for in vadose zones across numerous sites within the US nuclear weapons complex, including Los Alamos National Laboratory. The extraction, collection, and laboratory analysis of tritium from subterranean soil gas presents numerous technical challenges that have not been fully studied. Particularly, the lack of moisture in the soil gas in the vadose zone makes it difficult to obtain enough sample (e.g., > 5 g) to provide for the required measurement sensitivity, and often, only small amounts of moisture can be collected. Further, although silica gel has high affinity for water vapor and is prebaked prior to sampling, there is still sufficient residual moisture in the prebaked gel to dilute the relatively small amount of sampled moisture; thereby, significantly lowering the "true" tritium concentration in the soil gas. This paper provides an evaluation of the magnitude of the bias from dilution, provides methods to correct past measurements by applying a correction factor (CF), and evaluates the uncertainty of the CF values. For this, 10,000 Monte Carlo calculations were performed, and distribution parameters of CF values were determined and evaluated. The mean and standard deviation of the distribution of CF values were 1.53 ± 0.36, and the minimum, median, and maximum values were 1.14, 1.43, and 5.27, respectively. PMID:20140505

11. A large response range reflectometric urea biosensor made from silica-gel nanoparticles.

PubMed

Alqasaimeh, Muawia; Heng, Lee Yook; Ahmad, Musa; Raj, A S Santhana; Ling, Tan Ling

2014-07-22

A new silica-gel nanospheres (SiO2NPs) composition was formulated, followed by biochemical surface functionalization to examine its potential in urea biosensor development. The SiO2NPs were basically synthesized based on sol-gel chemistry using a modified Stober method. The SiO2NPs surfaces were modified with amine (-NH2) functional groups for urease immobilization in the presence of glutaric acid (GA) cross-linker. The chromoionophore pH-sensitive dye ETH 5294 was physically adsorbed on the functionalized SiO2NPs as pH transducer. The immobilized urease determined urea concentration reflectometrically based on the colour change of the immobilized chromoionophore as a result of the enzymatic hydrolysis of urea. The pH changes on the biosensor due to the catalytic enzyme reaction of immobilized urease were found to correlate with the urea concentrations over a linear response range of 50-500 mM (R2 = 0.96) with a detection limit of 10 mM urea. The biosensor response time was 9 min with reproducibility of less than 10% relative standard deviation (RSD). This optical urea biosensor did not show interferences by Na+, K+, Mg2+ and NH4+ ions. The biosensor performance has been validated using urine samples in comparison with a non-enzymatic method based on the use of p-dimethylaminobenzaldehyde (DMAB) reagent and demonstrated a good correlation between the two different methods (R2 = 0.996 and regression slope of 1.0307). The SiO2NPs-based reflectometric urea biosensor showed improved dynamic linear response range when compared to other nanoparticle-based optical urea biosensors.

12. A Large Response Range Reflectometric Urea Biosensor Made from Silica-Gel Nanoparticles

PubMed Central

Alqasaimeh, Muawia; Heng, Lee Yook; Ahmad, Musa; Raj, A.S. Santhana; Ling, Tan Ling

2014-01-01

A new silica-gel nanospheres (SiO2NPs) composition was formulated, followed by biochemical surface functionalization to examine its potential in urea biosensor development. The SiO2NPs were basically synthesized based on sol–gel chemistry using a modified Stober method. The SiO2NPs surfaces were modified with amine (-NH2) functional groups for urease immobilization in the presence of glutaric acid (GA) cross-linker. The chromoionophore pH-sensitive dye ETH 5294 was physically adsorbed on the functionalized SiO2NPs as pH transducer. The immobilized urease determined urea concentration reflectometrically based on the colour change of the immobilized chromoionophore as a result of the enzymatic hydrolysis of urea. The pH changes on the biosensor due to the catalytic enzyme reaction of immobilized urease were found to correlate with the urea concentrations over a linear response range of 50–500 mM (R2 = 0.96) with a detection limit of 10 mM urea. The biosensor response time was 9 min with reproducibility of less than 10% relative standard deviation (RSD). This optical urea biosensor did not show interferences by Na+, K+, Mg2+ and NH4+ ions. The biosensor performance has been validated using urine samples in comparison with a non-enzymatic method based on the use of p-dimethylaminobenzaldehyde (DMAB) reagent and demonstrated a good correlation between the two different methods (R2 = 0.996 and regression slope of 1.0307). The SiO2NPs-based reflectometric urea biosensor showed improved dynamic linear response range when compared to other nanoparticle-based optical urea biosensors. PMID:25054632

13. Adsorption of desflurane by the silica gel filters in breathing circuits: an in vitro study

PubMed Central

Song, Seok Young; Lim, Bo Reum

2015-01-01

Background During general anesthesia, a heated breathing circuit (HBC) is used to replace the heat and moisture exchange function of the upper airway. One HBC uses an air dryer filter that employs silica gel (SG) as a desiccant. SG is capable of adsorbing many organic compounds. Therefore, we undertook an in vitro study of the adsorption of desflurane by SG filters. Methods An HBC was connected to an anesthesia machine, and a test lung was connected to the circuit. The test lung was mechanically ventilated with 2 or 4 L/min of fresh gas flow, with and without the air dryer filter. Desflurane was administered at a 6 vol% on the vaporizer dial setting. The experiment was repeated 15 times in each group. The end-tidal concentrations were measured during the experiments. The air dryer filter weights were measured before and after the experiments, and the times required to achieve the specific end-tidal desflurane concentrations were determined. Results Significant differences in the end-tidal concentrations of desflurane were observed between the control and filter groups (P < 0.001). The filter weights increased significantly after the experiments (P < 0.001). The times required to achieve the same end-tidal desflurane concentrations were different with the application of the air dryer filter (P < 0.001). Conclusions The adsorption of desflurane with the use of an air dryer filter was verified in this in vitro study. Careful attention is needed when using air dryer gel filters during general anesthesia. PMID:26045931

14. Determination of arsenate in water by anion selective membrane electrode using polyurethane-silica gel fibrous anion exchanger composite.

PubMed

Khan, Asif Ali; Shaheen, Shakeeba

2014-01-15

Polyurethane (PU)-silica (Si gel) based fibrous anion exchanger composites were prepared by solid-gel polymerization of polyurethane in the presence of different amounts of silica gel. The formation of PU-Si gel fibrous anion exchanger composite was characterized by Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTA), scanning electron microscopy (SEM) and elemental analysis. The membrane having a composition of 5:3 (PU:Si gel) shows best results for water content, porosity, thickness and swelling. Our studies show that the present ion selective membrane electrode is selective for arsenic, having detection limit (1×10(-8)M to 1×10(-1)M), response time (45s) and working pH range (5-8). The selectivity coefficient values for interfering ions indicate good selectivity for arsenate (AsO4(3-)) over interfering anions. The accuracy of the detection limit results was compared by PCA-Arsenomat. PMID:24275475

15. Determination of arsenate in water by anion selective membrane electrode using polyurethane-silica gel fibrous anion exchanger composite.

PubMed

Khan, Asif Ali; Shaheen, Shakeeba

2014-01-15

Polyurethane (PU)-silica (Si gel) based fibrous anion exchanger composites were prepared by solid-gel polymerization of polyurethane in the presence of different amounts of silica gel. The formation of PU-Si gel fibrous anion exchanger composite was characterized by Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTA), scanning electron microscopy (SEM) and elemental analysis. The membrane having a composition of 5:3 (PU:Si gel) shows best results for water content, porosity, thickness and swelling. Our studies show that the present ion selective membrane electrode is selective for arsenic, having detection limit (1×10(-8)M to 1×10(-1)M), response time (45s) and working pH range (5-8). The selectivity coefficient values for interfering ions indicate good selectivity for arsenate (AsO4(3-)) over interfering anions. The accuracy of the detection limit results was compared by PCA-Arsenomat.

16. Immobilization of Chlorosulfonyl-Calix[4]arene onto the surface of silica gel through the directly estrification

Taghvaei-Ganjali, Saeed; Zadmard, Reza; Saber-Tehrani, Mandana

2012-06-01

For the first time Chlorosulfonyl-Calix[4]arene has been chemically bonded to silica gel through the directly estrification without silane coupling agent to prepare Chlorosulfonyl-Calix[4]arene-bonded silica gel. Sample characterization was performed by various techniques such as elemental analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), powder X-ray diffraction (XRD), N2 adsorption-desorption, thermal gravimetric analysis (TGA), 29Si CP/MAS spectroscopy and acid-base titration. All data approve the successful incorporation of organic group via covalent bond. From the comparison between sulfur content determined by elemental analysis and the number of H+ determined by acid-base titration, it was shown that two ester units took place onto the new synthesized sample and two acidic sites exist on the surface.

17. Static Analysis of Double Effect Adsorption Refrigeration Cycle Using Silica gel/Water Pair

Marlinda; Miyazaki, Takahiko; Ueda, Yuki; Akisawa, Atsushi

In this paper,a static analysis of double effect adsorption refrigeration cycle utilizing condensation heat is discussed. Double effect adsorption refrigeration cycle consists of two cycles, High Temperature Cycle (HTC) which is driven from external heat sources, and Low Temperature Cycle (LTC) which is driven by condensation heat from HTC. Both of HTC and LTC are using silica gel and water as working pairs. The effect of heat source temperature on cycle performance was investigated in terms of coefficient of performance (COP) and specific cooling energy (SCE). Results showed that double effect cycle would produce higher COP than single effect cycle for driving temperature observed between 80-150°C with the same operating condition. However, the value of SCE is lower than single effect, despite that the SCE of double effect cycle is improved with heat source temperature higher than 100°C. Further, it was also observed that adsorbent mass ratio of HTC and LTC affected performance of chiller. When adsorbent mass ratio of HTC and LTC was unity, it was found that SCE and COP took the maximum.

18. Computational Analysis of Silica gel-Water Adsorption Refrigeration Cycle with Mass Recovery

Akahira, Akira; Alam, K. C. Amanul; Hamamoto, Yoshinori; Akisawa, Atsushi; Kashiwagi, Takao

The study aims at clarifying the performance of silica gel-water adsorption refrigeration cycle with mass recovery process.Two kinds of heat exchanger were examined and the performances were compared with each other. One type of heat exchanger was a spiral tube and it was immersed in a low temperature thermostatic bath. The other was coil-shaped double tube heat exchanger using two tubes. The emulsion was circulated to make ice continuously. These systems were operated under various cooling conditions (flow rates of the emulsion and brine temperatures). The effects of the tube materials (fluororesin and non-fluororesin) and thickness were also examined. Slurry ice was formed continuously without adhesion of ice to the cooling wall under certain conditions. Using the fluororesin tube prevented ice from the adhesion and it enlarged the range of the cooling conditions under which slurry ice was formed continuously. Furthermore, by making thickness of the tube thinner and increasing the heat transfer coefficient on the outside of the tube, ice was made continuously without lowering the rate of ice formation at a higher brine temperature.

19. Heterogeneous polycyclic aromatic hydrocarbon degradation with ozone on silica gel carrier

SciTech Connect

Alebic-Juretic, A. ); Cvitas, T.; Klasinc, L. )

1990-01-01

Heterogeneous degradation of five polycyclic aromatic hydrocarbons (PAHs), perylene (Pe), pyrene (Py), benzo(a)pyrene (BaP), benz(a)anthracene (BaA), and fluoranthene (Flo), adsorbed on nonactivated (moisture-containing) silica gel with ozone in a fluidized-bed reactor has been studied. The concentrations of ozone employed varied from 0.050 to 0.400 ppm. The results obtained show that, concerning their kinetics, there is a clear difference between reactions with less than and more than monolayer coverage of the particle surface with PAHs, those carrying a submonomolecular layer being faster and indicating the effect of the particle surface. In more highly covered samples, the observed degradation obeys two distinct first-order laws, the slow one changing into the faster at monomolecular coverage; the relative reactivities are as follows: Pe > BaP > BaA > Py >> Flo, and BaP > Pe > BaA > Py >> Flo, respectively. According to the present results, heterogeneous degradation of PAHs by ozone on particle surfaces is one of important pathways for their removal from the atmosphere.

20. Adsorption properties of carbonized polyacrylonitrile deposited on {gamma}-alumina and silica gel by precipitation polymerization

SciTech Connect

Kustrowski, Piotr; Janus, Rafal; Kochanowski, Andrzej; Chmielarz, Lucjan; Dudek, Barbara; Piwowarska, Zofia; Michalik, Marek

2010-07-15

The precipitation polymerization method was used for the deposition of various contents of polyacrylonitrile on two oxide-type supports ({gamma}-alumina and silica gel). The synthesized materials were characterized by thermal analysis performed in inert and oxidizing atmospheres. The mechanism of polyacrylonitrile decomposition was proposed. In order to gain effective adsorbents of volatile organic compounds the polyacrylonitrile/support composites were carbonized at elevated temperatures. The texture and morphology of the calcined materials were examined by low-temperature sorption of N{sub 2} and scanning electron microscopy, respectively. An influence of thermal treatment conditions and carbonaceous species loading on adsorption capacity of methyl-ethyl ketone vapour was also determined. Attenuated total reflection Fourier transform infrared spectroscopy measurements revealed that the ladder-type polyacrylonitrile species formed above 250 {sup o}C and stable up to about 350-400 {sup o}C are the most effective sites for methyl-ethyl ketone sorption. The carbonaceous species dispersion was found to be an additional factor influencing the adsorption capacity of the carbonized polyacrylonitrile/support composites.

1. A Novel Parametric Analysis of a Conventional Silica-Gel Water Adsorption Chiller

Alam, K. C. A.; Saha, B. B.; Akisawa, Atsushi; Kashiwagi, Takao

A conventional adsorption chiller with silica gel as adsorbent and water as adsorbate has been analyzed numerically. In the present study, a non-dimensional simulation model has been presented and a set of non-dimensional parameters for conventional adsorption chiller has been derived. The results obtained by simulation method are confirmed by the experimental results. Simulation results show that switching speed is most influential parameter and there is an optimum switching speed for cooling capacity and COP. Results also show that system performance (cooling capacity and COP) is strongly affected by the number of transfer unit of adsorber/desorber, NTUa due to severe sensible heating/cooling requirements. The model is somewhat sensitive to the number of transfer unit of evaporator, NTUe. The number of transfer unit of condenser, NTUc is the least sensitive parameter. Finally, an investigation is made parametrically to obtain the optimum value of switching speed and the number of transfer unit, NTU of different component. The present model can be employed to analyze and to optimize the adsorption cooling/heat pump system.

2. Silica gel as a support for inorganic ion- exchangers for the determination of caesium-137 in natural waters.

PubMed

1970-10-01

The preparation and characteristics of ammonium molybdophosphate and potassium or ammonium hexacyanocobalt ferrate supported in silica gel, and their application to the determination of (137)Cs in natural waters are described. Use of columns of these materials gives better recovery of (137)Cs from natural waters (in comparison with co-precipitation with ammonium molybdophosphate), requires less exchanger, so raising the gamma-counting efficiency of (137)Cs, and permits elimination of other radionuclides by washing with hydrofluoric acid.

3. Immobilized chiral tropine ionic liquid on silica gel as adsorbent for separation of metal ions and racemic amino acids.

PubMed

Qian, Guofei; Song, Hang; Yao, Shun

2016-01-15

Tropine-type chiral ionic liquid with proline anion was immobilized on silica gel by chemical modification method for the first time, which was proved by elemental, infrared spectrum and thermogravimetric analysis. Secondly, the performance of this kind of ionic liquid-modified silica gel was investigated in the adsorption of some metal ions, which included Cu(2+), Fe(3+), Mn(2+) and Ni(2+). Then the effects of time, initial concentration and temperature on adsorption for Cu(2+) ions were studied in detail, which was followed by the further research of adsorption kinetics and thermodynamics. The adsorption could be better described by pseudo-second-order kinetics model and that the process was spontaneous, exothermic and entropy decreasing. In the mode of 'reuse after adsorption', the ionic liquid-modified silica gel with saturated adsorption of Cu(2+) was finally used in resolution of racemic amino acids for the first time. The static experiment showed that adsorption rate of two enantiomers was obviously different. Inspired by this, the complex was packed in chromatographic column for the separation of racemic amino acids and d-enantiomers were firstly eluted by water or ethanol. Steric hindrance was found as one of key influencing factors for its effect on the stability of the complex.

4. Yeast-based self-organized hybrid bio-silica sol-gels for the design of biosensors.

PubMed

Ponamoreva, O N; Kamanina, O A; Alferov, V A; Machulin, A V; Rogova, T V; Arlyapov, V A; Alferov, S V; Suzina, N E; Ivanova, E P

2015-05-15

The methylotrophic Pichia angusta VKM Y-2559 and the oleaginous Cryptococcus curvatus VKM Y-3288 yeast cells were immobilized in a bimodal silica-organic sol-gel matrix comprised of tetraethoxysilane (TEOS), the hydrophobic additive methyltriethoxysilane (MTES) and the porogen polyethylene glycol (PEG). Under carefully optimized experimental conditions, employing basic catalysts, yeast cells have become the nucleation centers for a silica-organic capsule assembled around the cells. The dynamic process involved in the formation of the sol-gel matrix has been investigated using optical and scanning electron microscopic techniques. The results demonstrated the influence of the MTES composition on the nature of the encapsulation of the yeast cells, together with the architecture of the three-dimensional (3D) sol-gel biomatrix that forms during the encapsulation process. A silica capsule was found to form around each yeast cell when using 85 vol% MTES. This capsule was found to protect the microorganisms from the harmful effects that result from exposure to heavy metal ions and UV radiation. The encapsulated P. angusta BKM Y-2559 cells were then employed as a biosensing element for the detection of methanol. The P. angusta-based biosensor is characterized by high reproducibility (Sr, 1%) and operational stability, where the biosensor remains viable for up to 28 days.

5. Immobilized chiral tropine ionic liquid on silica gel as adsorbent for separation of metal ions and racemic amino acids.

PubMed

Qian, Guofei; Song, Hang; Yao, Shun

2016-01-15

Tropine-type chiral ionic liquid with proline anion was immobilized on silica gel by chemical modification method for the first time, which was proved by elemental, infrared spectrum and thermogravimetric analysis. Secondly, the performance of this kind of ionic liquid-modified silica gel was investigated in the adsorption of some metal ions, which included Cu(2+), Fe(3+), Mn(2+) and Ni(2+). Then the effects of time, initial concentration and temperature on adsorption for Cu(2+) ions were studied in detail, which was followed by the further research of adsorption kinetics and thermodynamics. The adsorption could be better described by pseudo-second-order kinetics model and that the process was spontaneous, exothermic and entropy decreasing. In the mode of 'reuse after adsorption', the ionic liquid-modified silica gel with saturated adsorption of Cu(2+) was finally used in resolution of racemic amino acids for the first time. The static experiment showed that adsorption rate of two enantiomers was obviously different. Inspired by this, the complex was packed in chromatographic column for the separation of racemic amino acids and d-enantiomers were firstly eluted by water or ethanol. Steric hindrance was found as one of key influencing factors for its effect on the stability of the complex. PMID:26711153

6. Preparation of silver nanoparticle containing silica micro beads and investigation of their antibacterial activity

Quang, Dang Viet; Sarawade, Pradip B.; Hilonga, Askwar; Kim, Jong-Kil; Chai, Young Gyu; Kim, Sang Hoon; Ryu, Jae-Yong; Kim, Hee Taik

2011-05-01

Silver nanoparticle containing silica micro beads (Ag-NPBs) were successfully prepared by using sodium silicate, a cheap precursor, involving chemical reductive method. First, silica gel was synthesized and crushed into micro beads which have sizes ranging from 0.5 to 1 mm. Silica micro beads were then modified with 3-aminopropyltriethoxysilane to graft amino functional groups onto their surface. Silver ions were loaded onto the surface of the modified silica and reduced to silver crystal by adding NaBH 4. The presence of silver nanoparticles as well as structure of materials was characterized with FT-IR, XRD, BET, FE-SEM, TEM, UV-vis spectrophotometer, and optical microscope. Silver nanoparticles with an average size about 5 nm were found in the pore and on the surface of amino functionalized silica beads. Ag-NPBs samples were tested for their antibacterial activity against Escherichia coli ( E. coli). The antibacterial activity was examined by both zone inhibition and test tube test method. Biological results indicated that the synthesized materials have an excellent antibacterial performance against E. coli which was completely inhibited after 5 min contact with Ag-NPBs.

7. Mesoporous and biocompatible surface active silica aerogel synthesis using choline formate ionic liquid.

PubMed

Meera, Kamal Mohamed Seeni; Sankar, Rajavelu Murali; Jaisankar, Sellamuthu N; Mandal, Asit Baran

2011-09-01

In this paper, we report the preparation and characterization of mesoporous and biocompatible transparent silica aerogel by the sol-gel polymerization of tetraethyl orthosilicate using ionic liquid. Choline cation based ionic liquid allows the silica framework to form in a non collapsing environment and controls the pore size of the gel. FT-IR spectra reveal the interaction of ionic liquid with surface -OH of the gel. DSC thermogram giving the evidence of confinement of ionic liquid within the silica matrix, which helps to avoid the shrinkage of the gel during the aging process. Nitrogen sorption measurements of gel prepared with ionic liquid exhibit a low surface area of 100.53 m2/g and high average pore size of 3.74 nm. MTT assay proves the biocompatibility and cell viability of the prepared gels. This new nanoporous silica material can be applied to immobilize biological molecules, which may retain their stability over a longer period.

8. Superhydrophobic films on glass surface derived from trimethylsilanized silica gel nanoparticles.

PubMed

Goswami, Debmita; Medda, Samar Kumar; De, Goutam

2011-09-01

The paper deals with the fabrication of sol-gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH(3))(3)-functionalized SiO(2) nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO(2) nanoparticles of average size ∼9.4 nm in the sols. TEM studies showed presence of interconnected SiO(2) NPs of ∼10 nm in size. The films were formed with uniformly packed SiO(2) aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO(2) and the surface roughness (rms ≈30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 ± 3° with 6 μL of water. These superhydrophobic films were found to be stable up to about 230-240 °C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance. PMID:21823656

9. Isotopic exchange between 2,2-dimethylbutane and deuterium on rhodium/silica gel catalysts

SciTech Connect

Takehara, D.K.; Butt, J.B.; Burwell, R.L. Jr. )

1992-02-01

Isotropic exchange between 2.2-dimethylbutane and deuterium has been investigated at 75 C on 10 rhodium on wide-pore silica gel catalysts with H(chemisorbed)/Rh(D{sub h}) ranging from 11 to 108% and subjected to a variety of pretreatment conditions. Some catalysts were prepared by ion exchange with Rh(NH{sub 3}){sub 5}(H{sub 2}O){sup 3-} and some by impregnation to incipient wetness with Rh{sub 4}(CO){sub 12} or Rh{sub 6}(CO){sub 16}. The turnover frequency (N{sub t}) is affected both by D{sub h} and by the conditions of pretreatment. The extreme variation was a factor of 330. Exchange into the ethyl group was about 10 times faster than into the t-butyl group. In general, the catalysts of largest D{sub h} gave the largest N{sub t} and the smallest degree of multiple exchange in the ethyl group. The pretreatment, H{sub 2}, 450 C gave the largest N{sub t}. Mere removal of H* from catalysts so treated by He, 300 C had little effect, but He, 450 C led to a substantial decrease in N{sub t} except for 11-Rh/SiO{sub 2}. The various coupled values of N{sub t} and selectivity resulting from variations in D{sub h} and pretreatment require a minimum of eight different sites. N{sub t}'s and selectivities in the hydrogenolysis of methylcyclopropane on these same catalysts parallel those in the exchange of neohexane.

10. Superhydrophobic films on glass surface derived from trimethylsilanized silica gel nanoparticles.

PubMed

Goswami, Debmita; Medda, Samar Kumar; De, Goutam

2011-09-01

The paper deals with the fabrication of sol-gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH(3))(3)-functionalized SiO(2) nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO(2) nanoparticles of average size ∼9.4 nm in the sols. TEM studies showed presence of interconnected SiO(2) NPs of ∼10 nm in size. The films were formed with uniformly packed SiO(2) aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO(2) and the surface roughness (rms ≈30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 ± 3° with 6 μL of water. These superhydrophobic films were found to be stable up to about 230-240 °C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance.

11. Investigation of passive and active silica-tin oxide nanostructured optical fibers fabricated by "inverse dip-coating" and "powder in tube" method based on the chemical sol-gel process and laser emission

Granger, G.; Restoin, C.; Roy, P.; Jamier, R.; Rougier, S.; Duclere, J.-R.; Lecomte, A.; Dauliat, R.; Blondy, J.-M.

2015-05-01

This paper presents a study of original nanostructured optical fibers based on the SiO2-SnO2-(Yb3+) system. Two different processes have been developed and compared: the sol-gel chemical method associated to the "inverse dip-coating" (IDC) and the "powder in tube" (PIT). The microstructural and optical properties of the fibers are studied according to the concentration of SnO2. X-Ray Diffraction as well as Transmission Electron Microscopy studies show that the SnO2 crystallizes into the cassiterite phase as nanoparticles with a diameter ranging from 4 to 50 nm as a function of tin oxide concentration. A comparative study highlights a better conservation of SnO2 into the fiber core with the PIT approach according to the refractive index profile and energy dispersive X-Ray spectrometry measurement. The attenuation evaluated by the classic cut-back method gives respectively values higher than 3 dB/m and 0.2 dB/m in the visible (VIS) and infrared (IR) ranges for the PIT fibers whereas background losses reach 0.5 dB/m in the VIS range for IDC fibers. The introduction of ytterbium ions into the core of PIT fibers, directly in the first chemical step, leads to a laser emission (between 1050 and 1100 nm) according to the fiber length under 850 nm wavelength pumping. Luminescence studies have demonstrated the influence of the tin oxide on the rare earth optical properties especially by the modification of the absorption (850 to 1000 nm) and emission (950 to 1100 nm) by discretization of the bands, as well as on the IR emission lifetime evaluated to 10 μs.

12. Antioxidative and antiinflammatory activities of quercetin-loaded silica nanoparticles.

PubMed

Lee, Ga Hyun; Lee, Sung June; Jeong, Sang Won; Kim, Hyun-Chul; Park, Ga Young; Lee, Se Geun; Choi, Jin Hyun

2016-07-01

Utilizing the biological activities of compounds by encapsulating natural components in stable nanoparticles is an important strategy for a variety of biomedical and healthcare applications. In this study, quercetin-loaded silica nanoparticles were synthesized using an oil-in-water microemulsion method, which is a suitable system for producing functional nanoparticles of controlled size and shape. The resulting quercetin-loaded silica nanoparticles were spherical, highly monodispersed, and stable in an aqueous system. Superoxide radical scavenging effects were found for the quercetin-loaded silica nanoparticles as well as free quercetin. The quercetin-loaded silica nanoparticles showed cell viability comparable to that of the controls. The amounts of proinflammatory cytokines produced by macrophages, such as interleukin 1 beta, interleukin 6, and tumor necrosis factor alpha, were reduced significantly for the quercetin-loaded silica nanoparticles. These results suggest that the antioxidative and antiinflammatory activities of quercetin are maintained after encapsulation in silica. Silica nanoparticles can be used for the effective and stable incorporation of biologically active natural components into composite biomaterials. PMID:27038916

13. Silica dust exposures during selected construction activities.

PubMed

Flanagan, Mary Ellen; Seixas, Noah; Majar, Maria; Camp, Janice; Morgan, Michael

2003-01-01

This study characterized exposure for dust-producing construction tasks. Eight common construction tasks were evaluated for quartz and respirable dust exposure by collecting 113 personal task period samples for cleanup; demolition with handheld tools; concrete cutting; concrete mixing; tuck-point grinding; surface grinding; sacking and patching concrete; and concrete floor sanding using both time-integrating filter samples and direct-reading respirable dust monitors. The geometric mean quartz concentration was 0.10 mg/m(3) (geometric standard deviation [GSD]=4.88) for all run time samples, with 71% exceeding the threshold limit value. Activities with the highest exposures were surface grinding, tuck-point grinding, and concrete demolition (GM[GSD] of 0.63[4.12], 0.22[1.94], and 0.10[2.60], respectively). Factors recorded each minute were task, tool, work area, respiratory protection and controls used, estimated cross draft, and whether anyone nearby was making dust. Factors important to exposure included tool used, work area configuration, controls employed, cross draft, and in some cases nearby dust. More protective respirators were employed as quartz concentration increased, although respiratory protection was found to be inadequate for 42% of exposures. Controls were employed for only 12% of samples. Exposures were reduced with three controls: box fan for surface grinding and floor sanding, and vacuum/shroud for surface grinding, with reductions of 57, 50, and 71%, respectively. Exposures were higher for sweeping compound, box fan for cleanup, ducted fan dilution, and wetted substrate. Construction masons and laborers are frequently overexposed to silica. The usual protection method, respirators, was not always adequate, and engineering control use was infrequent and often ineffective.

14. Silica nanoparticles increase human adipose tissue-derived stem cell proliferation through ERK1/2 activation

PubMed Central

Kim, Ki Joo; Joe, Young Ae; Kim, Min Kyoung; Lee, Su Jin; Ryu, Yeon Hee; Cho, Dong-Woo; Rhie, Jong Won

2015-01-01

15. Structural, Optical and Magnetic Properties of Nickel-Silica Nanocomposite Prepared by a Sol-Gel Route

Saha, Mrinal; Soumya Mukherjee; Gayen, Arup; Siddhartha Mukherjee

2015-10-01

Nickel-silica nanocomposites have been synthesized by a sol-gel method using dextrose (C6H12O6) as the reducing agent. The dried gel is heat treated at 850 and 900 °C for 30 min in an inert atmosphere by N2 purging to obtain the composite material. The samples have been characterized by powder X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, transmission electron microscopy and selected area electron diffraction. Pure polycrystalline nickel granular particle has been found to form with face-centered cubic structure and is entrapped in amorphous silica matrix with particle sizes in between 10 and 30 nm and is almost spherical in shape. The strong ferromagnetic nature of Ni-SiO2 composite became evident from the M-H curve which is quite different from the bulk nickel. The band gap of the synthesized Ni-SiO2 nanocomposite is found to be 2.35 eV. The reported sol-gel technique is a convenient and effective method to prepare high purity nanopowders with uniform size distribution.

16. Nanostructuring an erbium local environment inside sol-gel silica glasses: toward efficient erbium optical fiber lasers

Savelii, Inna; El Hamzaoui, Hicham; Bigot, Laurent; Bouwmans, Géraud; Fsaifes, Ihsan; Capoen, Bruno; Bouazaoui, Mohamed

2016-02-01

To extend the use of erbium- (Er-)/aluminum- (Al-) codoped optical fibers in hostile environments, the reduction of the Al amount has been identified as a serious way to harden them against harsh radiation. In this work, sol-gel monolithic Er3+-doped and Er3+/Al3+-codoped silica glasses were prepared from nanoporous silica xerogels soaked in a solution containing an Er salt together or not with an Al salt. After sintering, these glasses were used as the core material of microstructured optical fibers made by the stack-and-draw method. The influence of Al incorporation on the optical properties of Er3+-doped silica glasses and fibers is investigated. This approach enabled the preparation of silica glasses containing dispersed Er3+ ions with low Al content. The obtained fibers have been tested in an all-fibered cavity laser architecture. The Er3+/Al3+-codoped fiber laser presents a maximum efficiency of 27% at 1530 nm. We show that without Al doping, the laser exhibits lower performances that depend on Er content inside the doped fiber core. The effect of Er pair-induced quenching also has been investigated through nonsaturable absorption experiments, which clearly indicate that the fraction of Er ion pairs is significantly reduced in the Al-codoped fiber.

17. Silica-gel Particles Loaded with an Ionic Liquid for Separation of Zr(IV) Prior to Its Determination by ICP-OES

PubMed Central

Marwani, Hadi M.; Alsafrani, Amjad E.; Asiri, Abdullah M.; Rahman, Mohammed M.

2016-01-01

A new ionic liquid loaded silica gel amine (SG-APTMS-N,N-EPANTf2) was developed, as an adsorptive material, for selective adsorption and determination of zirconium, Zr(IV), without the need for a chelating intermediate. Based on a selectivity study, the SG-APTMS-N,N-EPANTf2 phase showed a perfect selectivity towards Zr(IV) at pH 4 as compared to other metallic ions, including gold [Au(III)], copper [Cu(II)], cobalt [Co(II)], chromium [Cr(III)], lead [Pb(II)], selenium [Se(IV)] and mercury [Hg(II)] ions. The influence of pH, Zr(IV) concentration, contact time and interfering ions on SG-APTMS-N,N-EPANTf2 uptake for Zr(IV) was evaluated. The presence of incorporated donor atoms in newly synthesized SG-APTMS-N,N-EPANTf2 phase played a significant role in enhancing its uptake capacity of Zr(IV) by 78.64% in contrast to silica gel (activated). The equilibrium and kinetic information of Zr(IV) adsorption onto SG-APTMS-N,N-EPANTf2 were best expressed by Langmuir and pseudo second-order kinetic models, respectively. General co-existing cations did not interfere with the extraction and detection of Zr(IV). Finally, the analytical efficiency of the newly developed method was also confirmed by implementing it for the determination of Zr(IV) in several water samples. PMID:27367692

18. Silica-gel Particles Loaded with an Ionic Liquid for Separation of Zr(IV) Prior to Its Determination by ICP-OES.

PubMed

Marwani, Hadi M; Alsafrani, Amjad E; Asiri, Abdullah M; Rahman, Mohammed M

2016-01-01

A new ionic liquid loaded silica gel amine (SG-APTMS-N,N-EPANTf₂) was developed, as an adsorptive material, for selective adsorption and determination of zirconium, Zr(IV), without the need for a chelating intermediate. Based on a selectivity study, the SG-APTMS-N,N-EPANTf₂ phase showed a perfect selectivity towards Zr(IV) at pH 4 as compared to other metallic ions, including gold [Au(III)], copper [Cu(II)], cobalt [Co(II)], chromium [Cr(III)], lead [Pb(II)], selenium [Se(IV)] and mercury [Hg(II)] ions. The influence of pH, Zr(IV) concentration, contact time and interfering ions on SG-APTMS-N,N-EPANTf₂ uptake for Zr(IV) was evaluated. The presence of incorporated donor atoms in newly synthesized SG-APTMS-N,N-EPANTf₂ phase played a significant role in enhancing its uptake capacity of Zr(IV) by 78.64% in contrast to silica gel (activated). The equilibrium and kinetic information of Zr(IV) adsorption onto SG-APTMS-N,N-EPANTf₂ were best expressed by Langmuir and pseudo second-order kinetic models, respectively. General co-existing cations did not interfere with the extraction and detection of Zr(IV). Finally, the analytical efficiency of the newly developed method was also confirmed by implementing it for the determination of Zr(IV) in several water samples. PMID:27367692

19. Thermo-optic characterization of neodymium/nickel doped silica glasses prepared via sol-gel route.

PubMed

Manuel, Ancy; Kumar, B Rajesh; Basheer, N Shemeena; Kumari, B Syamala; Paulose, P I; Kurian, Achamma; George, Sajan D

2012-12-01

Intrinsic as well as rare earth (Neodymium) doped silica glasses with various molar ratio of dopant and a metallic (Nickel) co-dopant is prepared via sol-gel route. The structural characterization of the sample is carried out using X-ray diffraction and Fourier Transform Infrared Spectroscopy. The influence of dopant and doping concentration on the optical properties of silica matrix is investigated via UV-VIS absorption spectroscopy. Effect of dopant on thermal effusivity value of the host matrix is carried out by laser induced open cell photoacoustic technique. Analysis of the results showed that doping affect the thermal effusivity value and results are interpreted in terms of structural modification of the lattice and phonon assisted heat transport mechanism.

20. Adjustable rheology of fumed silica dispersion in urethane prepolymers: Composition-dependent sol and gel behaviors and energy-mediated shear responses

SciTech Connect

Zheng, Zhong Song, Yihu Wang, Xiang Zheng, Qiang

2015-07-15

Variation of colloidal and interfacial interactions leads to a microstructural diversity in fumed silica dispersions exhibiting absolutely different sol- or gel-like rheological responses. In this study, fumed silicas with different surface areas (200–400 m{sup 2}/g) and surface characteristics (hydrophilic or hydrophobic) are dispersed into moisture-cured polyurethane. The microstructures investigated using transmission electron microscope are associated perfectly with three different rheological behaviors: (i) Sols with well-dispersed silica aggregates, (ii) weak gels with agglomerate-linked networks, and (iii) strong gels with concentrated networks of large agglomerates. Though sols and gels are well distinguished by shear thickening or sustained thinning response through steady shear flow test, it is interesting that the sols and weak gels exhibit a uniform modulus plateau-softening-hardening-softening response with increasing dynamic strain at frequency 10 rad s{sup −1} while the strong gels show a sustained softening beyond the linear regime. Furthermore, the onset of softening and hardening can be normalized: The two softening are isoenergetic at mechanical energies of 0.3 J m{sup −3} and 10 kJ m{sup −3}. On the other hand, the hardening is initiated by a critical strain of 60%. The mechanisms involved in the generation of the sol- and the gel-like dispersions and their structural evolutions during shear are thoroughly clarified in relation to the polyols, the characteristic and content of silica and the curing catalysts.

1. A new precursor for the immobilization of enzymes inside sol-gel-derived hybrid silica nanocomposites containing polysaccharides.

PubMed

Shchipunov, Yurii A; Karpenko, Tat'yana Yu; Bakunina, Irina Yu; Burtseva, Yuliya V; Zvyagintseva, Tat'yana N

2004-01-30

Tetrakis(2-hydroxyethyl) orthosilicate (THEOS) introduced by Hoffmann et al. (J. Phys. Chem. B., 106 (2002) 1528) was first used to prepare hybrid nanocomposites containing various polysaccharides and immobilize enzymes in these materials. Two different types of O-glycoside hydrolyses (EC3.2.1), 1-->3-beta-D-glucanase LIV from marine mollusk Spisula sacchalinensis and alpha-D-galactosidase from marine bacterium Pseudoalteromonas sp. KMM 701, were taken for the immobilization. To reveal whether the polysaccharide inside the hybrid material influences the enzyme entrapment and functioning, negatively charged xanthan, cationic derivative of hydroxyethylcellulose and uncharged locust bean gum were examined. The mechanical properties of these nanocomposites were characterized by a dynamic rheology and their structure by a scanning electron microscopy. It was found that 1-->3-beta-D-glucanase was usually immobilized without the loss of its activity, while the alpha-D-galactosidase activity in the immobilized state depended on the polysaccharide type of material. An important point is that the amount of immobilized enzymes was small, comparable to their content in the living cells. It was shown by the scanning electron microscopy that the hybrid nanocomposites are sufficiently porous that allows the enzymatic substrates and products to diffuse from an external aqueous solution to the enzymes, whereas protein molecules were immobilized firmly and not easily washed out of the silica matrix. A sharp increase of the enzyme lifetime (more than a hundred times) was observed after the immobilization. As established, the efficient entrapment of enzymes is caused by few advantages of new precursor over the currently used TEOS and TMOS: (i) organic solvents and catalysts are not needed owing to the complete solubility of THEOS in water and the catalytic effect of polysaccharides on the sol-gel processes; (ii) the entrapment of enzymes can be performed at any pH which is suitable

2. In vitro bioactivity and structural features of mildly heat-treated sol-gel-derived silica fibers.

PubMed

Peltola, T; Jokinen, M; Veittola, S; Simola, J; Yli-Urpo, A

2001-03-15

The ability of sol-gel-derived silica fibers heat treated at a low temperature to induce formation of bone-like calcium phosphate (HCA) on their surfaces provides alternatives for the design of novel biomaterials, for example as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers, which were heat-treated at 175 degrees and 250 degrees C. In addition, the differences in the surface topography (in a nanometer scale) of different fibers with respect to their in vitro bioactivity were studied. The structure of the fibers was varied using three different factors: (1) spinnable sols having varying structures and sizes of silica polymers to establish varying viscosity levels; (2) aging of green-state fibers; and (3) heat treatment of fibers. The in vitro bioactivity and solubility tests were done in simulated body fluid (SBF). To monitor surface topography and roughness of the heat-treated silica fibers, a scanning probe microscopy (SPM) with tapping mode AFM was used. Different fibers obtained clearly different properties. The fibers spun at about eta > 3.0 Pas had the best properties with respect to bioactivity, especially when they were heat-treated at 175 degrees C. It was found that surface structure in a nanometer scale was the most important factor controlling the in vitro bioactivity of heat-treated silica fibers. The correct proportions between the peaks and peak distances at the surfaces are suggested to be important with respect to in vitro bioactivity. The results indicate that peak distance distribution between 5-50 nm, especially between 5-20 nm, together with a peak height > or = 1 nm is most favorable for calcium phosphate formation.

3. Electroassisted codeposition of sol-gel derived silica nanocomposite directs the fabrication of coral-like nanostructured porous gold.

PubMed

Farghaly, Ahmed A; Collinson, Maryanne M

2014-05-13

Herein, we report on a one-step coelectrodeposition method to form gold-silica nanocomposite materials from which high surface area nanostructured gold electrodes can be produced. The as-prepared Au-SiO2 films possess an interconnected three-dimensional porous framework with different silica-gold ratios depending on the deposition solutions and parameters. Chemical etching of the nanocomposite films using hydrofluoric acid resulted in the formation of nanostructured porous gold films with coral-like structures and pores in the nanometer range. The cross-linkage of the gold coral branches resulted in the generation of a porous framework. X-ray photoelectron spectroscopy confirms the complete removal of silica. Well-controlled surface area enhancement, film thickness, and morphology were achieved by manipulating the deposition parameters, such as potential, time, and gold ion and sol-gel monomer concentrations in the deposition solution. An enhancement in the surface area of the electrode up to 57 times relative to the geometric area has been achieved. The thickness of the as-prepared Au-SiO2 nanocomposite films is relatively high and varied from 8 to 15 μm by varying the applied deposition potential while the thickness of the coral-like nanostructured porous gold films ranged from 0.22 to 2.25 μm. A critical sol-gel monomer concentration (CSGC) was determined at which the deposited silica around the gold coral was able to stabilize the coral-like gold nanostructures, while below the CSGC, the coral-like gold nanostructures were unstable and the surface area of the nanostructured porous gold electrodes decreased. PMID:24766096

4. Phase behavior and 13C NMR spectroscopic analysis of the mixed methane + ethane + propane hydrates in mesoporous silica gels.

PubMed

Lee, Seungmin; Cha, Inuk; Seo, Yongwon

2010-11-25

In this study, the phase behavior and quantitative determination of hydrate composition and cage occupancy for the mixed CH(4) + C(2)H(6) + C(3)H(8) hydrates were closely investigated through the experimental measurement of three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria and (13)C NMR spectra. To examine the effect of pore size and salinity, we measured hydrate phase equilibria for the quaternary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + water mixtures in silica gel pores of nominal diameters of 6.0, 15.0, and 30.0 nm and for the quinary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + NaCl + water mixtures of two different NaCl concentrations (3 and 10 wt %) in silica gel pores of a nominal 30.0 nm diameter. The value of hydrate-water interfacial tension for the CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) hydrate was found to be 47 ± 4 mJ/m(2) from the relation of the dissociation temperature depression with the pore size of silica gels at a given pressure. At a specified temperature, three-phase H-L(W)-V equilibrium curves of pore hydrates were shifted to higher pressure regions depending on pore sizes and NaCl concentrations. From the cage-dependent (13)C NMR chemical shifts of enclathrated guest molecules, the mixed CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) gas hydrate was confirmed to be structure II. The cage occupancies of each guest molecule and the hydration number of the mixed gas hydrates were also estimated from the (13)C NMR spectra.

5. Grafting of molecularly imprinted polymers from the surface of silica gel particles via reversible addition-fragmentation chain transfer polymerization: a selective sorbent for theophylline.

PubMed

Li, Yong; Zhou, Wen-Hui; Yang, Huang-Hao; Wang, Xiao-Ru

2009-07-15

Molecularly imprinted polymers (MIPs) were grafted successfully from the surface of silica gel particles via surface initiated reversible addition-fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized silica gel as the chain transfer agent. The intrinsic characteristics of the controlled/living polymerization mechanism of RAFT allowed for the effective control of the grafting process. Thus the grafting copolymerization of methacrylic acid and divinyl benzene in the presence of template theophylline led to thin MIP film coating silica gel (MIP-Silica). The thickness of MIP film prepared in this study is about 1.98 nm, which was calculated from the nitrogen sorption analysis results. Measured binding kinetics for theophylline to the MIP-Silica and MIPs prepared by conventional bulk polymerization demonstrated that MIP-Silica had improved mass-transfer properties. In addition, the theophylline-imprinted MIP-Silica was used as the sorbent in solid-phase extraction to determine theophylline in blood serum with satisfactory recovery higher than 90%. Nonspecific adsorption of interfering compounds can be eliminated by a simple elution with acetonitrile, without sacrificing the selective binding of theophylline.

6. Crystallized alkali-silica gel in concrete from the late 1890s

SciTech Connect

Peterson, Karl . E-mail: cee@mtu.edu; Gress, David . E-mail: dlgress@unh.edu; Van Dam, Tom . E-mail: cee@mtu.edu; Sutter, Lawrence . E-mail: cee@mtu.edu

2006-08-15

The Elon Farnsworth Battery, a concrete structure completed in 1898, is in an advanced state of disrepair. To investigate the potential for rehabilitation, cores were extracted from the battery. Petrographic examination revealed abundant deposits of alkali silica reaction products in cracks associated with the quartz rich metasedimentary coarse aggregate. The products of the alkali silica reaction are variable in composition and morphology, including both amorphous and crystalline phases. The crystalline alkali silica reaction products are characterized by quantitative X-ray energy dispersive spectrometry (EDX) and X-ray diffraction (XRD). The broad extent of the reactivity is likely due to elevated alkali levels in the cements used.

7. Direct Evidence for Percolation of Immobilized Polymer Layer around Nanoparticles Accounting for Sol-Gel Transition in Fumed Silica Dispersions.

PubMed

Zheng, Zhong; Song, Yihu; Yang, Ruiquan; Zheng, Qiang

2015-12-22

Immobilized polymer fractions have been claimed to be of vital importance for sol-gel transitions generally observed in nanoparticle dispersions but remain a matter of debate regarding mechanism and difficulty for prediction. Here we investigate the immobilized layer structures of trifunctionality polyether polyol (PPG) near the surfaces of hydrophilic and hydrophobic fumed silica (FS) nanoparticles to reveal the role of surface chemistry on the molecular dynamics and sol-gel transitions of the dispersions. Using modulated differential scanning calorimetry, we measure the specific heat capacity during glass transition and the enthalpy during cold-crystallization. Comparing with hydrophobic FS that forms a fully immobilized (glassy) layer, we find that hydrophilic FS immobilizes more PPG, forming a partially immobilized outer layer being unable to crystallize next to the inner glassy layer. By correlating the thickness of the glassy layer with half of the minimum spacing between nanoparticles, we directly evidence the percolation of this layer along the nearest neighbor nanoparticles responsible for the sol-gel transition. Using effective volume fraction including the glassy layer, we successfully construct master curves of relative viscosity of both hydrophilic and hydrophobic FS dispersions, pointing to a common sol-gel transition mechanism mediated by the surface chemistry.

8. Encapsulation of biomolecules for bioanalytical purposes: preparation of diclofenac antibody-doped nanometer-sized silica particles by reverse micelle and sol-gel processing.

PubMed

Tsagkogeorgas, Fotios; Ochsenkühn-Petropoulou, Maria; Niessner, Reinhard; Knopp, Dietmar

2006-07-28

In recent years, the sol-gel technique has attracted increasing interest as a unique approach to immobilize biomolecules for bioanalytical applications as well as biochemical and biophysical studies. For this purpose, crushed biomolecule-doped sol-gel glass monoliths have been widely used. In the present work, for the first time, the encapsulation of anti-diclofenac antibodies in silica nanoparticles was carried out by a combination of reverse micelle and sol-gel technique. Cyclohexane was used for the preparation of the microemulsion as organic solvent, while surfactant Igepal CO-520 was found to be the optimal stabilizer. The antibody source was a purified IgG fraction originating from a polyclonal rabbit antiserum. Tetramethyl orthosilicate (TMOS) was used as precursor. Rather uniform, monodispersed and spherical silica particles of about 70nm diameter size were fabricated, as was demonstrated by transmission electron microscopy (TEM) and scanning electron microscopy/energy dispersive X-ray fluorescence analysis (SEM/EDX). The biological activity of the encapsulated antibodies was evaluated by incubation of the nanoparticles with a diclofenac standard solution and analysis of the filtrate and followed washing solutions by a highly sensitive enzyme-linked immunosorbent assay (ELISA), using non-doped particles as blanks. While only about 6% of the added diclofenac was nonspecifically retained by the blank, the corresponding amount of about 66% was much higher with the antibody-doped particles. An obvious advantage of this approach is the general applicability of the developed technique for a mild immobilization of different antibody species.

9. Designing photobioreactors based on living cells immobilized in silica gel for carbon dioxide mitigation.

PubMed

Rooke, Joanna C; Léonard, Alexandre; Meunier, Christophe F; Su, Bao-Lian

2011-09-19

Atmospheric carbon dioxide levels have been rising since the industrial revolution, with the most dramatic increase occurring since the end of World War II. Carbon dioxide is widely regarded as one of the major factors contributing to the greenhouse effect, which is of major concern in today's society because it leads to global warming. Photosynthesis is Nature's tool for combating elevated carbon dioxide levels. In essence, photosynthesis allows a cell to harvest solar energy and convert it into chemical energy through the assimilation of carbon dioxide and water. Therefore photosynthesis is regarded as an ideal way to harness the abundance of solar energy that reaches Earth and convert anthropologically generated carbon dioxide into useful carbohydrates, providing a much more sustainable energy source. This Minireview aims to tackle the idea of immobilizing photosynthetic unicellular organisms within inert silica frameworks, providing protection both to the fragile cells and to the external ecosystem, and to use this resultant living hybrid material in a photobioreactor. The viability and activity of various unicellular organisms are summarized alongside design issues of a photobioreactor based on living hybrid materials.

PubMed

Zeng, Minfeng; Wang, Yudong; Liu, Qi; Yuan, Xia; Feng, Ruokun; Yang, Zhen; Qi, Chenze

2016-08-01

In this study, a heterogeneous catalyst including palladium nanoparticles supported on nitrogen-doped mesoporous carbon (Pd@N-C) is synthesized from palladium salts as palladium precursor, colloidal silica as template, and chitosan as carbon source. N2 sorption isotherm results show that the prepared Pd@N-C had a high BET surface area (640m(2)g(-1)) with large porosity. The prepared Pd@N-C is high nitrogen-rich as characterized with element analysis. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy characterization of the catalyst shows that the palladium species with different chemical states are well dispersed on the nitrogen-containing mesoporous carbon. The Pd@N-C is high active and shows excellent stability as applied in Heck coupling reactions. This work supplies a successful method to prepare Pd heterogeneous catalysts with high performance from bulk biopolymer/Pd to high porous nitrogen-doped carbon supported palladium catalytic materials. PMID:27155234

11. Tunable dynamics of microtubule-based active isotropic gels

PubMed Central

Henkin, Gil; DeCamp, Stephen J.; Chen, Daniel T. N.; Sanchez, Tim; Dogic, Zvonimir

2014-01-01

We investigate the dynamics of an active gel of bundled microtubules (MTs) that is driven by clusters of kinesin molecular motors. Upon the addition of ATP, the coordinated action of thousands of molecular motors drives the gel to a highly dynamical turbulent-like state that persists for hours and is only limited by the stability of constituent proteins and the availability of the chemical fuel. We characterize how enhanced transport and emergent macroscopic flows of active gels depend on relevant molecular parameters, including ATP, kinesin motor and depletant concentrations, MT volume fraction, as well as the stoichiometry of the constituent motor clusters. Our results show that the dynamical and structural properties of MT-based active gels are highly tunable. They also indicate existence of an optimal concentration of molecular motors that maximize far-from-equilibrium activity of active isotropic MT gels. PMID:25332391

12. Disiloxanes and Functionalized Silica Gels: One Route, Two Complementary Outcomes—Guanidinium and Pyridinium Ion-Exchangers

PubMed Central

Tabisz, Łukasz

2015-01-01

Five novel disiloxane compounds comprising guanidinium and pyridinium moieties were obtained with high yields and purity. The verified synthetic pathways were then applied for modification of pre-functionalized silica gel, producing materials with the analogous organic side-chains. These halide-containing compounds and materials were then compared as to their ion-exchange properties: two disiloxanes proved to be effective in leaching different anions (nitrate, benzoate and ascorbate) from solid to organic phase, and pyridinium-functionalized silica gels showed selectivity towards perchlorate ion, removing it from methanolic solutions with preference to other singly charged anions. The results presented demonstrate that both compounds and materials containing silicon-carbon bonds can be produced using the same methodology, but offer strikingly different application opportunities. Comparison of their properties provides additional insight into the binding mode of different anions and hints at how the transition from a flexible siloxane bridge to immobilization on solid surface influences anion-binding selectivity. Additionally, one of the siloxane dipodands was found to form a crystalline and poorly soluble nitrate salt (1.316 g/L, water), although it was miscible with a wide range of solvents as a hydrochloride. A possible explanation is given with the help of semi-empirical calculations. A simple, time- and cost-efficient automated potentiometric titration methodology was used as a viable analytical tool for studying ion-exchange processes for both compounds and materials, in addition to standard NMR, FT-IR and ESI-MS methods. PMID:26714187

13. Disiloxanes and Functionalized Silica Gels: One Route, Two Complementary Outcomes-Guanidinium and Pyridinium Ion-Exchangers.

PubMed

Tabisz, Łukasz; Tukibayeva, Ainur; Pankiewicz, Radoslaw; Dobielska, Marta; Leska, Boguslawa

2015-01-01

Five novel disiloxane compounds comprising guanidinium and pyridinium moieties were obtained with high yields and purity. The verified synthetic pathways were then applied for modification of pre-functionalized silica gel, producing materials with the analogous organic side-chains. These halide-containing compounds and materials were then compared as to their ion-exchange properties: two disiloxanes proved to be effective in leaching different anions (nitrate, benzoate and ascorbate) from solid to organic phase, and pyridinium-functionalized silica gels showed selectivity towards perchlorate ion, removing it from methanolic solutions with preference to other singly charged anions. The results presented demonstrate that both compounds and materials containing silicon-carbon bonds can be produced using the same methodology, but offer strikingly different application opportunities. Comparison of their properties provides additional insight into the binding mode of different anions and hints at how the transition from a flexible siloxane bridge to immobilization on solid surface influences anion-binding selectivity. Additionally, one of the siloxane dipodands was found to form a crystalline and poorly soluble nitrate salt (1.316 g/L, water), although it was miscible with a wide range of solvents as a hydrochloride. A possible explanation is given with the help of semi-empirical calculations. A simple, time- and cost-efficient automated potentiometric titration methodology was used as a viable analytical tool for studying ion-exchange processes for both compounds and materials, in addition to standard NMR, FT-IR and ESI-MS methods. PMID:26714187

14. Hydroxylamine-doping effect on the Tg of 160 K for water confined in silica-gel nanopores.

PubMed

Nagoe, A; Oguni, M

2013-11-20

The glass transition behavior of hydroxylamine (HA) aqueous solutions in bulk and confined in silica-gel nanopores with average width of 1.1 nm was studied by means of differential scanning calorimetry measurements and adiabatic calorimetry. The glass transition temperature (Tg) of the confined solution with high HA mole-fraction (xHA) was essentially the same as the value of the bulk. This suggests that the nano-size confinement affects the Tg of HA aqueous solution little. Meanwhile, the bulk solution with xHA < 0.3 revealed partial crystallization on cooling and, on the other hand, the confined solution with the same xHA did not crystallize. The Tg of the xHA = 0.076 confined solution was 174 K which is higher than the value of 160 K for pure water confined in the same silica-gel pores. This demonstrates that HA doping leads to no abrupt Tg-decrease, unlike doping of all the other second components reported so far, suggesting that HA is set neatly in a hydrogen-bond network formed by water molecules. We discuss the xHA dependence of Tg for the HA aqueous solutions from a viewpoint related to peculiar phase-behavior of pure water. Considering that the xHA = 0.076 aqueous solution revealed no anomaly compared with pure water, it was recognized as corresponding to the high-temperature phase of pure water. PMID:24162332

15. Removal of lindane from an aqueous solution by using aminopropyl silica gel-immobilized calix[6]arene.

PubMed

Tor, Ali; Aydin, Mehmet Emin; Aydin, Senar; Tabakci, Mustafa; Beduk, Fatma

2013-11-15

An aminopropyl silica gel-immobilized calix[6]arene (C[6]APS) has been used for the removal of lindane from an aqueous solution in batch sorption technique. The C[6]APS was synthesized with p-tert-butylcalix[6]arene hexacarboxylate derivative and aminopropyl silica gel in the presence of N,N'-diisopropyl carbodiimide coupling reagent. The sorption study was carried out as functions of solution pH, contact time, initial lindane concentration, C[6]APS dosage and ionic strength of solution. The matrix effect of natural water samples on the sorption efficiency of C[6]APS was also investigated. Maximum lindane removal was obtained at a wide pH range of 2-8 and sorption equilibrium was achieved in 2h. The isotherm analysis indicated that the sorption data can be represented by both Langmuir and Freundlich isotherm models. Increasing ionic strength of the solutions increased the sorption efficiency and matrix of natural water samples had no effect on the sorption of lindane. By using multilinear regression model, regression equation was also developed to explain the effects of the experimental variables.

16. Tubular ceramic-supported sol-gel silica-based membranes for flue gas carbon dioxide capture and sequestration.

SciTech Connect

Tsai, C. Y.; Xomeritakis, George K.; Brinker, C. Jeffrey; Jiang, Ying-Bing

2009-03-01

Pure, amine-derivatized and nickel-doped sol-gel silica membranes have been developed on tubular Membralox-type commercial ceramic supports for the purpose of carbon dioxide separation from nitrogen under coal-fired power plant flue gas conditions. An extensive synthetic and permeation test study was carried out in order to optimize membrane CO{sub 2} permeance, CO{sub 2}:N{sub 2} separation factor and resistance against densification. Pure silica membranes prepared under optimized conditions exhibited an attractive combination of CO{sub 2} permeance of 2.0 MPU (1 MPU = 1 cm{sup 3}(STP) {center_dot} cm{sup -2} min{sup -1} atm{sup -1}) and CO{sub 2}:N{sub 2} separation factor of 80 with a dry 10:90 (v/v) CO{sub 2}:N{sub 2} feed at 25 C. However, these membranes exhibited flux decline phenomena under prolonged exposure to humidified feeds, especially in the presence of trace SO{sub 2} gas in the feed. Doping the membranes with nickel (II) nitrate salt was effective in retarding densification, as manifested by combined higher permeance and higher separation factor of the doped membrane compared to the pure (undoped) silica membrane after 168 hours exposure to simulated flue gas conditions.

17. Characteristic coordination structure around Nd Ions in sol-gel-derived Nd-Al-codoped silica glasses.

PubMed

Funabiki, Fuji; Kajihara, Koichi; Kaneko, Ken; Kanamura, Kiyoshi; Hosono, Hideo

2014-07-24

Al codoping can improve the poor solubility of rare-earth ions in silica glasses. However, the mechanism is not well understood. The coordination structure around Nd ions in sol-gel-derived Nd-Al-codoped silica glasses with different Al content was investigated by optical and pulsed electron paramagnetic resonance spectroscopies. Both tetrahedral AlO4 and octahedral AlO6 units were observed around Nd ions as ligands. The average total number of these two types of ligands for each Nd(3+) ion was ∼ 2 irrespective of Al content and was larger by 1-2 orders of magnitude than that calculated for a uniform distribution of codopant ions (∼ 0.08-0.25). With increasing Al content, AlO4 units disappeared and AlO6 units became dominant. The preferential coordination of AlOx (x = 4, 6) units to Nd ions enabled the amount of Al necessary to dissolve Nd ions uniformly in silica glass at a relatively low temperature of 1150-1200 °C to be minimized, and the conversion of AlO4 units to AlO6 units around Nd ions caused the asymmetry of the crystal field at the Nd sites to increase and the site-to-site distribution to decrease.

18. Development and characterization of colloidal silica-based slow-release permanganate gel (SRP-G): laboratory investigations.

PubMed

Lee, Eung Seok; Gupta, Neha

2014-08-01

Slow-release permanganate (MnO4(-)) gel (SRP-G) is a hyper-saline KMnO4 solution that can be used for treating large, dilute, or deep plumes of chlorinated solvents in groundwater. Ideally, the SRP-G injected into aquifers will slowly gelate to form MnO4(-) gel in situ, and the gel will slowly releases MnO4(-). Objectives of this study were to develop SRP-G using colloidal silica as gelling solution, characterize its gelation and release kinetics, and delineate its dynamics in a saturated sandy media. The SRP-G exhibited a two-phase increase in viscosity: a lag phase characterized by little increase in viscosity followed by a short gelation phase. Gelation lag times of SRP-G solutions increased (from 0.5h to 13d) with decreasing KMnO4 concentrations (from 25 to 8 g L(-1)). Permanganate release from gelated SRP-G increased with increasing KMnO4 concentrations, and was characterized as asymptotic release with initial peak (0.9-2.2 mg min(-1)) followed by more attenuated release. Gelation lag times of SRP-G flowing in sands (linear velocity=2.1md(-1)) increased (1, 3, and 6h) with decreasing KMnO4 concentrations (25.0, 23.0, and 22.9 g L(-1)). Permanganate release from gelated SRP-Gs continued for up to 3d and was characterized as asymptotic release with an initial peak release (∼1.2 g min(-1)) followed by more attenuated release over 70h. Dilution of SRP-G by dispersion in porous media affects gelation and release kinetics. Increasing the silica concentration in the SRP-G may facilitate gelation and extend the duration of MnO4(-) release from emplaced SRP-G in porous media. PMID:24650708

19. Development and characterization of colloidal silica-based slow-release permanganate gel (SRP-G): laboratory investigations.

PubMed

Lee, Eung Seok; Gupta, Neha

2014-08-01

Slow-release permanganate (MnO4(-)) gel (SRP-G) is a hyper-saline KMnO4 solution that can be used for treating large, dilute, or deep plumes of chlorinated solvents in groundwater. Ideally, the SRP-G injected into aquifers will slowly gelate to form MnO4(-) gel in situ, and the gel will slowly releases MnO4(-). Objectives of this study were to develop SRP-G using colloidal silica as gelling solution, characterize its gelation and release kinetics, and delineate its dynamics in a saturated sandy media. The SRP-G exhibited a two-phase increase in viscosity: a lag phase characterized by little increase in viscosity followed by a short gelation phase. Gelation lag times of SRP-G solutions increased (from 0.5h to 13d) with decreasing KMnO4 concentrations (from 25 to 8 g L(-1)). Permanganate release from gelated SRP-G increased with increasing KMnO4 concentrations, and was characterized as asymptotic release with initial peak (0.9-2.2 mg min(-1)) followed by more attenuated release. Gelation lag times of SRP-G flowing in sands (linear velocity=2.1md(-1)) increased (1, 3, and 6h) with decreasing KMnO4 concentrations (25.0, 23.0, and 22.9 g L(-1)). Permanganate release from gelated SRP-Gs continued for up to 3d and was characterized as asymptotic release with an initial peak release (∼1.2 g min(-1)) followed by more attenuated release over 70h. Dilution of SRP-G by dispersion in porous media affects gelation and release kinetics. Increasing the silica concentration in the SRP-G may facilitate gelation and extend the duration of MnO4(-) release from emplaced SRP-G in porous media.

20. Study of the high-coercivity material based on ɛ-Fe2O3 nanoparticles in the silica gel matrix

Balaev, D. A.; Yakushkin, S. S.; Dubrovskii, A. A.; Bukhtiyarova, G. A.; Shaikhutdinov, K. A.; Martyanov, O. N.

2016-04-01

We report the results of investigations of ɛ-Fe2O3 magnetic nanoparticles obtained by incipient wetness impregnation of silica gel. It was established that the obtained samples with an iron content of 12‒16% mass % containing ɛ-Fe2O3 nanoparticles with an average size of 10 nm on the silica gel surface exhibit a room-temperature coercivity of about 10 kOe. Along with fabrication simplicity, this fact makes the prepared samples promising for application as a magnetically hard material.

1. A novel non-aqueous sol-gel route for the in situ synthesis of high loaded silica-rubber nanocomposites.

PubMed

Wahba, Laura; D'Arienzo, Massimiliano; Dirè, Sandra; Donetti, Raffaella; Hanel, Thomas; Morazzoni, Franca; Niederberger, Markus; Santo, Nadia; Tadiello, Luciano; Scotti, Roberto

2014-04-01

Silica-natural rubber nanocomposites were obtained through a novel non-aqueous in situ sol-gel synthesis, producing the amount of water necessary to induce the hydrolysis and condensation of a tetraethoxysilane precursor by esterification of formic acid with ethanol. The method allows the synthesis of low hydrophilic silica nanoparticles with ethoxy groups linked to the silica surface which enable the filler to be more dispersible in the hydrophobic rubber. Thus, high loaded silica composites (75 phr, parts per hundred rubber) were obtained without using any coupling agent. Transmission Electron Microscopy (TEM) showed that the silica nanoparticles are surrounded by rubber layers, which lower the direct interparticle contact in the filler-filler interaction. At the lowest silica loading (up to 30 phr) silica particles are isolated in rubber and only at a large amount of filler (>60 phr) the interparticle distances decrease and a continuous percolative network, connected by thin polymer films, forms throughout the matrix. The dynamic-mechanical properties confirm that the strong reinforcement of the rubber composites is related to the network formation at high loading. Both the improvement of the particle dispersion and the enhancement of the silica loading are peculiar to the non-aqueous synthesis approach, making the method potentially interesting for the production of high-loaded silica-polymer nanocomposites. PMID:24651692

2. Preparation of silane-functionalized silica films via two-step dip coating sol-gel and evaluation of their superhydrophobic properties

2014-10-01

In this paper, we study the two-step dip coating via a sol-gel process to prepare superhydrophobic silica films on the glass substrate. The water repellency of the silica films was controlled by surface silylation method using isooctyltrimethoxysilane (iso-OTMS) as a surface modifying agent. Silica alcosol was synthesized by keeping the molar ratio of ethyltriethoxysilane (ETES) precursor, ethanol (EtOH) solvent, water (H2O) was kept constant at 1:36:6.6 respectively, with 6 M NH4OH throughout the experiment and the percentages of hydrophobic agent in hexane bath was varied from 0 to 15 vol.%. The static water contact angle values of the silica films increased from 108° to 160° with an increase in the vol.% of iso-OTMS. At 15 vol%. of iso-OTMS, the silica film shows static water contact angle as high as 160°. The superhydrophobic silica films are thermally stable up to 440 °C and above this temperature, the silica films lose superhydrophobicity. By controlling the primer particle size of SiO2 about 26 nm, leading to decrease the final size of silica nanoparticles after modification of nanoparticles by isooctyltrimethoxysilane about 42 nm. The films are transparent and have uniform size on the surface. The silica films have been characterized by atomic force microscopy (AFM), fourier transform infrared spectroscopy (FT-IR), transparency, contact angle measurement (CA), Zeta-potential, Thermal stability by TG-DTA analysis.

3. Mechanical properties characterization and modeling of active polymer gels

Marra, Steven Paul

Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as actuators and "artificial muscles." While much work has been done to study the behavior and properties of these gels, little information is available regarding the full constitutive description of the mechanical and actuation properties. This work focuses on developing a means of characterizing the mechanical properties of active polymer gels and describing how these properties evolve as the gel actuates. Poly(vinyl alcohol)-poly(acrylic acid) (PVA-PAA) gel was chosen as the model material for this work because it is relatively simple and safe to both fabricate and actuate. PVA-PAA gels are fabricated on-site using a solvent-casting technique. These gels expand when moved from acidic to basic solutions, and contract when moved from basic to acidic solutions. Citric acid and sodium bicarbonate were used as the testing solutions for this work. The mechanical properties of the gel were characterized by conducting uniaxial and biaxial tests on thin PVA-PAA gel films. A biaxial testing system has been developed which can measure stresses and deformations of these films in a variety of liquid environments. The experimental results on PVA-PAA gels show these materials to be relatively compliant, and slightly viscoelastic and compressible. These gels are also capable of large recoverable deformations in both acidic and basic environments. A thermodynamically consistent finite-elastic constitutive model was developed to describe the mechanical and actuation behaviors of active polymer gels. The mechanical properties of the gel are characterized by a free-energy function, and the model utilizes an evolving internal variable to describe the actuation

4. Precise size control over ultrafine rutile titania nanocrystallites in hierarchical nanotubular silica/titania hybrids with efficient photocatalytic activity.

PubMed

Gu, Yuanqing; Huang, Jianguo

2013-08-12

Hierarchical-structured nanotubular silica/titania hybrids incorporated with particle-size-controllable ultrafine rutile titania nanocrystallites were realized by deposition of ultrathin titania sandwiched silica gel films onto each nanofiber of natural cellulose substances (e.g., common commercial filter paper) and subsequent flame burning in air. The rapid flame burning transforms the initially amorphous titania into rutile phase titania, and the silica gel films suppress the crystallite growth of rutile titania, thereby achieving nano-precise size regulation of ultrafine rutile titania nanocrystallites densely embedded in the silica films of the nanotubes. The average diameters of these nanocrystallites are adjustable in a range of approximately 3.3-16.0 nm by a crystallite size increment rate of about 2.4 nm per titania deposition cycle. The silica films transfer the electrons activated by crystalline titania and generate catalytic reactive species at the outer surface. The size-tuned ultrafine rutile titania nanocrystallites distributed in the unique hierarchical networks significantly improve the photocatalytic performance of the rutile phase titania, thereby enabling a highly efficient photocatalytic degradation of the methylene blue dye under ultraviolet light irradiation, which is even superior to the pure anatase-titania-based materials. The facile stepwise size control of the rutile titania crystallites described here opens an effective pathway for the design and preparation of fine-nanostructured rutile phase titania materials to explore potential applications.

5. Anomalous phase separation behavior of gel-derived soda-silica glasses

NASA Technical Reports Server (NTRS)

Neilson, G. F.; Weinberg, M. C.

1982-01-01

The effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide preparaed by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.

6. Synthesis of organic-inorganic hybrid sols with nano silica particles and organoalkoxysilanes for transparent and high-thermal-resistance coating films using sol-gel reaction.

PubMed

Na, Moonkyong; Park, Hoyyul; Ahn, Myeongsang; Lee, Hyeonhwa; Chung, Ildoo

2010-10-01

Organic-inorganic hybrid sols were synthesized from nano silica particles dispersed in water and from organoalkoxysilanes, using the sol-gel reaction. This work focuses on the effects of the three multifunctional organoalkoxysilanes dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), and tetramethoxysilane (TMOS) to form a transparent and high-thermal-resistance coating film. The stability of the hybrid sol was evaluated as a function of the reaction time for 10 d through the variation of the viscosity. The viscosity of the silica/DMDMS and silica/MTMS sol was slightly increased for 10 d. The multifunctional organoalkoxysilanes formed dense silica networks through hydrolysis and condensation reaction, which enhanced the thermal resistance of the coating films. No thermal degradation of the silica/DMDMS sample occurred up to 600 degrees C, and none of the silica/MTMS and silica/TMOS samples occurred either up to 700 degrees C. The organic-inorganic hybrid sols were coated on the glass substrate using a spin-coating procedure. The organic-inorganic hybrid sols formed flat coating films without cracks. The transmittance of the hybrid sol coating films using MTMS and DMDMS was shown to be over 90%. The transmittance of the silica/TMOS sol coating film reacted for 10 d abruptly decreased due to faster gelation. The silica/DMDMS and silica/MTMS hybrid sols formed smooth coating films while the surface roughness of the silica/TMOS coating film markedly increased when the hybrid sol reacted for 10 d. The increase of the surface roughness of the silica/TMOS coating film can be attributed to the degradation of the stability of the hybrid sol and to the loss of transmittance of the coating film. It was confirmed in this study that the use of organic-inorganic hybrid sol can yield transparent and high-thermal-resistance coating films.

7. Study of growth condition and characterization of bisthiourea-zinc acetate (BTZA) crystal grown in silica gel

Sivanandan, T.; Kalainathan, S.

2015-05-01

Semiorganic crystals of bisthiourea-zinc acetate (BTZA) having nonlinear optical properties was grown in silica gel medium by gel technique at room temperature. The optimum pH, yielding maximum size (35 mm) of transparent title crystal was found to be 4.8 pH. Single crystal XRD analysis reveals that the crystal lattice of BTZA crystal belongs to monoclinic system with cell parameter, a = 7.1243 Å, b = 17.7292 Å and c = 11.1372 Å. The presence of functional groups in the crystals was confirmed by FTIR analysis, and also the presence of elements in the compound was identified by EDAX. The optical constants (lower cutoff wavelength λ = 297 nm, band gap energy = 4.4022 eV) were determined using the recorded UV-Vis-NIR spectrum of BTZA crystal. A surface feature of the crystal was analyzed using AFM (Atomic Force Microscope). The Vickers microhardness number was found to increase with increasing load, and the yield strength (σy), elastic stiffness constant (C11) of BTZA crystal were calculated. The laser damage threshold was measured using Nd:YAG laser (1064 nm). The dielectric properties of BTZA crystal was recorded in the frequency range of 50 Hz-5 MHz, and it shows that the dielectric constant and dielectric loss is found to be decreased with an increase of frequency at various temperature. Further, the valence electron, plasma energy and electronic polarizability for the gel grown BTZA crystal was calculated. Thermal behavior of the gel grown crystal was investigated by thermo gravimetric and differential scanning calorimetric analysis.

8. Solid-surface luminescence interactions of nitrogen heterocycles adsorbed on silica gel chromatoplates submerged in chloroform/n-hexane solvents

SciTech Connect

Burrell, G.J.; Hurtubise, R.J.

1988-03-15

The room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) of benzo(f)quinoline and benzo(h)quinoline, obtained from the samples adsorbed on silica gel chromatoplates submerged in chloroform/n-hexane solvents, revealed several of the interactions of the nitrogen heterocycles with the solid matrix. The RTP results showed the emitting phosphor was protected from collisional deactivation by the matrix and that the adsorbed chloroform minimally disrupted the phosphor adsorption interactions. In addition, at least two populations of phosphors were indicated. The RTF data and RTP data showed that different interactions were occurring in the singlet state compared to the triplet state. A comparison of RTF intensity and TRP intensity as a function of chromatographic solvent strength indicated that the protonated forms of the nitrogen heterocycles in their triplet states were interacting with the matrix more strongly than the protonated forms of the nitrogen heterocycles in their singlet states.

9. Simultaneous preconcentration of cadmium and lead in water samples with silica gel and determination by flame atomic absorption spectrometry.

PubMed

Xu, Hongbo; Wu, Yun; Wang, Jian; Shang, Xuewei; Jiang, Xiaojun

2013-12-01

A new method that utilizes pretreated silica gel as an adsorbent has been developed for simultaneous preconcentration of trace Cd(II) and Pb(II) prior to the measurement by flame atomic absorption spectrometry. The effects of pH, the shaking time, the elution condition and the coexisting ions on the separation/preconcentration conditions of analytes were investigated. Under optimized conditions, the static adsorption capacity of Cd(II) and Pb(II) were 45.5 and 27.1mg/g, the relative standard deviations were 3.2% and 1.7% (for n = 11), and the limits of detection obtained were 4.25 and 0.60 ng/mL, respectively. The method was validated by analyzing the certified reference materials GBW 07304a (stream sediment) and successfully applied to the analysis of various treated wastewater samples with satisfactory results.

10. Simultaneous preconcentration of cadmium and lead in water samples with silica gel and determination by flame atomic absorption spectrometry.

PubMed

Xu, Hongbo; Wu, Yun; Wang, Jian; Shang, Xuewei; Jiang, Xiaojun

2013-12-01

A new method that utilizes pretreated silica gel as an adsorbent has been developed for simultaneous preconcentration of trace Cd(II) and Pb(II) prior to the measurement by flame atomic absorption spectrometry. The effects of pH, the shaking time, the elution condition and the coexisting ions on the separation/preconcentration conditions of analytes were investigated. Under optimized conditions, the static adsorption capacity of Cd(II) and Pb(II) were 45.5 and 27.1mg/g, the relative standard deviations were 3.2% and 1.7% (for n = 11), and the limits of detection obtained were 4.25 and 0.60 ng/mL, respectively. The method was validated by analyzing the certified reference materials GBW 07304a (stream sediment) and successfully applied to the analysis of various treated wastewater samples with satisfactory results. PMID:25078838

11. Direct Patterning on Sol-Gel Low-k Porous Silica by Thermal Nanoimprinting

Makoto Okada,; Takahiro Nakayama,; Yuji Kang,; Yuichi Haruyama,; Kazuhiro Kanda,; Shinji Matsui,

2010-06-01

The direct patterning of low-dielectric constant (low-k) materials via nanoimprint lithography (NIL) has the potential to simplify fabrication processes and significantly reduce the manufacturing costs of semiconductor devices. It is known that a low k is realized by introducing a large number of nanoscale pores into a material. We demonstrated nanoimprinting on a sol-gel low-k material (k˜ 2.0) formed using methyl silicate as a siloxane oligomer source and surfactants as a pore template. As a result, 200-nm-linewidth mold patterns were successfully transferred onto the sol-gel low-k material by thermal nanoimprinting at 200 °C. However, pattern shrinkage was observed. The imprinted pattern linewidth was 180 nm. We assumed from the Fourier transform infrared spectroscopy (FT-IR) spectra of the sol-gel film before and after baking that the pattern shrinkage was induced by the condensation reaction.

12. Direct Patterning on Sol-Gel Low-k Porous Silica by Thermal Nanoimprinting

Okada, Makoto; Nakayama, Takahiro; Kang, Yuji; Haruyama, Yuichi; Kanda, Kazuhiro; Matsui, Shinji

2010-06-01

The direct patterning of low-dielectric constant (low-k) materials via nanoimprint lithography (NIL) has the potential to simplify fabrication processes and significantly reduce the manufacturing costs of semiconductor devices. It is known that a low k is realized by introducing a large number of nanoscale pores into a material. We demonstrated nanoimprinting on a sol-gel low-k material (k˜2.0) formed using methyl silicate as a siloxane oligomer source and surfactants as a pore template. As a result, 200-nm-linewidth mold patterns were successfully transferred onto the sol-gel low-k material by thermal nanoimprinting at 200 °C. However, pattern shrinkage was observed. The imprinted pattern linewidth was 180 nm. We assumed from the Fourier transform infrared spectroscopy (FT-IR) spectra of the sol-gel film before and after baking that the pattern shrinkage was induced by the condensation reaction.

13. Drastic selectivity reversal on crown-ether based ion-sensing membranes made of ordered mesoporous silica and conventional sol-gel derived one.

PubMed

Yajima, Setsuko; Nakajima, Takahito; Higashi, Mariko; Kimura, Keiichi

2010-03-21

A crown-ether based ion sensor, in which ordered mesoporous silica was used as a membrane material, was fabricated for the first time, and drastic selectivity reversal was attained in comparison with conventional sol-gel derived membrane based on the same crown ether.

14. Sorption of the organic cation metoprolol on silica gel from its aqueous solution considering the competition of inorganic cations.

PubMed

Kutzner, Susann; Schaffer, Mario; Börnick, Hilmar; Licha, Tobias; Worch, Eckhard

2014-05-01

Systematic batch experiments with the organic monovalent cation metoprolol as sorbate and the synthetic material silica gel as sorbent were conducted with the aim of characterizing the sorption of organic cations onto charged surfaces. Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na(+), NH4(+), Ca(2+), and Mg(2+)) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions. The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). In general, a decreasing sorption of metoprolol with increasing concentrations in inorganic cations was observed. Competing ions of the same valence showed similar effects. A significant sorption affinity of metoprolol with ion type dependent Freundlich coefficients KF,0.77 between 234.42 and 426.58 (L/kg)(0.77) could still be observed even at very high concentrations of competing inorganic cations. Additional column experiments confirm this behavior, which suggests the existence of further relevant interactions beside cation exchange. In subsequent batch experiments, the influence of mixtures with more than one competing ion and the effect of a reduced negative surface charge at a pH below the point of zero charge (pHPZC ≈ 2.5) were also investigated. Finally, the study demonstrates that cation exchange is the most relevant but not the sole mechanism for the sorption of metoprolol on silica gel. PMID:24584001

15. Adsorption of transition metal ions from aqueous solutions onto a novel silica gel matrix inorganic-organic composite material.

PubMed

Yin, Ping; Xu, Qiang; Qu, Rongjun; Zhao, Guifang; Sun, Yanzhi

2010-01-15

A novel inorganic-organic composite material silica gel microspheres encapsulated by imidazole functionalized polystyrene (SG-PS-azo-IM) has been synthesized and characterized. This composite material was used to investigate the adsorption of Cr(III), Mn(II), Fe(III), Ni(II), Cu(II), Zn(II), Hg(II), Pb(II), Pd(II), Pt(II), Ag(I), and Au(III) from aqueous solutions, and the research results displayed that SG-PS-azo-IM has the highest adsorption capacity for Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation, and the maximum adsorption capacity for Au(III) is 1.700 mmol/g. The adsorption selectivity, the dynamic adsorption and desorption properties of SG-PS-azo-IM for Au(III) have also been studied. The results showed that SG-PS-azo-IM had excellent adsorption for Au(III) in four binary ions system, especially in the systems of Au(III)-Zn(II) and Au(III)-Cu(II), and almost Au(III) could be desorbed with the eluent solution of 0.5% thiourea in 1 mol/L HCl. Moreover, this novel composite material was used to preconcentrate Au(III) before its determination by flame atomic adsorption spectrometry. In the initial concentration range of 0.10-0.20 microg/mL, multiple of enrichment could reach 5.28. Thus, silica gel encapsulated by polystyrene coupling with imidazole (SG-PS-azo-IM) is favorable and useful for the removal of transition metal ions, and the high adsorption capacity makes it a good promising candidate material for Au(III) removal.

16. Sorption of the organic cation metoprolol on silica gel from its aqueous solution considering the competition of inorganic cations.

PubMed

Kutzner, Susann; Schaffer, Mario; Börnick, Hilmar; Licha, Tobias; Worch, Eckhard

2014-05-01

Systematic batch experiments with the organic monovalent cation metoprolol as sorbate and the synthetic material silica gel as sorbent were conducted with the aim of characterizing the sorption of organic cations onto charged surfaces. Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na(+), NH4(+), Ca(2+), and Mg(2+)) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions. The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). In general, a decreasing sorption of metoprolol with increasing concentrations in inorganic cations was observed. Competing ions of the same valence showed similar effects. A significant sorption affinity of metoprolol with ion type dependent Freundlich coefficients KF,0.77 between 234.42 and 426.58 (L/kg)(0.77) could still be observed even at very high concentrations of competing inorganic cations. Additional column experiments confirm this behavior, which suggests the existence of further relevant interactions beside cation exchange. In subsequent batch experiments, the influence of mixtures with more than one competing ion and the effect of a reduced negative surface charge at a pH below the point of zero charge (pHPZC ≈ 2.5) were also investigated. Finally, the study demonstrates that cation exchange is the most relevant but not the sole mechanism for the sorption of metoprolol on silica gel.

17. [Separation of purines, pyrimidines, pterins and flavonoids on magnolol-bonded silica gel stationary phase by high performance liquid chromatography].

PubMed

Chen, Hong; Li, Laishen; Zhang, Yang; Zhou, Rendan

2012-10-01

A new magnolol-bonded silica gel stationary phase (MSP) was used to separate the basic drugs including four purines, eight pyrimidines, four pterins and five flavonoids as polar representative samples by high performance liquid chromatography (HPLC). To clarify the separation mechanism, a commercial ODS column was also tested under the same chromatographic conditions. The high selectivities and fast baseline separations of the above drugs were achieved by using simple mobile phases on MSP. Although there is no end-caped treatment, the peak shapes of basic drugs containing nitrogen such as purines, pyrimidines and pterins were rather symmetrical on MSP, which indicated the the magnolol as ligand with multi-sites could shield the side effect of residual silanol groups on the surface of silica gel. Although somewhat different in the separation resolution, it was found that the elution orders of some drugs were generally similar on both MSP and ODS. The hydrophobic interaction should play a significant role in the separations of the above basic drugs, which was attributed to their reversed-phase property in the nature. However, MSP could provide the additional sites for many polar solutes, which was a rational explanation for the high selectivity of MSP. For example, in the separation of purines, pyrimidines and pterins on MSP, hydrogen-bonding and dipole-dipole interactions played leading roles besides hydrophobic interaction. Some solute molecules (such as mercaptopurine, vitexicarpin) and MSP can form the strong pi-pi stacking in the separation process. All enhanced the retention and improved the separation selectivity of MSP, which facilitated the separation of the basic drugs.

18. Diced electrophoresis gel assay for screening enzymes with specified activities.

PubMed

Komatsu, Toru; Hanaoka, Kenjiro; Adibekian, Alexander; Yoshioka, Kentaro; Terai, Takuya; Ueno, Tasuku; Kawaguchi, Mitsuyasu; Cravatt, Benjamin F; Nagano, Tetsuo

2013-04-24

We have established the diced electrophoresis gel (DEG) assay as a proteome-wide screening tool to identify enzymes with activities of interest using turnover-based fluorescent substrates. The method utilizes the combination of native polyacrylamide gel electrophoresis (PAGE) with a multiwell-plate-based fluorometric assay to find protein spots with the specified activity. By developing fluorescent substrates that mimic the structure of neutrophil chemoattractants, we could identify enzymes involved in metabolic inactivation of the chemoattractants.

19. Effect of the sol-gel route on the textural characteristics of silica imprinted with Rhodamine B.

PubMed

de Coelho Escobar, Cícero; dos Santos, João Henrique Zimnoch

2014-04-01

A series of silica xerogels that support Rhodamine B as a template were synthesized using distinct sol-gel routes, namely, acid-catalyzed routes, a base-catalyzed route, acid-catalyzed with base-catalyzed (two steps) hydrolytic routes, and a FeCl3 -catalyzed nonhydrolytic route. The extraction methods (thermal, Soxhlet, water washing, and ultrasound) were also evaluated. The resulting xerogels were characterized through porosimetry using nitrogen adsorption/desorption. The samples were further analyzed through small-angle X-ray scattering, Fourier transform infrared spectroscopy, and SEM. The preparation route affected the materials' textural properties. Extraction was optimized using acid and two-step routes. The acid route from Rhodamine B to Rhodamine 6G generated the highest selectivity factor (2.5). The nonhydrolytic route produced the best imprinting factor. Competitive adsorption was also used, from which the approximate imprinting factor was 2. The cavity shape generated during the production of the imprinted silica dictates the adsorption behavior, not the magnitude of the surface area. PMID:24478149

20. Trivalent chromium removal from aqueous solutions by a sol–gel synthesized silica adsorbent functionalized with sulphonic acid groups

SciTech Connect

Gomez-Gonzalez, Sergio Efrain; Carbajal-Arizaga, Gregorio Guadalupe; Manriquez-Gonzalez, Ricardo; De la Cruz-Hernandez, Wencel; Gomez-Salazar, Sergio

2014-11-15

Highlights: • Corpuscular sulphonic acid-functionalized silica holds improved uptake of chromium. • Mesopores on adsorbent facilitate (CH{sub 3}COO){sub 2}Cr{sup +} ion uptake on sulphonate sites. • Formation of chromium acetate sulphonate complex proposed from XPS results. • Fixed bed chromium uptake results suggest potential industrial use. - Abstract: A high capacity hybrid silica adsorbent was synthesized via sol–gel processing with sulphonic acid groups as trivalent chromium complex ions chelators from aqueous solutions. The synthesis included co-condensation of tetraethoxysilane (TEOS) with 3-(mercaptopropyl)trimethoxysilane (MPS), and oxidation of thiol to sulphonic acid groups. Chromium uptake kinetic, batch and fixed-bed experiments were performed to assess the removal of this metal from aqueous solutions. {sup 13}C, {sup 29}Si CPMAS NMR, FTIR, XPS were used to characterize the adsorbent structure and the nature of chromium complexes on the adsorbent surface. Chromium maximum uptake was obtained at pH 3 (72.8 mg/g). Elemental analysis results showed ligand density of 1.48 mmol sulphonic groups/g. About 407 mL of Cr(III) solution (311 mg/L) were treated to breakthrough point reaching ≤0.06 mg/L at the effluent. These results comply with USEPA regulation for chromium concentration in drinking water (≤0.1 mg/L). The adsorbent shows potential to be used in chromium separations to the industrial level.

1. Nanoparticles of KFeP2O7 implanted on silica gel beads for Cd2+ ion adsorption.

PubMed

2015-01-01

2. Large-area electrochromic coatings: Composites of polyaniline and polyacrylate-silica hybrid sol-gel materials

SciTech Connect

Jang, G.W.; Chen, C.; Gumbs, R.W.; Wei, Y.; Yeh, J.M.

1996-08-01

A low-cost technique for fabricating large-area electrochromic coatings is described. Polyaniline was incorporated into polyacrylate-silica hybrid sol-gel networks using suspended particles or solutions. A solution of polyaniline and poly[methyl methacrylate-co-3-(trimethoxysilyl)propyl methacrylate] can be spray- or brush-coated on transparent indium-tin oxide substrates to form robust electrochromic coatings. Silane functional groups on the polyacrylate chain act as coupling and cross-linking agents to improve surface adhesion and mechanical properties of the resulting composite coatings. These coatings showed reversible transparent to green color change when polarized at potentials between {minus}0.4 and +0.4 V vs. Ag/AgCl in a 0.2 M LiClO{sub 4}/acetonitrile electrolyte solution. The cycle lifetimes of polyaniline films were improved by incorporating the polymer in the polyacrylate-silica matrix. Electrochromic switching was demonstrated for the composite coatings in large-area all-solid-state devices.

3. Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)

SciTech Connect

Grattan-Bellew, P.E.; Chan, Gordon

2013-05-15

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate.

4. The dependence of phase change enthalpy on the pore structure and interfacial groups in hydrated salts/silica composites via sol-gel.

PubMed

Wu, Yuping; Wang, Tao

2015-06-15

It was found that the procedures for incorporating hydrated salts into silica, including mixing with sol in an instant (S1 procedure), mixing with sol via drop by drop (S2 procedure) and mixing until the sol forming the gel (S3 procedure), had pronounced effects on the phase change enthalpy of hydrated salts/silica composite via sol-gel process. The discrepancy of phase change enthalpies of the composites with the same content of hydrated salts can be as high as 40 kJ/kg. To unveil the mechanism behind, the pore structure of silica matrix and interfacial functional groups were investigated extensively. It was revealed that different incorporation procedures resulted in distinct pore structure of silica matrix and different intensities of interfacial Si-OH groups. The S3 procedure was beneficial to induce the silica matrix with bigger pore size and fewer Si-OH groups. Consequently, the phase change enthalpy of the hydrated salts/silica composite prepared by this procedure was the highest because of its lower size confinement effects and weaker adsorption by Si-OH groups. This study will provide insight into the preparation of shape-stabilized phase change materials for thermal energy storage applications.

5. Effects of capsid-modified oncolytic adenoviruses and their combinations with gemcitabine or silica gel on pancreatic cancer.

PubMed

Kangasniemi, Lotta; Parviainen, Suvi; Pisto, Tommi; Koskinen, Mika; Jokinen, Mika; Kiviluoto, Tuula; Cerullo, Vincenzo; Jalonen, Harry; Koski, Anniina; Kangasniemi, Anna; Kanerva, Anna; Pesonen, Sari; Hemminki, Akseli

2012-07-01

Conventional cancer treatments often have little impact on the course of advanced pancreatic cancer. Although cancer gene therapy with adenoviruses is a promising developmental approach, the primary receptor is poorly expressed in pancreatic cancers which might compromise efficacy and thus targeting to other receptors could be beneficial. Extended stealth delivery, combination with standard chemotherapy or circumvention of host antiadenoviral immune response might improve efficacy further. In this work, capsid-modified adenoviruses were studied for transduction of cell lines and clinical normal and tumor tissue samples. The respective oncolytic viruses were tested for oncolytic activity in vitro and in vivo. Survival was studied in a peritoneally disseminated pancreas cancer model, with or without concurrent gemcitabine while silica implants were utilized for extended intraperitoneal virus delivery. Immunocompetent mice and Syrian hamsters were used to study the effect of silica mediated delivery on antiviral immune responses and subsequent in vivo gene delivery. Capsid modifications selectively enhanced gene transfer to malignant pancreatic cancer cell lines and clinical samples. The respective oncolytic viruses resulted in increased cell killing in vitro, which translated into a survival benefit in mice. Early proinfammatory cytokine responses and formation of antiviral neutralizing antibodies was partially avoided with silica implants. The implant also shielded the virus from pre-existing neutralizing antibodies, while increasing the pancreas/liver gene delivery ratio six-fold. In conclusion, capsid modified adenoviruses would be useful for testing in pancreatic cancer trials. Silica implants might increase the safety and efficacy of the approach.

6. Silica/polyacrylonitrile hybrid nanofiber membrane separators via sol-gel and electrospinning techniques for lithium-ion batteries

Yanilmaz, Meltem; Lu, Yao; Zhu, Jiadeng; Zhang, Xiangwu

2016-05-01

Silica/polyacrylonitrile (SiO2/PAN) hybrid nanofiber membranes were fabricated by using sol-gel and electrospinning techniques and their electrochemical performance was evaluated for use as separators in lithium-ion batteries. The aim of this study was to design high-performance separator membranes with enhanced electrochemical performance and good thermal stability compared to microporous polyolefin membranes. In this study, SiO2 nanoparticle content up to 27 wt% was achieved in the membranes by using sol-gel technique. It was found that SiO2/PAN hybrid nanofiber membranes had superior electrochemical performance with good thermal stability due to their high SiO2 content and large porosity. Compared with commercial microporous polyolefin membranes, SiO2/PAN hybrid nanofiber membranes had larger liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO2/PAN hybrid nanofiber membranes with different SiO2 contents (0, 16, 19 and 27 wt%) were also assembled into lithium/lithium iron phosphate cells, and high cell capacities and good cycling performance were demonstrated at room temperature. In addition, cells using SiO2/PAN hybrid nanofiber membranes with high SiO2 contents showed superior C-rate performance compared to those with low SiO2 contents and commercial microporous polyolefin membrane.

7. Facile Synthesis of Silica-Encapsulated Gold Nanoflowers as Surface-Enhanced Raman Scattering Probes Using Silane-Mediated Sol-Gel Reaction.

PubMed

Yoo, Jihye; Park, Sang-Joon; Lee, Sang-Wha

2016-06-01

Flower-like gold nanoparticles, so called gold nanoflowers (AuNFs), were synthesized through the reduction of HAuC4 with ascorbic acid in the presence of chitosan polymers. Chitosan-mediated AuNFs exhibited the distinct SERS signals of 2-chlorothiophenol (CTP) due to the presence of many interstitial gaps (so called hot spots) on the surface. For the facile silica coating, the AuNFs were conjugated with terminal carboxylate groups of (3-glycidyloxypropyl)trimethoxysilane (GPTMS), consequently forming alkoxy-terminated AuNFs which could facilely participate in the sol-gel reaction for silica coating. The resulting core-shell particles, i.e., CTP-adsorbed AuNFs with silica coating, exhibited the distinct SERS signals of CTP embedded within silica layer, warranting the effectiveness of this chemical strategy for spectroscopic labeling of Raman probes. PMID:27427704

8. Facile Synthesis of Silica-Encapsulated Gold Nanoflowers as Surface-Enhanced Raman Scattering Probes Using Silane-Mediated Sol-Gel Reaction.

PubMed

Yoo, Jihye; Park, Sang-Joon; Lee, Sang-Wha

2016-06-01

Flower-like gold nanoparticles, so called gold nanoflowers (AuNFs), were synthesized through the reduction of HAuC4 with ascorbic acid in the presence of chitosan polymers. Chitosan-mediated AuNFs exhibited the distinct SERS signals of 2-chlorothiophenol (CTP) due to the presence of many interstitial gaps (so called hot spots) on the surface. For the facile silica coating, the AuNFs were conjugated with terminal carboxylate groups of (3-glycidyloxypropyl)trimethoxysilane (GPTMS), consequently forming alkoxy-terminated AuNFs which could facilely participate in the sol-gel reaction for silica coating. The resulting core-shell particles, i.e., CTP-adsorbed AuNFs with silica coating, exhibited the distinct SERS signals of CTP embedded within silica layer, warranting the effectiveness of this chemical strategy for spectroscopic labeling of Raman probes.

9. Photophysical properties of some fluorescent materials containing 3-methoxy-7H-benzo[de]anthracen-7-one embedded in sol-gel silica hybrids

Raditoiu, Alina; Raditoiu, Valentin; Culita, Daniela Cristina; Baran, Adriana; Anghel, Dan Florin; Spataru, Catalin Ilie; Amariutei, Viorica; Nicolae, Cristian Andi; Wagner, Luminita Eugenia

2015-07-01

Several fluorescent materials were prepared by embedding 3-methoxy-7H-benzo[de]anthracen-7-one in transparent sol-gel silica hybrids, in acid catalysis and at room temperature. The photophysical properties of the materials are studied in relationship with the structure and based on interactions established between the fluorophore, which display high sensitivity to minor changes in the local environments, and hybrid silica networks. Colored materials show marked differences in absorption and fluorescence spectra due to the environments around the dyestuff molecules created in the host matrices by grafting different organic moieties onto silica surface. The fluorescence emission spectrum of the obtained materials reveals a positive solvatochromism due to the intramolecular charge transfer character of the excited states and changes in the fluorophore dipole moment. Variations recorded in the fluorescence parameters of the hybrid materials confirm that some interactions are established between the fluorescent dyestuff and hybrid silica network.

10. The precipitation of silica gels along seismogenic faults due to sudden fluid pressure drops: an example from the Zuccale low angle normal fault, Italy

Holdsworth, R. E.; Smith, S.; Lloyd, G. E.

2012-04-01

Based on experimental and some field-based studies several authors have proposed that silica gel (hydrated amorphous silica) layers are generated by frictional slip along seismogenic faults. The precise mechanism(s) of formation have remained somewhat enigmatic, but most studies invoke a mixture of frictional and chemical processes simultaneous with seismogenic slip. In this presentation we describe a new occurrence of ultrafine grained silica fault rocks that are hosted along a number of detachment faults developed within the Zuccale low angle normal fault on the island of Elba, Italy. Based on the geological and microstructural observations, including very detailed EBSD measurements, we propose an alternative mechanism of formation in which the gels precipitate rapidly from supersaturated pore fluids formed due to sudden drops in fluid pressure along faults during or immediately following episodes of seismogenic slip. This mechanism may have widespread application to other examples of fault-hosted silica gels. Furthermore, given the field appearance of these layers (see figure) and the recognition of ultrafine quartz crystallites in thin section, it is possible that similar examples in other natural fault zones may have been mistakenly identified as pseudotachylytes. The implications for fault weakening will also be discussed.

11. 8-Hydroxyquinoline anchored to silica gel via new moderate size linker: synthesis and applications as a metal ion collector for their flame atomic absorption spectrometric determination.

PubMed

Goswami, Anupama; Singh, Ajai K; Venkataramani, B

2003-08-29

The silica gel modified with (3-aminopropyl-triethoxysilane) was reacted with 5-formyl-8-hydroxyquinoline (FHOQ(x)) to anchor 8-quinolinol ligand on the silica gel. It was characterised with cross polarisation magic angle spinning (CPMAS) NMR and diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy and used for the preconcentration of Cu(II), Pb(II), Ni(II), Fe(III), Cd(II), Zn(II) and Co(II) prior to their determination by flame atomic absorption spectrometry. The surface area of the modified silica gel has been found to be 227 m(2) g(-1) and the two pKa values as 3.8 and 8.0. The optimum pH ranges for quantitative sorption are 4.0-7.0, 4.5-7.0, 3.0-6.0, 5.0-8.0, 5.0-8.0, 5.0-8.0 and 4.0-7.0 for Cu, Pb, Fe, Zn, Co, Ni and Cd, respectively. All the metals can be desorbed with 2.5 mol l(-1) HCl or HNO(3). The sorption capacity for these metal ions is in range of 92-448.0 micromol g(-1) and follows the order Cdsilica gel and determined with flame atomic absorption spectrometer (R.S.D.< or =6.4%). Cobalt contents of pharmaceutical samples (vitamin tablet) were preconcentrated with the present chelating silica gel and estimated by flame AAS, with R.S.D. approximately 1.4%. The results are in the good agreement with the certified value, 1.99 microg g(-1) of the

12. [Preparation of 1 µm non-porous C18 silica gel stationary phase for chiral-pressurized capillary electrochromatography].

PubMed

Lu, Yangfang; Wang, Hui; Wang, Guiming; Wang, Yan; Gu, Xue; Yan, Chao

2015-03-01

Non-porous C18 silica gel stationary phase (1 µm) was prepared and applied to chiral separation in pressurized capillary electrochromatography (pCEC) for the enantioseparation of various basic compounds. The non-porous silica particles (1 µm) were synthesized using modified St6ber method. C18 stationary phase (1 µm) was prepared by immobilization of chloro-dimethyl-octadecylsilane. Using carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral additive, the pCEC conditions including the content of acetonitrile (ACN), concentration of buffer, pH, the concentration of chiral additive and flow rate as well as applied voltage were investigated to obtain the optimal pCEC conditions for the separation of four basic chiral compounds. The column provided an efficiency of up to 190,000 plates/m. Bupropion hydrochloride, clenbuterol hydrochloride, metoprolol tartrate, and esmolol hydrochloride were baseline separated under the conditions of 5 mmol/L ammonium acetate buffer at pH 4. 0 with 20% (v/ v) acetonitrile, and 15 mmol/L CM-β-CD as the chiral additive. The applied voltage was 2 kV and flow rate was 0.03 mL/min with splitting ratio of 300:1. The resolution were 1.55, 2.82, 1. 69, 1. 70 for bupropion hydrochloride, clenbuterol hydrochloride, metoprolol tartrate, esmolol hydrochloride, respectively. The C18 coverage was improved by repeating silylation method. The synthesized 1 µm C18 packings have better mechanical strength and longer service life because of the special, non-porous structure. The column used in pCEC mode showed better separation of the racemates and a higher rate compared with those used in the capillary liquid chromatography (cLC) mode. This study provided an alternative way for the method of pCEC enantioseparation with chiral additives in the mobile phase and demonstrated the feasibility of micron particle stationary phase in chiral separation. PMID:26182460

13. [Preparation of 1 µm non-porous C18 silica gel stationary phase for chiral-pressurized capillary electrochromatography].

PubMed

Lu, Yangfang; Wang, Hui; Wang, Guiming; Wang, Yan; Gu, Xue; Yan, Chao

2015-03-01

Non-porous C18 silica gel stationary phase (1 µm) was prepared and applied to chiral separation in pressurized capillary electrochromatography (pCEC) for the enantioseparation of various basic compounds. The non-porous silica particles (1 µm) were synthesized using modified St6ber method. C18 stationary phase (1 µm) was prepared by immobilization of chloro-dimethyl-octadecylsilane. Using carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral additive, the pCEC conditions including the content of acetonitrile (ACN), concentration of buffer, pH, the concentration of chiral additive and flow rate as well as applied voltage were investigated to obtain the optimal pCEC conditions for the separation of four basic chiral compounds. The column provided an efficiency of up to 190,000 plates/m. Bupropion hydrochloride, clenbuterol hydrochloride, metoprolol tartrate, and esmolol hydrochloride were baseline separated under the conditions of 5 mmol/L ammonium acetate buffer at pH 4. 0 with 20% (v/ v) acetonitrile, and 15 mmol/L CM-β-CD as the chiral additive. The applied voltage was 2 kV and flow rate was 0.03 mL/min with splitting ratio of 300:1. The resolution were 1.55, 2.82, 1. 69, 1. 70 for bupropion hydrochloride, clenbuterol hydrochloride, metoprolol tartrate, esmolol hydrochloride, respectively. The C18 coverage was improved by repeating silylation method. The synthesized 1 µm C18 packings have better mechanical strength and longer service life because of the special, non-porous structure. The column used in pCEC mode showed better separation of the racemates and a higher rate compared with those used in the capillary liquid chromatography (cLC) mode. This study provided an alternative way for the method of pCEC enantioseparation with chiral additives in the mobile phase and demonstrated the feasibility of micron particle stationary phase in chiral separation.

14. Active motion induced break-up of colloidal gels

Szakasits, Megan; Solomon, Michael

2015-03-01

We found that fractal gel networks of polystyrene colloids can be broken up by active motion of Janus colloids that have been incorporated into them. Janus particles were synthesized by electron beam deposition of platinum onto one micron carboxylate modified polystyrene particles. Through addition of the divalent salt magnesium chloride, an initially stable suspension of Janus and polystyrene colloids, present in equal proportion, underwent aggregation to yield a fractal gel. The Janus colloids were activated by addition of 30% v/v hydrogen peroxide through a porous hydrogel membrane. Changes in structure and dynamics were visualized by two channel confocal laser scanning microscopy (CLSM). By means of image analysis, we calculated the mean squared displacement (MSD) and radial distribution function (RDF) for gel samples before and after addition of hydrogen peroxide. The MSD confirmed the Janus particles we synthesized undergo active motion. The RDF and cluster size distribution of gel samples before and after addition of peroxide demonstrate how active motion broke apart the gel network into smaller clusters.

15. Antibacterial Activity of Copaiba Oil Gel on Dental Biofilm

PubMed Central

Simões, Cláudia A.C.G.; Conde, Nikeila C. de Oliveira; Venâncio, Gisely N.; Milério, Patrícia S.L.L.; Bandeira, Maria F.C.L.; da Veiga Júnior, Valdir F.

2016-01-01

Amazonian biodiversity products that have been used for years in folk medicine, have emerged as feasible and promising alternatives for the inhibition of microorganisms in dental biofilm. Copaiba oil, a phytotherapic agent widely used by the Amazonian populations, is known for its antibacterial, anti-inflammatory, anesthetic, healing and antitumor medicinal properties. Objective: The aim of this study was to evaluate the in vitro antibacterial activity of copaiba oil (Copaifera multijuga) gel against strains of Streptococcus sp present in dental biofilm. Materials and Methods: The copaiba oil was obtained and the chemical components were identified. The oil emulsions were formulated and used with the Brain Heart Infusion agar diffusion method with strains of Streptococcus mitis, Streptococcus constellatus and Streptococcus salivarius isolated from patients as well as standard strains of S. mitis (ATCC903), S. mutans (ATCC10449), S. sanguinis (ATCC15300) and S. oralis (ATCC10557). The study groups were as follows: experimental copaiba oil gel, 1% chlorhexidine gel (positive control) and base gel (negative control). The seeded plates were incubated at 37ºC for 12, 24 and 48 hours, respectively. The results obtained were analyzed by Shapiro-Wilk and Friedman Tests (p<0.05) for non parametric data and the Tukey test was used for pH values with 5% level of significance. Results: The experimental copaiba oil gel and 1% chlorhexidine gel showed antibacterial activity against the tested microorganisms. Conclusion: The copaiba oil gel demonstrated antibacterial activity against all the strains of Streptococcus sp tested, suggesting that it can be used for dental biofilm control. PMID:27386004

16. Photoluminescence from terbium doped silica-titania prepared by a sol-gel method

SciTech Connect

Ismail, Adel Ali; Abboudi, Mostafa . E-mail: abboudi14@hotmail.com; Holloway, Paul; El-Shall, Hassan

2007-01-18

Terbium doped (0.5 at.%) TiO{sub 2}-SiO{sub 2} (30%/70%) was prepared by a sol-gel method. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the powder calcined at two different temperatures. At a low temperature of 550 deg. C an amorphous phase was obtained, but at a higher temperature of 1000 deg. C, the anatase TiO{sub 2} phase was crystallized in the amorphous SiO{sub 2} phase. Green photoluminescence from ultraviolet excitation was detected after heating to either temperature, but the amorphous sample heated to 550 deg. C exhibited a higher intensity. X-ray diffraction and photoluminescence excitation data are discussed to explain these observations.

17. Silica-polyethylene glycol hybrids synthesized by sol-gel: Biocompatibility improvement of titanium implants by coating.

PubMed

Catauro, M; Bollino, F; Papale, F; Ferrara, C; Mustarelli, P

2015-10-01

Although metallic implants are the most used in dental and orthopaedic fields, they can early fail due to low tissue tolerance or osseointegration ability. To overcome this drawback, functional coatings can be applied on the metallic surface to provide a firm fixation of the implants. The objective of the present study was twofold: to synthesize and to characterize silica/polyethylene glycol (PEG) hybrid materials using sol-gel technique and to investigate their capability to dip-coat titanium grade 4 (Ti-gr4) substrates to improve their biological properties. Various hybrid systems have been synthesized by changing the ratio between the organic and inorganic phases in order to study the influence of the polymer amount on the structure and, thus, on the properties of the coatings. Fourier transform infrared (FTIR) spectroscopy and solid state Nuclear Magnetic Resonance (NMR) allowed us to detect the formation of hydrogen bonds between the inorganic sol-gel matrix and the organic component. SEM analysis showed that high PEG content enables to obtain crack free-coating. Moreover, the effective improvement in biological properties of Ti-gr4 implants has been evaluated by performing in vitro tests. The bioactivity of the hybrid coatings has been showed by the hydroxyapatite formation on the surface of SiO2/PEG coated Ti-gr4 substrates after soaking in a simulated body fluid and the lack of cytotoxicity by the WST-8 Assay. The results showed that the coated substrates are more bioactive and biocompatible than the uncoated ones and that the bioactivity is not significantly affected by PEG amount whereas its addition makes the films more biocompatible. PMID:26117745

18. Silica-polyethylene glycol hybrids synthesized by sol-gel: Biocompatibility improvement of titanium implants by coating.

PubMed

Catauro, M; Bollino, F; Papale, F; Ferrara, C; Mustarelli, P

2015-10-01

Although metallic implants are the most used in dental and orthopaedic fields, they can early fail due to low tissue tolerance or osseointegration ability. To overcome this drawback, functional coatings can be applied on the metallic surface to provide a firm fixation of the implants. The objective of the present study was twofold: to synthesize and to characterize silica/polyethylene glycol (PEG) hybrid materials using sol-gel technique and to investigate their capability to dip-coat titanium grade 4 (Ti-gr4) substrates to improve their biological properties. Various hybrid systems have been synthesized by changing the ratio between the organic and inorganic phases in order to study the influence of the polymer amount on the structure and, thus, on the properties of the coatings. Fourier transform infrared (FTIR) spectroscopy and solid state Nuclear Magnetic Resonance (NMR) allowed us to detect the formation of hydrogen bonds between the inorganic sol-gel matrix and the organic component. SEM analysis showed that high PEG content enables to obtain crack free-coating. Moreover, the effective improvement in biological properties of Ti-gr4 implants has been evaluated by performing in vitro tests. The bioactivity of the hybrid coatings has been showed by the hydroxyapatite formation on the surface of SiO2/PEG coated Ti-gr4 substrates after soaking in a simulated body fluid and the lack of cytotoxicity by the WST-8 Assay. The results showed that the coated substrates are more bioactive and biocompatible than the uncoated ones and that the bioactivity is not significantly affected by PEG amount whereas its addition makes the films more biocompatible.

19. Aluminosilicates with varying alumina-silica ratios: synthesis via a hybrid sol-gel route and structural characterisation.

PubMed

Nampi, Padmaja Parameswaran; Moothetty, Padmanabhan; Berry, Frank John; Mortimer, Michael; Warrier, Krishna Gopakumar

2010-06-01

Aluminosilicates with varying Al2O3:SiO2 molar ratios (3:1, 3:2, 3:3 and 3:4) have been synthesized using a hybrid sol-gel route using boehmite sol as the precursor for alumina and tetraethyl orthosilicate (TEOS) as the precursor for silica. The synthesis of boehmite sol from aluminium nitrate, and its use as the alumina precursor, is cost effective compared to alkoxide precursors. Structural aspects, including bonding and coordination, are studied in detail for samples calcined in the temperature range 400-1400 °C using both NMR and FTIR spectroscopy: the results are correlated with phase formation data (spinel and high temperature phases) obtained from XRD and thermal analysis. FTIR results show a broadening of peaks at 800 °C indicating a disordered distribution of octahedral sites caused by crosslinking between AlO6 octahedral and SiO4 tetrahedral units prior to the formation of mullite. (27)Al MAS NMR spectra are consistent with a progressive decrease in the number of AlO6 polyhedra with increasing temperature corresponding to Al in these units being forced to adopt a tetrahedral coordination due to the increasing presence of similarly coordinated Si species. XRD results confirm the formation of pure mullite at 1250 °C for a 3Al2O3:2SiO2 system. At 1400 °C, phase pure mullite is observed for all compositions except 3Al2O3:SiO2 where α-Al2O3 is the major phase with traces of mullite. The synthesis of aluminosilicates through a hybrid sol-gel route and the detailed insight into structural features gained from spectroscopic and diffraction techniques contributes further to the development of these materials in applications ranging from nanocatalysts to high-temperature ceramics.

20. Impact of carbon on the surface and activity of silica-carbon supported copper catalysts for reduction of nitrogen oxides

Spassova, I.; Stoeva, N.; Nickolov, R.; Atanasova, G.; Khristova, M.

2016-04-01

Composite catalysts, prepared by one or more active components supported on a support are of interest because of the possible interaction between the catalytic components and the support materials. The supports of combined hydrophilic-hydrophobic type may influence how these materials maintain an active phase and as a result a possible cooperation between active components and the support material could occur and affects the catalytic behavior. Silica-carbon nanocomposites were prepared by sol-gel, using different in specific surface areas and porous texture carbon materials. Catalysts were obtained after copper deposition on these composites. The nanocomposites and the catalysts were characterized by nitrogen adsorption, TG, XRD, TEM- HRTEM, H2-TPR, and XPS. The nature of the carbon predetermines the composite's texture. The IEPs of carbon materials and silica is a force of composites formation and determines the respective distribution of the silica and carbon components on the surface of the composites. Copper deposition over the investigated silica-carbon composites leads to formation of active phases in which copper is in different oxidation states. The reduction of NO with CO proceeds by different paths on different catalysts due to the textural differences of the composites, maintaining different surface composition and oxidation states of copper.

1. Heterogeneous copper-silica catalyst from agricultural biomass and its catalytic activity

Andas, Jeyashelly; Adam, Farook; Rahman, Ismail Ab.

2013-11-01

A series of highly mesoporous copper catalysts (5-20 wt.%) supported on silica rice husk were synthesized via sol-gel route at room temperature. The FT-IR and 29Si MAS NMR spectroscopic studies revealed the successful substitution of copper into the silica matrix. Copper in the +2 oxidation state was evidenced from the DR/UV-vis and XPS analyses. Introduction of copper up to 10 wt.% (RH-10Cu) results in a progressive enhancement in the BET surface area. The activity of the copper catalysts was studied in the liquid-phase oxidation of phenol with H2O2 yielding catechol (CAT) and hydroquinone (HQ). Phenol conversion was influenced by various experimental conditions such as temperature, catalyst dosage, molar ratio of reactants, nature of solvent and percentage metal loading. Excellent activity was achieved when 10 wt.% copper was used and decreased with further increase in the copper loading. RH-10Cu could be regenerated several times without significant loss in the catalytic activity.

2. Development of a bi-functional silica monolith for electro-osmotic pumping and DNA clean-up/extraction using gel-supported reagents in a microfluidic device.

PubMed

Oakley, Jennifer A; Shaw, Kirsty J; Docker, Peter T; Dyer, Charlotte E; Greenman, John; Greenway, Gillian M; Haswell, Stephen J

2009-06-01

A silica monolith used to support both electro-osmotic pumping (EOP) and the extraction/elution of DNA coupled with gel-supported reagents is described. The benefits of the combined EOP extraction/elution system were illustrated by combining DNA extraction and gene amplification using the polymerase chain reaction (PCR) process. All the reagents necessary for both processes were supported within pre-loaded gels that allow the reagents to be stored at 4 degrees C for up to four weeks in the microfluidic device. When carrying out an analysis the crude sample only needed to be hydrodynamically introduced into the device which was connected to an external computer controlled power supply via platinum wire electrodes. DNA was extracted with 65% efficiency after loading lysed cells onto a silica monolith. Ethanol contained within an agarose gel matrix was then used to wash unwanted debris away from the sample by EOP (100 V cm(-1) for 5 min). The retained DNA was subsequently eluted from the monolith by water contained in a second agarose gel, again by EOP using an electric field of 100 V cm(-1) for 5 min, and transferred into the PCR reagent containing gel. The eluted DNA in solution was successfully amplified by PCR, confirming that the concept of a complete self-contained microfluidic device could be realised for DNA sample clean up and amplification, using a simple pumping and on-chip reagent storage methodology.

3. Activation volumes of enzymes adsorbed on silica particles.

PubMed

Schuabb, Vitor; Czeslik, Claus

2014-12-30

The immobilization of enzymes on carrier particles is useful in many biotechnological processes. In this way, enzymes can be separated from the reaction solution by filtering and can be reused in several cycles. On the other hand, there is a series of examples of free enzymes in solution that can be activated by the application of pressure. Thus, a potential loss of enzymatic activity upon immobilization on carrier particles might be compensated by pressure. In this study, we have determined the activation volumes of two enzymes, α-chymotrypsin (α-CT) and horseradish peroxidase (HRP), when they are adsorbed on silica particles and free in solution. The experiments have been carried out using fluorescence assays under pressures up to 2000 bar. In all cases, activation volumes were found to depend on the applied pressure, suggesting different compressions of the enzyme-substrate complex and the transition state. The volume profiles of free and adsorbed HRP are similar. For α-CT, larger activation volumes are found in the adsorbed state. However, up to about 500 bar, the enzymatic reaction of α-CT, which is adsorbed on silica particles, is characterized by a negative activation volume. This observation suggests that application of pressure might indeed be useful to enhance the activity of enzymes on carrier particles.

4. Remaining Sites Verification Package for the 100-F-44:4, Discovery Pipeline in Silica Gel Pit, Waste Site Reclassification Form 2008-030

SciTech Connect

J. M. Capron

2008-09-23

The 100-F-44:4, Discovery Pipeline in Silica Gel Pit subsite is located in the 100-FR-1 Operable Unit of the Hanford Site, near the location of the former 110-F Gas Storage Tanks structure. The 100-F-44:4 subsite is a steel pipe discovered October 17, 2004, during trenching to locate the 118-F-4 Silica Gel Pit. Based on visual inspection and confirmatory investigation sampling data, the 100-F-44:4 subsite is a piece of non-hazardous electrical conduit debris. The 100-F-44:4 subsite supports unrestricted future use of shallow zone soil and is protective of groundwater and the Columbia River. No residual contamination exists within the deep zone. Therefore, no deep zone institutional controls are required.

5. Silver nanoparticles attached to silica gel as a new solid phase adsorbent for preconcentration and determination of iron from biological samples

Khajeh, Mostafa; Dastafkan, Kamran

2012-11-01

In this study, an easy and fast procedure based on solid phase extraction was developed that is intended to pre-concentrate, separate, and determine trace amounts of Fe(III) ions in biological samples using flame atomic absorption spectrometry (FAAS). Silver nanoparticles coated with silica gel were modified by morin and then used as a sorbent. It was synthesized by mixing slurried silica gel with silver nitrate and sodium citrate. The effects of experimental conditions, including pH, sample and eluent flow rates, and the type and least amount of an eluent to the elute iron from the sorbent were studied, and optimum values of these parameters have been found. Under the optimum conditions, the limit of detection of this procedure for Fe(III) was 67 ng/l. The relative standard deviation (RSD%) was 2.5 % (n = 10, C = 0.5 mg/l). The developed procedure was used to determine iron in biological samples.

6. Dithizone immobilized silica gel on-line preconcentration of trace copper with detection by flame atomic absorption spectrometry.

PubMed

Yu, Hong-Mei; Song, Hua; Chen, Ming-Li

2011-07-15

A novel adsorbent-silica gel bound dithizone (H(2)Dz-SG) was prepared and used as solid-phase extraction of copper from complex matrix. The H(2)Dz-SG is investigated by means of FT-IR spectra and the SEM images, demonstrating the bonding of dithizone. The H(2)Dz-SG quantitatively adsorb copper ions, and the retained copper is afterwards collected by elution of 10% (v/v) nitric acid. An on-line flow injection solid-phase extraction procedure was developed for trace copper separation and preconcentration with detection by flame atomic spectrometry. By loading 5.4 mL of sample solution, a liner range of 0.5-120 μg L(-1), an enrichment factor of 42.6, a detection limit of 0.2 μg L(-1) and a precision of 1.7% RSD at the 40 μg L(-1) level (n=11) were obtained, along with a sampling frequency of 47 h(-1). The dynamic sorption capacity of H(2)Dz-SG to Cu(2+) was 0.76 mg g(-1). The accuracy of the proposed procedure was evaluated by determination of copper in reference water sample. The potential applications of the procedure for extraction of trace copper were successfully accomplished in water samples (tap, rain, snow, sea and river). The spiking recoveries within 91-107% are achieved. PMID:21645750

7. Adsorption of pesticidal compounds bearing a single carboxyl functional group and biogenic amines by humic fraction-immobilized silica gel.

PubMed

Chen, Cheng-Sheng; Chen, Shushi

2013-04-17

8. Separation of human thymocytes at different stages of maturation by centrifugation on a discontinuous gradient of colloidal silica gel.

PubMed

Goust, J M; Perry, L R

1981-06-01

Separation of human intrathymic cells on a discontinuous gradient of colloidal silica gel (Percoll) yielded four layers. The first (density 1.054 +/- 0.002 g/ml) contained stromal cells and a few thymocytes positive for terminal deoxynucleotidyl transferase (Tdt), most of which were bound to large Tdt-negative non-T cells. The second layer (1.069+/- 0.003 g/ml) contained large Tdt-negative thymocytes. The third and forth layers (1.075 +/-0.004 and 1.085 +/- 0.003 g/ml, respectively) contained smaller T cells, more than 95% of which were Tdt-positive. Functional studies revealed that cells from the first layer had a high level of spontaneous [3H]thymidine uptake but did not respond to lectins; the second layer responded to PHA, ConA, and allogeneic stimuli; and the third and fourth layers did not respond to lectin stimulation. Addition of cells from the first layer to the other layers at a 1 : 10 ratio significantly increased the mitogenic responses of the cells from the second layer, but not of those from the third or fourth layer. These results suggest that, as in mice and rats, low-density intrathymic thymocytes in humans represent more mature T cells, the percentage of which increases with age. PMID:6973841

9. Organically nanoporous silica gel based on carbon paste electrode for potentiometric detection of trace Cr(III).

PubMed

Zhou, Wei; Chai, Yaqin; Yuan, Ruo; Guo, Junxiang; Wu, Xia

2009-08-11

A new ion-selective electrode (ISE) for the detection of trace chromium(III) was designed by using 2-acetylpyridine and nanoporous silica gel (APNSG)-functionalized carbon paste electrode (CPE). The presence of APNSG acted as not only a paste binder, but also a reactive material. With 7.5 wt% APNSG proportions, the developed electrode exhibited wide dynamic range of 1.0 x 10(-8) to 1.0 x 10(-3) M toward Cr(III) with a detection limit of 8.0 x 10(-9) M and a Nernstian slope of 19.8 +/- 0.2 mV decade(-1). The as-prepared electrode displayed rapid response (approximately 55 s), long-time stability, and high sensitivity. Moreover, the potentiometric responses could be carried out with wide pH range of 1.5-5.0. In addition, the content of Cr(III) in food samples, e.g. coffee and tea leaves, has been assayed by the developed electrode, atomic absorption spectrophotometer (AAS) and atomic emission spectrometer (ICP-AES), respectively, and consistent results were obtained. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance and UV-vis spectroscopy.

10. The effect of adding PDMS-OH and silica nanoparticles on sol-gel properties and effectiveness in stone protection

Li, Dan; Xu, Feigao; Liu, Zhenghua; Zhu, Jiaqi; Zhang, Qingjian; Shao, Li

2013-02-01

Inorganic-organic hybrid crack-free xerogels were obtained using di-n-butyltin dilaurate (DBTL) as a catalyst containing tetraethoxyorthosilicate (TEOS) and hydroxyl-terminated polydimethylsiloxane (PDMS-OH) as an additive. We studied the effect of gelling time and sol pH on DBTL concentration. The xerogels' structure was studied by FTIR, TGA-DTA and SEM techniques. The results showed that the catalyst (DBTL) would substantially shorten the gelling time of the sol. With the addition of PDMS-OH, the viscosity of the sol increased while the gel time decreased. In addition, we noticed an improvement in the cracking of the xerogel with the addition of PDMS-OH. However, the xerogels were opaque when mole ratio of PDMS/TEOS is higher than 0.153. Addition of silica nanoparticles at 0.1% (w/v) in sol could increase xerogels' surface roughness and hydrophobicity and did not change color of the xerogels. The protective performance evaluated by its ability to resist acid rain revealed that the protective effects were satisfying.

11. Dithizone immobilized silica gel on-line preconcentration of trace copper with detection by flame atomic absorption spectrometry.

PubMed

Yu, Hong-Mei; Song, Hua; Chen, Ming-Li

2011-07-15

A novel adsorbent-silica gel bound dithizone (H(2)Dz-SG) was prepared and used as solid-phase extraction of copper from complex matrix. The H(2)Dz-SG is investigated by means of FT-IR spectra and the SEM images, demonstrating the bonding of dithizone. The H(2)Dz-SG quantitatively adsorb copper ions, and the retained copper is afterwards collected by elution of 10% (v/v) nitric acid. An on-line flow injection solid-phase extraction procedure was developed for trace copper separation and preconcentration with detection by flame atomic spectrometry. By loading 5.4 mL of sample solution, a liner range of 0.5-120 μg L(-1), an enrichment factor of 42.6, a detection limit of 0.2 μg L(-1) and a precision of 1.7% RSD at the 40 μg L(-1) level (n=11) were obtained, along with a sampling frequency of 47 h(-1). The dynamic sorption capacity of H(2)Dz-SG to Cu(2+) was 0.76 mg g(-1). The accuracy of the proposed procedure was evaluated by determination of copper in reference water sample. The potential applications of the procedure for extraction of trace copper were successfully accomplished in water samples (tap, rain, snow, sea and river). The spiking recoveries within 91-107% are achieved.

12. Preparation and adsorption behavior of berberine hydrochloride imprinted polymers by using silica gel as sacrificed support material

Li, Hui; Li, Yuzhuo; Li, Zhiping; Peng, Xiyang; Li, Yanan; Li, Gui; Tan, Xianzhou; Chen, Gongxi

2012-03-01

Preparation of berberine hydrochloride (B-Cl) imprinted polymers (MIPs) based on surface imprinting technique with silica gel as sacrificial support material was performed successfully by using B-Cl as template, methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as functional monomer and cross-linker, respectively. The prepared polymers were characterized by Fourier transmission infrared spectrometry (FTIR) and scanning electron microscopy (SEM). Adsorption behavior of the MIPs for the template and its structural analogues was investigated. Sites distribution on the surface of MIPs was explored by using different isotherm adsorption models and thermodynamic parameters for the adsorption of B-Cl on the MIPs determined. Sample application and reusability for the MIPs was also evaluated. Results indicated the strong adsorption and high selectivity of the MIPs for B-Cl. Saturated adsorption capacity reached 27.2 μmol g-1 and the selectivity coefficient of the MIPs for B-Cl relative to jatrorrhizine hydrochloride (J-Cl) and palmatine palmatus hydrochloride (P-Cl) are 3.70 and 6.03, respectively. In addition, the MIPs were shown with good reusability and selectively retention ability in sample application.

13. Determination of fluoride and oxalate using the indicator reaction of Zr(IV) with methylthymol blue adsorbed on silica gel.

PubMed

Zaporozhets, Olga A; Tsyukalo, Lyudmila Ye

2007-07-30

Solid-phase spectrophotometric and visual test-methods of fluoride and oxalate determination are proposed. The methods are based on the competitive reactions of ZrOCl2 with methylthymol blue immobilized on silica gel and fluoride or oxalate in solution. Absorbance of the solid-phase reagent at 590 nm decreases with the growth of fluoride and oxalate contents in solution. The developed methods demonstrate high selectivity. The interference of Bi(III) and SO4(2-), PO4(3-) is eliminated by the addition of 0.01 mol L(-1) solution of ascorbic acid and 0.01 mol L(-1) of BaCl2, respectively. To eliminate the fluoride interference with oxalate determination 1x10(-3) mol L(-1) solution of Ca(NO3)2 at pH 1.5 was added. The anions of the organic acids were destructed prior to F- determination by ultrasonic exposition (44 kHz, intensity of < or = 10 W cm(-2) for 3 min). The proposed methods were applied to the analysis of mineral water, toothpaste and biological fluids.

14. Optical Degradation of Colloidal Eu-Complex Embedded in Silica Glass Film Using Reprecipitation and Sol-Gel Methods.

PubMed

Fukuda, Takeshi; Kurabayashi, Tomokazu; Yamaki, Tatsuki

2016-04-01

A reprecipitation method has been investigated for fabricating colloidal nanoparticles using Eu-complex. Herein, we investigated optical degradation characteristics of (1,10-phenanthroline)tris [4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) colloidal nanoparticles, which were embedded into a silica glass film fabricated by a conventional sol-gel process. At first, we tried several types of good solvents for the reprecipitation method, and dimethyl sulfoxide (DMSO) is found to be a suitable solvent for realizing the small diameter and the high long-term stability against the ultraviolet irradiation even though the boing point of DMSO is higher than that of water used as a poor solvent. By optimizing the good solvent and the concentration of Eu-complex, the relative photoluminescence intensity of 0.96 was achieved even though the ultraviolet light was continuously irradiated for 90 min. In addition, the average diameter of 106 nm was achieved when DMSO was used as a good solvent, resulting in the high transmittance at a visible wavelength region. Therefore, we can achieve the transparent emissive thin film with a center wavelength of 612 nm, and the optical degradation was drastically reduced by forming nanoparticles. PMID:27451610

15. Ion chromatographic determination of hydroxide ion on monolithic reversed-phase silica gel columns coated with nonionic and cationic surfactants.

PubMed

Xu, Qun; Mori, Masanobu; Tanaka, Kazuhiko; Ikedo, Mikaru; Hu, Wenzhi; Haddad, Paul R

2004-07-01

The determination of hydroxide by ion chromatography (IC) is demonstrated using a monolithic octadecylsilyl (ODS)-silica gel column coated first with a nonionic surfactant (polyoxyethylene (POE)) and then with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)). This stationary phase, when used in conjunction with a 10 mmol/l sodium sulfate eluent at pH 8.2, was found to be suitable for the rapid and efficient separation of hydroxide from some other anions, based on a conventional ion-exchange mechanism. The peak directions and detection responses for these ions were in agreement with their known limiting equivalent ionic conductance values. Under these conditions, a linear calibration plot was obtained for hydroxide ion over the range 16 micromol/l to 15 mmol/l, and the detection limit determined at a signal-to-noise ratio of 3 was 6.4 micromol/l. The double-coated stationary phase described above was shown to be superior to a single coating of cetyltrimethylammonium bromide alone, in terms of separation efficiency and stability of the stationary phase. A range of samples comprising solutions of some strong and weak bases was analyzed by the proposed method and the results obtained were in good agreement with those obtained by conventional potentiometric pH measurement.

16. Effect of complexing ligands on the adsorption of Cu(II) onto the silica gel surface. 1: Adsorption of ligands

SciTech Connect

Park, Y.J.; Jung, K.H.; Park, K.K.; Park, K.K.

1995-04-01

17. Sol-gel-derived silica films with tailored microstructures for applications requiring organic dyes

SciTech Connect

Logan, M.N.; Prabakar, S.; Brinker, C.J. |

1994-09-01

A three-step sol-gel process was developed to prepare organic dye-doped thin films with tailored porosity for applications in chemical sensing and optoelectronics. Varying the acid- and base-catalyzed hydrolysis steps of sols prepared from tetraethoxysilane with identical final H{sub 2}O/Si ratios, dilution factors and pH resulted in considerably different distributions of the silicate polymers in the sol (determined by {sup 29}Si NMR) and considerably different structures for the polymer clusters (determined by SAXS). During film formation these kinetic effects cause differences in the packing and collapse of the silicate network, leading to thin films with different refractive indices and volume fraction porosities. Under conditions where small pore-plugging species were avoided, the porosities of as-deposited films could be varied by aging the sol prior to film deposition. This strategy, which relies on the growth and aggregation of fractal polymeric clusters, is compatible with the low temperature and near neutral pH requirements of organic dyes.

18. Effect of ZrN coating by magnetron sputtering and sol-gel processed silica coating on titanium/porcelain interface bond strength.

PubMed

Xia, Yang; Zhou, Shu; Zhang, Feimin; Gu, Ning

2011-02-01

In this study, a coating technique was applied to improve the bond strength of titanium (Ti) porcelain. ZrN coating was prepared by magnetron sputtering, and silica coating was processed by a sol-gel method. The treated surfaces of the specimens were analyzed by X-ray diffraction, and the Ti/porcelain interface was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy. The coated specimens appeared fully coherent to the Ti substrate. The fractured bonding surface was also investigated by SEM. The residual porcelain on the metal surface could be observed in the ZrN group and silica group, but there was no obvious porcelain remaining in the control group. A three-point-bending test showed that the bonding strength of the ZrN group (45.99 ± 0.65 MPa) was higher than the silica group (37.77 ± 0.78 MPa) (P < 0.001) and control group (29.48 ± 1.01 MPa) (P < 0.001), while that of the silica group was significantly higher than the control group (P < 0.001). In conclusion, conditioning the ceramic surface with ZrN and silica coatings resulted in a stronger Ti/porcelain bond. ZrN coating by magnetron sputtering was a more effective way to improve the bond strength between Ti and porcelain compared with sol-gel processed silica coating in this study. PMID:21181240

19. Comparison of sulfuric acid treatment and multi-layer silica gel column chromatography in cleanup methods for determination of PCDDs, PCDFs and dioxin-like PCBs in foods.

PubMed

Amakura, Yoshiaki; Tsutsumi, Tomoaki; Sasaki, Kumiko; Toyoda, Masatake; Maitani, Tamio

2002-10-01

Two typical cleanup methods, sulfuric acid treatment and multi-layer silica gel column chromatography, for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in seventeen food samples were examined and compared. Vegetables, fruits, cereals, fish, meat and dairy foods were extracted by conventional methods (shaking with acetone/n-hexane or with n-hexane after alkaline treatment). The extracts were cleaned up by sulfuric acid treatment or multi-layer silica gel column chromatography, followed by several column chromatographic steps. Of the samples treated, the vegetable, fruit and cereal samples could be directly applied to the multi-layer silica gel column after extraction. However, the samples containing fats and oils such as fish, meat and dairy foods needed to be treated several times with concentrated sulfuric acid before multi-layer column chromatography, because these samples plugged the column with oily residues. Both cleanup methods gave similar values of isomeric concentrations and showed similar efficiency of purification, and the recoveries ranged from 40 to 120%. These results are considered to provide useful data for the efficient analysis of dioxins in foods which have wide-ranging compositions.

20. Densitometric HPTLC method for qualitative, quantitative analysis and stability study of Coenzyme Q10 in pharmaceutical formulations utilizing normal and reversed-phase silica gel plates.

PubMed

2016-03-01

Two simple, precise and stability-indicating densitometric HPTLC method were developed and validated for qualitative and quantitative analysis of Coenzyme Q10 in pharmaceutical formulations using normal-phase (Method I) and reversed phase (Method II) silica gel TLC plates. Both methods were developed and validated with 10×20 cm glass-backed plates coated with 0.2 mm layers of either silica gel 60 F254 (E-Merck, Germany) using hexane-ethyl acetate (8.5:1.5 v/v) as developing system (Method I) or RP-18 silica gel 60 F254 (E-Merck, Germany) using methanol-acetone (4:6 v/v) as mobile phase (Method II). Both analyses were scanned with a densitometer at 282 nm. Linearity was found in the ranges 50-800 ng/spot (r(2)=0.9989) and 50-800 ng/spot (r(2)=0.9987) for Method I and Method II respectively. Stability of Coenzyme Q10 was explored by the two methods using acid, base, hydrogen peroxide, temperature and different solvents. Due to the efficiency of the method in separating Coenzyme Q10 from other ingredients including its degradation products, it can be applied for quality control, standardization of different pharmaceutical formulations and stability study.

1. Nanosilver on nanostructured silica: Antibacterial activity and Ag surface area.

PubMed

Sotiriou, Georgios A; Teleki, Alexandra; Camenzind, Adrian; Krumeich, Frank; Meyer, Andreas; Panke, Sven; Pratsinis, Sotiris E

2011-06-01

Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide motivating research to better understand the relationship between Ag characteristics and antibacterial activity. Nanosilver immobilized on nanostructured silica facilitates such investigations as the SiO2 support hinders the growth of nanosilver during its synthesis and, most importantly, its flocculation in bacterial suspensions. Here, such composite Ag/silica nanoparticles were made by flame spray pyrolysis of appropriate solutions of Ag-acetate or Ag-nitrate and hexamethyldisiloxane or tetraethylorthosilicate in ethanol, propanol, diethylene glucolmonobutyl ether, acetonitrile or ethylhexanoic acid. The effect of solution composition on nanosilver characteristics and antibacterial activity against the Gram negative Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity pointing out that the nanosilver surface area concentration rather than its mass or molar or number concentration determine best its antibacterial activity. Nanosilver made from Ag-acetate showed a unimodal size distribution, while that made from inexpensive Ag-nitrate exhibited a bimodal one. Regardless of precursor composition or nanosilver size distribution, the antibacterial activity of nanosilver was correlated best with its surface area concentration in solution. PMID:23730198

2. Nanosilver on nanostructured silica: Antibacterial activity and Ag surface area.

PubMed

Sotiriou, Georgios A; Teleki, Alexandra; Camenzind, Adrian; Krumeich, Frank; Meyer, Andreas; Panke, Sven; Pratsinis, Sotiris E

2011-06-01

Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide motivating research to better understand the relationship between Ag characteristics and antibacterial activity. Nanosilver immobilized on nanostructured silica facilitates such investigations as the SiO2 support hinders the growth of nanosilver during its synthesis and, most importantly, its flocculation in bacterial suspensions. Here, such composite Ag/silica nanoparticles were made by flame spray pyrolysis of appropriate solutions of Ag-acetate or Ag-nitrate and hexamethyldisiloxane or tetraethylorthosilicate in ethanol, propanol, diethylene glucolmonobutyl ether, acetonitrile or ethylhexanoic acid. The effect of solution composition on nanosilver characteristics and antibacterial activity against the Gram negative Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity pointing out that the nanosilver surface area concentration rather than its mass or molar or number concentration determine best its antibacterial activity. Nanosilver made from Ag-acetate showed a unimodal size distribution, while that made from inexpensive Ag-nitrate exhibited a bimodal one. Regardless of precursor composition or nanosilver size distribution, the antibacterial activity of nanosilver was correlated best with its surface area concentration in solution.

3. Enzymatically active biomimetic micropropellers for the penetration of mucin gels

PubMed Central

Walker, Debora; Käsdorf, Benjamin T.; Jeong, Hyeon-Ho; Lieleg, Oliver; Fischer, Peer

2015-01-01

In the body, mucus provides an important defense mechanism by limiting the penetration of pathogens. It is therefore also a major obstacle for the efficient delivery of particle-based drug carriers. The acidic stomach lining in particular is difficult to overcome because mucin glycoproteins form viscoelastic gels under acidic conditions. The bacterium Helicobacter pylori has developed a strategy to overcome the mucus barrier by producing the enzyme urease, which locally raises the pH and consequently liquefies the mucus. This allows the bacteria to swim through mucus and to reach the epithelial surface. We present an artificial system of reactive magnetic micropropellers that mimic this strategy to move through gastric mucin gels by making use of surface-immobilized urease. The results demonstrate the validity of this biomimetic approach to penetrate biological gels, and show that externally propelled microstructures can actively and reversibly manipulate the physical state of their surroundings, suggesting that such particles could potentially penetrate native mucus. PMID:26824056

4. Boundaries steer the contraction of active gels

Schuppler, Matthias; Keber, Felix C.; Kröger, Martin; Bausch, Andreas R.

2016-10-01

Cells set up contractile actin arrays to drive various shape changes and to exert forces to their environment. To understand their assembly process, we present here a reconstituted contractile system, comprising F-actin and myosin II filaments, where we can control the local activation of myosin by light. By stimulating different symmetries, we show that the force balancing at the boundaries determine the shape changes as well as the dynamics of the global contraction. Spatially anisotropic attachment of initially isotropic networks leads to a self-organization of highly aligned contractile fibres, being reminiscent of the order formation in muscles or stress fibres. The observed shape changes and dynamics are fully recovered by a minimal physical model.

5. Boundaries steer the contraction of active gels

PubMed Central

Schuppler, Matthias; Keber, Felix C.; Kröger, Martin; Bausch, Andreas R.

2016-01-01

Cells set up contractile actin arrays to drive various shape changes and to exert forces to their environment. To understand their assembly process, we present here a reconstituted contractile system, comprising F-actin and myosin II filaments, where we can control the local activation of myosin by light. By stimulating different symmetries, we show that the force balancing at the boundaries determine the shape changes as well as the dynamics of the global contraction. Spatially anisotropic attachment of initially isotropic networks leads to a self-organization of highly aligned contractile fibres, being reminiscent of the order formation in muscles or stress fibres. The observed shape changes and dynamics are fully recovered by a minimal physical model. PMID:27739426

6. Formation of a supramolecular gel between alpha-cyclodextrin and free and adsorbed PEO on the surface of colloidal silica: effect of temperature, solvent, and particle size.

PubMed

Dreiss, Cécile A; Cosgrove, Terence; Newby, Francisco N; Sabadini, Edvaldo

2004-10-12

Aqueous solutions of alpha-cyclodextrin (alpha-CD) complex spontaneously with poly(ethylene oxide) (PEO), forming a supramolecular structure known as pseudopolyrotaxane. We have studied the formation of the complex obtained from the threading of alpha-CD onto PEO, both free in solution and adsorbed on colloidal silica. The kinetics of the reaction were studied by gravimetric methods and determined as a function of temperature and solvent composition for the PEO free in solution. PEO was then adsorbed on the surface of colloidal silica particles, and the monomers were displaced by systematically varying the degree of complexation, the concentration of particles, and the molecular weight of the polymer. The effect of the size of the silica particles on the yield of the reaction was also studied. With the adsorbed PEO, the complexation was found to be partial and to take place from the tails of the polymer. The formation of a gel network containing silica at high degrees of complexation was observed. Small-angle X-ray and neutron scattering experiments were performed to study the configuration of the polymeric chains and confirmed the partial desorption of the polymer from the surface of the silica upon complexation.

7. Effect of the size of silica nanoparticles on wettability and surface chemistry of sol-gel superhydrophobic and oleophobic nanocomposite coatings

Lakshmi, R. V.; Bera, Parthasarathi; Anandan, C.; Basu, Bharathibai J.

2014-11-01

Superhydrophobic sol-gel nanocomposite coatings have been fabricated by incorporating silica nanoparticles with different particle sizes separately in an acid-catalyzed sol of methyltriethoxysilane (MTEOS). Water contact angle (WCA) of the coatings increased with increase in the concentration of silica nanoparticles in both the cases. The coatings became superhydrophobic at an optimum silica concentration. The water repellency was further improved by the addition of fluoroalkylsilane (FAS). The optimum silica concentration was found to depend on the size of silica nanoparticles and FAS content and the coatings exhibited WCA of about 160° and water sliding angle (WSA) of <2°. FAS addition also improved the oleophobicity of the coatings. The coatings exhibited oil-repellency with a lubricant oil contact angle of 126° and ethylene glycol contact angle of 153.3°. Surface morphology of the coatings analyzed using field emission scanning electron microscopy (FESEM) showed a rough surface with microscale bumps and nanoscale pores. XPS was used to study the surface composition of the coatings. The superhydrophobic property of the coatings was due to the synergistic effect of surface chemistry and surface microstructure and can be explained using Cassie-Baxter model.

8. Organic-inorganic crosslinked and hybrid membranes derived from sulfonated poly(arylene ether sulfone)/silica via sol-gel process

Feng, Shaoguang; Shang, Yuming; Wang, Yingzi; Xie, Xiaofeng; Mathur, V. K.; Xu, Jingming

A series of covalently crosslinkable organic-inorganic hybrid membranes have been prepared from sulfonated poly(arylene ether sulfone) (SPAES) with pendant propenyl moiety and various amounts of vinyl substituted silica via sol-gel process which are then thermally crosslinked in the presence of benzoyl peroxide (BPO) initiator. The obtained membranes are characterized in terms of oxidative stability, thermal property, ion exchange capacity (IEC), water uptake, swelling ratio in methanol aqueous solution, proton conductivity, and methanol permeability coefficient. The results indicate that the oxidative stability and thermal stability of the hybrid membranes are improved. Moreover, introduction of silica reduces the water uptake and methanol swelling of membranes. The swelling ratio of membranes in 2 mol L -1 methanol aqueous solution at 80 °C slowly decreases from 26 to 19% with the increase of SiO 2 content from 0 to 12 wt.%. Furthermore, with the increase in silica content, the methanol permeability coefficient of the hybrid membranes decreases at first and then increases. When the silica content reaches 8 wt.%, the methanol permeability coefficient is at the minimum of 6.02 × 10 -7 cm 2 s -1, a 2.64-fold decrease compared with that of the pristine SPAES membrane. Moreover, the proton conductivity is found to be at about 95% of that of pristine polymer at that silica content.

9. Novel sol-gel synthesis of cerium-doped ZnO thin films for photocatalytic activity

SciTech Connect

Senthilvelan, S.; Chandraboss, V. L.; Karthikeyan, B.; Murugavelu, M.; Loganathan, B.; Natanapatham, L.

2012-07-23

The Ce-doped ZnO films on silica glass plates were prepared by sol-gel dip coating technique. The surface morphology of thin films was characterized by means of scanning electron microscopy (SEM). Optical properties of films have been investigated using UV-visible spectroscopy. The photocatalytic activity was established by testing the degradation of Alizarin Red (AR) from aqueous solution. The test of photocatalytic activity of the heat-treated Ce-doped ZnO films were also carried out under visible light irradiation.

10. Sol-gel derived silica/chitosan/Fe3O4 nanocomposite for direct electrochemistry and hydrogen peroxide biosensing

Satvekar, R. K.; Rohiwal, S. S.; Tiwari, A. P.; Raut, A. V.; Tiwale, B. M.; Pawar, S. H.

2015-01-01

A novel strategy to fabricate hydrogen peroxide third generation biosensor has been developed from sol-gel of silica/chitosan (SC) organic-inorganic hybrid material assimilated with iron oxide magnetic nanoparticles (Fe3O4). The large surface area of Fe3O4 and porous morphology of the SC composite facilitates a high loading of horseradish peroxidase (HRP). Moreover, the entrapped enzyme preserves its conformation and biofunctionality. The fabrication of hydrogen peroxide biosensor has been carried out by drop casting of the SC/F/HRP nanocomposite on glassy carbon electrode (GCE) for study of direct electrochemistry. The x-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) confirms the phase purity and particle size of as-synthesized Fe3O4 nanoparticles, respectively. The nanocomposite was characterized by UV-vis spectroscopy, fluorescence spectroscopy and Fourier transform infrared (FTIR) for the characteristic structure and conformation of enzyme. The surface topographies of the nanocomposite thin films were investigated by scanning electron microscopy (SEM). Dynamic light scattering (DLS) was used to determine the particle size distribution. The electrostatic interactions of the SC composite with Fe3O4 nanoparticles were studied by the zeta potential measurement. Electrochemical impedance spectroscopy (EIS) of the SC/F/HRP/GCE electrode displays Fe3O4 nanoparticles as an excellent candidate for electron transfer. The SC/F/HRP/GCE exhibited a pair of well-defined quasi reversible cyclic voltammetry peaks due to the redox couple of HRP-heme Fe (III)/Fe (II) in pH 7.0 potassium phosphate buffer. The biosensor was employed to detect H2O2 with linear range of 5 μM to 40 μM and detection limit of 5 μM. The sensor displays excellent selectivity, sensitivity, good reproducibility and long term stability.

11. Studies on chelating adsorption properties of novel composite material polyethyleneimine/silica gel for heavy-metal ions

Gao, Baojiao; An, Fuqiang; Liu, Kangkai

2006-12-01

12. Microstructure investigation on micropore formation in microporous silica materials prepared via a catalytic sol-gel process by small angle X-ray scattering.

PubMed

Shimizu, Wataru; Hokka, Junsuke; Sato, Takaaki; Usami, Hisanao; Murakami, Yasushi

2011-08-01

The so-called sol-gel technique has been shown to be a template-free, efficient way to create functional porous silica materials having uniform micropores. This appears to be closely linked with a postulation that the formation of weakly branched polymer-like aggregates in a precursor solution is a key to the uniform micropore generation. However, how such a polymer-like structure can precisely be controlled, and further, how the generated low-fractal dimension solution structure is imprinted on the solid silica materials still remain elusive. Here we present fabrication of microporous silica from tetramethyl orthosilicate (TMOS) using a recently developed catalytic sol-gel process based on a nonionic hydroxyacetone (HA) catalyst. Small angle X-ray scattering (SAXS), nitrogen adsorption porosimetry, and transmission electron microscope (TEM) allowed us to observe the whole structural evolution, ranging from polymer-like aggregates in the precursor solution to agglomeration with heat treatment and microporous morphology of silica powders after drying and hydrolysis. Using the HA catalyst with short chain monohydric alcohols (methanol or ethanol) in the precursor solution, polymer-like aggregates having microscopic correlation length (or mesh-size) < 2 nm and low fractal dimensions ∼2, which is identical to that of an ideal coil polymer, can selectively be synthesized, yielding the uniform micropores with diameters <2 nm in the solid materials. In contrast, the absence of HA or substitution of 1-propanol led to considerably different scattering behavior reflecting the particle-like aggregate formation in the precursor solution, which resulted in the formation of mesopores (diameter >2 nm) in the solid product due to apertures between the particle-like aggregates. The data demonstrate that the extremely fine porous silica architecture comes essentially from a gaussian polymer-like nature of the silica aggregates in the precursor having the microscopic mesh-size and

13. Fabrication of Hollow Porous Silica Using a Combined Emulsion Sol-Gel Process and Amphiphilic Triblock Copolymer for Loading of Quercetin.

PubMed

Lee, Sang Gil; Kim, Young Ho; Bae, Jun Tae; Lee, Chung Hee; Pyo, Hyeong Bae; Kang, Kuk Hyoun; Lee, Dong Kyu

2015-10-01

Flavonoids have recently attracted significant interest as potential reducing agents, hydrogen-donating antioxidants, and singlet oxygen-quenchers. Quercetin, in particular, induces the expression of a gene, known to be associated with cell protection, in dose- and time-dependent manners. Therefore, quercetin may be used as an effective cosmeceutical material useful in the protection of dermal skin. In this study, hollow porous silica spheres used to load quercetin were prepared by using a combined emulsion sol-gel process and triblock copolymer as a template. Fabrication of hollow porous silica spheres was performed under various conditions such as the molar ratios of H2O/TEOS (Rw) and weight ratios of poloxamer 184/poloxamer 407. Loading of quercetin in hollow porous silica spheres was devised to improve the stability of quercetin and to consider the possibility as a raw cosmetic material. The surface of inclusion complexes of quercetin in hollow porous silicas was modified to enhance the stability of quercetin. The physicochemical properties of the samples were investigated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA)-differential thermal analysis (DTA) and Brunauer-Emmett-Teller (BET) surface area and porosity analysis. Determination of quercetin concentration was carried out by high-performance liquid chromatography (HPLC) analysis. PMID:26726443

14. A needle trap device packed with a sol-gel derived, multi-walled carbon nanotubes/silica composite for sampling and analysis of volatile organohalogen compounds in air.

PubMed

Heidari, Mahmoud; Bahrami, Abdolrahman; Ghiasvand, Ali Reza; Shahna, Farshid Ghorbani; Soltanian, Ali Reza

2013-06-27

A needle trap device (NTD) packed with silica composite of multi-walled carbon nanotubes (MWCNTs) prepared based on sol-gel technique was utilized for sampling and analysis of volatile organohalogen compounds (HVOCs) in air. The performance of the NTD packed with MWCNTs/silica composite as sorbent was examined in a variety of sampling conditions and was compared with NTDs packed with PDMS as well as SPME with Carboxen/PDMS-coated fibers. The limit of detection of NTDs for the GC/MS detection system was 0.01-0.05 ng mL(-1) and the limit of quantitation was 0.04-0.18 ng mL(-1). The RSD were 1.1-7.8% for intra-NTD comparison intended for repeatability of technique. The NTD-MWCNTs/silica composite showed better analytical performances compared to the NTD-PDMS composite and had the same analytical performances when compared to the SPME-Carboxen/PDMS fibers. The results show that NTD-MWCNTs-GC/MS is a powerful technique for active sampling of occupational/environmental pollutants in air.

15. Detection of organophosphorus compound based on a sol-gel silica planar waveguide doped with a green fluorescent protein and an organophosphorus hydrolase

Enami, Y.; Tsuchiya, K.; Suye, S.

2011-06-01

In this letter, the authors report the real-time detection of an organophosphorus compound using a sol-gel silica planar waveguide doped with a green fluorescent protein and an organophosphorus hydrolase on a yeast-cell surface display. The waveguide was pumped at 488 nm, and it emitted green fluorescence at the far field. The green fluorescent light at 550 nm changed by 50% from the original power 1 min after application of the organophosphorus compound. The results enable the real-time detection of sarin and other biochemicals by using an in-line fiber sensor network.

16. External and Intraparticle Diffusion of Coumarin 102 with Surfactant in the ODS-silica Gel/water System by Single Microparticle Injection and Confocal Fluorescence Microspectroscopy.

PubMed

Nakatani, Kiyoharu; Matsuta, Emi

2015-01-01

The release mechanism of coumarin 102 from a single ODS-silica gel microparticle into the water phase in the presence of Triton X-100 was investigated by confocal fluorescence microspectroscopy combined with the single microparticle injection technique. The release rate significantly depended on the Triton X-100 concentration in the water phase and was not limited by diffusion in the pores of the microparticle. The release rate constant was inversely proportional to the microparticle radius squared, indicating that the rate-determining step is the external diffusion between the microparticle and the water phase.

17. Design of electro-active polymer gels as actuator materials

Popovic, Suzana

Smart materials, alternatively called active or adaptive, differ from passive materials in their sensing and activation capability. These materials can sense changes in environment such as: electric field, magnetic field, UV light, pH, temperature. They are capable of responding in numerous ways. Some change their stiffness properties (electro-rheological fluids), other deform (piezos, shape memory alloys, electrostrictive materials) or change optic properties (electrochromic polymers). Polymer gels are one of such materials which can change the shape, volume and even optical properties upon different applied stimuli. Due to their low stiffness property they are capable of having up to 100% of strain in a short time, order of seconds. Their motion resembles the one of biosystems, and they are often seen as possible artificial muscle materials. Despite their delicate nature, appropriate design can make them being used as actuator materials which can form controllable surfaces and mechanical switches. In this study several different groups of polymer gel material were investigated: (a) acrylamide based gels are sensitive to pH and electric field and respond in volume change, (b) polyacrylonitrile (PAN) gel is sensitive to pH and electric field and responds in axial strain and bending, (c) polyvinylalcohol (PVA) gel is sensitive to electric field and responds in axial strain and bending and (d) perfluorinated sulfonic acid membrane, Nafion RTM, is sensitive to electric field and responds in bending. Electro-mechanical and chemo-mechanical behavior of these materials is a function of a variety of phenomena: polymer structure, affinity of polymer to the solvent, charge distribution within material, type of solvent, elasticity of polymer matrix, etc. Modeling of this behavior is a task aimed to identify what is driving mechanism for activation and express it in a quantitative way in terms of deformation of material. In this work behavior of the most promising material as

18. Detection of Non-Equilibrium Fluctuations in Active Gels

Bacanu, Alexandru; Broedersz, Chase; Gladrow, Jannes; Mackintosh, Fred; Schmidt, Christoph; Fakhri, Nikta

Active force generation at the molecular scale in cells can result in stochastic non-equilibrium dynamics on mesoscpopic scales. Molecular motors such as myosin can drive steady-state stress fluctuations in cytoskeletal networks. Here, we present a non-invasive technique to probe non-equilibrium fluctuations in an active gel using single-walled carbon nanotubes (SWNTs). SWNTs are semiflexible polymers with intrinsic fluorescence in the near infrared. Both thermal and active motor-induced forces in the network induce transverse fluctuations of SWNTs. We demonstrate that active driven shape fluctuations of the SWNTs exhibit dynamics that reflect the non-equilibrium activity, in particular the emergence of correlations between the bending modes. We discuss the observation of breaking of detailed balance in this configurational space of the SWNT probes. Supported by National Defense Science and Engineering Graduate Student Fellowship (NDSEG).

19. Effect of Electrophoresis on the Efficiency of Graphite-Nano-TiO2 Modified Silica Sol-Gel Electrode.

PubMed

Hejazi, Mohammad Saeid; Majidi, Mir Reza; Gholizadeh, Sima; Hamidi-Asl, Ezat; Turner, Anthony P F; Golabi, Seyed Mahdi

2015-05-01

Electrophoresis treatment was used to improve the function of a nano-TiO2 modified sol-gel electrode. Electrodes were prepared using TiO2 nanoparticles and fine graphite powder and then treated by electrophoresis. The developed electrode was employed for the detection of lactate dehydrogenase (LDH) by following the decrease in the immobilised lactate peak current due to its LDH-mediated enzymatic oxidation. Detection was realised using square wave voltammetry (SWV). Experiments showed that the positive and negative heads of the electrophoresis-treated electrode displayed different activities, with the positive head response being remarkably improved. Parameters affecting the electrode response, such as applied potential value, electrophoresis time and percentage of TiO2, were investigated and optimised. The improved performance was dependent on TiO2 concentration as well as electrophoresis voltage and time. The prepared sensor, under optimised conditions, displayed a detection limit of 0.0073 U/μl for LDH.

20. [Kinetic study on the in situ synthesis of nickle phthalocyanine in silica gel glass matrix by UV/Vis absorption spectra].

PubMed

Huang, Juan; Zheng, Chan; Feng, Miao; Zhan, Hong-Bing

2009-01-01

In decades, metallo-phthalocyanines (MPcs) have undergone a renaissance because of their singular and unconventional physical properties. However, for the successful application of MPcs in practical devices, it is important to disperse MPc molecules into solid state matrix to fabricate MPc doped composite with desired properties. Inorganic glass is an ideal matrix because of its transparency and high environmental stability. One attractive approach to fabricating MPc/inorganic composite is sol-gel technique. In the present paper, silica gel glass matrix was prepared by hydrolysis and poly-condensation of tetraethyloxysilane. 1,2-dicyanobenzene and analytically pure soluble nickle salt were used as the nickle phthalocyanine (NiPc) reactants and chemical synthesis technique was used to prepare NiPc doped sol-gel materials at several temperatures. During the heat treatment, four 1, 2-dicyanobenzene molecules and one nickle ion collide to form a NiPc molecule. In-situ synthesizing process of NiPc in the pores of silica gel glass matrix was traced by UV/Vis absorption spectra. Owing to the remarkable absorption band of NiPc in visible region, quantity of in-situ synthesized NiPc was calculated by the absorbance at certain wavelength of 670 nm, using composites with physically doped NiPc as a reference. The in-situ synthesized kinetics was studied in detail and found to be consistent with Avrami-Erofeev equation The reaction grades were deduced to be 4.5, 4.5, 3.7, 3.2 and 1.9 respectively at temperatures of 180 degrees C, 185 degrees C, 190 degrees C, 195 degrees C and 200 degrees C, respectively.

1. Deactivation of photocatalytically active ZnO nanoparticle and enhancement of its compatibility with organic compounds by surface-capping with organically modified silica

Cao, Zhi; Zhang, Zhijun

2011-02-01

Tetraethyl orthosilicate (TEOS) and dimethyldiethoxysilane (DEDMS) were used as co-precursors to prepare organically modified silica (ormosil) via sol-gel process. The resultant ormosil was adopted for surface-capping of ZnO nanoparticle, where methyl (organic functional group) and silica (inorganic component) were simultaneously introduced onto the surface of the nanoparticles for realizing dual surface-modification. The ormosil-capped ZnO nanoparticle showed strong hydrophobicity and good compatibility with organic phases, as well as effectively decreased photocatalytic activity and almost unchanged ultraviolet (UV)-shielding ability. More importantly, the comprehensive properties of ormosil-capped ZnO nanoparticle could be manipulated by adjusting the molar ratio of TEOS to DEDMS during sol-gel process. This should help to open a wider window to better utilizing the unique and highly attractive properties such as high UV-shielding ability and high-visible light transparency of ZnO nanoparticle in sunscreen cosmetics.

2. The Solid Phase Extraction of Some Metal Ions Using Palladium Nanoparticles Attached to Silica Gel Chemically Bonded by Silica-Bonded N-Propylmorpholine as New Sorbent prior to Their Determination by Flame Atomic Absorption Spectroscopy

PubMed Central

Ghaedi, M.; Rezakhani, M.; Khodadoust, S.; Niknam, K.; Soylak, M.

2012-01-01

In this research at first palladium nanoparticle attached to a new chemically bonded silica gel has been synthesized and has been characterized with different techniques such as X-ray diffraction (XRD), fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Then, this new sorbent (chemically modified silica gel with N-propylmorpholine (PNP-SBNPM)) was efficiently used for preconcentration of some metal ions in various food samples. The influence of effective variables including mass of sorbent, flow rate, pH of sample solutions and condition of eluent such as volume, type and concentration on the recoveries of understudy metal ions were investigated. Following the optimization of variables, the interfering effects of some foreign ions on the preconcentration and determination of the investigated metal ions described. At optimum values of variables, all investigated metal ions were efficiently recovered with efficiency more than 95%, relative standard deviation (RSD) between 2.4 and 2.8, and detection limit in the range of 1.4–2.7 ng mL−1. The present method is simple and rapidly applicable for the determination of the understudied metal ions (ng mL−1) in different natural food samples. PMID:22666150

3. Assessing Kinase Activity in Plants with In-Gel Kinase Assays.

PubMed

Wang, Pengcheng; Zhu, Jian-Kang

2016-01-01

The in-gel protein kinase assay is a powerful method to measure the protein phosphorylation activity of specific protein kinases. Any protein substrate can be embedded in polyacrylamide gels where they can be phosphorylated by protein kinases that are separated in the gel under denaturing conditions and then renatured. The kinase activity can be visualized in situ in the gels by autoradiography. This method has been used to compare the activities of protein kinases in parallel samples or to identify their potential substrates. Here, we describe in detail an in-gel kinase assay to measure the activity of some protein kinases in plants.

4. Synthesis and properties of a newly obtained sorbent based on silica gel coated with a polyaniline film as the stationary phase for non-suppressed ion chromatography.

PubMed

Sowa, Ireneusz; Wójciak-Kosior, Magdalena; Drączkowski, Piotr; Strzemski, Maciej; Kocjan, Ryszard

2013-07-17

The new sorbent for non-suppressed ion chromatography based on silica gel coated with a film of polyaniline (PANI) was obtained in a process of in situ polymerization of aniline by oxidation with ammonium peroxydisulfate. Raman analyses performed using a Thermo Scientific DXR confocal Raman Microscope equipped with the Omnic 8 software from Thermo Fisher Scientific have proved a uniform distribution of PANI on the surface of chromatographic beads and in the pores of the particle. The obtained stationary phase was packed into a stainless steel HPLC column. The quality of the prepared column was verified on the basis of hydrodynamic parameters such as column efficiency index (Ip) and separation impedance (E). The potential application of silica gel modified with polyaniline for separation and determination of selected anions using non-suppressed ion chromatography was also investigated. Chromatographic analyses were performed using of the ion chromatograph Dionex DX-500. The best results were obtained for the mobile phase consisting of an aqueous or methanolic solution of hydrochloric acid. The tested column and optimized chromatographic system were successfully used for the analysis of nitrate, bromide and iodide in waters samples.

5. Quantitative determination of dimethyl fumarate in silica gel by solid-phase microextraction/gas chromatography/mass spectrometry and ultrasound-assisted extraction/gas chromatography/mass spectrometry.

PubMed

Bocchini, Paola; Pinelli, Francesca; Pozzi, Romina; Ghetti, Federica; Galletti, Guido C

2015-06-01

Dimethyl fumarate (DMF) is a chemical compound which has been added to silica gel bags used for preserving leather products during shipment. DMF has recently been singled out due to its ability to induce a number of medical problems in people which touch products contaminated by it. Its use as a biocide has been recently made illegal in Europe. Two different extraction techniques, namely ultrasound-assisted extraction (UAE) and solid-phase microextraction (SPME), both coupled with gas chromatography/mass spectrometry were applied to the quantitative determination of DMF in silica gel. Linearity of the methods, reproducibility and detection limits were determined. The two methods were applied to the quantification of DMF in thirty-four silica gel samples used as anti-mould agents in different leather products sold in Italy, and the obtained results were statistically compared. PMID:25939646

6. Nonaqueous sol-gel chemistry applied to atomic layer deposition: tuning of photonic band gap properties of silica opals.

PubMed

Marichy, Catherine; Dechézelles, Jean-Francois; Willinger, Marc-Georg; Pinna, Nicola; Ravaine, Serge; Vallée, Renaud

2010-05-01

Combining both electromagnetic simulations and experiments, it is shown that the photonic pseudo band gap (PPBG) exhibited by a silica opal can be fully controlled by Atomic Layer Deposition (ALD) of titania into the pores of the silica spheres constituting the opal. Different types of opals were assembled by the Langmuir-Blodgett technique: homogeneous closed packed structures set up of, respectively, 260 and 285 nm silica spheres, as well as opal heterostructures consisting of a monolayer of 430 nm silica spheres embedded within 10 layers of 280 nm silica spheres. For the stepwise infiltration of the opals with titania, titanium isopropoxide and acetic acid were used as metal and oxygen sources, in accordance with a recently published non-aqueous approach to ALD. A shift of the direct PPBG, its disappearance, and the subsequent appearance and shifting of the inverse PPBG are observed as the opal is progressively filled. The close agreement between simulated and experimental results is striking, and promising in terms of predicting the properties of advanced photonic materials. Moreover, this work demonstrates that the ALD process is rather robust and can be applied to the coating of complex nanostructures.

7. Injectable silica-permanganate gel as a slow-release MnO4(-) source for groundwater remediation: rheological properties and release dynamics.

PubMed

Yang, S; Oostrom, M; Truex, M J; Li, G; Zhong, L

2016-02-01

Injectable slow-release permanganate gels (ISRPGs), formed by mixing aqueous KMnO4 solution with fumed silica powders, may have potential applications in remediating chlorinated solvent plumes in groundwater. A series of batch, column, and two-dimensional (2-D) flow cell experiments has been completed to characterize the ISRPG and study the release of permanganate (MnO4(-)) under a variety of conditions. The experiments have provided information on ISRPG rheology, MnO4(-) release dynamics and distribution in porous media, and trichloroethene (TCE) destruction by the ISRPG-released oxidant. The gel possesses shear thinning characteristics, resulting in a relatively low viscosity during mixing, and facilitating subsurface injection and distribution. Batch tests clearly showed that MnO4(-) diffused out from the ISRPG into water. During this process, the gel did not dissolve or disperse into water, but rather maintained its initial shape. Column experiments demonstrated that MnO4(-) release from the ISRPG lasted considerably longer than that from an aqueous solution. In addition, due to the longer release duration, TCE destruction by ISRPG-released MnO4(-) was considerably more effective than that when MnO4(-) was delivered using aqueous solution injection. In the 2-D flow cell experiments, it was demonstrated that ISRPGs released a long-lasting, low-concentration MnO4(-) plume potentially sufficient for sustainable remediation in aquifers. PMID:26766607

8. Injectable silica-permanganate gel as a slow-release MnO4(-) source for groundwater remediation: rheological properties and release dynamics.

PubMed

Yang, S; Oostrom, M; Truex, M J; Li, G; Zhong, L

2016-02-01

Injectable slow-release permanganate gels (ISRPGs), formed by mixing aqueous KMnO4 solution with fumed silica powders, may have potential applications in remediating chlorinated solvent plumes in groundwater. A series of batch, column, and two-dimensional (2-D) flow cell experiments has been completed to characterize the ISRPG and study the release of permanganate (MnO4(-)) under a variety of conditions. The experiments have provided information on ISRPG rheology, MnO4(-) release dynamics and distribution in porous media, and trichloroethene (TCE) destruction by the ISRPG-released oxidant. The gel possesses shear thinning characteristics, resulting in a relatively low viscosity during mixing, and facilitating subsurface injection and distribution. Batch tests clearly showed that MnO4(-) diffused out from the ISRPG into water. During this process, the gel did not dissolve or disperse into water, but rather maintained its initial shape. Column experiments demonstrated that MnO4(-) release from the ISRPG lasted considerably longer than that from an aqueous solution. In addition, due to the longer release duration, TCE destruction by ISRPG-released MnO4(-) was considerably more effective than that when MnO4(-) was delivered using aqueous solution injection. In the 2-D flow cell experiments, it was demonstrated that ISRPGs released a long-lasting, low-concentration MnO4(-) plume potentially sufficient for sustainable remediation in aquifers.

9. Optically active silica and polymeric materials for microcavity lasers and sensors

Armani, A. M.; Deka, N.; Mehrabani, S.; Shi, C.; Maker, A.; Lee, M.; Kovach, A.; Gungor, E.; Kuo, K.; Diep, V.

2015-03-01

Silica and silica-doped high quality factor (Q) optical resonators have demonstrated ultra-low threshold lasers based on numerous mechanisms (eg rare earth dopants, Raman). To date, the key focus has been on maintaining a high Q, as that determines the lasing threshold and linewidth. However, equally important criteria are lasing efficiency and wavelength. These parameters are governed by the material, not the cavity Q. Therefore, to fully address this challenge, it is necessary to develop new materials. We have synthesized a suite of silica and polymeric materials with nanoparticle and rare-earth dopants to enable the development of microcavity lasers with emission from the near-IR to the UV. Additionally, the efficiencies and thresholds of many of these devices surpass the previous work. Specifically, the silica sol-gel lasers are co- and tri-doped with metal nanoparticles (eg Ti, Al) and rare-earth materials (eg Yb, Nb, Tm) and are fabricated using conventional micro/nanofabrication methods. The intercalation of the metal in the silica matrix reduces the clustering of the rare-earth ions and reduces the phonon energy of the glass, improving efficiency and overall device performance. Additionally, the silica Raman gain coefficient is enhanced due to the inclusion of the metal nanoparticles, which results in a lower threshold and a higher efficiency silica Raman laser. Finally, we have synthesized several polymer films doped with metal (eg Au, Ag) nanoparticles and deposited them on the surface of our microcavity devices. By pumping on the plasmonic resonant wavelength of the particle, we are able to achieve plasmonic-enhanced upconversion lasing.

10. Active gels: dynamics of patterning and self-organization

Backouche, F.; Haviv, L.; Groswasser, D.; Bernheim-Groswasser, A.

2006-12-01

The actin cytoskeleton is an active gel which constantly remodels during cellular processes such as motility and division. Myosin II molecular motors are involved in this active remodeling process and therefore control the dynamic self-organization of cytoskeletal structures. Due to the complexity of in vivo systems, it is hard to investigate the role of myosin II in the reorganization process which determines the resulting cytoskeletal structures. Here we use an in vitro model system to show that myosin II actively reorganizes actin into a variety of mesoscopic patterns, but only in the presence of bundling proteins. We find that the nature of the reorganization process is complex, exhibiting patterns and dynamical phenomena not predicted by current theoretical models and not observed in corresponding passive systems (excluding motors). This system generates active networks, asters and even rings depending on motor and bundling protein concentrations. Furthermore, the motors generate the formation of the patterns, but above a critical concentration they can also disassemble them and even totally prevent the polymerization and bundling of actin filaments. These results may suggest that tuning the assembly and disassembly of cytoskeletal structures can be obtained by tuning the local myosin II concentration/activity.

11. Examination of the haemolytic activity of sol-gel materials

Ulatowska-Jarza, Agnieszka; Podbielska, Halina; Holowacz, Iwona; Lechna-Marczynska, Monika I.; Szymonowicz, Maria; Staniszewska-Kus, Jolanta; Paluch, Danuta

2001-10-01

Recently, the sol-gel based biomaterials are extendedly investigated with emphasis on theirs various applications, including medical ones. In this respect it is important to investigate the influence of sol-gel matrices on biological systems. The results of laboratory and biological testing of aqueous extracts of sol-gels are presented in this work. It was proved that it is possible to produce the sol-gel derived materials that will be non-haemolytic. This can be achieved by heating the materials in elevated temperatures. This effect can also be reached by suitably long aging (minimum 6 months).

12. Effect of sintering temperature on mechanical behaviour and bioactivity of sol-gel synthesized bioglass-ceramics using rice husk ash as a silica source

Nayak, J. P.; Bera, J.

2010-11-01

Bioglass-ceramics with SiO2-Na2O-CaO composition was prepared by sol-gel method using rice husk ash as a silica source. Material was sintered at different temperatures ranging from 900 to 1050 °C for 2 h. Phase-formation behaviour, densification characteristics, and mechanical strength of glass-ceramics were investigated. The material sintered at 1000 °C showed a good mechanical strength. Mechanical properties were correlated with microstructural features. Both in vitro bioactivity and biodegradability of sintered material were investigated by incubating in simulated body fluid and Tris buffer solution, respectively. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to investigate the surface deposition during body fluid incubation. Both bioactivity and degradability decreased with increase in sintering temperature.

13. Silica-titania sol-gel hybrid materials: synthesis, characterization and potential application in solid phase extraction.

PubMed

de Moraes, Sandra V M; Passos, Joana B; Schossler, Patricia; Caramão, Elina B; Moro, Celso C; Costa, Tania M H; Benvenutti, Edilson V

2003-04-10

The biphenilaminepropylsilica and biphenilaminepropylsilicatitania were synthesized by sol-gel method, in two steps: (a) biphenylamine reacts with chloropropyltrimethoxysilane and (b) the product of reaction was polycondensed with tetraethylorthosilicate (TEOS) or TEOS and titanium isopropoxide. The sol-gel materials were characterized using infrared spectroscopy and N(2) adsorption-desorption isotherms and they were employed as sorbents for carcinogenic N-containing compound retention, in aqueous solution, using the SPE technique. The N-containing compounds adsorption was influenced by the titania presence and the sorption process seems to happen in the pores with higher organic density.

14. Syntheses, characterization and adsorption properties for Pb2+ of silica-gel functionalized by dendrimer-like polyamidoamine and 5-sulfosalicylic acid

Wu, Xiongzhi; Luo, Liangliang; Chen, Ziyan; Liang, Kailing

2016-02-01

15. Heavy metal adsorptivity of calcium-alginate-modified diethylenetriamine-silica gel and its application to a flow analytical system using flame atomic absorption spectrometry.

PubMed

Mori, Masanobu; Suzuki, Toshinobu; Sugita, Tsuyoshi; Nagai, Daisuke; Hirayama, Kazuo; Onozato, Makoto; Itabashi, Hideyuki

2014-08-20

16. Heavy metal adsorptivity of calcium-alginate-modified diethylenetriamine-silica gel and its application to a flow analytical system using flame atomic absorption spectrometry.

PubMed

Mori, Masanobu; Suzuki, Toshinobu; Sugita, Tsuyoshi; Nagai, Daisuke; Hirayama, Kazuo; Onozato, Makoto; Itabashi, Hideyuki

2014-08-20

17. Application of graphene nanoplatelets silica composite, prepared by sol-gel technology, as a novel sorbent in two microextraction techniques.

PubMed

Heidari, Mahmoud; Bahrami, Abdolrahman; Ghiasvand, Ali Reza; Shahna, Farshid Ghorbani; Soltanian, Ali Reza; Rafieiemam, Maryam

2015-12-01

In this study, the application of a novel nanomaterial composite was investigated in two microextraction techniques of solid-phase microextraction and a needle trap device in a variety of sampling conditions. The optimum sampling temperature and relative humidity were 10°C and 20%, respectively, for both techniques with two sorbents of graphene/silica composite and polydimethyl siloxane. The two microextraction techniques with the proposed sorbent showed recoveries of 95.2 and 94.6% after 7 days. For the needle trap device the optimums desorption time and temperature were 3 min at 290°C and for SPME these measures were 1 and 1.5 min at 240-250°C for the graphene/silica composite and polydimethyl siloxane, respectively. The relative standard division obtained in inter- and intra-day comparative studies were 3.3-14.3 and 5.1-25.4, respectively. For four sample the limit of detection was 0.021-0.25 ng/mL, and the limit of quantitation was 0.08-0.75 ng/mL. The results show that the graphene/silica composite is an appropriate extraction media for both techniques. Combining an appropriate sorbent with microextraction techniques, and using these in conjunction with a sensitive analytical instrument can introduce a strong method for sampling and analysis of occupational and environmental pollutants in air.

18. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

Janaun, J.; Safie, N. N.; Siambun, N. J.

2016-07-01

The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

19. Physicochemical properties of silica gel coated with a thin layer of polyaniline (PANI) and its application in non-suppressed ion chromatography.

PubMed

Sowa, Ireneusz; Kocjan, Ryszard; Wójciak-Kosior, Magdalena; Swieboda, Ryszard; Zajdel, Dominika; Hajnos, Mieczysław

2013-10-15

Physicochemical properties of a new sorbent and its potential application in non-suppressed ion chromatography (IC) have been investigated. The sorbent was obtained in a process of covering silica gel particles with a film of polyaniline (PANI). The properties of silica modified with polyaniline such as particle size, porosity, average quantity of polyaniline covering carrier and density of sorbent were determined. In our study the following methods were used: microscopic analysis, laser diffraction technique, combustion analysis, mercury porosimetry and helium pycnometry. Column with the newly obtained packing was used for the separation of inorganic anions. Optimized chromatographic system was successfully employed for analysis of iodide and bromide in selected pharmaceutical products (Bochnia salt and Iwonicz salt) applied in chronic respiratory disease. Analysis was carried out using 0.1M solution of HCl in mixture of methanol/water (50:50v/v) as a mobile phase; the flow rate was 0.3 mL min(-1), temperature was 24°C and λ=210 nm. Validation parameters such as correlation coefficient, RSD values, recovery, detection and quantification limits were found to be satisfactory.

20. Dual mode signaling responses of a rhodamine based probe and its immobilization onto a silica gel surface for specific mercury ion detection.

PubMed

2015-09-14

A 3-aminomethyl-(2-amino-1-pyridyl) coupled amino-ethyl-rhodamine-B based probe (2) exhibited simultaneous chromogenic and fluorogenic dual mode signaling responses in the presence of Hg(II) ions only among all the metal ions investigated in an organic aqueous medium. The spiro-cyclic rhodamine signaling subunit undergoes complexation induced structural transformation to result in absorption and fluorescence modulation. Its complexation induced signaling exhibited reversibility with various contrasting reagents having higher affinity towards Hg(II) ions, such as anions (AcO(-)) and competing chelating agents (En). It also exhibited Hg(II)-specific photophysical signaling responses when immobilized onto a silica gel surface attached through its amino-ethyl-receptor end, owing to its structure-conformational advantages for effective coordination. The surface modified silica appended with 2 (SiR-1), as evaluated through the FTIR spectral pattern, thermogravimetric analysis, FESEM images, elemental analysis, X-ray diffraction, surface area determination and particle size analysis, also exhibited reversible Hg(II)-specific signaling in its suspension state in an aqueous medium, enhancing the probe's utility for practical applications such as the detection, isolation and extraction of Hg(II) ions in the presence of other competitive metal ions.

1. Living organisms as an alternative to hyphenated techniques for metal speciation. Evaluation of baker's yeast immobilized on silica gel for Hg speciation*1

Pérez-Corona, Teresa; Madrid-Albarrán, Yolanda; Cámara, Carmen; Beceiro, Elisa

1998-02-01

The use of living organisms for metal preconcentration and speciation is discussed. Among substrates, Saccharomyces cerevisiae baker's yeast has been successfully used for the speciation of mercury [Hg(II) and CH 3Hg +], selenium [Se(IV) and Se(VI)] and antimony [Sb(III) and Sb(V)]. To illustrate the capabilities of these organisms, the analytical performance of baker's yeast immobilized on silica gel for on-line preconcentration and speciation of Hg(II) and methylmercury is reported. The immobilized cells were packed in a PTFE microcolumn, through which mixtures of organic and inorganic mercury solutions were passed. Retention of inorganic and organic mercury solutions took place simultaneously, with the former retained in the silica and the latter on the yeast. The efficiency uptake for both species was higher than 95% over a wide pH range. The speciation was carried out by selective and sequential elution with 0.02 mol L -1 HCl for methylmercury and 0.8 mol L -1 CN - for Hg(II). This method allows both preconcentration and speciation of mercury. The preconcentration factors were around 15 and 100 for methylmercury and mercury(II), respectively. The method has been successfully applied to spiked sea water samples.

2. Autophagy deficiency in macrophages enhances NLRP3 inflammasome activity and chronic lung disease following silica exposure.

PubMed

Jessop, Forrest; Hamilton, Raymond F; Rhoderick, Joseph F; Shaw, Pamela K; Holian, Andrij

2016-10-15

Autophagy is an important metabolic mechanism that can promote cellular survival following injury. The specific contribution of autophagy to silica-induced inflammation and disease is not known. The objective of these studies was to determine the effects of silica exposure on the autophagic pathway in macrophages, as well as the general contribution of autophagy in macrophages to inflammation and disease. Silica exposure enhanced autophagic activity in vitro in Bone Marrow derived Macrophages and in vivo in Alveolar Macrophages isolated from silica-exposed mice. Impairment of autophagy in myeloid cells in vivo using Atg5(fl/fl)LysM-Cre(+) mice resulted in enhanced cytotoxicity and inflammation after silica exposure compared to littermate controls, including elevated IL-18 and the alarmin HMGB1 in the whole lavage fluid. Autophagy deficiency caused some spontaneous inflammation and disease. Greater silica-induced acute inflammation in Atg5(fl/fl)LysM-Cre(+) mice correlated with increased fibrosis and chronic lung disease. These studies demonstrate a critical role for autophagy in suppressing silica-induced cytotoxicity and inflammation in disease development. Furthermore, this data highlights the importance of basal autophagy in macrophages and other myeloid cells in maintaining lung homeostasis.

3. Autophagy deficiency in macrophages enhances NLRP3 inflammasome activity and chronic lung disease following silica exposure.

PubMed

Jessop, Forrest; Hamilton, Raymond F; Rhoderick, Joseph F; Shaw, Pamela K; Holian, Andrij

2016-10-15

Autophagy is an important metabolic mechanism that can promote cellular survival following injury. The specific contribution of autophagy to silica-induced inflammation and disease is not known. The objective of these studies was to determine the effects of silica exposure on the autophagic pathway in macrophages, as well as the general contribution of autophagy in macrophages to inflammation and disease. Silica exposure enhanced autophagic activity in vitro in Bone Marrow derived Macrophages and in vivo in Alveolar Macrophages isolated from silica-exposed mice. Impairment of autophagy in myeloid cells in vivo using Atg5(fl/fl)LysM-Cre(+) mice resulted in enhanced cytotoxicity and inflammation after silica exposure compared to littermate controls, including elevated IL-18 and the alarmin HMGB1 in the whole lavage fluid. Autophagy deficiency caused some spontaneous inflammation and disease. Greater silica-induced acute inflammation in Atg5(fl/fl)LysM-Cre(+) mice correlated with increased fibrosis and chronic lung disease. These studies demonstrate a critical role for autophagy in suppressing silica-induced cytotoxicity and inflammation in disease development. Furthermore, this data highlights the importance of basal autophagy in macrophages and other myeloid cells in maintaining lung homeostasis. PMID:27594529

4. Mesoporous CLEAs-silica composite microparticles with high activity and enhanced stability

PubMed Central

Cui, Jiandong; Jia, Shiru; Liang, Longhao; Zhao, Yamin; Feng, Yuxiao

2015-01-01

A novel enzyme immobilization approach was used to generate mesoporous enzymes-silica composite microparticles by co-entrapping gelatinized starch and cross-linked phenylalanine ammonia lyase (PAL) aggregates (CLEAs) containing gelatinized starch into biomemitic silica and subsequently removing the starch by α-amylase treatment. During the preparation process, the gelatinzed starch served as a pore-forming agent to create pores in CLEAs and biomimetic silica. The resulting mesoporous CLEAs-silica composite microparticles exhibited higher activity and stability than native PAL, conventional CLEAs, and PAL encapsulated in biomimetic silica. Furthermore, the mesoporous CLEAs-silica composite microparticles displayed good reusability due to its suitable size and mechanical properties, and had excellent stability for storage. The superior catalytic performances were attributed to the combinational unique structure from the intra-cross-linking among enzyme aggregates and hard mesoporous silica shell, which not only decreased the enzyme-support negative interaction and mass-transfer limitations, but also improved the mechanical properties and monodispersity. This approach will be highly beneficial for preparing various bioactive mesoporous composites with excellent catalytic performance. PMID:26374188

5. Photocatalytic activity of erbium-doped TiO{sub 2} nanoparticles immobilized in macro-porous silica films

SciTech Connect

Castaneda-Contreras, J.; Maranon-Ruiz, V.F.; Chiu-Zarate, R.; Perez-Ladron de Guevara, H.; Rodriguez, R.; Michel-Uribe, C.

2012-02-15

Highlights: Black-Right-Pointing-Pointer Erbium-doped TiO{sub 2} nanoparticles were immobilized on macro-porous silica films. Black-Right-Pointing-Pointer The films were obtained by a phase separation process. Black-Right-Pointing-Pointer The samples exhibited photo-catalytic activity under visible light. Black-Right-Pointing-Pointer The sensitization of TiO{sub 2} was attributed to a red shift in the TiO{sub 2} band-gap. -- Abstract: A macro-porous silica film served as mechanical support to immobilize TiO{sub 2} nanoparticles, which were doped with erbium. The films and the nanoparticles were prepared by sol-gel route. The nanoparticles exhibited photocatalytic activity under visible light. We obtained a degradation rate of methylene blue that followed first order kinetics. The sensitization of the nanoparticles to visible light was attributed to a red shift in the band-gap of the TiO{sub 2} due to the addition of erbium ions.

6. Influence of mechanochemical activation in various media on structure of porous and non-porous silicas

Sydorchuk, V.; Khalameida, S.; Zazhigalov, V.; Skubiszewska-Zięba, J.; Leboda, R.; Wieczorek-Ciurowa, K.

2010-11-01

Influence of mechanochemical activation on porous structure and surface properties of porous and non-porous silicas in air, water and ethanol has been studied. Milled samples have been investigated with help of nitrogen adsorption-desorption, mercury porometry, thermogravimetric analysis, FTIR and ESR spectroscopy. It has been revealed that destruction of porous structure of silicagel at dry milling and, on the contrary, formation of porous silica from non-porous powders (aerosils) during treatment in liquid media occurs.

7. Bifunctionalized mesoporous silica-supported gold nanoparticles: intrinsic oxidase and peroxidase catalytic activities for antibacterial applications.

PubMed

Tao, Yu; Ju, Enguo; Ren, Jinsong; Qu, Xiaogang

2015-02-11

Bifunctionalized mesoporous silica-supported gold nanoparticles as oxidase and peroxidase mimics for antibacterial applications are demonstrated. For the first time, these mesoporous silica-supported gold nanoparticles are applied as oxidase and peroxidase mimics. Taking advantage of their prominent enzyme activities, the MSN-AuNPs show excellent antibacterial properties against both Gram-negative and Gram-positive bacteria. Furthermore, MSN-AuNPs also exhibit outstanding performance in biofilm elimination . PMID:25655182

8. Mineralogical characteristics of the silica polymorphs in relation to their biological activities

SciTech Connect

Guthrie, G.D. Jr.; Heaney, P.J.

1993-10-01

Numerous aspects of minerals (including the silica polymorphs) can effect their biological activities. These include periodic structures, compositional variations, dissolution characteristics, surface properties, and particle size/shape. In order to understand mineral-induced pathogenesis in a mechanistic way, the links between these properties and biochemical processes must be elucidated. This paper presents some of the basic properties of the silica polymorphs that may relate to pathogenicity and mineralogical strategies for designing biological assays to evaluate these properties.

9. SBA-15 Mesoporous Silica Modified with Gallic Acid and Evaluation of Its Cytotoxic Activity

PubMed Central

Lewandowski, Dawid

2015-01-01

Gallic acid has been covalently conjugated to SBA-15 mesoporous silica surface through different linkers. Cytotoxic activity of the hybrid organic-inorganic systems against HeLa and KB cell lines has been analyzed. Up to 67% of HeLa or KB tumor cells growth inhibition has been achieved at low silica concentration used (10 μg mL-1). PMID:26151908

10. Modification of the sensitivity and selectivity of thin porous layers coated by the sol-gel method on silica optical fibers to gases

Matejec, Vlastimil; Berkova, Daniela; Chomat, Miroslav; Kuncova, Gabriela

1999-12-01

It has been found that thin layers of aerogels applied by the sol-gel method on silica optical fibers change their optical properties due to the interaction with gases such as hydrocarbons. This paper deals with modification of the sensitivity and selectivity to vapors of hydrocarbons and chlorinated hydrocarbons of siloxane aerogel layers based on their doping with TiOTi chains and/or immobilizing in them Cu-ephedrine and Cu-phthalocyanine. The sensing fibers were prepared by the sol-gel application of porous siloxane and doped-siloxane layers on bare cores of PCS fibers. By using the excitation of the fiber with inclined laser beams it is experimentally shown that there are positive or negative changes of the output optical power from the fibers due to bringing the prepared layers into contact with vapors of aliphatic, aromatic and chlorinated hydrocarbons in nitrogen. These effects may be related to a difference between the refractive index of the layer and refractive index of liquid hydrocarbon or hydrocarbon its derivative. It is shown experimentally that doping porous siloxane layers with copper complexes changes their refractive index and optical losses changing thus their sensitivity and selectivity to hydrocarbons and hydrocarbon derivatives.

11. Improved Mobility Control for Carbon Dioxide (CO{sub 2}) Enhanced Oil Recovery Using Silica-Polymer-Initiator (SPI) Gels

SciTech Connect

Oglesby, Kenneth

2014-01-31

SPI gels are multi-component silicate based gels for improving (areal and vertical) conformance in oilfield enhanced recovery operations, including water-floods and carbon dioxide (CO{sub 2}) floods, as well as other applications. SPI mixtures are like-water when pumped, but form light up to very thick, paste-like gels in contact with CO{sub 2}. When formed they are 3 to 10 times stronger than any gelled polyacrylamide gel now available, however, they are not as strong as cement or epoxy, allowing them to be washed / jetted out of the wellbore without drilling. This DOE funded project allowed 8 SPI field treatments to be performed in 6 wells (5 injection wells and 1 production well) in 2 different fields with different operators, in 2 different basins (Gulf Coast and Permian) and in 2 different rock types (sandstone and dolomite). Field A was in a central Mississippi sandstone that injected CO{sub 2} as an immiscible process. Field B was in the west Texas San Andres dolomite formation with a mature water-alternating-gas miscible CO{sub 2} flood. Field A treatments are now over 1 year old while Field B treatments have only 4 months data available under variable WAG conditions. Both fields had other operational events and well work occurring before/ during / after the treatments making definitive evaluation difficult. Laboratory static beaker and dynamic sand pack tests were performed with Ottawa sand and both fields’ core material, brines and crude oils to improve SPI chemistry, optimize SPI formulations, ensure SPI mix compatibility with field rocks and fluids, optimize SPI treatment field treatment volumes and methods, and ensure that strong gels set in the reservoir. Field quality control procedures were designed and utilized. Pre-treatment well (surface) injectivities ranged from 0.39 to 7.9 MMCF/psi. The SPI treatment volumes ranged from 20.7 cubic meters (m{sup 3}, 5460 gallons/ 130 bbls) to 691 m{sup 3} (182,658 gallons/ 4349 bbls). Various size and types

12. Interference sources in ATP bioluminescence assay of silica nanoparticle toxicity to activated sludge.

PubMed

Sibag, Mark; Kim, Seung Hwan; Kim, Choah; Kim, Hee Jun; Cho, Jinwoo

2015-06-01

ATP measurement provides an overview of the general state of microbial activity, and thus it has proven useful for the evaluation of nanoparticle toxicity in activated sludge. ATP bioluminescence assay, however, is susceptible to interference by the components of activated sludge other than biomass. This paper presents the interference identified specific to the use of this assay after activated sludge respiration inhibition test of silica nanoparticles (OECD 209). We observed a high degree of interference (90%) in the presence of 100 mg/L silica nanoparticles and a low level of ATP being measured (0.01 μM); and 30% interference by the synthetic medium regardless of silica nanoparticle concentration and ATP level in the samples. ATP measurement in activated sludge with different MLSS concentrations revealed interference of high biomass content. In conclusion, silica nanoparticles, synthetic medium and activated sludge samples themselves interfere with ATP bioluminescence; this will need to be considered in the evaluation of silica nanoparticle toxicity to activated sludge when this type of assay is used. PMID:25892589

13. Interference sources in ATP bioluminescence assay of silica nanoparticle toxicity to activated sludge.

PubMed

Sibag, Mark; Kim, Seung Hwan; Kim, Choah; Kim, Hee Jun; Cho, Jinwoo

2015-06-01

ATP measurement provides an overview of the general state of microbial activity, and thus it has proven useful for the evaluation of nanoparticle toxicity in activated sludge. ATP bioluminescence assay, however, is susceptible to interference by the components of activated sludge other than biomass. This paper presents the interference identified specific to the use of this assay after activated sludge respiration inhibition test of silica nanoparticles (OECD 209). We observed a high degree of interference (90%) in the presence of 100 mg/L silica nanoparticles and a low level of ATP being measured (0.01 μM); and 30% interference by the synthetic medium regardless of silica nanoparticle concentration and ATP level in the samples. ATP measurement in activated sludge with different MLSS concentrations revealed interference of high biomass content. In conclusion, silica nanoparticles, synthetic medium and activated sludge samples themselves interfere with ATP bioluminescence; this will need to be considered in the evaluation of silica nanoparticle toxicity to activated sludge when this type of assay is used.

14. One-pot preparation of silica-supported hybrid immobilized metal affinity adsorbent with macroporous surface based on surface imprinting coating technique combined with polysaccharide incorporated sol--gel process.

PubMed

Li, Feng; Li, Xue-Mei; Zhang, Shu-Sheng

2006-10-01

15. Method for preparing high activity silica supported hydrotreating catalysts

SciTech Connect

Thompson, M.S.

1986-03-04

A method is described for preparing a silica supported hydrotreating catalyst containing from about 10-25%w molybdenum and from about 1-5%w nickel and/or cobalt as hydrogenation metals. The method consists of: (a) reacting a mixture of MoCl/sub 5/ and a compound selected from the group consisting of Ni(H/sub 2/O)/sub 6/Cl/sub 2/, Co(H/sub 2/O)/sub 6/Cl/sub 2/ and mixutres in amounts to provide a desired catalytic metals concentration of the support in the presence of a solubilizing amount of acetonitrile; (b) heating the mixture to between about 25/sup 0/ and 80/sup 0/C until most of the metal compounds have reacted and/or dissolved; (c) removing any undissolved solids from the solution; (d) impregnating the dried silica support with the hydrogenation metals-containing solution in one or more steps; and (e) drying the impregnated silica support at elevated temperature.

16. Novel Sol–Gel Precursors for Thin Mesoporous Eu3+-Doped Silica Coatings as Efficient Luminescent Materials.

PubMed Central

2012-01-01

Europium(III) ions containing mesoporous silica coatings have been prepared via a solvent evaporation-induced self-assembly (EISA) approach of different single-source precursors (SSPs) in the presence of Pluronic P123 as a structure-directing agent, using the spin-coating process. A deliberate tailoring of the chemical composition of the porous coatings with various Si:Eu ratios was achieved by processing mixtures of tetraethylorthosilicate (TEOS) and Eu3+-coordinated SSPs. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses demonstrate that the thin metal oxide-doped silica coatings consist of a porous network with a short-range order of the pore structure, even at high europium(III) loadings. Furthermore, luminescence properties were investigated at different temperatures and different degrees of Eu3+ contents. The photoluminescence spectra clearly show characteristic emission peaks corresponding to the 5D0 → 7FJ (J = 0–5) transitions resulting in a red luminescence visible by the eyes, although the films have a very low thickness (150–200 nm). PMID:23503160

17. Functionalisation of mesoporous silica gel with 2-[(phosphonomethyl)-amino]acetic acid functional groups. Characterisation and application

Caldarola, Dario; Mitev, Dimitar P.; Marlin, Lucile; Nesterenko, Ekaterina P.; Paull, Brett; Onida, Barbara; Bruzzoniti, Maria Concetta; Carlo, Rosa Maria De; Sarzanini, Corrado; Nesterenko, Pavel N.

2014-01-01

A new complexing adsorbent was prepared by chemical modification of mesoporous silica Kieselgel 60 (dp = 37-63 μm, average pore size 6 nm, specific surface area 425 m2 g-1) with 3-glycidoxypropyltrimethoxysilane and 2-[(phosphonomethyl)amino]acetic acid (PMA), commonly known as glyphosate. The prepared adsorbent was fully characterised using elemental analysis, thermal gravimetric analysis (TGA), acid-base potentiometric titration, Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption isotherms at 77 K (BET), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The concentration of bonded PMA groups calculated from the nitrogen content was 0.38 mmol per gram. The adsorption of transition metal ions on PMA functionalised silica (HEPMAS) was studied from aqueous solutions having different pH and the following selectivity was established, Zn(II) < Co(II) < Cd(II) < Mn(II) < Ni(II) < Cu(II). The calculated values of distribution coefficients D for the adsorption of ecotoxic metal ions on HEPMAS are 5.0 × 104, 4.9 × 105 and 2.6 × 104 for Zn(II), Pb(II) and Cd(II), respectively.

18. Biological activity of insulin in GMO gels and the effect of agitation.

PubMed

1999-11-25

Glyceryl monooleate (GMO)-water cubic phase gel was previously shown to protect insulin from agitation induced aggregation. However, it is not known if insulin is biologically active in the gel and what effect agitation has on insulin in the gel. Therefore, the objective was to determine the stability of insulin in cubic phase gel in terms of its biological activity in a suitable animal model such as Sprague-Dawley rats. Effect of agitation on biological activity of insulin in cubic phase GMO gel was determined by subcutaneous injections of the agitated and non-agitated gels to two groups of previously fasted rats and measuring the effect on their blood glucose levels. Two groups of rats administered with agitated insulin solution and normal saline were used as controls. The biological activity of insulin was evaluated by comparing AAC (area above the blood glucose level-time curve, in %-h), C(max) (maximum % decrease in blood glucose levels) and t(max) (time required to attain C(max), in h) values for the four groups of rats. Since cubic phase gel is highly viscous, therapeutic equivalency of insulin in the lamellar phase gel, which converts in situ into cubic phase gel, was compared to insulin solution with normal saline as the control, using AAC, C(max) and t(max) of the blood glucose profile. Insulin was biologically active in both agitated and non-agitated gels; however, upon agitation, insulin in solution totally lost its hypoglycemic activity. Agitation of insulin in the cubic phase gel was seen to have very little deleterious effect on its biological activity. Insulin in the lamellar phase gel was not only biologically active but also therapeutically equivalent to insulin solution based on AAC (327.9+/-100.8 and 431.7+/-113.3), C(max) (57. 1+/-7.0 and 70.2+/-6.5) and t(max) (2.8+/-0.7 and 4.0+/-1.7) for the lamellar phase gel and insulin solution, respectively (no significant difference, P0.05). In summary, GMO cubic phase gel protected insulin from

19. Preparation of phenothiazine bonded silica gel as sorbents of solid phase extraction and their application for determination of nitrobenzene compounds in environmental water by gas chromatography-mass spectrometry.

PubMed

Peng, Xi-Tian; Zhao, Xing; Feng, Yu-Qi

2011-12-30

In this paper, two phenothiazine bonded silica (PTZ-Si) sorbents were prepared and used as sorbents of solid-phase extraction (SPE) for the determination of nitrobenzene compounds in environmental water samples by gas chromatography-mass spectrometry (GC-MS). Different synthesis routes were proposed to obtain high bonded amount of PTZ on the surface of silica gel. PTZ molecule was derived to its amino or acyl chloride derivatives for reacting with isocyanate or amino silane coupling agent, which was further reacted with the surface silanol groups of silica gel to obtain the PTZ-Si sorbents. The resultant PTZ-Si sorbents were characterized by nitrogen sorption porosimetry (NSP), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA) to assure the successful bonding of PTZ on the surface of silica gel. Then the PTZ-Si sorbents were served as SPE sorbents for the enrichment of nitrobenzene compounds. Several parameters affecting the extraction performance were investigated. Under the optimized conditions, the proposed method was applied to the analysis of six nitrobenzene compounds in environmental water samples. Good linearities were obtained for all nitrobenzene compounds with R(2) larger than 0.9958. The limits of detection were found to be in the range of 0.06-0.3 ng/mL. The method recoveries of nitrobenzene compounds spiked in water samples were from 71.4% to 124.3%, with relative standard deviations (RSDs) less than 10.1%. PMID:22129571

20. Fiber optic chemical microsensors employing optically active silica microspheres

Pope, Edward J. A.

1995-05-01

Dye-doped porous silica microspheres can be prepared from liquid solution at temperatures near ambient. Microsphere diameter can be controlled between approximately 5.0 microns to in excess of a millimeter. The resulting microspheres can be attached to the distal end of an optical fiber in which the proximal end is attached to a spectrophotometer. Depending upon the organic species doped into the microsphere, a wide variety of sensing functions are possible. In this paper, the use of microsensors for measuring pH, temperature, and solvent content of aqueous solutions is demonstrated. Potential utility of this type of sensor to heavy metals detection and biomedical diagnostics is also discussed.

1. Sol-gel silica-based nanocomposites containing a high PEG amount: Chemical characterization and study of biological properties

Catauro, Michelina; Bollino, Flavia; Gloria, Antonio

2016-05-01

The objective of the present study was to synthesize and to characterize Silica/polyethylene glycol (SiO2/PEG) organic-inorganic hybrid materials containing a high polymer amount (60 and 70 wt%) for biomedical applications. Scanning electron microscopy (SEM) showed that the samples are homogeneous on the nanometer scale, confirming that they are nanocomposites. Fourier transform infrared spectroscopy (FT-IR) proved that the materials are class I hybrids because the two phases (SiO2 and PEG) interact by hydrogen bonds. To evaluate the possibility of using them in the biomedical field, the bioactivity and biocompatibility of the synthesized hybrids have been ascertained. The formation of a hydroxyapatite layer was observed on the hybrid surface by SEM/EDX and FTIR after soaking in simulated body fluid (SBF). Moreover, their biocompatibility was assessed by performing WST-8 cytotoxicity assay in vitro.

2. Passive and active sol-gel materials and devices

Andrews, Mark P.; Najafi, S. Iraj

1997-07-01

This paper examines sol-gel materials for photonics in terms of partnerships with other material contenders for processing optical devices. The discussion in four sections identifies semiconductors, amorphous and crystalline inorganic dielectrics, and amorphous and crystalline organic dielectrics as strategic agents in the rapidly evolving area of materials and devices for data communications and telecommunications. With Zyss, we trace the hierarchical lineage that connects molecular hybridization (chemical functionality), through supramolecular hybridization (collective properties and responses), to functional hybridization (device and system level constructs). These three concepts thread their way through discussions of the roles sol-gel glasses might be anticipated to assume in a photonics marketplace. We assign a special place to glass integrated optics and show how high temperature consolidated sol-gel derived glasses fit into competitive glass fabrication technologies. Low temperature hybrid sol-gel glasses that combine attractive features of organic polymers and inorganic glasses are considered by drawing on examples of our own new processes for fabricating couplers, power splitters, waveguides and gratings by combining chemical synthesis and sol-gel processing with simple photomask techniques.

3. Elaboration, activity and stability of silica-based nitroaromatic sensors.

PubMed

Mercier, Dimitri; Pereira, Franck; Méthivier, Christophe; Montméat, Pierre; Hairault, Lionel; Pradier, Claire-Marie

2013-08-21

Functionalized silica-based thin films, modified with hydrophobic groups, were synthesized and used as sensors for nitroaromatic compound (NAC) specific detection. Their performance and behavior, in terms of stability, ageing and regeneration, have been fully characterized by combining chemical characterization techniques and electron microscopy. NAC was efficiently and specifically detected using these silica-based sensors, but showed a great degradation in the presence of humidity. Moreover, the sensor sensitivity seriously decreases with storage time. Methyl- and phenyl-functionalization helped to overcome this humidity sensitivity. Surface characterization enabled us to establish a direct correlation between the appearance, and increasing amount, of adsorbed carbonyl-containing species, and sensor efficiency. This contamination, appearing after only one month, was particularly important when sensors were stored in plastic containers. Rinsing with cyclohexane enables us to recover part of the sensor performance but does not yield a complete regeneration of the sensors. This work led us to the definition of optimized elaboration and storage conditions for nitroaromatic sensors. PMID:23812282

4. Sol-gel combustion synthesis, particle shape analysis and magnetic properties of hematite (α-Fe2O3) nanoparticles embedded in an amorphous silica matrix

Kopanja, Lazar; Milosevic, Irena; Panjan, Matjaz; Damnjanovic, Vesna; Tadic, Marin

2016-01-01

We report the synthesis and magnetic properties of hematite/amorphous silica nanostructures. Raman spectroscopy showed the formation of a hematite phase. A transmission electron microscopy (TEM) revealed spherically shaped hematite nanoparticles, well-dispersed in an amorphous silica matrix. In order to quantitatively describe morphological properties of nanoparticles, we use the circularity of shapes as a measure of how circular a shape is. Diameters of about 5 nm and a narrow size distribution of nanoparticles are observed. The obtained hematite nanoparticles exhibit superparamagnetic properties at room temperature (SPION). The sample does not display the Morin transition. The FC hysteresis loop at 5 K has shown an exchange bias effect. These results have been compared to those previously reported for α-Fe2O3/SiO2 nanosystems in the literature. These comparisons reveal that the sol-gel combustion method yields hematite nanoparticles with a higher magnetization and magnetic moment. These data indicate the existence of an additional factor that contributes to magnetization. We suggest that the increased magnetization is due to an increased number of the surface spins caused by the breaking of large numbers of exchange bonds between surface atoms (disordered structure). This leads to an increase in the magnetic moment per a hematite nanoparticle and an exchange bias effect. We have concluded that the combustion-related part of this synthesis method enhances surface effects, i.e. it promotes the breaking of bonds and surface disordered layers, which results in these magnetic properties. Such interesting structural and magnetic properties of hematite might be important in future practical applications and fundamental research.

5. Silica-Based Carbon Source Delivery for In-situ Bioremediation Enhancement

Zhong, L.; Lee, M. H.; Lee, B.; Yang, S.

2015-12-01

Colloidal silica aqueous suspensions undergo viscosity increasing and gelation over time under favorable geochemical conditions. This property of silica suspension can potentially be applied to deliver remedial amendments to the subsurface and establish slow release amendment sources for enhanced remediation. In this study, silica-based delivery of carbon sources for in-situ bioremediation enhancement is investigated. Sodium lactate, vegetable oil, ethanol, and molasses have been studied for the interaction with colloidal silica in aqueous suspensions. The rheological properties of the carbon source amendments and silica suspension have been investigated. The lactate-, ethanol-, and molasses-silica suspensions exhibited controllable viscosity increase and eventually became gels under favorable geochemical conditions. The gelation rate was a function of the concentration of silica, salinity, amendment, and temperature. The vegetable oil-silica suspensions increased viscosity immediately upon mixing, but did not perform gelation. The carbon source release rate from the lactate-, ethanol-, and molasses-silica gels was determined as a function of silica, salinity, amendment concentration. The microbial activity stimulation and in-situ bioremediation enhancement by the slow-released carbon from the amendment-silica gels will be demonstrated in future investigations planned in this study.

6. Simple route to enhanced photocatalytic activity of p25 titanium dioxide nanoparticles by silica addition.

PubMed

Jafry, Huma R; Liga, Michael V; Li, Qilin; Barron, Andrew R

2011-02-15

Silica doped TiO2(P25) nanoparticles are tested for its photocatalytic activity in the degradation of bacteriophage MS2. During our studies it was found that treatment of TiO2(P25) in the glass flasks sealed with silicone grease resulted in a significant improvement in the catalytic activity of the titania. Further improvement can be made by the purposeful reaction of TiO2(P25) with 2.5 wt % silica. This non in situ method of incorporating silica to TiO2(P25) nanoparticles is tested for their role in killing of viruses, and it is found that the rate constant is three times higher to kill viruses with the addition of silica. BET measurements show no significant change/increase in the surface area of silica doped TiO2(P25)-SiO2, compared to the undoped TiO2(P25). Further studies show that the addition of silica increases the adsorption of viruses onto the catalyst. There is a significant difference in the activity of the TiO2(P25)-SiO2 samples in the presence of methanol, supporting the notion that hydroxide radical (HO·) is responsible for the antiviral action. The TiO2(P25)-SiO2 either produces more HO· than non silica-doped material, or the enhanced adsorption of MS2 to the catalyst results in greater exposure to the HO·, or both mechanisms may work in concert. XPS studies suggest the formation of silica species on the surface of the TiO2(P25), while UV-visible spectroscopy suggests that the presence of the silica results in a small increase in the measured band gap. We suggest that the enhanced catalytic activity is a result of increased adsorption and/or band bending which can occur at the interface within TiO2(P25)-SiO2. One result of this would be a reduction of the electron-hole recombination, the formation of a greater concentration of OH·, and hence an improved catalytic performance.

7. Development and characterization of ultra-porous silica films made by the sol-gel method. Application to biosensing

Desfours, Caroline; Calas-Etienne, Sylvie; Horvath, Robert; Martin, Marta; Gergely, Csilla; Cuisinier, Frédéric; Etienne, Pascal

2014-02-01

The aim of this work is to demonstrate the sensing ability of reverse-symmetry waveguides to investigate adsorption of casein and build-up of poly-L-lysine mediated casein multilayers. A first part of this study is dedicated to the elaboration and characterization of ultra-porous thin films with very low refractive indices by an appropriate sol-gel method. This will form the basis of our planar optical sensors. Optical waveguide light mode spectroscopy is a real-time and sensitive method to study protein adsorption kinetics and lipid bilayers. We used it to test the obtained waveguides for in-situ monitoring of biomolecule adsorption. As a result, significant changes in the incoupling peak position were observed during the layer-by-layer adsorption. Finally, refractive index and thickness of the adsorbed layers were established.

8. Sensitive detection of influenza viruses with Europium nanoparticles on an epoxy silica sol-gel functionalized polycarbonate-polydimethylsiloxane hybrid microchip.

PubMed

Liu, Jikun; Zhao, Jiangqin; Petrochenko, Peter; Zheng, Jiwen; Hewlett, Indira

2016-12-15

In an effort to develop new tools for diagnosing influenza in resource-limited settings, we fabricated a polycarbonate (PC)-polydimethylsiloxane (PDMS) hybrid microchip using a simple epoxy silica sol-gel coating/bonding method and employed it in sensitive detection of influenza virus with Europium nanoparticles (EuNPs). The incorporation of sol-gel material in device fabrication provided functionalized channel surfaces ready for covalent immobilization of primary antibodies and a strong bonding between PDMS substrates and PC supports without increasing background fluorescence. In microchip EuNP immunoassay (µENIA) of inactivated influenza viruses, replacing native PDMS microchips with hybrid microchips allowed the achievement of a 6-fold increase in signal-to-background ratio, a 12-fold and a 6-fold decreases in limit-of-detection (LOD) in influenza A and B tests respectively. Using influenza A samples with known titers, the LOD of influenza µENIA on hybrid microchips was determined to be ~10(4) TCID50 titer/mL and 10(3)-10(4) EID50 titer/mL. A comparison test indicated that the sensitivity of influenza µENIA enhanced using the hybrid microchips even surpassed that of a commercial laboratory influenza ELISA test. In addition to the sensitivity improvement, assay variation was clearly reduced when hybrid microchips instead of native PDMS microchips were used in the µENIA tests. Finally, infectious reference viruses and nasopharyngeal swab patient specimens were successfully tested using μENIA on hybrid microchip platforms, demonstrating the potential of this unique microchip nanoparticle assay in clinical diagnosis of influenza. Meanwhile, the tests showed the necessity of using nucleic acid confirmatory tests to clarify ambiguous test results obtained from prototype or developed point-of-care testing devices for influenza diagnosis.

9. Sensitive detection of influenza viruses with Europium nanoparticles on an epoxy silica sol-gel functionalized polycarbonate-polydimethylsiloxane hybrid microchip.

PubMed

Liu, Jikun; Zhao, Jiangqin; Petrochenko, Peter; Zheng, Jiwen; Hewlett, Indira

2016-12-15

In an effort to develop new tools for diagnosing influenza in resource-limited settings, we fabricated a polycarbonate (PC)-polydimethylsiloxane (PDMS) hybrid microchip using a simple epoxy silica sol-gel coating/bonding method and employed it in sensitive detection of influenza virus with Europium nanoparticles (EuNPs). The incorporation of sol-gel material in device fabrication provided functionalized channel surfaces ready for covalent immobilization of primary antibodies and a strong bonding between PDMS substrates and PC supports without increasing background fluorescence. In microchip EuNP immunoassay (µENIA) of inactivated influenza viruses, replacing native PDMS microchips with hybrid microchips allowed the achievement of a 6-fold increase in signal-to-background ratio, a 12-fold and a 6-fold decreases in limit-of-detection (LOD) in influenza A and B tests respectively. Using influenza A samples with known titers, the LOD of influenza µENIA on hybrid microchips was determined to be ~10(4) TCID50 titer/mL and 10(3)-10(4) EID50 titer/mL. A comparison test indicated that the sensitivity of influenza µENIA enhanced using the hybrid microchips even surpassed that of a commercial laboratory influenza ELISA test. In addition to the sensitivity improvement, assay variation was clearly reduced when hybrid microchips instead of native PDMS microchips were used in the µENIA tests. Finally, infectious reference viruses and nasopharyngeal swab patient specimens were successfully tested using μENIA on hybrid microchip platforms, demonstrating the potential of this unique microchip nanoparticle assay in clinical diagnosis of influenza. Meanwhile, the tests showed the necessity of using nucleic acid confirmatory tests to clarify ambiguous test results obtained from prototype or developed point-of-care testing devices for influenza diagnosis. PMID:27362253

10. Study on CM-chitosan/activated carbon hybrid gel films formed with EB irradiation

Zhao, Long; Luo, Fang; Zhai, Maolin; Mitomo, Hiroshi; Yoshii, Fumio

2008-05-01

A series of novel hybrid gel films were prepared from carboxymethylated chitosan (CM-chitosan) and activated carbon (AC) by irradiation of compression-molded CM-chitosan/AC mixture in physical gel state with electron beam (EB) at room temperature. The formation, properties and structure of CM-chitosan/AC hybrid gel films were discussed in terms of gel fraction, swelling, mechanical property, SEM image and XPS spectra. Compared with pure crosslinked CM-chitosan gel, the gel fraction and mechanical property of the hybrid sample were obviously improved after adding AC into CM-chitosan film. The morphology analyses indicated that the hybrid gel films exhibited a rough and folded surface and a relatively interior uniform structure was sustained between CM-chitosan and AC. XPS revealed that the content of protonated amino groups of CM-chitosan macromolecule was promoted by AC. In addition, the adsorptive property of the gel films against humic acid was investigated by batch adsorption method. It was found that the adsorption efficiency of CM-chitosan is significantly improved by adding AC. These preliminary evaluations suggest that the CM-chitosan/AC gel films have great potential for applications in industrial field and biomedical field.

11. Synthesis of organic/inorganic hybrid gel with acid activated clay after γ-ray radiation.

PubMed

Kim, Donghyun; Lee, Hoik; Sohn, Daewon

2014-08-01

A hybrid gel was prepared from acid activated clay (AA clay) and acrylic acid by gamma ray irradiation. Irradiated inorganic particles which have peroxide groups act as initiator because it generates oxide radicals by increasing temperature. Inorganic nanoparticles which are rigid part in hybrid gel also contribute to increase the mechanical property as a crosslinker. We prepared two hybrid gels to compare the effect of acid activated treatment of clay; one is synthesized with raw clay particles and another is synthesized with AA clay particles. The composition and structure of AA clay particles and raw clay particles were confirmed by X-ray diffraction (XRD), X-ray fluorescence instrument and surface area analyzer. And chemical and physical property of hybrid gel with different ratios of acrylic acid and clay particle was tested by Raman spectroscope and universal testing machine (UTM). The synthesized hydrogel with 76% gel contents can elongated approximately 1000% of its original size.

12. Switching on the Metathesis Activity of Re Oxo Alkylidene Surface Sites through a Tailor-Made Silica-Alumina Support.

PubMed

Valla, Maxence; Stadler, David; Mougel, Victor; Copéret, Christophe

2016-01-18

Re oxo alkylidene surface species are putative active sites in classical heterogeneous Re-based alkene-metathesis catalysts. However, the lack of evidence for such species questions their existence and/or relevance as reaction intermediates. Using Re(O)(=CH-CH=CPh2)(OtBuF6)3(THF), the corresponding well-defined Re oxo alkylidene surface species can be generated on both silica and silica-alumina supports. While inactive on the silica support, it displays very good activity, even for functionalized olefins, on the silica-alumina support. PMID:26756446

13. Comparison of analgesic and anti-inflammatory activity of meloxicam gel with diclofenac and piroxicam gels in animal models: pharmacokinetic parameters after topical application.

PubMed

Gupta, S K; Bansal, P; Bhardwaj, R K; Jaiswal, J; Velpandian, T

2002-01-01

Meloxicam, a non-steroidal anti-inflammatory drug, is a preferential inhibitor of cyclooxygenase-2 and has demonstrated potent analgesic and anti-inflammatory activity after oral administration. The present work was carried out to elucidate the anti-inflammatory and analgesic activity of a newer topical gel formulation of meloxicam (1% w/w gel) and compare it with 0.5% w/w piroxicam and 1% w/w diclofenac gels in experimental animal models. The study was also extended to determine the pharmacokinetic profile of a newer formulation of meloxicam gel after topical application on depilated skin of rats. The anti-inflammatory activities of meloxicam, piroxicam and diclofenac gels were compared using carrageenan-induced acute paw oedema and complete Freund's adjuvant-induced chronic paw oedema in rats. Meloxicam gel showed increased protection against inflammation as compared to piroxicam and diclofenac gels. Acetic acid-induced writhing and formalin-induced phase I and phase II pain models were used to compare their analgesic activity. Meloxicam gel showed significant protection in formalin-induced phase II pain whereas its analgesic activity was less as compared to diclofenac and piroxicam gels in writhing test and formalin-induced phase I pain. The pharmacokinetic studies showed peak plasma drug concentration (C(max)) of 48.48 +/- 6.57 microg/ml at 2 h (T(max)) after topical application of 500 mg of meloxicam gel formulation. The area under the curve as calculated from 0 to 6 h was found to be 114.18 +/- 4.23 and 194.13 +/- 3.78 microg x h/ml for 0 to infinity. The results indicate that topical preparation of meloxicam could be an effective alternative to diclofenac and piroxicam gels in inflammatory conditions and its associated pain with the possibility of less systemic side-effects.

14. Isolation of two new prenylated flavonoids from Sinopodophyllum emodi fruit by silica gel column and high-speed counter-current chromatography.

PubMed

Sun, Yanjun; Sun, Yinshi; Chen, Hui; Hao, Zhiyou; Wang, Junmin; Guan, Yanbin; Zhang, Yanli; Feng, Weisheng; Zheng, Xiaoke

2014-10-15

Two new prenylated flavonoids, sinoflavonoids A-B, were isolated from the dried fruits of Sinopodophyllum emodi by silica gel column chromatography (SGCC) and high-speed counter-current chromatography (HSCCC). The 95% ethanol extract was partitioned with petroleum ether, dichloromethane, ethyl acetate, and n-butanol in water, respectively. The ethyl acetate fraction was pre-separated by SGCC with a petroleum ether-acetone gradient. The eluates containing target compounds were further separated by HSCCC with n-hexane-ethyl acetate-methanol-water (4:6:4:4, v/v). Finally, 17.3mg of sinoflavonoid A and 25.9mg of sinoflavonoid B were obtained from 100mg of the pretreated concentrate. The purities of sinoflavonoid A and sinoflavonoid B were 98.47% and 99.38%, respectively, as determined by HPLC. Their structures were elucidated on the basis of spectroscopic evidences (HR-ESI-MS, (1)H-NMR, (13)C-NMR, HSQC, HMBC). The separation procedures proved to be efficient, especially for trace prenylated flavonoids.

15. Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler

Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y.; Huo, Fengwei

2015-11-01

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

16. Extrathermodynamic interpretation of retention equilibria in reversed-phase liquid chromatography using octadecylsilyl-silica gels bonded to C1 and C18 ligands of different densities.

PubMed

Miyabe, Kanji; Guiochon, Georges

2005-12-16

The retention behavior on silica gels bonded to C18 and C1 alkyl ligands of different densities was studied in reversed-phase liquid chromatography (RPLC) from the viewpoints of two extrathermodynamic relationships, enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, the four tests proposed by Krug et al. were applied to the values of the retention equilibrium constants (K) normalized by the alkyl ligand density. These tests showed that a real EEC of the retention equilibrium originates from substantial physico-chemical effects. Second, we derived a new model based on the EEC to explain the LFER between the retention equilibria under different RPLC conditions. The new model indicates how the slope and intercept of the LFER are correlated to the compensation temperatures derived from the EEC analyses and to several parameters characterizing the molecular contributions to the changes in enthalpy and entropy. Finally, we calculated K under various RPLC conditions from only one original experimental K datum by assuming that the contributions of the C18 and C1 ligands to K are additive and that their contributions are proportional to the density of each ligand. The estimated K values are in agreement with the corresponding experimental data, demonstrating that our model is useful to explain the variations of K due to changes in the RPLC conditions.

17. Solid phase extraction of gold(III) on silica gel modified with benzoylthiourea prior to its determination by flame atomic absorption spectrometry.

PubMed

Bozkurt, Serap Seyhan; Merdivan, Melek

2009-11-01

A new method has been developed for the determination of gold based on separation and preconcentration using silica gel modified with benzoylthiourea. The optimum experimental parameters for preconcentration of gold, such as acid concentration, sample flow rate, eluent and matrix ions, have been investigated. Gold could be quantitatively retained in the 0.25-2.0 mol L(-1) HCl and HNO(3) concentrations, and then eluted completely with 0.5 mol L(-1) thiourea in 1.0 mol L(-1) HCl. The sorption capacity of gold(III) is 0.92 +/- 0.04 mmol g(-1) with a high enrichment factor of 267. The relative standard deviation of the method, RSD%, was found as 1.2% for 0.1 microg mL(-1). The detection limit for gold was 1.4 microg L(-1). The validation of the proposed method was checked by the analysis of certified reference soil materials. The presented procedure was applied to the determination of gold in some environmental samples.

18. Simultaneous Determination of Se and Te in Ores by HG-AFS After Online Preconcentration with Nano-TiO2 Immobilized on Silica Gel.

PubMed

Zhou, Jing-rong; Deng, Dong-yan; Huang, Ke; Tian, Yun-fei; Hou, Xian-deng

2015-09-01

A simple, sensitive and interference-free method was established for simultaneous determination of trace selenium and tellurium in ore samples by HG-AFS, by using nano-TiO2 immobilized on a silica gel packed microcolumn for online preconcentration. Selenium and tellurium were selectively adsorbed to the microcolumn in acidic condition and then completely eluted with 2% (m/v) NaOH solution. The experimental conditions for hydride generation, adsorption, elution and potential interference were investigated in detail. Under the optimum conditions, the detection limits of selenium and tellurium by the proposed method with 180 s sampling time were 4.0 and 3.6 ng · L(-1), with sensitivity enhancement of 20- and 13-fold compared to conventional hydride generation method, respectively. The relative standard deviation (RSD, n=5) of this method for 1 μg · L(-1) Se(IV) and Te(IV) were 0.7% and 2.3%, respectively. This method was applied to determination of selenium and tellurium in several ore samples. PMID:26669138

19. A comparison study of carbon dioxide adsorption on polydimethylsiloxane, silica gel, and Illinois No. 6 coal using in situ infrared spectroscopy

SciTech Connect

A.L. Goodman

2009-01-15

Adsorption of supercritical carbon dioxide (CO{sub 2}) on polydimethylsiloxane (PDMS), silica gel (SiO{sub 2}), and Illinois No. 6 coal was compared using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy at pressures up to 14 MPa and temperatures at 40{sup o}C and 50{sup o}C. Only physical adsorption of CO{sub 2} was recorded for PDMS, SiO{sub 2}, and Illinois no. 6. There was no evidence of the formation of carbonic acid, bicarbonates, carbonates, or any other reaction product between CO{sub 2} and PDMS, SiO{sub 2}, and Illinois No. 6 coal. Carbon dioxide adsorption on PDMS and SiO{sub 2} produced a linear isotherm while a typical Langmuir-like isotherm was observed for Illinois No. 6 coal. Attempts to measure CO{sub 2} induced swelling of the three materials was unsuccessful due to the design of the ATR-FTIR cell. 51 refs., 7 figs., 1 tab.

20. Effect of complexing ligands on the adsorption of Cu(II) onto the silica gel surface. 2: Adsorption of Cu(II)-ligand complexes

SciTech Connect

Park, Y.J.; Jung, K.H.; Park, K.K.

1995-06-15

The effect of complexing ligands on the adsorption of Cu(II) onto silica gel was investigated in aqueous solution. The adsorption was conspicuously enhanced by 2,2{prime},6{prime},2{double_prime}-terpyridine, 2-pyridine methanol and 2-aminomethyl pyridine, as compared to non-complexed Cu{sup 2+} ions. This enhancement was attributed to both hydrophobic interaction in the low pH region and the formation of ternary surface complexes in the high pH region. It was attenuated by picolinic acid, salicylic acid, and 5-sulfosalicylic acid due to the competition of dissolved ligands and silanol groups with Cu{sup 2+} ions. In the presence of pyridine or 3,4-lutidine, the adsorption was slightly increased, as compared to non-complexed Cu{sup 2+} ions. In both cases, the adsorption at low pH was interpreted in terms of the type B ternary surface complex formation. For 2-pyridine methanol, the formation of cyclic ternary surface complexes was proposed. The Stern model was adopted for the treatment of the adsorption data in the present study.

1. Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler.

PubMed

Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y; Huo, Fengwei

2015-11-23

The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

2. Evaluation of silica gel cartridges coated in situ with acidified 2,4-dinitrophenylhydrazine for sampling aldehydes and ketones in air.

PubMed

1986-01-01

A procedure for coating in situ silica gel in prepacked cartridges with 2,4-dinitrophenylhydrazine (DNPH) acidified with hydrochloric acid is described. The coated cartridge was compared with a validated DNPH impinger method for sampling organic carbonyl compounds (aldehydes and ketones) in diluted automotive exhaust emissions and in ambient air for subsequent analysis of the DNPH derivatives by high performance liquid chromatography. Qualitative and quantitative data are presented that show that the two sampling devices are equivalent. The coated cartridge is ideal for long-term sampling of carbonyls at sub to low parts-per-billion level in ambient air or for short-term sampling of carbonyls at low ppb to parts-per-million level in diluted automotive exhaust emissions. An unknown degradation product of acrolein has been tentatively identified as x-acrolein. The disappearance of acrolein in the analytical sample matrix correlates quantitatively almost on a mole for mole basis with the growth of x-acrolein. The sum of the concentration of acrolein and x-acrolein appears to be invariant with time. PMID:3019907

3. Silver clusters onto nanosized colloidal silica as novel surface-enhanced Raman scattering active substrates.

PubMed

Muniz-Miranda, Maurizio

2003-06-01

A new method is proposed for obtaining surface-enhanced Raman scattering (SERS)-active substrates by photochemical reduction of silver nitrate onto colloidal silica. Transmission electron microscopy (TEM) and UV-visible absorption spectroscopy are employed to investigate the nanoscale structure of the materials. High quality SERS spectra are obtained from different organic ligands to check the efficiency of these substrates. A marked stability of the colloidal suspension is ensured by the scarce tendency of the Ag-doped silica particles to aggregate by either aging or adsorption of ligand.

4. RADIOLOGICAL RELEASES DUE TO AIR AND SILICA DUST ACTIVATION IN EMPLACEMENT DRIFTS

SciTech Connect

J.S. Tang

2003-05-07

The purpose of this calculation is to determine the quantity and significance of annual Monitored Geologic Repository (MGR) subsurface normal radiological releases due to neutron activation of air and silica dust in emplacement drifts. This calculation includes the following items: (1) Calculate activation of ventilation airflow through emplacement drifts to quantify radioactive gaseous releases; and (2) Calculate the bounding potential activated silica dust concentration and releases. The sources of silica dust may arise from air supply to emplacement drifts as well as host rock around emplacement drifts. For this calculation, the source of dust is conservatively assumed to be the host rock (Assumption 3.6), which is subject to long-term neutron exposure resulting in saturated radioactivity. The scope of this calculation is limited to releases from activated air and silica dust only, excluding natural radioactive releases such as radon or releases from defective waste packages (breached or contaminated). This work supports the repository ventilation system design and Preclosure Safety Analysis. This includes MGR items classified as Quality Level 1, for example, the Uncanistered Spent Nuclear Fuel Waste Package (CRWMS M&O [Civilian Radioactive Waste Management and Operation Contractor] 1999a, page 7). Therefore, this calculation is subject to the requirements of the ''Quality Assurance Requirements and Description'' (DOE [U.S. Department of Energy] 2003). The performance of the calculation and development of this document are carried out in accordance with AP-3.12Q, ''Design Calculation and Analyses'' and LP-3.30Q-BSC, ''Hazards Analysis System''.

5. Shape control of mesoporous silica nanomaterials templated with dual cationic surfactants and their antibacterial activities.

PubMed

Hao, Nanjing; Chen, Xuan; Jayawardana, Kalana W; Wu, Bin; Sundhoro, Madanodaya; Yan, Mingdi

2016-01-01

Mesoporous silica nanomaterials of different shapes (film, platelet, sphere, rod) were synthesized simply by tuning the mole ratio of dual cationic surfactant templates, cetyltrimethylammonium bromide (CTAB) and tetrabutylammonium iodine (TBAI). The film showed the most potent antibacterial activity against mycobacteria. PMID:26364920

6. Shape Control of Mesoporous Silica Nanomaterials Templated with Dual Cationic Surfactants and Their Antibacterial Activities

PubMed Central

Hao, Nanjing; Chen, Xuan; Jayawardana, Kalana W.; Wu, Bin; Sundhoro, Madanodaya; Yan, Mingdi

2015-01-01

Mesoporous silica nanomaterials of different shapes (film, platelet, sphere, rod) were synthesized simply by tuning the mole ratio of dual cationic surfactant templates, cetyltrimethylammonium bromide (CTAB) and tetrabutylammonium iodine (TBAI). The film showed the most potent antibacterial activities against mycobacteria. PMID:26364920

7. Solid-phase extraction method for preconcentration of trace amounts of some metal ions in environmental samples using silica gel modified by 2,4,6-trimorpholino-1,3,5-triazin.

PubMed

2008-12-30

A method was proposed for the preconcentration of some transition elements at trace levels using a column packed with silica gel modified by a synthetic ligand. Metal ions were adsorbed on 2,4,6-trimorpholino-1,3,5-triazin modified silica gel, then analytes retained on the adsorbent were eluted by 1molL(-1) hydrochloric acid and determined by flame atomic absorption spectrometry (FAAS). The influences of some experimental parameters including pH of the sample solution, weight of adsorbent, type, concentration and volume of eluent, flow rates of the sample solution and eluent, and sample volume on the preconcentration efficiency have been investigated. The influences of some matrix elements were also examined. The method also was used for simultaneous preconcentration of these elements and the method was successfully applied to the preconcentration and determination of them. The detection limits of the method for Ni2+, Co2+, Cd2+ and Zn2+were 0.29, 0.20, 0.23 and, 0.30ngmL(-1), respectively. The application of this modified silica gel to preconcentration of investigated cation from tap water, lake water, urine and apple leaves gave high accuracy and precision (relative standard deviation (R.S.D.) <3%). PMID:18420343

8. Kraft lignin/silica-AgNPs as a functional material with antibacterial activity.

PubMed

Klapiszewski, Łukasz; Rzemieniecki, Tomasz; Krawczyk, Magdalena; Malina, Dagmara; Norman, Małgorzata; Zdarta, Jakub; Majchrzak, Izabela; Dobrowolska, Anna; Czaczyk, Katarzyna; Jesionowski, Teofil

2015-10-01

Advanced functional silica/lignin hybrid materials, modified with nanosilver, were obtained. The commercial silica Syloid 244 was used, modified with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to increase its chemical affinity to lignin. Similarly, kraft lignin was oxidized using a solution of sodium periodate to activate appropriate functional groups on its surface. Silver nanoparticles were grafted onto the resulting silica/lignin hybrids. The systems obtained were comprehensively tested using available techniques and methods, including transmission electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, elemental analysis and atomic absorption spectroscopy. An evaluation was also made of the electrokinetic stability of the systems with and without silver nanoparticles. Conclusions were drawn concerning the chemical nature of the bonds between the precursors and the effectiveness of the method of binding nanosilver to the hybrid materials. The antimicrobial activity of the studied materials was tested against five species of Gram-positive and Gram-negative bacteria. The addition of silver nanoparticles to the silica/lignin hybrids led to inhibition of the growth of the analyzed bacteria. The best results were obtained against Pseudomonas aeruginosa, a dangerous human pathogen.

9. Detection of protein kinase activity by renaturation in sodium dodecyl sulfate-polyacrylamide gels

SciTech Connect

Anostario, M. Jr.; Harrison, M.L.; Geahlen, R.L.

1986-05-01

The authors have developed a procedure for identifying protein kinase activity in protein samples following electrophoresis on SDS-polyacrylamide gels. Proteins are allowed to renature directly in the gel by removal of detergent. The gel is then incubated with (..gamma..-/sup 32/P)ATP to allow renatured protein kinases to autophosphorylate or to phosphorylate various substrates which can be incorporated into the gel. The positions of the radiolabeled proteins can then be detected by autoradiography. With this technique, using purified catalytic subunit of cAMP-dependent protein kinase, enzyme concentrations as low as 0.01 ..mu..g can be detected on gels containing 1.0 mg/ml casein. The procedure is also applicable for the determination of active subunits of multisubunit protein kinases. For example, when the two subunits of casein kinase II are separated by SDS-polyacrylamide gel electrophoresis and allowed to renature, only the larger ..cap alpha.. subunit shows activity. This procedure can also be used to detect and distinguish kinases present in heterogeneous mixtures. Starting with a particulate fraction from LSTRA, a murine T cell lymphoma, several distinct enzymes were detected, including a 30,000 Dalton protein with protein-tyrosine kinase activity. This same enzyme has also been detected in T lymphocytes and other T lymphoid cell lines.

10. A slow-release system of bacterial cellulose gel and nanoparticles for hydrophobic active ingredients.

PubMed

Numata, Yukari; Mazzarino, Leticia; Borsali, Redouane

2015-01-01

A combination of bacterial cellulose (BC) gel and amphiphilic block copolymer nanoparticles was investigated as a drug delivery system (DDS) for hydrophobic active ingredients. Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) and retinol were used as the block copolymer and hydrophobic active ingredient, respectively. The BC gel was capable of incorporating copolymer nanoparticles and releasing them in an acetic acid-sodium acetate buffer solution (pH 5.2) at 37 °C. The percentage of released copolymer reached a maximum value of approximately 60% after 6h and remained constant after 24h. The percentage of retinol released from the copolymer-containing BC gel reached a maximum value at 4h. These results show that the combination of BC gel and nanoparticles is a slow-release system that may be useful in the cosmetic and biomedical fields for skin treatment and preparation. PMID:25840273

11. A slow-release system of bacterial cellulose gel and nanoparticles for hydrophobic active ingredients.

PubMed

Numata, Yukari; Mazzarino, Leticia; Borsali, Redouane

2015-01-01

A combination of bacterial cellulose (BC) gel and amphiphilic block copolymer nanoparticles was investigated as a drug delivery system (DDS) for hydrophobic active ingredients. Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) and retinol were used as the block copolymer and hydrophobic active ingredient, respectively. The BC gel was capable of incorporating copolymer nanoparticles and releasing them in an acetic acid-sodium acetate buffer solution (pH 5.2) at 37 °C. The percentage of released copolymer reached a maximum value of approximately 60% after 6h and remained constant after 24h. The percentage of retinol released from the copolymer-containing BC gel reached a maximum value at 4h. These results show that the combination of BC gel and nanoparticles is a slow-release system that may be useful in the cosmetic and biomedical fields for skin treatment and preparation.

12. Solid phase extraction of lead (II), copper (II), cadmium (II) and nickel (II) using gallic acid-modified silica gel prior to determination by flame atomic absorption spectrometry.

PubMed

Xie, Fazhi; Lin, Xucong; Wu, Xiaoping; Xie, Zenghong

2008-01-15

The immobilization of gallic acid on the surface of amino group-containing silica gel phases for the formation of a newly chelating matrix (GASG) is described. The newly synthesized extractant, characterized by the diffuse reflectance infrared Fourier transformation spectroscopy and elemental analysis, was used to preconcentrate Pb(II), Cu(II), Cd(II) and Ni(II). The pH ranges for quantitative sorption and the concentrations of HCl for eluting Pb(II), Cd(II), Cu(II) and Ni(II) were opimized, respectively. The sorption capacity of the matrix has been found to be 12.63, 6.09, 15.38, 4.62mg/g for Pb(II), Cd(II), Cu(II) and Ni(II), respectively, with the preconcentration factor of approximately 200 ( approximately 100 for Cd(II)). The effects of flow rates, the eluants, the electrolytes and cations on the metal ions extraction, as well as the chelating matrix stability and reusability, were also studied. The extraction behavior of the matrix was conformed with Langmuir's equation. The present preconcentration and determination method was successfully applied to the analysis of synthetic metal mixture solution and river water samples. The 3sigma detection limit and 10sigma quantification limit for Pb(II), Cu(II), Cd(II) and Ni(II) were found to be 0.58, 0.86, 0.65, 0.92microg/L and 1.08, 1.23, 0.87, 1.26microg/L, respectively. PMID:18371717

13. An ion-imprinted amino-functionalized silica gel sorbent prepared by hydrothermal assisted surface imprinting technique for selective removal of cadmium (II) from aqueous solution

Fan, Hong-Tao; Li, Jing; Li, Zhan-Chao; Sun, Ting

2012-02-01

A new ion-imprinted amino-functionalized silica gel sorbent was synthesized by the hydrothermal-assisted surface imprinting technique using Cd2+ as the template, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AAAPTS) as the functional monomer, and epichlorohydrin as the cross-linking agent (IIP-AAAPTS/SiO2) for the selective removal of Cd2+ from aqueous solution, and was characterized by FTIR, SEM, nitrogen adsorption and the static adsorption-desorption experiment method. The specific surface area of the IIP-AAAPTS/SiO2 sorbents was found to be 149 m2 g-1. The results showed that the maximum static adsorption capacities of IIP-AAAPTS/SiO2 sorbents by hydrothermal heating method and by the conventional heating method were 57.4 and 31.6 mg g-1, respectively. The IIP-AAAPTS/SiO2 sorbents offered a fast kinetics for the adsorption and desorption of Cd(II). The relative selectivity coefficients of IIP-AAAPTS/SiO2 sorbents for Cd2+/Co2+, Cd2+/Ni2+, Cd2+/Zn2+, Cd2+/Pb2+ and Cd2+/Cu2+ were 30.68, 14.02, 3.00, 3.12 and 6.17, respectively. IIP-AAAPTS/SiO2 sorbents had a substantial binding capacity in the range of pH 4-8 and could be used repeatedly. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. Kinetic studies indicated that adsorption followed a pseudo-second-order model. Negative values of ΔG° indicated spontaneous adsorption and the degree of spontaneity of the reaction increased with increasing temperature. ΔH° of 26.13 kJ mol-1 due to the adsorption of Cd2+ on the IIP-AAAPTS/SiO2 sorbents indicated that the adsorption was endothermic in the experimental temperature range.

14. Structural and optical properties of silver-doped zirconia and mixed zirconia-silica matrices obtained by sol-gel processing

SciTech Connect

Gonella, F.; Mattei, G.; Mazzoldi, P.; Battaglin, G.; Quaranta, A.; De, G.; Montecchi, M.

1999-03-01

The annealing behavior of zirconia and mixed zirconia-silica matrices (with different ZrO{sub 2}/SiO{sub 2} molar ratios) containing silver nanoclusters, synthesized by the sol-gel technique has been investigated. The film samples of the general formula (SiO{sub 2}){sub x}(ZrO{sub 2}){sub (0.9{minus}x)}Ag{sub 0.1} (x = 0, 0.225, 0.45, 0.675, and 0.9) were treated in different atmospheres (air, N{sub 2}, and 5%H{sub 2}-95%N{sub 2}) at temperatures ranging from 200--900 C. The ZrO{sub 2} matrix undergoes a structural phase transition from amorphous to cubic-tetragonal polycrystalline between 400 and 500 C and on further raising the temperature near 600--700 C the monoclinic phase also develops. On the contrary, the ZrO{sub 2}:SiO{sub 2} system remains amorphous up to {approximately}700 C. Ag nanoclusters are formed in all the systems. It has been observed that the change in the ZrO{sub 2}/SiO{sub 2} molar ratio is an effective way to control not only the overall refractive index of the matrix but also the Ag cluster size. The shifting of the surface plasma resonance position of Ag nanoclusters is observed as a function of the refractive indices of the matrix following the Mie theory. Samples were characterized by transmission electron microscopy, Rutherford backscattering spectrometry, and optical spectrometry to correlate the cluster structure to their optical properties.

15. Interactions of silica surfaces

SciTech Connect

Vigil, G.; Xu, Z.; Steinberg, S.; Israelachvili, J. . Dept. of Chemical and Nuclear Engineering and Materials Dept.)

1994-07-01

Adhesion, friction, and colloidal forces in air and aqueous salt solutions have been measured between various silica surfaces prepared by depositing amorphous but highly smooth silica films on mica. The results show four interesting and interrelated phenomena: (i) the adhesion of silica surfaces in air increases slowly with contact time, especially in humid air where the contacting surfaces become separated by an [approximately]20-[angstrom]-thick layer of hydrated silica or silica gel; (ii) the friction of two silica surfaces exhibits large sticking or stiction spikes, whose magnitude increases in the presence of water and when the surfaces are kept in contact longer before sliding; (iii) the non-DLVO repulsion commonly seen at short range (<40 A) between silica surfaces immersed in aqueous solutions is monotonically repulsive, with no oscillatory component, and is quite unlike theoretical expectations and previous measurements of forces due to solvent structure; (iv) dynamic contact angle measurements reveal time-dependent effects which cannot be due to a fixed surface chemical heterogeneity or roughness. The results indicate that silica surfaces undergo slow structural and chemical changes during interactions with water and with each other. More specifically, the authors propose that the unusual interfacial and colloidal properties of silica are due, not to hydration effects, but to the presence of an [approximately]10-[angstrom]-thick gel-like layer of protruding silanol and silicilic acid groups that grow on the surfaces in the presence of water. These protruding groups react chemically (sinter) with similar groups located on an opposing surface and give rise to the unusual time-dependent adhesion, friction, and non-DLVO forces observed. The proposed mechanism in terms of a surface layer of silica gel is consistent with the known surface chemistry of silica and accounts for the results reported and for other unusual surface and colloidal properties of silica.

16. Assessment of Anti HSV-1 Activity of Aloe Vera Gel Extract: an In Vitro Study

PubMed Central

2016-01-01

Statement of the Problem Herpes simplex virus (HSV) infection is one of the most common and debilitating oral diseases; yet, there is no standard topical treatment to control it. The extract of Aloe vera leaves has been previously reported to have anti-inflammatory, antibacterial, and also antiviral effects. There is no data on anti-Herpes simplex virus type 1 (HSV-1) activity of Aloe vera gel. Purpose This study aimed to evaluate the anti-HSV-1 activity of Aloe vera gel in Vero cell line. Materials and Method In this study, gel extraction and cytotoxicity of various increasing concentrations of Aloe vera gel (0.2, 0.5, 1, 2, and 5%) was evaluated in Dulbecco’s Modified Eagle Medium (DMEM) containing 2% fetal bovine serum (FBS). Having been washed with phosphate buffered saline, 50 plaque-forming units (PFU) of HSV-1 was added to each well. After 1 hour of incubation at 37°C, cell monolayers in 24 well plates were exposed to different increasing concentrations of Aloe vera gel. The anti-HSV-1 activity of Aloe vera gel in different concentrations was assessed by plaque reduction assays. Data were analyzed by using One-way ANOVA. Results The cytotoxicity assay showed that Aloe vera in prearranged concentrations was cell-compatible. The inhibitory effect of various concentrations of Aloe vera was observed one hour after the Vero cell was infected with HSV-1. However, there was no significant difference between two serial concentrations (p> 0.05). One-way ANOVA also revealed no significant difference between the groups. The findings indicated a dose-dependent antiviral effect of Aloe vera. Conclusion The findings showed significant inhibitory effect of 0.2-5% Aloe vera gel on HSV-1 growth in Vero cell line. Therefore, this gel could be a useful topical treatment for oral HSV-1 infections without any significant toxicity. PMID:26966709

17. "JCE" Classroom Activity Connections: NaCl or CaCl[subscript 2], Smart Polymer Gel Tells More

ERIC Educational Resources Information Center

Chen, Yueh-Huey; Lin, Jia-Ying; Wang, Yu-Chen; Yaung, Jing-Fun

2010-01-01

This classroom activity connection demonstrates the differences between the effects of NaCl (a salt of monovalent metal ions) and CaCl[subscript 2] (a salt of polyvalent metal ions) on swollen superabsorbent polymer gels. Being ionic compounds, NaCl and CaCl[subscript 2] both collapse the swollen polymer gels. The gel contracted by NaCl reswells…

18. Inhibitory activity of Aloe vera gel on some clinically isolated cariogenic and periodontopathic bacteria.

PubMed

2012-03-01

Aloe vera is a medicinal plant with anti-inflammatory, antimicrobial, antidiabetic and immune-boosting properties. In the present study we investigated the inhibitory activities of Aloe vera gel on some cariogenic (Streptococcus mutans), periodontopathic (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis) and an opportunistic periodontopathogen (Bacteroides fragilis) isolated from patients with dental caries and periodontal diseases. Twenty isolates of each of these bacteria were investigated for their sensitivity to Aloe vera gel using the disk diffusion and microdilution methods. S. mutans was the species most sensitive to Aloe vera gel with a MIC of 12.5 µg/ml, while A. actinomycetemcomitans, P. gingivalis, and B. fragilis were less sensitive, with a MIC of 25-50 µg/ml (P < 0.01). Based on our present findings it is concluded that Aloe vera gel at optimum concentration could be used as an antiseptic for prevention of dental caries and periodontal diseases.

19. Spectrum of antimicrobial activity and user acceptability of the hand disinfectant agent Sterillium Gel.

PubMed

Kampf, G; Rudolf, M; Labadie, J-C; Barrett, S P

2002-10-01

The antimicrobial efficacy of alcohol-based hand gels has been shown to be significantly less than liquid hand rubs probably because of a lower concentration of alcohol. Sterillium Gel is the first hand gel with 85% ethanol. Its antimicrobial efficacy and user acceptability was studied. Bactericidal activity was tested according to prEN 12054 against Staphylococcus aureus, Enterococcus hirae, Pseudomonas aeruginosa and Escherichia coli (suspension test) and EN 1500 (15 volunteers; four replicates), fungicidal activity according to EN 1275 against Candida albicans and spores of Aspergillus niger (suspension test) and tuberculocidal activity against Mycobacterium terrae using the DGHM suspension test. Virucidal activity was determined in suspension tests based on reduction of infectivity with and without interfering substances (10% fetal calf serum; 0.3% erythrocytes and 0.3% bovine serum albumin). Ninety-six healthcare workers in hospitals in France and the UK used the gel for four weeks and assessed it by filling out a questionnaire. The gel was bactericidal (a reduction factor of > 10(5)-fold), tuberculocidal (reduction factor > 10(5)) and fungicidal (reduction factor > 10(4)) in 30 s. Irrespective of interfering substances the gel inactivated orthopoxvirus and herpes simplex virus type 1 and 2 in 15 s, adenovirus in 2 min, poliovirus in 3 min and papovavirus in 15 min by a factor of > 10(4)-fold. Rotavirus and human immunodeficiency virus were inactivated in 30 s (without interfering substances). Under practical use conditions it was as effective in 30 s as the reference alcohol in 60 s. Most users described the tackiness, aggregation, skin feeling after use and smell as positive or acceptable. A total of 65.6% assessed the new gel to be better than a comparator irrespective of its type (gel or liquid). Overall Sterillium Gel had a unique spectrum of antimicrobial activity. It is probably the first alcohol-based hand gel to pass EN 1500 in 30 s. Due to the

20. Spectrum of antimicrobial activity and user acceptability of the hand disinfectant agent Sterillium Gel.

PubMed

Kampf, G; Rudolf, M; Labadie, J-C; Barrett, S P

2002-10-01

The antimicrobial efficacy of alcohol-based hand gels has been shown to be significantly less than liquid hand rubs probably because of a lower concentration of alcohol. Sterillium Gel is the first hand gel with 85% ethanol. Its antimicrobial efficacy and user acceptability was studied. Bactericidal activity was tested according to prEN 12054 against Staphylococcus aureus, Enterococcus hirae, Pseudomonas aeruginosa and Escherichia coli (suspension test) and EN 1500 (15 volunteers; four replicates), fungicidal activity according to EN 1275 against Candida albicans and spores of Aspergillus niger (suspension test) and tuberculocidal activity against Mycobacterium terrae using the DGHM suspension test. Virucidal activity was determined in suspension tests based on reduction of infectivity with and without interfering substances (10% fetal calf serum; 0.3% erythrocytes and 0.3% bovine serum albumin). Ninety-six healthcare workers in hospitals in France and the UK used the gel for four weeks and assessed it by filling out a questionnaire. The gel was bactericidal (a reduction factor of > 10(5)-fold), tuberculocidal (reduction factor > 10(5)) and fungicidal (reduction factor > 10(4)) in 30 s. Irrespective of interfering substances the gel inactivated orthopoxvirus and herpes simplex virus type 1 and 2 in 15 s, adenovirus in 2 min, poliovirus in 3 min and papovavirus in 15 min by a factor of > 10(4)-fold. Rotavirus and human immunodeficiency virus were inactivated in 30 s (without interfering substances). Under practical use conditions it was as effective in 30 s as the reference alcohol in 60 s. Most users described the tackiness, aggregation, skin feeling after use and smell as positive or acceptable. A total of 65.6% assessed the new gel to be better than a comparator irrespective of its type (gel or liquid). Overall Sterillium Gel had a unique spectrum of antimicrobial activity. It is probably the first alcohol-based hand gel to pass EN 1500 in 30 s. Due to the

1. Silica nanoparticles as indicator of hydrothermal activities at Enceladus ocean floor

Postberg, F.; Hsu, S.; Sekine, Y.; Kempf, S.; Juhasz, A.; Horanyi, M.; Moragas-Klostermeyer, G.; Srama, R.

2013-12-01

Silica nanoparticles as indicator of hydrothermal activities at Enceladus ocean floor F. Postberg, H.-W. Hsu, Y. Sekine, S. Kempf, A. Juhasz, M. Horanyi, G. Moragas-Klostermeyer, R. Srama Silica serves as a unique indicator of hydrothermal activities on Earth as well as on Mars. Here we report the Cassini Cosmic Dust Analyser (CDA) observation of nanosilica particles from the Saturnian system. Based on their interaction with the solar wind electromagnetic fields, these charged nanosilica particles, so-called stream particles, are found to be originated in Saturn's E ring, indicating Enceladus being their ultimate source. CDA stream particle mass spectra reveal a metal-free but silicon-rich composition that is only plausible for nearly pure silica particles. The size range derived from our measurements confines the size of these particles to a radius of 2 - 8 nm. The unique properties of nano-grains with the observed composition and size are a well-known phenomenon on Earth and their formation requires specific hydrothermal rock-water interactions. The observation of Saturnian nanosilica particles thus serves as an evidence of hydrothermal activities at the interface of Enceladus subsurface ocean and its rocky core. Considering plasma erosion as the major mechanism of releasing embedded nanosilica particles from their carriers, the much larger E ring ice grains, our dynamical model and CDA observation provide a lower limit on the average nanosilica concentration in E ring grains. Together with dedicated hydrothermal experiments (Sekine at al., 2013) this can be translated into constraints on the hydrothermal activities on Enceladus. Measurements and experiments both point at dissolved silica concentrations at the ocean floor in the order of 1 - 3 mMol. The hydrothermal reactions likely take place with a pristine, chondritic rock composition at temperature higher than 130°C (Sekine at al. 2013). Colloidal nano-silica forms upon supersaturation during cooling of the

2. Thermal Stability and Catalytic Activity of Gold Nanoparticles Supported on Silica

SciTech Connect

Veith, G.; Lupini, A; Rashkeev, S; Pennycook, S; Mullins, D; Schwartz, V; Bridges, C; Dudney, N

2009-01-01

2.5 nm gold nanoparticles were grown on a fumed silica support, using the physical vapor deposition technique of magnetron sputtering, that are thermally stable when annealed in an oxygen containing environment up to at least 500 C. Traditional Au/TiO{sub 2} catalysts rapidly sinter to form large 13.9 nm gold clusters under these annealing conditions. This surprising stability of Au/SiO{sub 2} is attributed to the absence of residual impurities (ensured by the halide-free production method) and a strong bond between gold and defects at the silica surface (about 3 eV per bond) estimated from density functional theory (DFT) calculations. The Au/SiO{sub 2} catalysts are less active for CO oxidation than the prototypical Au/TiO2 catalysts, however they can be regenerated far more easily, allowing the activity of a catalyst to be fully recovered after deactivation.

3. Influence of calcination temperature on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate as precursor

PubMed Central

2011-01-01

Effects of calcination temperatures varying from 400 to 1000°C on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in the sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate (THEOS) as water-soluble silica precursor have been investigated. Studies carried out using XRD, FT-IR, TEM, STA (TG-DTG-DTA) and VSM techniques. Results indicated that magnetic properties of samples such as superparamagnetism and ferromagnetism showed great dependence on the variation of the crystallinity and particle size caused by the calcination temperature. The crystallization, saturation magnetization Ms and remenant magnetization Mr increased as the calcination temperature increased. But the variation of coercivity Hc was not in accordance with that of Ms and Mr, indicating that Hc is not determined only by the crystallinity and size of CoFe2O4 nanoparticles. TEM images showed spherical nanoparticles dispersed in the silica network with sizes of 10-30 nm. Results showed that the well-established silica network provided nucleation locations for CoFe2O4 nanoparticles to confinement the coarsening and aggregation of nanoparticles. THEOS as silica matrix network provides an ideal nucleation environment to disperse CoFe2O4 nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS as water-soluble silica precursor over the currently used TEOS and TMOS, the organic solvents are not needed owing to the complete solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of Co-ferrite even more versatile. PMID:21486494

4. Effects of Al(3+) Ions on Formation of Silica Framework and Surface Active Sites for SO4(2-) Ions.

PubMed

Sasahara, Shigeo; Ozeki, Sumio

2016-07-19

Al(3+) ions were introduced into silica framework at 318 K in order to make active Al sites for SO4(2-) by the addition of aqueous sodium silicate solution to aqueous sulfuric acid solution of Al2(SO4)3. The (27)Al and (29)Si NMR spectra of aluminosilicates were measured at 278 K with reaction time. (29)Si NMR spectra were analyzed by the multivariate curve resolution. The addition of Al(3+) ions to aqueous silicate solution promoted gel formation. Small amounts of Al(3+) ions were incorporated as a four-coordinated complex at early stage of polymerization reaction of silicates and during subsequent reaction six-coordinated Al complex increased, suggesting reversible conversion between 4- and 6-coordinated complexes. SO4(2-) ions interact with positive surfaces of aluminosilicates and are specifically adsorbed on the surface sites of 6-coordinated Al(3+) species, which may be stabilized on silicate surfaces as [Al(H2O)5SO4](+). PMID:27352046

5. Effects of Al(3+) Ions on Formation of Silica Framework and Surface Active Sites for SO4(2-) Ions.

PubMed

Sasahara, Shigeo; Ozeki, Sumio

2016-07-19

Al(3+) ions were introduced into silica framework at 318 K in order to make active Al sites for SO4(2-) by the addition of aqueous sodium silicate solution to aqueous sulfuric acid solution of Al2(SO4)3. The (27)Al and (29)Si NMR spectra of aluminosilicates were measured at 278 K with reaction time. (29)Si NMR spectra were analyzed by the multivariate curve resolution. The addition of Al(3+) ions to aqueous silicate solution promoted gel formation. Small amounts of Al(3+) ions were incorporated as a four-coordinated complex at early stage of polymerization reaction of silicates and during subsequent reaction six-coordinated Al complex increased, suggesting reversible conversion between 4- and 6-coordinated complexes. SO4(2-) ions interact with positive surfaces of aluminosilicates and are specifically adsorbed on the surface sites of 6-coordinated Al(3+) species, which may be stabilized on silicate surfaces as [Al(H2O)5SO4](+).

6. The coexistence of geopolymeric gel and calcium silicate hydrate at the early stage of alkaline activation

SciTech Connect

Yip, C.K.; Lukey, G.C.; Deventer, J.S.J. van . E-mail: jannie@unimelb.edu.au

2005-09-01

Scanning electron microscopy was used to study the effects of the addition of ground granulated blast furnace slag (GGBFS) on the microstructure and mechanical properties of metakaolin (MK) based geopolymers. It was found that it is possible to have geopolymeric gel and calcium silicate hydrate (CSH) gel forming simultaneously within a single binder. The coexistence of these two phases is dependent on the alkalinity of the alkali activator and the MK / GGBFS mass ratio. It has been found that the formation of CSH gel together with the geopolymeric gel occurs only in a system at low alkalinity. In the presence of high concentrations of NaOH (> 7.5 M), the geopolymeric gel is the predominant phase formed with small calcium precipitates scattered within the binder. The coexistence of the two phases is not observed unless a substantial amount of a reactive calcium source is present initially. It is thought that voids and pores within the geopolymeric binder become filled with the CSH gel. This helps to bridge the gaps between the different hydrated phases and unreacted particles; thereby resulting in the observed increase in mechanical strength for these binders.

7. Light activated, In situ Forming Gel for Sustained Suprachoroidal Delivery of Bevacizumab

PubMed Central

Tyagi, Puneet; Barros, Matthew; Stansbury, Jeffrey W.; Kompella, Uday B.

2014-01-01

Purpose To develop a light activated polycaprolactone dimethacrylate and hydroxyethyl methacrylate based gel network that sustains the release of stable, active bevacizumab (an anti-VEGF antibody used to treat choroidal neovascularization) and to assess sustained ex vivo delivery in rabbit eyes and in vivo delivery in rat eyes following in situ gel formation in the suprachoroidal space. Methods Polycaprolactone dimethacrylate (PCM) was synthesized from polycaprolactone diol (PCD) and evaluated using NMR spectroscopy. PCM was used to cross-link hydroxyethyl methacrylate (HEMA) in the presence of 365 nm UV light and 2, 2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator. Bevacizumab was entrapped in the gel using 3 different cross-linking durations of 3, 7, and 10 minutes. In vitro release of bevacizumab in PBS pH 7.4 at 37°C during a 4 months study was quantified using a VEGF-binding based ELISA. Stability of released bevacizumab was monitored by size exclusion chromatography (SEC) and circular dichroism. Alexa Fluor® 488 dye conjugated bevacizumab mixed with polymers was injected suprachoroidally in rabbit eyes to study the effect of different cross-linking durations on the spread of the dye conjugated bevacizumab. In vivo delivery was assessed in Sprague Dawley (SD) rats by injecting Alexa Fluor® 488 dye conjugated bevacizumab mixed with polymers followed by cross-linking for 10 minutes. Spread in the rabbit eyes and in vivo delivery in rat eyes was monitored noninvasively using a fundus camera and Fluorotron Master™. Results Formation of PCM was confirmed by the disappearance of hydroxyl peak in NMR spectra. Cross-linking duration of 10 minutes resulted in a burst release of 21 % of bevacizumab. Other cross-linking durations had ≥ 62 % burst release. Bevacizumab release from 10 minute cross-linked gel was sustained for ∼ 4 months. Release samples contained ≥ 96.1 % of bevacizumab in the monomeric form as observed in SEC chromatograms. Circular

8. Silica gel modified with N-(3-propyl)-O-phenylenediamine: functionalization, metal sorption equilibrium studies and application to metal enrichment prior to determination by flame atomic absorption spectrometry.

PubMed

Akl, Magda Ali Abd-elAziz; Kenawy, Ibraheim Mohamed; Lasheen, Rabab Ramadan

2005-08-01

The use of the chemically modified silica gel N-(3-propyl)-O-phenylenediamine (SiG-NPPDA) adsorbent, for the preconcentration and separation of trace heavy metals, was described. SiG-NPPDA sorbs quantitatively (90-100% recovery) trace amounts of nine heavy metals, viz., Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) at pH 7-8. The sorption capacity varies from 350 to 450 micromol g(-1). Desorption was found to be quantitative with 1-2 M HNO3 or 0.05 M Na2EDTA. The distribution coefficient, Kd and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C(M,eqm)% (Recovery, R%), were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, log Kd, ranges between 4.0 and 6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS). The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance), potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the SiG-NPPDA adsorbent and the investigated metal ions is proposed to be due to the reaction of the investigated metal ions with the two nitrogen atoms of the SiG-NPPDA adsorbent. The present adsorbent coupled with flame AAS has been used to enrich and determine the nine metal ions in natural aqueous systems and in certified reference materials (RSD < or = 5%). The copper, iron, manganese and zinc present in some pharmaceutical vitamin samples were also preconcentrated on SiG-NPPDA adsorbent and determined by flame AAS (RSD < or = 4.2%). Nanogram concentrations (0.07-0.14 ng ml(-1)) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.

9. Thermodynamic analysis of sol-gel transition of gelatin in terms of water activity in various solutions.

PubMed

Miyawaki, Osato; Omote, Chiaki; Matsuhira, Keiko

2015-12-01

Sol-gel transition of gelatin was analyzed as a multisite stoichiometric reaction of a gelatin molecule with water and solute molecules. The equilibrium sol-gel transition temperature, Tt , was estimated from the average of gelation and melting temperature measured by differential scanning calorimetry. From Tt and the melting enthalpy, ΔHsol , the equilibrium sol-to-gel ratio was estimated by the van't Hoff equation. The reciprocal form of the Wyman-Tanford equation, which describes the sol-to-gel ratio as a function of water activity, was successfully applied to obtain a good linear relationship. From this analysis, the role of water activity on the sol-gel transition of gelatin was clearly explained and the contributions of hydration and solute binding to gelatin molecules were separately discussed in sol-gel transition. The general solution for the free energy for gel-stabilization in various solutions was obtained as a simple function of solute concentration.

10. An electrochemical double layer capacitor using an activated carbon electrode with gel electrolyte binder

SciTech Connect

Osaka, Tetsuya, Liu, X.; Nojima, Masashi; Momma, Toshiyuki

1999-05-01

An electric double layer capacitor (EDLC) was prepared with an activated carbon powder electrode with poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) based gel electrolyte. Ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizer and tetraethylammonium tetrafluoroborate (TEABF{sub 4}) was used as the supporting electrolyte. An optimized gel electrolyte of PVdF-HFP/PC/EC/TEABF{sub 4} - 23/31/35/11 mass ratio exhibited high ionic conductivity of 5 {times} 10{sup {minus}3} S/cm, high electrode capacitance, and good mechanical strength. An electrode consisting of activated carbon (AC) with the gel electrolyte as the binder (AC/PVdF-HFP based gel, 7/3 mass ratio) showed a higher specific capacitance and a lower ion diffusion resistance within the electrode than a carbon electrode, prepared with PVdF-HFP binder without plasticizer. This suggests that an electrode mixed with the gel electrolyte has a lower ion diffusion resistance inside the electrode. The highest specific capacitance of 123 F/g was achieved with an electrode containing AC with a specific surface area of 2500 m{sup 2}/g. A coin-type EDLC cell with optimized components showed excellent cycleability exceeding 10{sup 4} cycles with ca. 100% coulombic efficiency achieved when charging and discharging was repeated between 1.0 and 2.5 V at 1.66 mA/cm{sup 2}.

11. Electrically-controlled polymeric gels as active materials in adaptive structures

SciTech Connect

Segalman, D.; Witkowski, W.; Adolf, D. ); Shahinpoor, M. . Dept. of Mechanical Engineering)

1991-01-01

This paper presents several applications of ionizable polymeric gels that are capable of undergoing substantial expansions and contractions when subjected to changing pH environments, temperature, or solvent. Conceptual designs for smart, electrically activated devices exploiting this phenomenon are discussed. These devices have the possibility of being manipulated via active computer control as large displacement actuators for use in adaptive structures. The enabling technology of these novel devices is the use of compliant containers for the gels and their solvents, removing the difficulties associated with maintaining a bath for the gels. Though most of these devices are designed using properties well discussed in the literature, some presented near the end of this paper make use of conclusions that the authors have drawn form the literature and their own experimental work. Those conclusions about the basic mechanisms of electromechanical gels are discussed in the third part of this paper and a complete set of governing equations describing these mechanisms are presented in the fourth section. This paper concludes with a discussion of some of the ramifications of the above system of equations and a discussion on gel-driven devices and on the control of such devices. 24 refs., 6 figs., 1 tab.

12. Repetitive Dosing of Fumed Silica Leads to Profibrogenic Effects through Unique Structure-Activity Relationships and Biopersistence in the Lung.

PubMed

Sun, Bingbing; Wang, Xiang; Liao, Yu-Pei; Ji, Zhaoxia; Chang, Chong Hyun; Pokhrel, Suman; Ku, Justine; Liu, Xiangsheng; Wang, Meiying; Dunphy, Darren R; Li, Ruibin; Meng, Huan; Mädler, Lutz; Brinker, C Jeffrey; Nel, André E; Xia, Tian

2016-08-23

Contrary to the notion that the use of fumed silica in consumer products can "generally (be) regarded as safe" (GRAS), the high surface reactivity of pyrogenic silica differs from other forms of synthetic amorphous silica (SAS), including the capacity to induce membrane damage and acute proinflammatory changes in the murine lung. In addition, the chain-like structure and reactive surface silanols also allow fumed silica to activate the NLRP3 inflammasome, leading to IL-1β production. This pathway is known to be associated with subchronic inflammation and profibrogenic effects in the lung by α-quartz and carbon nanotubes. However, different from the latter materials, bolus dose instillation of 21 mg/kg fumed silica did not induce sustained IL-1β production or subchronic pulmonary effects. In contrast, the NLRP3 inflammasome pathway was continuously activated by repetitive-dose administration of 3 × 7 mg/kg fumed silica, 1 week apart. We also found that while single-dose exposure failed to induce profibrotic effects in the lung, repetitive dosing can trigger increased collagen production, even at 3 × 3 mg/kg. The change between bolus and repetitive dosing was due to a change in lung clearance, with recurrent dosing leading to fumed silica biopersistence, sustained macrophage recruitment, and activation of the NLRP3 pathway. These subchronic proinflammatory effects disappeared when less surface-reactive titanium-doped fumed silica was used for recurrent administration. All considered, these data indicate that while fumed silica may be regarded as safe for some applications, we should reconsider the GRAS label during repetitive or chronic inhalation exposure conditions. PMID:27483033

13. Enhanced removal of detergent and recovery of enzymatic activity following sodium dodecyl sulfate-polyacrylamide gel electrophoresis: UUse of casein in gel wash buffer

SciTech Connect

McGrew, B.R.; Green, D.M. )

1990-08-15

The inclusion of 1% casein or bovine serum albumin in buffer used to reactivate enzymes subjected to sodium dodecyl sulfate (SDS)-polyacrylamide electrophoresis resulted in accelerated removal of SDS and restoration of nuclease and beta-galactosidase enzyme activities. Nuclease and beta-galactosidase activities which are absent from gels after longer wash procedures are detectable with this technique. Enzyme activity in gels prepared with SDS which contained inhibitory contaminants was partially restored by the casein wash procedure. The threshold of detection of two-dimensionally separated deoxyribonuclease I using the casein wash procedure was 1 picogram.

14. Chemical and biochemical activities of sonochemically synthesized poly(N-isopropyl acrylamide)/silica nanocomposite

Chowdhury, Pranesh; Saha, Swadhin Kr; Guha, Arun; Saha, Samar Kr

2012-11-01

Poly(N-isopropyl acrylamide) (PNIPA) grafted mesoporous silica nanoparticles (MPSNP) leading to novel inorganic/organic core-shell nanocomposite has been synthesized sonochemically in an aqueous medium without additives like cross-linker, hydrophobic agent, organic solvent. The colloidal stability of MPSNP is enhanced significantly due to encapsulation of the polymer. The composites are characterized by TEM, FTIR and TGA. The chemical and biochemical activities of the sonochemically synthesized materials have been studied in the light of reaction with acid-base, protein adsorption, antimicrobial activity, biocompatibility and nonthrombogenic property. Advantages of sonochemical synthesis compared to other techniques have been evaluated.

15. Influence of surface composition on hydrogen peroxide decomposition catalyzed by Co(II) aminopyridine-supported compounds on amorphous silica gel.

PubMed

de Farias, Robson F; Gonçalves, Afonso S; Airoldi, Claudio

2002-03-01

Cobalt compounds supported on 2-, 3-, and 4-aminopyridine-modified silica surfaces, named Sil2Co, Sil3Co, and Sil4Co, respectively, were used to catalyze the decomposition of hydrogen peroxide on ethanolic solutions at 293, 298, and 303 K. The calculated k values (x10(-4) s(-1)) for Sil2Co, Sil3Co, and Sil4Co are 0.65, 1.24, and 4.78 (293 K); 1.23, 1.87, and 6.33 (298 K); and 1.80, 2.80, and 10.30 (303 K), respectively. All obtained results evidence that such decomposition is a first-order reaction. Zinc-, nickel-, and copper-supported compounds were also tested, but exhibited a very low catalytic activity. By using the k values at 298 and 303 K, and employing the equation ln (k1/k2) = E(a)/R(1/T2-1/T1), the activation energy values for the considered reaction were Sil2Co = 57.20, Sil3Co = 60.60, and Sil4Co = 73.10 kJ mol(-1), respectively. The low values calculated for E(a) are in agreement with a free-radical mechanism.

16. Surface activity and flocculation behavior of polyethylene glycol-functionalized silica nanoparticles.

PubMed

Björkegren, Sanna Maria Sofi; Nordstierna, Lars; Törncrona, Anders; Persson, Michael E; Palmqvist, Anders E C

2015-08-15

Colloidal silica nanoparticles have been functionalized with methyl polyethylene glycol silane (mPEG silane) and the PEGylated particles have been characterized with focus on exploring their surface chemical properties. The degree of surface functionalization was quantified using NMR diffusometry, and the measurements showed that the silane binds covalently to the silica surface. Samples with surface coverages ranging from 0.068 to 0.315 μmol silane/m(2) have been analyzed. The functionalized particles proved to be surface active and showed a significant reduction in surface charge and zeta potential with increasing degree of PEG functionalization. All samples showed colloidal stability at neutral pH and above within the range studied. At lower pH, the samples with low surface coverage displayed a reversible flocculation behavior, while samples with a high surface coverage and samples without functionalization remained stable. This suggests that steric stabilization is effective at low pH when the surface coverage is high enough; electrostatic stabilization is effective for samples without functionalization; and that inter-particle PEG-silica interactions cause flocculation of particles with too low degrees of PEG functionalization.

17. Asters, Vortices, and Rotating Spirals in Active Gels of Polar Filaments

Kruse, K.; Joanny, J. F.; Jülicher, F.; Prost, J.; Sekimoto, K.

2004-02-01

We develop a general theory for active viscoelastic materials made of polar filaments. This theory is motivated by the dynamics of the cytoskeleton. The continuous consumption of a fuel generates a nonequilibrium state characterized by the generation of flows and stresses. Our theory applies to any polar system with internal energy consumption such as active chemical gels and cytoskeletal networks which are set in motion by active processes at work in cells.

18. Sustainability of the Catalytic Activity of a Silica-Titania Composite (STC) for Long-Term Indoor Air Quality Control

NASA Technical Reports Server (NTRS)

Coutts, Janelle L.; Levine, Lanfang H.; Richards, Jeffrey T.

2011-01-01

TiO2-assisted photocatalytic oxidation (PCO) is an emerging technology for indoor air quality control and is also being evaluated as an alternative trace contaminant control technology for crew habitats in space exploration. Though there exists a vast range of literature on the development of photocatalysts and associated reactor systems, including catalyst performance and performance-influencing factors, the critical question of whether photocatalysts can sustain their initial catalytic activity over an extended period of operation has not been adequately addressed. For a catalyst to effectively serve as an air quality control product, it must be rugged enough to withstand exposure to a multitude of low concentration volatile organic compounds (VOCs) over long periods of time with minimal loss of activity. The objective of this study was to determine the functional lifetime of a promising photocatalyst - the silica-titania composite (STC) from Sol Gel Solutions, LLC in a real-world scenario. A bench-scale STC-packed annular reactor under continuous irradiation by a UV-A fluorescent black-light blue lamp ((lambda)max = 365 nm) was exposed to laboratory air continuously at an apparent contact time of 0.27 sand challenged with a known concentration of ethanol periodically to assess any changes in catalytic activity. Laboratory air was also episodically spiked with halocarbons (e.g., octafluoropropane), organosulfur compounds (e.g., sulfur hexafluoride), and organosilicons (e.g., siloxanes) to simulate accidental releases or leaks of such VOCs. Total organic carbon (TOC) loading and contaminant profiles of the laboratory air were also monitored. Changes in STC photocatalytic performance were evaluated using the ethanol mineralization rate, mineralization efficiency, and oxidation intermediate (acetaldehyde) formation. Results provide insights to any potential catalyst poisoning by trace halocarbons and organosulfur compounds.

19. Dynamics of self-oscillating cilia designed from active polymer gels

Dayal, Pratyush; Bhattacharya, Amitabh; Kuksenok, Olga; Balazs, Anna C.

2012-02-01

Using theory and simulations, we design active synthetic surfaces which are capable of replicating functionalities of biological cilia. In order to design such exquisite biomimetic systems we harness unique properties of polymer gels that undergo photosensitive Belousov-Zhabotinsky (BZ) reaction. Powered by internalized BZ reaction these polymer gels swell and de-swell autonomously by chemo-mechanical transduction and therefore are ideal materials for designing our system. In order to simulate the dynamics of the BZ cilia in surrounding fluid we have developed a nonlinear hybrid 3D model which captures elasto-dynamics of polymer gel and diffusive exchange of BZ reagents between the gel and the fluid. Here we show that the geometrical arrangement of cilia and the distribution of BZ activator in the fluid determine the dynamic response of the cilia. We further show that using light as an external stimulus we can sequentially modulate height of individual cilium and thereby create the piano effect''. Finally, we demonstrate that synchronized oscillations in the cilia result from the distribution of BZ-activator in the surrounding fluid. Our findings can be used to design active surfaces which can be remotely tuned depending upon the magnitude of external stimuli.

20. In vitro activity of Aloe vera inner gel against microorganisms grown in planktonic and sessile phases.

PubMed

Cataldi, V; Di Bartolomeo, S; Di Campli, E; Nostro, A; Cellini, L; Di Giulio, M

2015-12-01

The failure of traditional antimicrobial treatments is becoming a worldwide problem. The use of Aloe vera is of particular interest for its role as curative agent and its efficacy in complementary therapies for a variety of illnesses. This study evaluated the antimicrobial activity of A. vera inner gel against a panel of microorganisms, Gram-positive and -negative bacteria, and Candida albicans. In addition to A. vera inner gel being used in the treatment of peptic ulcers, in dermatological treatments, and wound healing, it was also tested on the sessile phase of clinical Helicobacter pylori strains (including multi-drug-resistant strains) and on planktonic and sessile phase of Staphylococcus aureus/Pseudomonas aeruginosa clinical isolates from venous leg ulcers.A. vera inner gel expresses its prevalent activity against Gram-negative bacteria and C. albicans in respect to Gram-positive bacteria. The results of the A. vera antibiofilm activity showed a decrease of the produced biomass in a concentration-dependent-way, in each analyzed microorganism. The data obtained show that A. vera inner gel has both an antimicrobial and antibiofilm activity suggesting its potential use for the treatment of microbial infections, in particular for H. pylori gastric infection, especially in case of multi-drug-resistance, as well as for an effective wound dressing. PMID:26526205

1. In vitro activity of Aloe vera inner gel against microorganisms grown in planktonic and sessile phases.

PubMed

Cataldi, V; Di Bartolomeo, S; Di Campli, E; Nostro, A; Cellini, L; Di Giulio, M

2015-12-01

The failure of traditional antimicrobial treatments is becoming a worldwide problem. The use of Aloe vera is of particular interest for its role as curative agent and its efficacy in complementary therapies for a variety of illnesses. This study evaluated the antimicrobial activity of A. vera inner gel against a panel of microorganisms, Gram-positive and -negative bacteria, and Candida albicans. In addition to A. vera inner gel being used in the treatment of peptic ulcers, in dermatological treatments, and wound healing, it was also tested on the sessile phase of clinical Helicobacter pylori strains (including multi-drug-resistant strains) and on planktonic and sessile phase of Staphylococcus aureus/Pseudomonas aeruginosa clinical isolates from venous leg ulcers.A. vera inner gel expresses its prevalent activity against Gram-negative bacteria and C. albicans in respect to Gram-positive bacteria. The results of the A. vera antibiofilm activity showed a decrease of the produced biomass in a concentration-dependent-way, in each analyzed microorganism. The data obtained show that A. vera inner gel has both an antimicrobial and antibiofilm activity suggesting its potential use for the treatment of microbial infections, in particular for H. pylori gastric infection, especially in case of multi-drug-resistance, as well as for an effective wound dressing.

2. Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation

SciTech Connect

Bernal, Susan A.; Provis, John L.; Walkley, Brant; San Nicolas, Rackel; Gehman, John D.; Brice, David G.; Kilcullen, Adam R.; Duxson, Peter; Deventer, Jannie S.J. van

2013-11-15

Binders formed through alkali-activation of slags and fly ashes, including ‘fly ash geopolymers’, provide appealing properties as binders for low-emissions concrete production. However, the changes in pH and pore solution chemistry induced during accelerated carbonation testing provide unrealistically low predictions of in-service carbonation resistance. The aluminosilicate gel remaining in an alkali-activated slag system after accelerated carbonation is highly polymerised, consistent with a decalcification mechanism, while fly ash-based binders mainly carbonate through precipitation of alkali salts (bicarbonates at elevated CO{sub 2} concentrations, or carbonates under natural exposure) from the pore solution, with little change in the binder gel identifiable by nuclear magnetic resonance spectroscopy. In activated fly ash/slag blends, two distinct gels (C–A–S–H and N–A–S–H) are formed; under accelerated carbonation, the N–A–S–H gel behaves comparably to fly ash-based systems, while the C–A–S–H gel is decalcified similarly to alkali-activated slag. This provides new scope for durability optimisation, and for developing appropriate testing methodologies. -- Highlights: •C-A-S-H gel in alkali-activated slag decalcifies during accelerated carbonation. •Alkali-activated fly ash gel changes much less under CO{sub 2} exposure. •Blended slag-fly ash binder contains two coexisting gel types. •These two gels respond differently to carbonation. •Understanding of carbonation mechanisms is essential in developing test methods.

3. Mushroom tyrosinase inhibition activity of Aloe vera L. gel from different germplasms.

PubMed

Gupta, S Dutta; Masakapalli, S K

2013-11-01

In this study, lyophilized and methanolic extracts of aloe gel from different germplasms were evaluated for their potential to inhibit mushroom tyrosinase activity. The results showed potent inhibitory effect of Aloe vera gel extracts on L-dihydroxyphenylalanine (L-DOPA) oxidation catalyzed by tyrosinase in a dose-dependent manner. Significant differences in % inhibition of tyrosinase among the extraction methods and the germplasms were observed. The relative performance of the germplasms was evaluated with the help of posthoc multicomparison test. The methanolic extract was more effective than the lyophilized crude gel in all the germplasms. The inhibitory effect of the lyophilized gel and methanolic extract tested from five germplasms followed the order: RM > TN > S24 > OR > RJN. The germplasm RM showed the highest tyrosinase inhibition, and the maximum % inhibition noted was 26.04% and 41.18%, respectively for the lyophilized and methanolic extracts at 6 mg · mL(-1) concentration. Lineweaver-Burk plots of the different concentrations of L-DOPA in the absence and presence of lyophilized gel extract showed competitive inhibition of mushroom tyrosinase in all the germplasms. This study suggests that the germplasm RM could potentially be used for the isolation and identification of the effective tyrosinase inhibitory component, and ascertains the critical role of selecting the best source of germplasm for natural product isolation and characterization.

4. The antioxidant activity of Clitoria ternatea flower petal extracts and eye gel.

PubMed

Kamkaen, N; Wilkinson, J M

2009-11-01

Extracts of Clitoria ternatea (butterfly pea) flowers are used in Thailand as a component of cosmetics and the chemical composition of the flowers suggest that they may have antioxidant activity. In this study the potential antioxidant activity of C. ternatea extracts and an extract containing eye gel formulation was investigated. Aqueous extracts were shown to have stronger antioxidant activity (as measured by DPPH scavenging activity) than ethanol extracts (IC(50) values were 1 mg/mL and 4 mg/mL, respectively). Aqueous extracts incorporated in to an eye gel formulation were also shown to retain this activity, however, it was significantly less than a commercial antiwrinkle cream included for comparison. The total phenolic content was 1.9 mg/g extract as gallic acid equivalents. The data from this study support the use of C. ternatea extracts as antioxidant inclusions in cosmetic products. PMID:19367668

5. A hybrid particle-mesh method for incompressible active polar viscous gels

Ramaswamy, Rajesh; Bourantas, George; Jülicher, Frank; Sbalzarini, Ivo F.

2015-06-01

We present a hybrid particle-mesh method for numerically solving the hydrodynamic equations of incompressible active polar viscous gels. These equations model the dynamics of polar active agents, embedded in a viscous medium, in which stresses are induced through constant consumption of energy. The numerical method is based on Lagrangian particles and staggered Cartesian finite-difference meshes. We show that the method is second-order and first-order accurate with respect to grid and time-step sizes, respectively. Using the present method, we simulate the hydrodynamics in rectangular geometries, of a passive liquid crystal, of an active polar film and of active gels with topological defects in polarization. We show the emergence of spontaneous flow due to Fréedericksz transition, and transformation in the nature of topological defects by tuning the activity of the system.

6. Effect of conductive additives to gel electrolytes on activated carbon-based supercapacitors

Barzegar, Farshad; Dangbegnon, Julien K.; Bello, Abdulhakeem; Momodu, Damilola Y.; Johnson, A. T. Charlie; Manyala, Ncholu

2015-09-01

This article is focused on polymer based gel electrolyte due to the fact that polymers are cheap and can be used to achieve extended potential window for improved energy density of the supercapacitor devices when compared to aqueous electrolytes. Electrochemical characterization of a symmetric supercapacitor devices based on activated carbon in different polyvinyl alcohol (PVA) based gel electrolytes was carried out. The device exhibited a maximum energy density of 24 Wh kg-1 when carbon black was added to the gel electrolyte as conductive additive. The good energy density was correlated with the improved conductivity of the electrolyte medium which is favorable for fast ion transport in this relatively viscous environment. Most importantly, the device remained stable with no capacitance lost after 10,000 cycles.

7. Composites of silica with immobilized cholinesterase incorporated into polymeric shell

Payentko, Victoriya; Matkovsky, Alexander; Matrunchik, Yulia

2015-02-01

Synthetic approaches for new nanocomposite materials with relatively high cholinesterase activity have been developed. The peculiarity of the formation of such systems is the introduction of cholinesterase into polymer with subsequent incorporation on the ready-made silica particles and into the polysiloxane matrixes during sol-gel synthesis. Evaluation of the cholinesterase activity has been fulfilled through the imitation of the acetylcholine chloride decomposition reaction. Values of activity for cholinesterase nanocomposites demonstrated in this work are higher than those for the native cholinesterase. The higher activity of cholinesterase contained in nanocomposites was found for those prepared using highly dispersed silica.

8. Preparation of a novel ionic hybrid stationary phase by non-covalent functionalization of single-walled carbon nanotubes with amino-derivatized silica gel for fast HPLC separation of aromatic compounds.

PubMed

Aral, Hayriye; Çelik, K Serdar; Aral, Tarık; Topal, Giray

2016-03-01

Single-walled carbon nanotubes (SWCNTs) were immobilized on spherical silica gel with a 4-μm average particle size and a 60-Å average pore size. The amino-derivatized silica gel was non-covalently coated with carboxylated SWCNTs to preserve the structure of the nanotubes and their physico-chemical properties. The novel ionic hybrid stationary phase was characterized by scanning electron microscopy (SEM), infra-red (IR) spectroscopy and elemental analysis, and then, it was used to fill an empty 150×4.6mm(2) high-performance liquid chromatography (HPLC) column. Chromatographic parameters, such as the theoretical plate number, retention factor and peak asymmetry factor, and analytical parameters, such as the limit of detection (LOD), limit of quantification (LOQ), linear range, calibration equation, and R(2) value, and quantitative analysis parameters were calculated for all of the analytes. Using different mobile phases, five different classes of aromatic hydrocarbons were separated in a very short analysis time of 4-8min. Furthermore, a high theoretical plate number (up to 25000) and an excellent peak asymmetry factor (1.0) were obtained. The results showed that the surface of the SWNTs had very strong interactions with aromatic groups, therefore providing high selectivity for the separation of different classes of aromatic compounds. This study indicates that SWCNTs enable the extension of the application range of the newly prepared stationary phases for the fast separation of aromatic compounds by HPLC.

9. Monodisperse Mesoporous Carbon Nanoparticles from Polymer/Silica Self-Aggregates and Their Electrocatalytic Activities.

PubMed

Huang, Xiaoxi; Zhou, Li-Jing; Voiry, Damien; Chhowalla, Manish; Zou, Xiaoxin; Asefa, Tewodros

2016-07-27

In our quest to make various chemical processes sustainable, the development of facile synthetic routes and inexpensive catalysts can play a central role. Herein we report the synthesis of monodisperse, polyaniline (PANI)-derived mesoporous carbon nanoparticles (PAMCs) that can serve as efficient metal-free electrocatalysts for the hydrogen peroxide reduction reaction (HPRR) as well as the oxygen reduction reaction (ORR) in fuel cells. The materials are synthesized by polymerization of aniline with the aid of (NH4)2S2O8 as oxidant and colloidal silica nanoparticles as templates, then carbonization of the resulting PANI/silica composite material at different high temperatures, and finally removal of the silica templates from the carbonized products. The PAMC materials that are synthesized under optimized synthetic conditions possess monodisperse mesoporous carbon nanoparticles with an average size of 128 ± 12 nm and an average pore size of ca. 12 nm. Compared with Co3O4, a commonly used electrocatalyst for HPRR, these materials show much better catalytic activity for this reaction. In addition, unlike Co3O4, the PAMCs remain relatively stable during the reaction, under both basic and acidic conditions. The nanoparticles also show good electrocatalytic activity toward ORR. Based on the experimental results, PAMCs' excellent electrocatalytic activity is attributed partly to their heteroatom dopants and/or intrinsic defect sites created by vacancies in their structures and partly to their high porosity and surface area. The reported synthetic method is equally applicable to other polymeric precursors (e.g., polypyrrole (PPY)), which also produces monodisperse, mesoporous carbon nanoparticles in the same way. The resulting materials are potentially useful not only for electrocatalysis of HPRR and ORR in fuel cells but also for other applications where high surface area, small sized, nanostructured carbon materials are generally useful for (e.g., adsorption

10. Monodisperse Mesoporous Carbon Nanoparticles from Polymer/Silica Self-Aggregates and Their Electrocatalytic Activities.

PubMed

Huang, Xiaoxi; Zhou, Li-Jing; Voiry, Damien; Chhowalla, Manish; Zou, Xiaoxin; Asefa, Tewodros

2016-07-27

In our quest to make various chemical processes sustainable, the development of facile synthetic routes and inexpensive catalysts can play a central role. Herein we report the synthesis of monodisperse, polyaniline (PANI)-derived mesoporous carbon nanoparticles (PAMCs) that can serve as efficient metal-free electrocatalysts for the hydrogen peroxide reduction reaction (HPRR) as well as the oxygen reduction reaction (ORR) in fuel cells. The materials are synthesized by polymerization of aniline with the aid of (NH4)2S2O8 as oxidant and colloidal silica nanoparticles as templates, then carbonization of the resulting PANI/silica composite material at different high temperatures, and finally removal of the silica templates from the carbonized products. The PAMC materials that are synthesized under optimized synthetic conditions possess monodisperse mesoporous carbon nanoparticles with an average size of 128 ± 12 nm and an average pore size of ca. 12 nm. Compared with Co3O4, a commonly used electrocatalyst for HPRR, these materials show much better catalytic activity for this reaction. In addition, unlike Co3O4, the PAMCs remain relatively stable during the reaction, under both basic and acidic conditions. The nanoparticles also show good electrocatalytic activity toward ORR. Based on the experimental results, PAMCs' excellent electrocatalytic activity is attributed partly to their heteroatom dopants and/or intrinsic defect sites created by vacancies in their structures and partly to their high porosity and surface area. The reported synthetic method is equally applicable to other polymeric precursors (e.g., polypyrrole (PPY)), which also produces monodisperse, mesoporous carbon nanoparticles in the same way. The resulting materials are potentially useful not only for electrocatalysis of HPRR and ORR in fuel cells but also for other applications where high surface area, small sized, nanostructured carbon materials are generally useful for (e.g., adsorption

11. Modeling the dynamics of a tracer particle in an elastic active gel.

PubMed

Ben-Isaac, E; Fodor, É; Visco, P; van Wijland, F; Gov, Nir S

2015-07-01

The internal dynamics of active gels both in artificial (in vitro) model systems and inside the cytoskeleton of living cells has been extensively studied with experiments of recent years. These dynamics are probed using tracer particles embedded in the network of biopolymers together with molecular motors, and distinct nonthermal behavior is observed. We present a theoretical model of the dynamics of a trapped active particle, which allows us to quantify the deviations from equilibrium behavior, using both analytic and numerical calculations. We map the different regimes of dynamics in this system and highlight the different manifestations of activity: breakdown of the virial theorem and equipartition, different elasticity-dependent "effective temperatures," and distinct non-Gaussian distributions. Our results shed light on puzzling observations in active gel experiments and provide physical interpretation of existing observations, as well as predictions for future studies.

12. Modeling the dynamics of a tracer particle in an elastic active gel

Ben-Isaac, E.; Fodor, É.; Visco, P.; van Wijland, F.; Gov, Nir S.

2015-07-01

The internal dynamics of active gels both in artificial (in vitro) model systems and inside the cytoskeleton of living cells has been extensively studied with experiments of recent years. These dynamics are probed using tracer particles embedded in the network of biopolymers together with molecular motors, and distinct nonthermal behavior is observed. We present a theoretical model of the dynamics of a trapped active particle, which allows us to quantify the deviations from equilibrium behavior, using both analytic and numerical calculations. We map the different regimes of dynamics in this system and highlight the different manifestations of activity: breakdown of the virial theorem and equipartition, different elasticity-dependent "effective temperatures," and distinct non-Gaussian distributions. Our results shed light on puzzling observations in active gel experiments and provide physical interpretation of existing observations, as well as predictions for future studies.

13. Modeling the dynamics of a tracer particle in an elastic active gel.

PubMed

Ben-Isaac, E; Fodor, É; Visco, P; van Wijland, F; Gov, Nir S

2015-07-01

The internal dynamics of active gels both in artificial (in vitro) model systems and inside the cytoskeleton of living cells has been extensively studied with experiments of recent years. These dynamics are probed using tracer particles embedded in the network of biopolymers together with molecular motors, and distinct nonthermal behavior is observed. We present a theoretical model of the dynamics of a trapped active particle, which allows us to quantify the deviations from equilibrium behavior, using both analytic and numerical calculations. We map the different regimes of dynamics in this system and highlight the different manifestations of activity: breakdown of the virial theorem and equipartition, different elasticity-dependent "effective temperatures," and distinct non-Gaussian distributions. Our results shed light on puzzling observations in active gel experiments and provide physical interpretation of existing observations, as well as predictions for future studies. PMID:26274211

14. Antimicrobial activity of silica coated silicon nano-tubes (SCSNT) and silica coated silicon nano-particles (SCSNP) synthesized by gas phase condensation.

PubMed

Tank, Chiti; Raman, Sujatha; Karan, Sujoy; Gosavi, Suresh; Lalla, Niranjan P; Sathe, Vasant; Berndt, Richard; Gade, W N; Bhoraskar, S V; Mathe, Vikas L

2013-06-01

Silica-coated, silicon nanotubes (SCSNTs) and silica-coated, silicon nanoparticles (SCSNPs) have been synthesized by catalyst-free single-step gas phase condensation using the arc plasma process. Transmission electron microscopy and scanning tunneling microscopy showed that SCSNTs exhibited a wall thickness of less than 1 nm, with an average diameter of 14 nm and a length of several 100 nm. Both nano-structures had a high specific surface area. The present study has demonstrated cheaper, resistance-free and effective antibacterial activity in silica-coated silicon nano-structures, each for two Gram-positive and Gram-negative bacteria. The minimum inhibitory concentration (MIC) was estimated, using the optical densitometric technique, and by determining colony-forming units. The MIC was found to range in the order of micrograms, which is comparable to the reported MIC of metal oxides for these bacteria. SCSNTs were found to be more effective in limiting the growth of multidrug-resistant Staphylococcus aureus over SCSNPs at 10 μg/ml (IC 50 = 100 μg/ml).

15. Activated charcoal-carboxymethylcellulose gel formulation as an antidotal agent for orally ingested aspirin.

PubMed

Mathur, L K; Jaffe, J M; Colaizzi, J L; Moriarty, R W

1976-07-01

The in vivo effect on aspirin absorption of a potentially more palatable form of activated charcoal was compared to that of a simple aqueous slurry of activated charcoal. The experimental formulation consisted of 20.0 g of activated charcoal, 2.25 g of carboxymethylcellulose (CMC) and 42.8 ml of water; it was tested with and without chocolate syrup as a flavoring agent added just prior to administration. Six subjects were treated in crossover fashion following an aspirin dose of 972 mg. Total urinary excretion of salicylate was measured over 48 hours. Although all three treatments appeared to be effective in reducing the rate and extent of aspirin absorption, the slurry was significantly more effective in reducing the total amount absorbed than the charcoal-CMC gel with chocolate syrup. The slight difference in effectiveness between the gel formulation with and without the chocolate syrup was not significant. PMID:941924

16. Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon.

PubMed

Alvarez, Jon; Lopez, Gartzen; Amutio, Maider; Bilbao, Javier; Olazar, Martin

2014-10-01

The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500°C. Extraction with Na2CO3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800°C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365m(2)g(-1) at the end of 15min.

17. Encapsulation of nanoclusters in dried gel materials via an inverse micelle/sol gel synthesis

DOEpatents

Martino, Anthony; Yamanaka, Stacey A.; Kawola, Jeffrey S.; Showalter, Steven K.; Loy, Douglas A.

1998-01-01

A dried gel material sterically entrapping nanoclusters of a catalytically active material and a process to make the material via an inverse micelle/sol-gel synthesis. A surfactant is mixed with an apolar solvent to form an inverse micelle solution. A salt of a catalytically active material, such as gold chloride, is added along with a silica gel precursor to the solution to form a mixture. To the mixture are then added a reducing agent for the purpose of reducing the gold in the gold chloride to atomic gold to form the nanoclusters and a condensing agent to form the gel which sterically entraps the nanoclusters. The nanoclusters are normally in the average size range of from 5-10 nm in diameter with a monodisperse size distribution.

18. Encapsulation of nanoclusters in dried gel materials via an inverse micelle/sol gel synthesis

DOEpatents

Martino, A.; Yamanaka, S.A.; Kawola, J.S.; Showalter, S.K.; Loy, D.A.

1998-09-29

A dried gel material sterically entrapping nanoclusters of a catalytically active material and a process to make the material via an inverse micelle/sol-gel synthesis are disclosed. A surfactant is mixed with an apolar solvent to form an inverse micelle solution. A salt of a catalytically active material, such as gold chloride, is added along with a silica gel precursor to the solution to form a mixture. To the mixture are then added a reducing agent for the purpose of reducing the gold in the gold chloride to atomic gold to form the nanoclusters and a condensing agent to form the gel which sterically entraps the nanoclusters. The nanoclusters are normally in the average size range of from 5--10 nm in diameter with a monodisperse size distribution. 1 fig.

19. Silica nanoparticles in E ring ice grains as an indicator for hydrothermal activities at Enceladus

Postberg, F.; Hsu, H. W.; Sekine, Y.

2013-09-01

Since 2004 the Cosmic Dust Analyser (CDA) on board the Cassini spacecraft detects nano-meter sized dust particles, so called stream particles, in the Saturnian system. Recently it has been shown that they are released from E ring ice grains in which they were previously embedded [1]. As a consequence the nanograins must have been generated at Saturns active moon Enceladus which feeds the E ring by its spectacular jets of vapour and ice grains. Liquid water below the moons icy crust is known to be the dominant source of these jets [2, 3]. New results from CDA presented here indicate that stream particles actually are nano-silica grains. The most prominent geological process which produces nano-phase silica are hydrothermal rock-water interactions. This process has recently been intensely studied for hydrothermal systems on Earth [e.g. 4, 5]. The measured concentration, composition and size range observed at in the Saturnian system precisely matches a hydrothermal synthesis origin. Thus, we propose nano-colloidal silica to be present at mMol concentrations in Enceladus' subsurface waters. We were able to reproduce the proposed hydrothermal serpentinisation processes in a geochemical long term experiment in the laboratory. As there are no alternative formation scenarios which are in agreement with the CDA observations our results indicate ongoing rock-water interactions inside Enceladus at temperatures clearly exceeding 100°C. We discuss implications for Enceladus geochemistry, like salinity, possible ranges of temperature and pH, as well as the mineral composition of the Enceladian rock core.

20. Enzyme renaturation to higher activity driven by the sol-gel transition: Carbonic anhydrase

2015-09-01

We describe a so-far unknown route for renaturing denatured enzymes, namely subjecting the denatured enzyme to an oxide sol-gel transition. The phenomenon was revealed in a detailed study of denatured carbonic anhydrase which was subjected to an alumina sol-gel transition, up to the thermally stabilizing entrapment in the final xerogel. Remarkably, not only that the killed enzyme regained its activity during the sol-gel process, but its activity increased to 180% of the native enzyme. To the best of our knowledge, this is the first report of enhanced activity following by renaturing (a “Phoenix effect”). Kinetic study which revealed a five-orders of magnitude (!) increase in the Arrhenius prefactor upon entrapment compared to solution. Circular dichroism analysis, differential scanning calorimetry, zeta potential analyses as well as synchronous fluorescence measurements, all of which were used to characterize the phenomenon, are consistent with a proposed mechanism which is based on the specific orienting interactions of the active site of the enzyme with respect to the alumina interface and its pores network.

1. In vitro and in vivo antioxidant activities of polysaccharide purified from aloe vera (Aloe barbadensis) gel.

PubMed

Kang, Min-Cheol; Kim, Seo Young; Kim, Yoon Taek; Kim, Eun-A; Lee, Seung-Hong; Ko, Seok-Chun; Wijesinghe, W A J P; Samarakoon, Kalpa W; Kim, Young-Sun; Cho, Jin Hun; Jang, Hyeang-Su; Jeon, You-Jin

2014-01-01

The in vitro and in vivo antioxidant potentials of a polysaccharide isolated from aloe vera gel were investigated. Enzymatic extracts were prepared from aloe vera gel by using ten digestive enzymes including five carbohydrases and five proteases. Among them, the highest yield was obtained with the Viscozyme extract and the same extract showed the best radical scavenging activity. An active polysaccharide was purified from the Viscozyme extract using ethanol-added separation and anion exchange chromatography. Purified aloe vera polysaccharide (APS) strongly scavenged radicals including DPPH, hydroxyl and alkyl radicals. In addition, APS showed a protective effect against AAPH-induced oxidative stress and cell death in Vero cells as well as in the in vivo zebrafish model. In this study, it is proved that both the in vitro and in vivo antioxidant potentials of APS could be further utilized in relevant industrial applications.

2. Photocatalytic activity of titania coatings synthesised by a combined laser/sol–gel technique

SciTech Connect

Adraider, Y.; Pang, Y.X.; Nabhani, F.; Hodgson, S.N.; Sharp, M.C.; Al-Waidh, A.

2014-06-01

Highlights: • Sol–gel method was used to prepare titania coatings. • Titania thin films were coated on substrate surface by dip coating. • Fibre laser was employed to irradiate the titania coated surfaces. • Photocatalytic efficiency of titania coatings was significantly improved after laser processing. - Abstract: Titania coatings were prepared using sol–gel method and then applied on the substrate surface by dip coating. Fibre laser (λ = 1064 nm) in continuous wave mode was used to irradiate the titania coated surfaces at different specific energies. The ATR-FTIR, XRD, SEM, EDS and contact angle measurement were employed to analyse surface morphology, phase composition and crystalline structure of laser-irradiated titania coatings, whilst the photocatalytic activity was evaluated by measuring the decomposition of methylene blue (MB) after exposure to the visible light for various illumination times. Results showed that the laser-irradiated titania coatings demonstrate significant different composition and microstructure in comparison with the as-coated from the same sol–gel titania. Photocatalytic efficiency of titania coatings was significantly improved after laser processing. The photocatalytic activity of laser-irradiated titania coatings was higher than that of the as-coated titania. The titania coating processed at laser specific energy of 6.5 J/mm{sup 2} exhibited the highest photocatalytic activity among all titania samples.

3. IPEC Gels for Remediating Soils Contaminated as Result of Nuclear and Industrial Activities

SciTech Connect

Mikheykin, S.V.; Anciferova, E.Yu.; Simonov, V.P.; Zezin, A.B.; Rogacheva, V.B.; Bolusheva, T.N.

2006-07-01

be highly erosion-resistant. It showed that new kinds of IPECs based with micro-gels are very useful as soil stabilizers and applicable as activating agent of grass vegetation in the remediation activities. It may successfully apply also in the post-accidental activities in the case of spray radioactive materials onto topsoils. (authors)

4. [Preparation and anti-cancer activity in vitro of curcumin loaded mesoporous silica nanoparticle].

PubMed

He, Li-li; Gu, Jian

2015-11-01

This paper is to prepare curcumin (Cur) loaded mesoporous silica nanoparticle (Cur-MSN), evaluate its release behavior and anti-cancer activity in vitro. Mesoporous silica nanoparticle (MSN) was prepared by polymerization method and Cur-MSN was obtained using solvent evaporation method and impregnation centrifugation method. The preparation method was optimized using entrapment efficiency (EE) and loading efficiency (LE) as indexes. Cur-MSN was characterized with scanning electron microscope and its particle size and zeta potential were determined. Finally, in vitro release behavior in 0.2% SDS solution and its cell-killing effect on HeLa cells were also evaluated. The Cur-MSN prepared with process optimization method was round and uniform and exhibited typical mesoporous characterization. The mean particle size and Zeta potential of Cur-MSN were 75.8 nm and -30.1 mV, respectively. EE and LE of three batches of Cur-MSN were (72.55 ± 2.01)% and (16.21 ± 1.12)%, respectively. In vitro release behavior of Cur-MSN showed a sustained release profile with 83.5% cumulative release within 96 h. The killing effect of Cur-MSN on HeLa cells was dose-dependent with IC50 of 19.40 mg x L(-1), which was similar to that of Cur. PMID:27071254

5. Live Diatom Silica Immobilization of Multimeric and Redox-Active Enzymes

PubMed Central

Sheppard, V. C.; Scheffel, A.; Poulsen, N.

2012-01-01

Living organisms are adept in forming inorganic materials (biominerals) with unique structures and properties that exceed the capabilities of engineered materials. Biomimetic materials syntheses are being developed that aim at replicating the advantageous properties of biominerals in vitro and endow them with additional functionalities. Recently, proof-of-concept was provided for an alternative approach that allows for the production of biomineral-based functional materials in vivo. In this approach, the cellular machinery for the biosynthesis of nano-/micropatterned SiO2 (silica) structures in diatoms was genetically engineered to incorporate a monomeric, cofactor-independent (“simple”) enzyme, HabB, into diatom silica. In the present work, it is demonstrated that this approach is also applicable for enzymes with “complex” activity requirements, including oligomerization, metal ions, organic redox cofactors, and posttranslational modifications. Functional expression of the enzymes β-glucuronidase, glucose oxidase, galactose oxidase, and horseradish peroxidase in the diatom Thalassiosira pseudonana was accomplished, and 66 to 78% of the expressed enzymes were stably incorporated into the biosilica. The in vivo incorporated enzymes represent approximately 0.1% (wt/wt) of the diatom biosilica and are stabilized against denaturation and proteolytic degradation. Furthermore, it is demonstrated that the gene construct for in vivo immobilization of glucose oxidase can be utilized as the first negative selection marker for diatom genetic engineering. PMID:22057862

6. Live diatom silica immobilization of multimeric and redox-active enzymes.

PubMed

Sheppard, V C; Scheffel, A; Poulsen, N; Kröger, N

2012-01-01

Living organisms are adept in forming inorganic materials (biominerals) with unique structures and properties that exceed the capabilities of engineered materials. Biomimetic materials syntheses are being developed that aim at replicating the advantageous properties of biominerals in vitro and endow them with additional functionalities. Recently, proof-of-concept was provided for an alternative approach that allows for the production of biomineral-based functional materials in vivo. In this approach, the cellular machinery for the biosynthesis of nano-/micropatterned SiO₂ (silica) structures in diatoms was genetically engineered to incorporate a monomeric, cofactor-independent ("simple") enzyme, HabB, into diatom silica. In the present work, it is demonstrated that this approach is also applicable for enzymes with "complex" activity requirements, including oligomerization, metal ions, organic redox cofactors, and posttranslational modifications. Functional expression of the enzymes β-glucuronidase, glucose oxidase, galactose oxidase, and horseradish peroxidase in the diatom Thalassiosira pseudonana was accomplished, and 66 to 78% of the expressed enzymes were stably incorporated into the biosilica. The in vivo incorporated enzymes represent approximately 0.1% (wt/wt) of the diatom biosilica and are stabilized against denaturation and proteolytic degradation. Furthermore, it is demonstrated that the gene construct for in vivo immobilization of glucose oxidase can be utilized as the first negative selection marker for diatom genetic engineering.

7. A Silica-Supported Iron Oxide Catalyst Capable of Activating Hydrogen Peroxide at Neutral pH Values

PubMed Central

Pham, Anh Le-Tuan; Lee, Changha; Doyle, Fiona M.; Sedlak, David L.

2009-01-01

Iron oxides catalyze the conversion of hydrogen peroxide (H2O2) into oxidants capable of transforming recalcitrant contaminants. Unfortunately, the process is relatively inefficient at circumneutral pH values due to competing reactions that decompose H2O2 without producing oxidants. Silica- and alumina-containing iron oxides prepared by sol-gel processing of aqueous solutions containing Fe(ClO4)3, AlCl3 and tetraethyl orthosilicate efficiently catalyzed the decomposition of H2O2 into oxidants capable of transforming phenol at circumneutral pH values. Relative to hematite, goethite and amorphous FeOOH, the silica-iron oxide catalyst exhibited a stoichiometric efficiency, defined as the number of moles of phenol transformed per mole of H2O2 consumed, that was 10 to 40 times higher than that of the iron oxides. The silica-alumina-iron oxide catalyst had a stoichiometric efficiency that was 50 to 80 times higher than that of the iron oxides. The significant enhancement in oxidant production is attributable to the interaction of Fe with Al and Si in the mixed oxides, which alters the surface redox processes, favoring the production of strong oxidants during H2O2 decomposition. PMID:19943668

8. Mesostructured Silica for Optical Functionality, Nanomachines, and Drug Delivery

PubMed Central

Klichko, Yaroslav; Liong, Monty; Choi, Eunshil; Angelos, Sarah; Nel, Andre E.; Stoddart, J. Fraser; Tamanoi, Fuyuhiko; Zink, Jeffrey I.

2009-01-01

Silica thin films and nanoparticles prepared using sol–gel chemistry are derivatized with active molecules to generate new functional materials. The mild conditions associated with sol–gel processing allow for the incorporation of a range of dopants including organic or inorganic dyes, biomolecules, surfactants, and molecular machines. Silica nanoparticles embedded with inorganic nanocrystals, and films containing living cells have also been synthesized. Silica templated with surfactants to create mesostructure contains physically and chemically different regions that can be selectively derivatized using defined techniques to create dynamic materials. Using two different techniques, donor–acceptor pairs can be doped into separated regions simultaneously and photo-induced electron transfer between the molecules can be measured. Mesoporous silica materials are also useful supports for molecular machines. Machines including snap-tops and nanoimpellers that are designed to control the release of guest molecules trapped within the pores are described. Mesoporous silica nanoparticles are promising materials for drug delivery and other biomedical applications because they are nontoxic and can be taken up by living cells. Through appropriate design and synthesis, multifunctional mesoporous silica nanoparticles for sophisticated bio-applications are created. PMID:19834571

9. Mesostructured Silica for Optical Functionality, Nanomachines, and Drug Delivery.

PubMed

Klichko, Yaroslav; Liong, Monty; Choi, Eunshil; Angelos, Sarah; Nel, Andre E; Stoddart, J Fraser; Tamanoi, Fuyuhiko; Zink, Jeffrey I

2009-01-01

Silica thin films and nanoparticles prepared using sol-gel chemistry are derivatized with active molecules to generate new functional materials. The mild conditions associated with sol-gel processing allow for the incorporation of a range of dopants including organic or inorganic dyes, biomolecules, surfactants, and molecular machines. Silica nanoparticles embedded with inorganic nanocrystals, and films containing living cells have also been synthesized. Silica templated with surfactants to create mesostructure contains physically and chemically different regions that can be selectively derivatized using defined techniques to create dynamic materials. Using two different techniques, donor-acceptor pairs can be doped into separated regions simultaneously and photo-induced electron transfer between the molecules can be measured. Mesoporous silica materials are also useful supports for molecular machines. Machines including snap-tops and nanoimpellers that are designed to control the release of guest molecules trapped within the pores are described. Mesoporous silica nanoparticles are promising materials for drug delivery and other biomedical applications because they are nontoxic and can be taken up by living cells. Through appropriate design and synthesis, multifunctional mesoporous silica nanoparticles for sophisticated bio-applications are created.

10. Increasing the activity and enantioselectivity of lipases by sol-gel immobilization: further advancements of practical interest.

PubMed

Tielmann, Patrick; Kierkels, Hans; Zonta, Albin; Ilie, Adriana; Reetz, Manfred T

2014-06-21

The entrapment of lipases in hydrophobic silicate matrices formed by sol-gel mediated hydrolysis of RSi(OCH3)3/Si(OCH3)4 as originally reported in 1996 has been improved over the years by a number of modifications. In the production of second-generation sol-gel lipase immobilizates, a variety of additives during the sol-gel process leads to increased activity and enhanced stereoselectivity in esterifying kinetic resolution. Recent advances in this type of lipase immobilization are reviewed here, in addition to new results regarding the sol-gel entrapment of the lipase from Burkholderia cepacia. It constitutes an excellent heterogeneous biocatalyst in the acylating kinetic resolution of two synthetically and industrially important chiral alcohols, rac-sulcatol and rac-trans-2-methoxycyclohexanol. The observation that the catalyst can be used 10 times in recycling experiments without losing its significant activity or enantioselectivity demonstrates the practical viability of the sol-gel approach.

11. Transparent gels: study of their formation and assimilation of active ingredients through phase diagrams.

PubMed

Comelles, F; Caelles, J; Parra, J L; Leal, J S

1992-08-01

Synopsis Multicomponent gel formulations capable of assimilating, simultaneously, several active ingredients of potential application in the cosmetic field were studied. The possibility of formation of a transparent gel was determined using a method which consisted in the optimization of several lipophilic basic compositions, composed of oil, a mixture of surfactants, a sunscreen agent, several vitamins and antioxidants situated in the base of a regular tetrahedron that symbolized the considered system. To this, a polar phase made of water, a cosolvent and urea in appropriate proportions and situated in the fourth vertex, was progressively added. It may be concluded, that the use of phase diagrams on cosmetic systems, constitutes a useful way to select the components and their mutual ratios, allowing an adaptation to the specific requested conditions of formulation.

12. Application of factorial design and Doehlert matrix for determination of trace lead in environmental samples by on-line column preconcentration FAAS using silica gel chemically modified with niobium(V) oxide.

PubMed

Roux, Kalya Cravo Di Pietro; Maltez, Heloisa França; Carletto, Jeferson Schneider; Martendal, Edmar; Carasek, Eduardo

2008-03-01

In this study a new method for Pb determination in water using solid phase extraction coupled to a flow injection system and flame atomic absorption spectrometry was developed. The sorbent used for Pb preconcentration and extraction was silica gel chemically modified with niobium(V) oxide. Flow and chemical variables of the system were optimized through a multivariate procedure. The factors selected were buffer type, eluent concentration, and sample and eluent flow rates. It was verified that the aforementioned factors as well as their interactions were statistically significant at the 95% confidence level. The effect of foreign ions was evaluated using a fractionary factorial experimental design. The detection limit was 0.35 microg L(-1) and the precision was 1.6%. Results for recovery tests using different environmental samples were between 90 and 104%. Certified reference materials were analyzed in order to check the accuracy of the proposed method. PMID:18332544

13. The adsorption of CO(2)/H(2)O/N(2) on 5A zeolite and silica gel in a packed column in one and two-dimensional flows

The purpose of this work is to develop a computer model that simulates the dynamic behavior of a Four-Bed Molecular Sieves (4-BMS) system. The system will be installed on the International Space Station for removal of CO 2/H2O/N2 on four beds that consist of 5A zeolite, 13X zeolite, and Silica gel. Due to the complexity of the actual 4-BMS, separately packed columns of 5A and Silica gel were built and tested using the model results to obtain the mass and heat transfer coefficients necessary for the development of the 4-BMS. This work begins by introducing the adsorption/desorption process in a packed column. The formulation of the simplest model of adsorption in a packed bed is developed assuming that Darcy's law. In this model, the mass and heat transport gradients are assumed to vary only in the axial direction, i.e., one-dimensional flow. The results of temperature and mass transfer breakthrough of one-dimensional flow are compared with the test results for adsorption of CO2/N2 and CO2/H2O/N2 on 5A zeolite. In the packed column near the wall boundary, the velocity decreases due to the viscous forces and the porosity increases exponentially. This near-wall region of higher porosity results in the channeling of fluid close to the wall surface. This channeling causes an early solute breakthrough relative to the center of the column. In order to accommodate the effect of porosity variation on the breakthrough, a two-dimensional model of the packed column is developed. The results of two-dimensional flow are compared with the test results for adsorption of CO2/N2 and CO2/H 2O/N2 on 5A zeolite. This work also investigates the dynamics of H2O adsorption on Silica gel material. A one-dimensional flow of a packed column bed is developed with the assumption that Darcy's law governs the momentum transport. The results of both models are compared with the test results for adsorption of H 2O/N2 on Silica gel. Finally, a computer model based on the obtained parameters of

14. Determination of anionic surface active agents using silica coated magnetite nanoparticles modified with cationic surfactant aggregates.

PubMed

Pena-Pereira, Francisco; Duarte, Regina M B O; Trindade, Tito; Duarte, Armando C

2013-07-19

The development of a novel methodology for extraction and preconcentration of the most commonly used anionic surface active agents (SAAs), linear alkylbenzene sulfonates (LAS), is presented herein. The present method, based on the use of silica-magnetite nanoparticles modified with cationic surfactant aggregates, was developed for determination of C10-C13 LAS homologues. The proposed methodology allowed quantitative recoveries of C10-C13 LAS homologues by using a reduced amount of magnetic nanoparticles. Limits of detection were in the range 0.8-1.9μgL(-1) for C10-C13 LAS homologues, while the repeatability, expressed as relative standard deviation (RSD), ranged from 2.0 to 3.9% (N=6). Finally, the proposed method was successfully applied to the analysis of a variety of natural water samples.

15. Photosynthetic activity of spinach chloroplasts after isopycnic centrifugation in gradients of silica.

PubMed

Morgenthaler, J J; Price, C A

1974-10-01

Chloroplast suspensions from spinach (Spinacia oleracea L.) were clearly resolved into intact and stripped chloroplasts by isopycnic centrifugation in density gradients of silica sol ("Ludox") and polyethlene glycol. The intact chloroplasts fixed CO(2) and evolved O(2) more rapidly than the crude suspensions; the stripped chloroplasts were inactive. During the photosynthetic fixation of (14)CO(2) in the intact chloroplasts recovered from the gradient, the (14)C label was observed to spread through the photosynthetic intermediate pools, as well as into starch, which indicates that the purified chloroplasts are metabolically competent. This appears to be the first report of the retention of photosynthetic activity following the purification of chloroplasts in density gradients. PMID:16658922

16. Substrate effect on nanoporous structure of silica wires by channel-confined self-assembly of block-copolymer and sol-gel precursors

DOE PAGES

Hu, Michael Z.; Lai, Peng

2015-09-22

Nanoporous silica wires of various wire diameters were developed by space-confined molecular self-assembly of triblock copolymer ethylene/propylene/ethylene (P123) and silica alkoxide precursor (tetraethylorthosilicate, TEOS). Two distinctive hard-templating substrates, anodized aluminum oxide (AAO) and track-etched polycarbonate (EPC), with channel diameters in the range between 10 nm and 200 nm were employed for space-confinement of soft molecular self-assembly driven by the block-copolymer microphase separation. It was observed in the scanning and transmission electron microscope (STEM) studies that the substrate geometry and material characteristics had pronounced effects on the structure and morphology of the silica nanowires. A substrate wall effect was proposed tomore » explain the ordering and orientation of the intra-wire mesostructure. Circular and spiral nanostructures were found only in wires formed in AAO substrate, not in EPC. Pore-size differences and distinctive wall morphologies of the nanowires relating to the substrates were discussed. It was shown that the material and channel wall characteristics of different substrates play key roles in the ordering and morphology of the intra-wire nanostructures.« less

17. Substrate effect on nanoporous structure of silica wires by channel-confined self-assembly of block-copolymer and sol-gel precursors

SciTech Connect

Hu, Michael Z.; Lai, Peng

2015-09-22

Nanoporous silica wires of various wire diameters were developed by space-confined molecular self-assembly of triblock copolymer ethylene/propylene/ethylene (P123) and silica alkoxide precursor (tetraethylorthosilicate, TEOS). Two distinctive hard-templating substrates, anodized aluminum oxide (AAO) and track-etched polycarbonate (EPC), with channel diameters in the range between 10 nm and 200 nm were employed for space-confinement of soft molecular self-assembly driven by the block-copolymer microphase separation. It was observed in the scanning and transmission electron microscope (STEM) studies that the substrate geometry and material characteristics had pronounced effects on the structure and morphology of the silica nanowires. A substrate wall effect was proposed to explain the ordering and orientation of the intra-wire mesostructure. Circular and spiral nanostructures were found only in wires formed in AAO substrate, not in EPC. Pore-size differences and distinctive wall morphologies of the nanowires relating to the substrates were discussed. It was shown that the material and channel wall characteristics of different substrates play key roles in the ordering and morphology of the intra-wire nanostructures.

18. Poly(lactic) acid fibers loaded with mesoporous silica for potential applications in the active food packaging

Cacciotti, Ilaria; Nanni, Francesca

2016-06-01

Multifunctional fibrous systems based on poly(lactic) acid (PLA), mesoporous silica (SiO2) and ascorbic acid (AA) were produced by means of electrospinning technique, for potential applications in the active food packaging sector, as platform for the controlled release of antioxidant and/or antimicrobial agents with the additional filtering function. The ascorbic acid was physisorbed on the surface of mesoporous silica in order to stabilize it and to extend its antioxidant action. The influence of mesoporous silica and ascorbic acid on the microstructural and mechanical properties was investigated, revealing a revelant mechanical reinforcement in the case of fibers loaded only with SiO2 and a decrement in the case of SiO2 with physisorbed ascorbic acid, due to the worse interface between the fillers and the polymeric matrix.

19. Sol-Gel Glasses

NASA Technical Reports Server (NTRS)

Mukherjee, S. P.

1985-01-01

Multicomponent homogeneous, ultrapure noncrystalline gels/gel derived glasses are promising batch materials for the containerless glass melting experiments in microgravity. Hence, ultrapure, homogeneous gel precursors could be used to: (1) investigate the effect of the container induced nucleation on the glass forming ability of marginally glass forming compositions; and (2) investigate the influence of gravity on the phase separation and coarsening behavior of gel derived glasses in the liquid-liquid immiscibility zone of the nonsilicate systems having a high density phase. The structure and crystallization behavior of gels in the SiO2-GeO2 as a function of gel chemistry and thermal treatment were investigated. As are the chemical principles involved in the distribution of a second network former in silica gel matrix being investigated. The procedures for synthesizing noncrystalline gels/gel-monoliths in the SiO2-GeO2, GeO2-PbO systems were developed. Preliminary investigations on the levitation and thermal treatment of germania silicate gel-monoliths in the Pressure Facility Acoustic Levitator were done.

20. Nonequilibrium structure and dynamics in a microscopic model of thin-film active gels

Head, D. A.; Briels, W. J.; Gompper, Gerhard

2014-03-01

In the presence of adenosine triphosphate, molecular motors generate active force dipoles that drive suspensions of protein filaments far from thermodynamic equilibrium, leading to exotic dynamics and pattern formation. Microscopic modeling can help to quantify the relationship between individual motors plus filaments to organization and dynamics on molecular and supramolecular length scales. Here, we present results of extensive numerical simulations of active gels where the motors and filaments are confined between two infinite parallel plates. Thermal fluctuations and excluded-volume interactions between filaments are included. A systematic variation of rates for motor motion, attachment, and detachment, including a differential detachment rate from filament ends, reveals a range of nonequilibrium behavior. Strong motor binding produces structured filament aggregates that we refer to as asters, bundles, or layers, whose stability depends on motor speed and differential end detachment. The gross features of the dependence of the observed structures on the motor rate and the filament concentration can be captured by a simple one-filament model. Loosely bound aggregates exhibit superdiffusive mass transport, where filament translocation scales with lag time with nonunique exponents that depend on motor kinetics. An empirical data collapse of filament speed as a function of motor speed and end detachment is found, suggesting a dimensional reduction of the relevant parameter space. We conclude by discussing the perspectives of microscopic modeling in the field of active gels.

1. Anti-inflammatory activity of Achillea and Ruscus topical gel on carrageenan-induced paw edema in rats.

PubMed

2006-01-01

The anti-inflammatory activity of Achillea and Ruscus extracts was studied in comparison with diclofenac sodium topical gel (diclosal Emulgel), using the carrageenan induced paw edema model in Albino rats. Gel formulation was prepared containing 6% of each extract in gel base, namely sodium carboxymethylcellulose (NaCMC). The kinetics of drug release from the prepared formulation was studied separately in each case. Results showed that the release follows the Higuchi square root equation. The pharmacological screening revealed that the percent reduction of edema for Achillea extract and Ruscus extract were 48.1% and 18.8%, respectively, while diclosal Emulgel produced 47% reduction of edema.

2. Water-compatible silica sol-gel molecularly imprinted polymer as a potential delivery system for the controlled release of salicylic acid.

PubMed

Li, Bin; Xu, Jingjing; Hall, Andrew J; Haupt, Karsten; Tse Sum Bui, Bernadette

2014-09-01

Molecularly imprinted polymers (MIPs) for salicylic acid were synthesized and evaluated in aqueous environments in the aim to apply them as drug delivery carriers. One organic MIP and one inorganic MIP based on the sol-gel process were synthesized. The organic MIP was prepared by radical polymerization using the stoichiometric functional monomer, 1-(4-vinylphenyl)-3-(3,5-bis(trifluoromethyl)phenyl)urea, which can establish strong electrostatic interactions with the -COOH of salicylic acid. The sol-gel MIP was prepared with 3-(aminopropyl)triethoxysilane and trimethoxyphenylsilane, as functional monomers and tetraethyl orthosilicate as the crosslinker. While the organic MIPs bound the target specifically in acetonitrile, they exhibited lower binding in the presence of water, although the imprinting factor increased under these conditions, due to reduced non-specific binding. The sol-gel MIP has a high specificity and capacity for the drug in ethanol, a solvent compatible with drug formulation and biomedical applications. In vitro release profiles of the polymers in water were evaluated, and the results were modelled by Fick's law of diffusion and the power law. Analysis shows that the release mechanism was predominantly diffusion-controlled. PMID:25042710

3. Water-compatible silica sol-gel molecularly imprinted polymer as a potential delivery system for the controlled release of salicylic acid.

PubMed

Li, Bin; Xu, Jingjing; Hall, Andrew J; Haupt, Karsten; Tse Sum Bui, Bernadette

2014-09-01

Molecularly imprinted polymers (MIPs) for salicylic acid were synthesized and evaluated in aqueous environments in the aim to apply them as drug delivery carriers. One organic MIP and one inorganic MIP based on the sol-gel process were synthesized. The organic MIP was prepared by radical polymerization using the stoichiometric functional monomer, 1-(4-vinylphenyl)-3-(3,5-bis(trifluoromethyl)phenyl)urea, which can establish strong electrostatic interactions with the -COOH of salicylic acid. The sol-gel MIP was prepared with 3-(aminopropyl)triethoxysilane and trimethoxyphenylsilane, as functional monomers and tetraethyl orthosilicate as the crosslinker. While the organic MIPs bound the target specifically in acetonitrile, they exhibited lower binding in the presence of water, although the imprinting factor increased under these conditions, due to reduced non-specific binding. The sol-gel MIP has a high specificity and capacity for the drug in ethanol, a solvent compatible with drug formulation and biomedical applications. In vitro release profiles of the polymers in water were evaluated, and the results were modelled by Fick's law of diffusion and the power law. Analysis shows that the release mechanism was predominantly diffusion-controlled.

4. Mesoporous silica coatings for cephalosporin active release at the bone-implant interface

Rădulescu, Dragoş; Voicu, Georgeta; Oprea, Alexandra Elena; Andronescu, Ecaterina; Grumezescu, Valentina; Holban, Alina Maria; Vasile, Bogdan Stefan; Surdu, Adrian Vasile; Grumezescu, Alexandru Mihai; Socol, Gabriel; Mogoantă, Laurenţiu; Mogoşanu, George Dan; Balaure, Paul Cătălin; Rădulescu, Radu; Chifiriuc, Mariana Carmen

2016-06-01

In this study, we investigated the potential of MAPLE-deposited coatings mesoporous silica nanoparticles (MSNs) to release Zinforo (ceftarolinum fosmil) in biologically active form. The MSNs were prepared by using a classic procedure with cetyltrimethylammonium bromide as sacrificial template and tetraethylorthosilicate as the monomer. The Brunauer-Emmett-Teller (BET) and transmission electron microscopy (TEM) analyses revealed network-forming granules with diameters under 100 nm and an average pore diameter of 2.33 nm. The deposited films were characterized by SEM, TEM, XRD and IR. Microbiological analyses performed on ceftaroline-loaded films demonstrated that the antibiotic was released in an active form, decreasing the microbial adherence rate and colonization of the surface. Moreover, the in vitro and in vivo assays proved the excellent biodistribution and biocompatibility of the prepared systems. Our results suggest that the obtained bioactive coatings possess a significant potential for the design of drug delivery systems and antibacterial medical-use surfaces, with great applications in bone implantology.

5. Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica.

PubMed

Ji, Yazhou; Caskey, Christopher; Richards, Ryan M

2015-01-01

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties of the materials were investigated. We used a one pot sol-gel approach to intercalate gold nano particles in the walls of mesoporous silica. To start with the synthesis, P123 was used as template to form micelles. Then TESPTS was used as a surface modification agent to intercalate gold nano particles. Following this process, TEOS was added in as a silica source which underwent a polymerization process in acid environment. After hydrothermal processing and calcination, the final product was acquired. Several techniques were utilized to characterize the porosity, morphology and structure of the gold intercalated mesoporous silica. The results showed a stable structure of mesoporous silica after gold intercalation. Through the oxidation of benzyl alcohol as a benchmark reaction, the GMS materials showed high selectivity and recyclability.

6. Controllable formation of high density SERS-active silver nanoprism layers on hybrid silica-APTES coatings

Pilipavicius, J.; Kaleinikaite, R.; Pucetaite, M.; Velicka, M.; Kareiva, A.; Beganskiene, A.

2016-07-01

In this work sol-gel process for preparation of the uniform hybrid silica-3-aminopropyltriethoxysilane (APTES) coatings on glass surface is presented from mechanistic point of view. The suggested synthetic approach is straightforward, scalable and provides the means to tune the amount of amino groups on the surface simply by changing concentration of APTES in the initial sol. Deposition rate of different size silver nanoprisms (AgNPRs) on hybrid silica coatings of various amounts of APTES were studied and their performance as SERS materials were probed. The acquired data shows that the deposition rate of AgNPRs can be tuned by changing the amount of APTES. The optimal amount of APTES was found to be crucial for successful AgNPRs assembly and subsequent uniformity of the final SERS substrate-too high APTES content may result in rapid non-stable aggregation and non-uniform assembly process. SERS study revealed that SERS enhancement is the strongest at moderate AgNPRs aggregation level whereas it significantly drops at high aggregation levels.

7. Increasing the activity and enantioselectivity of lipases by sol-gel immobilization: further advancements of practical interest

Tielmann, Patrick; Kierkels, Hans; Zonta, Albin; Ilie, Adriana; Reetz, Manfred T.

2014-05-01

The entrapment of lipases in hydrophobic silicate matrices formed by sol-gel mediated hydrolysis of RSi(OCH3)3/Si(OCH3)4 as originally reported in 1996 has been improved over the years by a number of modifications. In the production of second-generation sol-gel lipase immobilizates, a variety of additives during the sol-gel process leads to increased activity and enhanced stereoselectivity in esterifying kinetic resolution. Recent advances in this type of lipase immobilization are reviewed here, in addition to new results regarding the sol-gel entrapment of the lipase from Burkholderia cepacia. It constitutes an excellent heterogeneous biocatalyst in the acylating kinetic resolution of two synthetically and industrially important chiral alcohols, rac-sulcatol and rac-trans-2-methoxycyclohexanol. The observation that the catalyst can be used 10 times in recycling experiments without losing its significant activity or enantioselectivity demonstrates the practical viability of the sol-gel approach.The entrapment of lipases in hydrophobic silicate matrices formed by sol-gel mediated hydrolysis of RSi(OCH3)3/Si(OCH3)4 as originally reported in 1996 has been improved over the years by a number of modifications. In the production of second-generation sol-gel lipase immobilizates, a variety of additives during the sol-gel process leads to increased activity and enhanced stereoselectivity in esterifying kinetic resolution. Recent advances in this type of lipase immobilization are reviewed here, in addition to new results regarding the sol-gel entrapment of the lipase from Burkholderia cepacia. It constitutes an excellent heterogeneous biocatalyst in the acylating kinetic resolution of two synthetically and industrially important chiral alcohols, rac-sulcatol and rac-trans-2-methoxycyclohexanol. The observation that the catalyst can be used 10 times in recycling experiments without losing its significant activity or enantioselectivity demonstrates the practical viability of

8. Evaluation of silica-gel cartridges coated in situ with acidified 2,4-dinitrophenylhydrazine for sampling aldehydes and ketones in air

SciTech Connect

1986-01-01

A procedure for coating in-situ silica in commercially available prepacked cartridges with 2,4-dinitrophenylhydrazine (DNPH) acidified with hydrochloric acid is described. The coated cartridge was compared with a validated DNPH impinger method for sampling organic carbonyl compounds (aldehydes and ketones) in diluted automotive exhaust emissions and in ambient air for subsequent analysis of the DNPH derivatives by high performance liquid chromatography. Qualitative and quantitative results show that the two sampling devices are equivalent. An unknown degradation product of acrolein has been tentatively identified as x-acrolein. The disappearance of acrolein in the analytical sample matrix correlated quantitatively almost on a mole-for-mole basis with the growth of x-acrolein. The sum of the concentration of acrolein and x-acrolein appears to be invariant with time. This sum could possibly be used as a more-accurate value of the concentration of acrolein in the integratated sample.

9. Assembly of acid and sintering resistant honeycomb washcoat and catalytically active phase using sols of silica, zirconia, and platinum

SciTech Connect

Felthouse, T.R. |; Berkel, D.A.; Jost, S.R.

1995-12-01

Development of high performance honeycomb catalysts containing platinum active phase for gas phase air oxidation of sulfur dioxide is described. Stepwise assembly of these washcoated honeycombs consists of: (1) selection of honeycomb composition (mullite substrate) and cell density based on pressure drop requirements; (2) identification of washcoat slurry composition (silica-precursor sol, silica powder, and surfactants if needed); (3) processing of the washcoat-substrate by dip coating, drying, and calcining; (4) loading of the platinum active phase through a facilitated adsorption technique followed by drying and activation steps; and (5) reactor loading and evaluation. Details of these steps will be presented that include thermal and chemical stability tests. Characterization by transmission electron microscopy of the final Pt/(ZrO{sub 2}-SiO{sub 2}) composite attached to the mullite substrate will be reported.

10. Activators generated by electron transfer for atom transfer radical polymerization of styrene in the presence of mesoporous silica nanoparticles

SciTech Connect

Khezri, Khezrollah; Roghani-Mamaqani, Hossein

2014-11-15

Graphical abstract: Effect of mesoporous silica nanoparticles (MCM-41) on the activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is investigated. Decrement of conversion and number average molecular weight and also increment of polydispersity index (PDI) values are three main results of addition of MCM-41 nanoparticles. Incorporation of MCM-41 nanoparticles in the polystyrene matrix can clearly increase thermal stability and decrease glass transition temperature of the nanocomposites. - Highlights: • Spherical morphology, hexagonal structure, and high surface area with regular pore diameters of the synthesized MCM-41 nanoparticles are examined. • AGET ATRP of styrene in the presence of MCM-41 nanoparticles is performed. • Effect of MCM-41 nanoparticles addition on the polymerization rate, conversion and molecular weights of the products are discussed. • Improvement in thermal stability of the nanocomposites and decreasing T{sub g} values was also observed by incorporation of MCM-41 nanoparticles. - Abstract: Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol{sup −1}. However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric

11. Staining electrophoretic gels for laccase and peroxidase activity using 1,8-diaminonaphthalene.

PubMed

Hoopes, J T; Dean, J F

2001-06-01

A new chromogenic substrate for laccases and peroxidases, 1,8-diaminonapthalene, was used to detect phenoloxidase activity in gels after SDS-PAGE. This substrate has several advantages over other widely used phenoloxidase stains in that it is inexpensive, and the oxidized product has both high molar absorptivity and very low solubility. Furthermore, neither the substrate nor the product is known to have toxicity problems of the type associated with many other phenoloxidase stains. The sensitivity of detection using 1,8-diaminonapthalene was comparable to that obtained using the most sensitive stains commonly used for phenoloxidases, e.g., 3,3-diaminobenzidine, and was close to that attainable for protein detection using silver staining. Zymograms developed with 1,8-diaminonapthalene can be used with video densitometry to monitor the specific enzymatic activity of phenoloxidases during enzyme purification. PMID:11373084

12. Microbicidal activity of TiO2 nanoparticles synthesised by sol-gel method.

PubMed

Priyanka, Karathan Parakkandi; Sukirtha, Thiruvangium Henry; Balakrishna, Kagalagodu Manjunthiah; Varghese, Thomas

2016-04-01

In this study, the authors investigated antimicrobial activity of TiO2 nanoparticles (NPs) synthesised by sol-gel method. As synthesised TiO2 NPs were characterised by X-ray diffraction, scanning electron microscopy and ultraviolet-visible absorption spectroscopy. The antimicrobial activity of calcined TiO2 nanoparticle samples was examined in day light on Gram positive bacteria (Staphylococcus aureus, Streptococcus pneumonia and Bacillus subtilis), Gram negative bacteria (Proteus vulgaris, Pseudomonas aeruginosa and Escherichia coli) and fungal test pathogen Candida albicans. The synthesised TiO2 NPs were found to be effective in visible light against Streptococcus pneumonia, Staphylococcus aureus, Proteus vulgaris, Pseudomonas aeruginosa and Candida albicans. PMID:27074858

13. Effect of chemical activation of 10% carbamide peroxide gel in tooth bleaching.

PubMed

Batista, Graziela Ribeiro; Arantes, Paula Tamiao; Attin, Thomas; Wiegand, Annette; Torres, Carlos Rocha

2013-01-01

This study aimed to evaluate the efficacy of chemical agents to increase the bleaching effectiveness of 10% carbamide peroxide. Two hundred and ninety enamel-dentin discs were prepared from bovine incisors. The color measurement was performed by a spectrophotometer using the CIE L*a*b*system. The groups were divided according to the bleaching treatment: negative control group (NC): without bleaching; positive control group (PC): bleached with 10% carbamide peroxide gel without any chemical activator; Manganese gluconate (MG); Manganese chloride (MC); Ferrous gluconate (FG); Ferric chloride (FC); and Ferrous sulphate (FS). Three different concentrations (MG, MC, FG, FC: 0.01, 0.02 and 0.03% w/w; FS: 0.001, 0.002 and 0.003% w/w) for each agent were tested. The bleaching gel was applied on the specimens for 8 h, after which they were immersed in artificial saliva for 16 h, during 14 days. Color assessments were made after 7 and 14 days. The data were analyzed by repeated measures analysis of variance and Tukey's test (5%). Generally, the test groups were unable to increase the bleaching effect (ΔE) significantly compared to the PC group. Only for ΔL, significant higher values compared to the PC group could be seen after 7 days in groups MG (0.02%), and FS (0.002 and 0.003%). The NC group showed significantly lower values than all tested groups. It was concluded that for home bleaching procedures, the addition of chemical activators did not produce a bleaching result significantly higher than the use of 10% carbamide peroxide without activation, and that the concentration of chemical activators used did not significantly influence the effectiveness of treatment.

14. Study on third order nonlinear optical properties of a metal organic complex-Monothiourea-cadmium Sulphate Dihydrate single crystals grown in silica gel

Sivanandan, T.; Kalainathan, S.

2015-04-01

The third order nonlinear optical properties of Monothiourea-cadmium Sulphate Dihydrate crystal were measured using a He-Ne laser (λ=632.8 nm) by a Z-scan technique. The magnitude of nonlinear refractive index (n2) and nonlinear absorption coefficient was found to be 4.4769×10-11 m2/W and 1.233×10-2 m/W respectively. The third order non-linear optical susceptibility χ(3) was found to be in the order of 3.6533×10-2 esu. The negative sign of non-linear refractive index shows the self-defocusing nature of the gel grown crystal. The second-order molecular hyperpolarizability γ of the grown crystal is 1.2822×10-33 esu. Laser damage threshold was measured by using an Nd: YAG laser (1064 nm). Photoconductivity studies of the gel grown crystal revealed that the crystal possesses positive photoconducting nature. The results obtained from Z-scan, laser damage threshold and photoconducting studies reveal that the crystal can be a possible candidate material for photonics device, optical switches, and optical power limiting application.

15. Activation of snap-top capped mesoporous silica nanocontainers using two near-infrared photons.

PubMed

Guardado-Alvarez, Tania M; Sudha Devi, Lekshmi; Russell, Melissa M; Schwartz, Benjamin J; Zink, Jeffrey I

2013-09-25

Photoactivation of "snap-top" stoppers over the pore openings of mesoporous silica nanoparticles releases intact cargo molecules from the pores. The on-command release can be stimulated by either one UV photon or two coherent near-IR photons. Two-photon activation is particularly desirable for use in biological systems because it enables good tissue penetration and precise spatial control. Stoppers were assembled by first binding photolabile coumarin-based molecules to the nanoparticle surface. Then, after the particles were loaded with cargo, bulky β-cyclodextrin (CD) molecules were noncovalently associated with the substituted coumarin molecule, blocking the pores and preventing the cargo from escaping. One-photon excitation at 376 nm or two-photon excitation at 800 nm cleaves the bond holding the coumarin to the nanopore, releasing both the CD cap and the cargo. The dynamics of both the cleavage of the cap and the cargo release was monitored using fluorescence spectroscopy. This system traps intact cargo molecules without the necessity of chemical modification, releases them with tissue-penetrating near-IR light, and has possible applications in photostimulated drug delivery.

16. Light- and pH-activated intracellular drug release from polymeric mesoporous silica nanoparticles.

PubMed

Tian, Ye; Kong, Yi; Li, Xiaojian; Wu, Jun; Ko, Alex C-T; Xing, Malcolm

2015-10-01

Surface modified mesoporous silica nanoparticles (MSNs) with reduced toxicity were prepared for light and pH dual triggerable drug delivery system. Both 413 nm light and acidic environment can activate the drug release process, improving the pharmacological action. By applying rhodamine B (RhB) as a model drug, the accumulative RhB release is as high as 95% in pH 5.0 and in irradiation of 413 nm light, compared to only 55% in pH 7.4 and in dark. The anti-cancer drug camptothecin (CPT) loaded nanoparticles can kill cancer cells with IC₅₀ value of 0.02 μg mL(-1) in exposure of 413 nm light, which is much lower than free CPT (about 0.1 μg mL(-1)). Multimodal nonlinear optical imaging microscopy (NLOM) was employed to acquire in vitro coherent anti-Stokes Raman (CARS) and two-photon excited fluorescence (TPEF) images of live MCF-7 cells and showed that the nanoparticles can be taken up by breast tumor cell MCF-7 with high efficiency, indicating its great potential for anti-cancer drug delivery system. PMID:26188470

17. Reactive simulations of the activation barrier to dissolution of amorphous silica in water.

PubMed

Kagan, Michael; Lockwood, Glenn K; Garofalini, Stephen H

2014-05-28

Molecular dynamics simulations employing reactive potentials were used to determine the activation barriers to the dissolution of the amorphous SiO2 surface in the presence of a 2 nm overlayer of water. The potential of mean force calculations of the reactions of water molecules with 15 different starting Q4 sites (Qi is the Si site with i bridging oxygen neighbors) to eventually form the dissolved Q0 site were used to obtain the barriers. Activation barriers for each step in the dissolution process, from the Q4 to Q3 to Q2 to Q1 to Q0 were obtained. Relaxation runs between each reaction step enabled redistribution of the water above the surface in response to the new Qi site configuration. The rate-limiting step observed in the simulations was in both the Q32 reaction (a Q3 site changing to a Q2 site) and the Q21 reaction, each with an average barrier of ∼14.1 kcal mol(-1). However, the barrier for the overall reaction from the Q4 site to a Q0 site, averaged over the maximum barrier for each of the 15 samples, was 15.1 kcal mol(-1). This result is within the lower end of the experimental data, which varies from 14-24 kcal mol(-1), while ab initio calculations using small cluster models obtain values that vary from 18-39 kcal mol(-1). Constraints between the oxygen bridges from the Si site and the connecting silica structure, the presence of pre-reaction strained siloxane bonds, and the location of the reacting Si site within slight concave surface contours all affected the overall activation barriers.

18. Synthesis, characterization and catalytic activity of ordered macroporous silicas functionalized with organosulfur groups

SciTech Connect

Wu Quanzhou Liao Jufang; Yin Qiang; Li Yuguang

2008-05-06

Hybrid three-dimensionally ordered macroporous (3DOM) SiO{sub 2}-SO{sub 3}H materials with different S/Si ratio have been prepared by colloidal crystal templating method. The process involved preparation of 3DOM SiO{sub 2}-SH materials by co-condensation of (3-mercaptopropyl)triethoxysilane and tetraethoxysilane via sol-gel transformation, and following oxidation of -SH group to -SO{sub 3}H group by H{sub 2}O{sub 2}. Materials were characterized by scanning electron microscopy (SEM), Fourier transform infra-red spectrometer (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption measurement. SEM observation shows that the macropores are highly ordered with a typical 'surface-templated' structure. The surface area of 3DOM SiO{sub 2}-SH material is 25.1 m{sup 2}/g and SiO{sub 2}-SO{sub 3}H material is 18.6 m{sup 2}/g. Catalytic activity test shows that 3DOM SiO{sub 2}-SO{sub 3}H materials possess a high activity for the esterification of acetic acid and n-butanol, and the activity is increased with the amount of sulfur in the materials. This study provided significant results for developing new application of 3DOM materials.

19. Gel barrier formation in unsaturated porous media

Kim, Meejeong; Corapcioglu, M. Yavuz

2002-05-01

The gel barrier formation by a gelling liquid (Colloidal Silica) injection in an unsaturated porous medium is investigated by developing a mathematical model and conducting numerical simulations. Gelation process is initiated by adding electrolytes such as NaCl, and the gel phase consisting of cross-linked colloidal silica particles grows as the gelation process proceeds. The mathematical model describing the transport and gelation of Colloidal Silica (CS) is based on coupled mass balance equations for the gel mixture (the sol phase plus the gel phase), gel phase (cross-linked colloidal silica particles plus water captured between cross-linked particles), and colloidal silica particles (discrete and cross-linked) and NaCl in the sol (suspension of discrete colloidal silica particles in water) and gel phases. The solutions in terms of volumetric fraction of the gel phase yield the gel mixture viscosity via the dependency on the volumetric fraction of gel phase. This dependency is determined from a kinetic gelation model with time-normalized viscosity curves. The proposed model is verified by comparing experimentally and numerically determined hydraulic conductivities of gel-treated soil columns at different CS injection volumes. The numerical experiments indicate that an impermeable gel layer is formed within the time period twice the gel-point in a one-dimensional flow system. At the same normalized time corresponding to twice the gel-point, the CS solutions with lower NaCl concentrations result in further migration and poor performance in plugging the pore space. The viscosity computation proposed in this study is compared with another method available in the literature. It is observed that the other method estimates the viscosity at the mixing zone higher than the one proposed by the authors. The proposed model can simulate realistic injection scenarios with various combinations of operating parameters such as NaCl concentration and NaCl mixing time, and thus

20. Gel barrier formation in unsaturated porous media.

PubMed

Kim, Meejeong; Corapcioglu, M Yavuz

2002-05-01

The gel barrier formation by a gelling liquid (Colloidal Silica) injection in an unsaturated porous medium is investigated by developing a mathematical model and conducting numerical simulations. Gelation process is initiated by adding electrolytes such as NaCl, and the gel phase consisting of cross-linked colloidal silica particles grows as the gelation process proceeds. The mathematical model describing the transport and gelation of Colloidal Silica (CS) is based on coupled mass balance equations for the gel mixture (the sol phase plus the gel phase), gel phase (cross-linked colloidal silica particles plus water captured between cross-linked particles), and colloidal silica particles (discrete and cross-linked) and NaCl in the sol (suspension of discrete colloidal silica particles in water) and gel phases. The solutions in terms of volumetric fraction of the gel phase yield the gel mixture viscosity via the dependency on the volumetric fraction of gel phase. This dependency is determined from a kinetic gelation model with time-normalized viscosity curves. The proposed model is verified by comparing experimentally and numerically determined hydraulic conductivities of gel-treated soil columns at different CS injection volumes. The numerical experiments indicate that an impermeable gel layer is formed within the time period twice the gel-point in a one-dimensional flow system. At the same normalized time corresponding to twice the gel-point, the CS solutions with lower NaCl concentrations result in further migration and poor performance in plugging the pore space. The viscosity computation proposed in this study is compared with another method available in the literature. It is observed that the other method estimates the viscosity at the mixing zone higher than the one proposed by the authors. The proposed model can simulate realistic injection scenarios with various combinations of operating parameters such as NaCl concentration and NaCl mixing time, and thus
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