One of the challenges for the non-oxidative coupling of methane (NOCM) is to effectively remove the deposited coke over catalysts owing to the over-dehydrogenation of methane. Herein, we show that an in-situ growth of carbon nanotubes (CNTs) instead of coke were observed during NOCM over a CuSO4/γ-Al2O3 catalyst. The as-grown CNTs depict an unexpected promoting effect for NOCM with a highest activity of 0.48 mol kg cat-1·h-1, and maintained 85% activity after 200 h running time. The equilibrium methane conversion is 9.8 % with a selectivity of 78.2 % for C2 (C2H4 + C2H6) products. Highly dispersed Cu nanoparticles distributed on the top of CNTs measured by transmission electron microscopy is proposed to result in high catalyst stability during NOCM for 200 h instead of deactivation in several hours. Here, we firstly prove that the as-grown CNTs can promote the catalytic activity of NOCM instead of deactivation by coking over catalysts.
The electronic properties, bonding structure and magnetic behaviours of oxygen- and chlorine-treated nitrogenated carbon nanotubes (N-CNTs) were studied using x-ray absorption near-edge structure (XANES), scanning photoelectron microscopy (SPEM) and PPMS measurements. The C and N K-edge XANES spectra of chlorine-treated N-CNTs consistently reveal the formation of pyridinelike N-CNTs by the observation of 1s→π*(e2u) antibonding and 1s→π*(b2g) bonding states. Features in the C K-edge XANES spectra are shifted by ~0.3 eV toward higher energies and by ~1.1 eV toward lower energies relatively to those of the more symmetrical pyridinelike and graphitelike structured N-CNTs upon chlorination and oxidation, respectively. Increases in N K-edge XANES intensities for both chlorination and oxidation reveal substitution of C–C bonds by C–N bonds consistent with the observed valence-band photoemission spectra of the decrease of the C 2s bond and the increase of the N 2s bond. The valence-band photoemission spectra obtained from SPEM images indicate that chlorination of the nanotubes enhances the C–N bonding. First-principles calculations of the partial densities of states in conjunction with C K-edge XANES data identify the presence of C–Cl bonding in chlorine treated N-CNTs. In the electron field emission of chlorination (N-CNT:Cl) and oxidation (N-CNT:O) of N-CNT shows a high current density (J) of 15.0 mA/cm2 has been achieved on chlorination, whereas low J of 0.0052 mA/cm2 is observed on oxidation compared to J = 1.3 mA/cm2 for untreated N-CNT at an applied electric field EA of ~1.9 V/mm. The turn-on electric field (ETO) was ~0.875 and 1.25 V/mm was achieved for N-CNT:Cl and N-CNT:O, respectively, with respect to ETO = 1.0 V/mm for untreated one. The magnetic behavioural changes occurs when N-CNTs are functionalized with Cl and O respectively.
Understanding the criteria warranting the existence, stability, and activity of a given configuration of atoms has pivotal relevance in chemical and materials science. Photocatalysts, traditionally semiconductors, are essential for processes ranging from water purification to water splitting, air filtration, and surgical instrument sterilization, and harvest optical energy to drive chemical reactions. These semiconductors harvest optical energy to drive chemical reactions. With chemical reactions dictated by atomic and molecular interactions at the nanoscale, examining these processes with near-atomic resolution is necessary to understand photochemical processes in depth and to improve materials for next-generation catalysts. The performance and key electronic properties of semiconductors are dictated by the interplay between the surface chemistry and morphology, whose manipulation has inspired experimental and theoretical researchers. This interplay has been clarified by theoretical studies based on atomic-scale modelling with particular attention given to two sets of degrees-of-freedom: the atomic positions and chemical configuration. This perspective article presents the major computational challenges and modern methodological strategies toward advancing the field. The ZnWO4 material was selected as a case study, and the key concepts developed in recent years are discussed to clarify the morphology, i.e., the exposed surfaces of materials, and explain its functional properties or performance. First-principle calculations capture the geometric and electronic effects on the photocatalytic activity in agreement with experimental data. Indeed, important and often surprising structure-function relations have been observed based in depth atomistic modelling on morphological analysis. An overview of past achievements and future directions is provided according to the authors’ outlook.
The present study deals with the synthesis of two structurally different azomethine polyamides and their effect as inhibitor for a steel rebar in chloride containing pore solution. The amorphous and crystalline natures of the polymers were evaluated based on the XRD analysis. Potentiodynamic polarisation and impedance spectroscopy were employed to investigate the inhibition efficiency of the polymers for the protection of the rebar during corrosion. Scanning electron microscopic and atomic force microscopic techniques were used for the surface characterization of the steel in presence of the adsorbed layer formed by the polymer molecule leading to the inhibition from corrosion. The adsorption of the polyamide inhibitors on the steel rebar obeyed Langmuir adsorption isotherm. Two polyamide inhibitors showed similar inhibition efficiency at concentration ranging from 10 to 1000 ppm and maximum efficiency of 99.62% was achieved by the polymer PAMA1. Formation of protective layer on the surface of steel rebar by the inhibitors was attributed to be the reason for corrosion protection under chloride contaminated pore solution.
This article reviews two reasonably novel approaches for remarkable corrosion resistance of metallic material, and discusses challenges and future opportunities. In the first approach, the nanaocrystalline structure of a corrosion resistant alloy has been found to bring about remarkable improvement in oxidation/corrosion resistance of alloys, as a result of the enhancement in diffusivity of the alloying element that is responsible for theformation of a corrosion barrier layer of protective oxide, due to the nanocrystalline structure (vis-à-vis the microcrystalline counterpart of the same alloy). In the second approach, just a monolayer or a few atomic layer thick graphene coating was found to improve corrosion resistance of copper, nickel and copper nickel alloys in aggressive chloride solution by up to two orders of magnitude, because of the unique characteristics of graphene, i.e., impermeability and inertness to aggressive fluids.
We report an investigation into the magnetic and electronic properties of partially hydrogen functionalized vertically aligned few layers graphene (FLG) synthesized by microwave plasma enhanced chemical vapor deposition process. The FLG samples are hydrogenated at different substrate temperatures (50oC - 200oC) to alter the degree of hydrogenation and their depth profile. The unique morphology of the structure gives rise to a unique geometry in which graphane (full hydrogenation) / graphone (partial hydrogenation) is supported by graphene layers in the bulk, which is very different from other widely studied structures such as one-dimensional nanoribbons. Synchrotron based x-ray absorption fine structure spectroscopy measurements have been used to investigate the electronic structure and the underlying hydrogenation mechanism responsible for the magnetic properties. While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed. Free spins available via the conversion of sp2 to sp3-hybridized structures and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observed ferromagnetic orders. Theoretical point of view different possible reason for the formation of magnetism in Graphene materials also discussed elaborately.
Functional ligand-protected metal cluster nanomaterials with increased two-photon absorption and two-photon excited emission might result in new technologies within the fields of bio-imaging applications. During this article, I review the two-photon absorption/emission properties of atomically precise ligand-protected silver and gold nanoclusters, coined “ligand-core” NLO-phores. This includes quantum-chemical methodologies using time-dependent density theory. I will analyze physical phenomena and trends resulting in giant two-photon absorption/emission responses of a number of series of model nanoclusters. I will then focus my review on the effects of the relaxation pathways within the linear and nonlinear optical regime, similarly as innovative ways aiming at enhancing their two-photon emission responses.