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Applications of chitin- and chitosan-derivatives for the detoxification of water and
wastewater — A short review
Amit Bhatnagar⁎, Mika Sillanpää
Laboratory of Applied Environmental Chemistry, Department of Environmental Sciences, University of Kuopio, FI-50100 Mikkeli, Finland
a b s t r a c ta r t i c l e i n f o
Available online 1 October 2009
Water treatment
Chitin and chitosan-derivatives have gained wide attention as effective biosorbents due to low cost and high
contents of amino and hydroxyl functional groups which show significant adsorption potential for the
removal of various aquatic pollutants. In this review, an extensive list of chitin- and chitosan-derivatives
from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as
available in the literature are presented. This paper will give an overview of the principal results obtained
during the treatment of water and wastewater utilizing chitin and chitosan-derivatives for the removal of:
(a) metal cations and metal anions; (b) radionuclides; (c) different classes of dyes; (d) phenol and
substituted phenols; (e) different anions and other miscellaneous pollutants. The review provides a
summary of recent information obtained using batch studies and deals with the various adsorption
mechanisms involved. It is evident from the literature survey that chitin- and chitosan-derivatives have
shown good potential for the removal of various aquatic pollutants. However, still there is a need to find out
the practical utility of such developed adsorbents on commercial scale.
© 2009 Elsevier B.V. All rights reserved.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chitin- and chitosan-derivatives for detoxification of water and wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.1.Chitin- and chitosan-derivatives for metals (cations and anions) and radionuclides removal . . . . . . . . . . . . . . . . . . . . . . 27
2.2.Chitin- and chitosan-derivatives for dyes removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.Chitin- and chitosan-derivatives for phenols removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4.Chitin- and chitosan-derivatives for anions removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.5.Chitin- and chitosan-derivatives for miscellaneous pollutants removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Conclusions and future perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction
Water is one of the basic necessities required for the sustenance
and continuation of life. It is therefore important that supply of good
quality water should be available for various activities. However, this
is becoming increasingly difficult in view of large scale pollution
caused by industrial, agricultural and domestic activities. These
activities generate wastewater which contains both inorganic and
organic pollutants. Some of the common pollutants are phenols, dyes,
detergents, insecticides, pesticides and heavy metals [1]. The nature of
pollutants in wastewater depends on the source of generation and
varies from place to place. These pollutants are often toxic and cause
adverse affects on human and animal life if present above certain
concentration levels. In order to avoid pollution of natural water
bodies, it is essential to treat wastewater for the removal of pollutants
before being discharged into them. A number of methods such as
coagulation, membrane process, adsorption, dialysis, foam flotation,
osmosis, photocatalytic degradation and biological methods have
generally been used for the removal of toxic pollutants from water
and wastewater [2]. The type of the process to be employed may
depend on nature of pollutant. However, adsorption process is often
considered most appropriate as it can remove both inorganic and
organic pollutants and the operation of the process is convenient.
Advances in Colloid and Interface Science 152 (2009) 26–38
⁎ Corresponding author. Tel.: +358 40 355 3405.
E-mail addresses: email@example.com, firstname.lastname@example.com (A. Bhatnagar).
0001-8686/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
Advances in Colloid and Interface Science
journal homepage: www.elsevier.com/locate/cis
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Activated carbon has been found to be a universal adsorbent for
effluent treatment and is commonly used for the removal of various
pollutants from water [3]. However, its widespread use in wastewater
treatment is sometimes restricted due to its higher cost. It is now
economic method for water decontamination. A large variety of non-
various types of pollutants from water and wastewater. Biosorbents
gain wide attention as these are available in large quantities worldwide
has receivedreorganization,in particular polysaccharides suchaschitin
and its derivate chitosan.
Chitin was first discovered in mushrooms by the French Professor,
Henrni Braconnot, in 1811. In 1820s chitin was also isolated from
insects. Chitin contains 2-acetamido-2-deoxy-β-D-glucose through a β
(1→4) linkage. Chitin is the most abundant natural fiber next to the
sourceof chitin isthe shell of craband shrimp. Chitosan wasdiscovered
β-D-glucopyranose and 2-amino-2-deoxy-β-D-glucopyranose residues.
its lowcostcompared to activated carbonand its highcontents ofamino
and hydroxyl functional groups showing high adsorption potential for
alternative to other biomaterials because of its physico-chemical
characteristics, chemical stability, high reactivity, excellent chelation
behavior and high selectivity toward pollutants [4–8]. Natural chitosan
has been modified by several methods (either physically or chemically)
in order to enhance the adsorption capacity for various types of pollut-
ants. Different shapes of chitosan, e.g. membranes, microspheres, gel
beads and films have been prepared and examined for the removal of
various pollutants from water and wastewater. The detailed description
about structures of chitin and chitosan and their physical and chemical
modification by various techniques has been documented in detail in
earlier reviews [4–10].
is to compile and present the adsorption potential (adsorption
capacities) of chitin- and chitosan-derivatives for various other aquatic
pollutants e.g. phenol and substituted phenols; different anions and
miscellaneous pollutants such as pesticides, fungicides, humic sub-
stances etc. This review provides, besides the critical discussions, the
recent literature of about the past 10–15 years to demonstrate the
usefulness of chitin- and chitosan-derivatives in water and wastewater
applications. A summary of relevant published data (in terms of
adsorption capacities of chitin and chitosan-derivatives for the removal
of various different pollutants) with some of the latest important
findings and giving a source of up-to-date literature on the adsorption
properties of chitin and chitosan for diverse types of pollutants is
presented and some of the results have been discussed here.
2. Chitin- and chitosan-derivatives for detoxification of water
and wastewater
2.1. Chitin- and chitosan-derivatives for metals (cations and anions) and
radionuclides removal
Metal ions are one of the important categories of water pollutants,
which are toxic for humans through the food-chain pyramid. Various
toxic heavy metal ions discharged into the environment through
different industrial activities, constituting one of the major causes of
environmental pollution. Chitin- and chitosan-derivatives have been
extensively investigated as adsorbents for the removal of metal ions
from water and wastewater. The high adsorption potential of chitosan
for heavy metals can be attributed to (1) high hydrophilicity due to
large number of hydroxyl groups of glucose units, (2) presence of a
large number of functional groups, (3) high chemical reactivity of
these groups, and (4) flexible structure of the polymer chain [10].
Cadmium and its compounds are extremely toxic even in low
concentrations, and bioaccumulate in organisms and ecosystems. A
disease known as "Itai Itai" in Japan is associated with cadmium
poisoning, which results in multiple fractures in the body. Chitin has
been explored as adsorbent for the removal of cadmium (Cd) ions
from aqueous solutions by batch experiments [11]. An adsorption
capacity of 14 mg/g of chitin for Cd(II) ions was observed. Scanning
electron microscopy coupled with X-ray energy dispersed analysis
was used to demonstrate that cadmium-containing nodules existed
on the chitin surface for cadmium-equilibrated chitin. They also
examined the effect of co-ions (Cu2+and Zn2+) on the cadmium
biosorption at free solution pH and 25 °C, in static conditions [12].
Biosorption of individual metals followed the sequence: Cu>Cd>Zn.
Zn2+ions had little affect on cadmium uptake capacity of chitin under
the conditions examined, whereas, the presence of Cu2+ions
decreased the affinity of chitin for cadmium.
The efficiency of cadmium removal using chitosan has also been
investigated by Jha et al. [13]. An adsorption capacity of 5.93 mg of
Cd(II)/g of chitosan at a pH range of 4.0–8.3 was reported and the
presence of ethylenediaminetetraacetic acid (EDTA) was found to
significantly decrease cadmium removal. This is expectable, because
EDTA and other aminopolycarboxylic acids are known to form
extremely stable complexes with heavy metals [14,15].
Mercury (Hg), copper (Cu), nickel (Ni), zinc (Zn), lead (Pb) and
concern when present at higher concentrations in the environment.
by chitin and chitosan-derivatives. McKay et al. investigated the
adsorption of some metal ions by chitosan [16]. It was found that the
815, 222, 164 and 75 mg/g, respectively. The ability of chitin or
into account kinetic, equilibrium, and mass transfer aspects [17].
Equilibrium isotherm studies revealed that the Cu(II) sorption onto
chitin and chitosan was best described by the Langmuir and Redlich-
Peterson models. The sorption capacity of chitosan for Cu(II) ions was
four to five times higher than that of chitin.
The use of chitosan flakes for the removal of Cu2+from water has
been examined [18]. Chitosan showed excellent ability for Cu2+
adsorption with a capacity of 1.8–2.2 mmol/g dry mass. However, the
capacitysharply riseswhenthe solutions containa high concentration
of chloride ions. The variation of solution pH leads to competition
between the coordination of Cu2+with chitosan. The optimal pH
range for copper adsorption onto chitosan flakes was 5.4–6.0.
The performance of commercially available sources of chitin,
chitosan and chitosan cross-linked with benzoquinone for various
metal ions has also been explored [19]. Initial pH of the metal solution
significantly influenced metal uptake capacity. The highest metal
uptake values (137, 108, 58, and 124 mg/g for copper, zinc, arsenic,
and chromium, respectively) were achieved with chitosan (1 g/L, at
pH 4) with initial metal concentrations of 400 mg/L.
Simultaneous removal of various metal ions (zinc, copper,
cadmium, and lead) using commercially available chitosan flakes
from aqueous solutions under variable physico-chemical conditions
has also been reported [20]. The results obtained from the adsorption
studies showed that there was significant uptake of these metal ions
by chitosan. Chitosan flakes exhibited maximum uptake capacity for
copper ions. The order of metal ion adsorption by chitosan decreased
from Cu2+to Zn2+as follows: copper>lead>cadmium>zinc. The
heavy metal uptake by chitosan was found to be pH dependent. The
uptake of metal ions by chitosan was enhanced by increasing the pH
from 4 to 7. This was attributed to the greater availability of amino
groups at higher pH. On the other hand, the reduced adsorption of
metal ions at acidic pH values could be attributed to the fact that at
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lower pH, the metal ions that would coordinate with the lone pair of
nitrogen would have to compete with H3O+for an active site.
Several chemical modifications have been carried out to increase
aminated chitosan beads formed by the chemical reaction of
ethylenediamine and carbodiimide showed the highest uptake
capacity for mercury (Hg2+) ions. The uptake capacity of aminated
chitosanbeadswasca.2.26 mmolHg2+/gdrymassatpH7.Thisvalue
wasthoughttobe oneofthehighestuptakecapacitiesamongvarious
biosorbents. Beads also showed the characteristic of competitive
sorption between mercury and hydrogen ions and finally it was
successfully modelled by an equilibrium model based on isothermal
sorption data. Recently, Hg(II) removal from water by chitosan and
its derivatives has extensively been reviewed by Miretzky and Cirelli
To enhance the sorption capacity of chitosan for Cd removal,
Rorrer et al. performed experiments to increase the porosity of the
chitosan beads by adding acidic chitosan solution into a sodium
hydroxide solution precipitation bath [22]. The gelled chitosan beads
were cross-linked with glutaraldehyde and then freeze dried. Beads of
1- and 3-mm diameter were prepared. Beads of 1-mm diameter
possessed surface areas exceeding 150 m2/g and mean pore sizes of
560 Å and were insoluble in acid media at pH 2. Adsorption isotherms
at 25 °C and pH 6.5 over the concentration range 1–1690 mg Cd2+/L
possessed a stepped shape and maximum adsorption capacities for
the 1- and 3-mm beads were found to be 518 and 188 mg of Cd/g of
beads, respectively. The stepped shape of the isotherm was explained
by a pore-blockage mechanism. The modified chitosan showed many
advantages over flaked or powdered chitosan e.g. higher internal
surface area, and cross-linkage of beads making them insoluble in
low-pH solutions, thus proving their suitability over a broad pH range.
A new composite chitosan biosorbent was prepared by coating
chitosan on to perlite ore and investigated for Cu(II) and Ni(II)
removal [23]. Maximum removal of Cu(II) and Ni(II) on chitosan
coated on perlite was at pH 5.0. The maximum monolayer adsorption
capacity of chitosan coated on perlite was 196.07 mg/g for Cu(II) and
114.94 mg/g for Ni(II).
Chitosan obtained from silkworm chrysalides (ChSC) was exam-
ined for the removal of Pb2+and Cu2+from battery manufacture
wastewater [24]. The best pure ChSC deacetylation degrees (DDs)
obtained for the removal of Pb2+and Cu2+from battery wastewater
were 80% (90 min ChSC deacetylation) and 92% (180 min ChSC
deacetylation), respectively. The maximum adsorption capacities for
Pb2+and Cu2+using pure ChSC with 80% and 92% DD were 72 mg/g
and 87 mg/g, respectively, under the experimental conditions: pH 5.0,
particle size from 300 to 425 µm, temperature 20.0±0.1 °C, and
250 rpm stirring.
removal of Cu(II) from aqueous solutions [25]: (i) Ch, without grafting;
(ii) Ch-g-Aam, grafted with acrylamide; and (iii) Ch-g-Aa, grafted with
Cu(II) removal (318 mg/g at pH 6) among the studied and earlier cited
chitosan materials. The interaction between Cu(II) and the prepared
sorbents was confirmed by FTIR spectroscopy. The peaks of amino
non-loaded ones (Ch, 1665–1660 cm−1; Ch-g-Aam, 1672–1674 cm−1;
Ch-g-Aa, 1674–1670 cm−1), suggesting a chelated complex.
New chitosan-derivative has been synthesized by cross-linking a
metal complexing agent, [6,6′-piperazine-1,4-diyldimethylenebis
(4-methyl-2-formyl) phenol] (L), with chitosan (CTS) by Krishna-
priya and Kandaswamy [26]. Adsorption experiments (pH depen-
dency, kinetics, and equilibrium) of the cross-linked chitosan ligand
(CCTSL) of various metal ions such as Mn(II), Fe(II), Co(II), Cu(II), Ni
(II), Cd(II) and Pb(II) were carried out at 25 °C. The results showed
that the adsorption was dependent on pH of the solution, with
maximum capacity between pH 6.5 and 8.5. The order of adsorption
capacities for the metal ions studied was found to be Cu(II)>Ni(II)>
Cd(II)≥Co(II)≥Mn(II)≥Fe(II)≥Pb(II). Chemical sorption was sug-
gested as the rate-limiting step of adsorption mechanism.
A new biosorbent was developed by coating chitosan on to
polyvinyl chloride (PVC) beads [27]. Equilibrium and column flow
adsorption characteristics of copper(II) and nickel(II) ions on the
biosorbent were studied. The maximum monolayer adsorption
capacity of chitosan-coated PVC sorbent as obtained from Langmuir
adsorption isotherm was found to be 87.9 mg/g for Cu(II) and
120.5 mg/g for Ni(II) ions, respectively. The results indicated that
the maximum uptake of Cu(II) ions took place at pH 4.0 while the
maximumuptakeofNi(II)ionsoccurredat an initialpHof5.0. Column
experiments exhibited that it was possible to remove the metal ions
from aqueous medium by biosorption on to chitosan-coated PVC
The magnetic chitosan nanocomposites were synthesized on the
basis of amine-functionalized magnetite nanoparticles [28]. These
nanocomposites provide a very efficient, fast, and convenient tool for
removing Pb2+, Cu2+, and Cd2+from water. It was suggested that
synthesized magnetic chitosan nanocomposites can be used as a
recyclable tool for heavy metal ion removal.
The adsorption of Al(III) from aqueous solutions onto chitosan was
found to be 45.45 mg/g at 30 °C. [29]. The adsorption of Al(III)
increased with the rise in adjusted pH of the solution from 3.0 to 4.0
and decreased after pH 4.0. The pseudo-second-order kinetic model
was used to describe the kinetics which is based on the assumption
that the rate-limiting step may be chemisorption involving valency
forces through sharing or exchange of electrons between the –NH2
groups in chitosan and Al(III). It was observed by the authors that
before equilibrium was reached, an increase in temperature led to an
increase in adsorption rate which indicated a kinetically controlled
process, while the adsorption of Al(III) on chitosan was controlled by
an exothermic process.
Metal anions are another class of aquatic pollutants which pose
of metal anions by chitin and chitosan-derivatives has been examined
by many researchers. Chitosan was found very efficient for the removal
to be in the range 3.0 to 3.5. Sorption capacity under optimum
experimental conditions reached 8–9 mmol/g (ca. 400–450 mg/g),
which corresponds to a molar ratio of ca. 1.3–1.5 between vanadate
and –NH3
the sorption isotherm curves, which was correlated to the predomi-
nance of anionic species, indicated that sorption occurred through the
reaction of protonated amine sites with decavanadate species (prefer-
entially to other polynuclear anionic species of lower vanadium unit
number). In acidic solutions, the predominance of decavanadate
solutions lead to almost rectangular sorption isotherm curves. In near
resulted in negligible adsorption up to a concentration, dependent on
pH, at which decavanadate species appeared in solution. At this limit
the protonation of amine groups was significantly reduced and the
or to attract anionic species. Thus, the protonation of the polymer
revealed a key parameter, as does the distribution of metal species, on
the efficiency of vanadium sorption on chitosan. Sorption kinetics was
also strongly controlled by the pH and the metal concentration. The
predominance of decavanadate species had been correlated to fastest
kinetics. Desorption was optimum in alkaline solutions, in which
vanadium took the form of vanadate species in solution.
Cross-linked chitosan gel beads were used for molybdate sorption
and were found to show enhanced sorption performance in batch
systems [31]. The authors reported that, in continuous systems,
sorption capacities could reach 700 mg/g, a level close to that
+groups. This stoichiometric ratio, together with the shape of
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obtained in batch studies. They also suggested that the sorption of
molybdate (MoO4
decreased from the range 300–800 to 150–400 mg Mo/g when the
chitosan flakes were cross-linked with glutaraldehyde.
Cross-linking of chitosan particles, in glutaraldehyde, epichlorhy-
drine, or EGDE (ethylene glycol glycidyl ether) enhances the
resistance of sorbent beads against acids, alkali or chemicals. This
property of glutaraldehyde cross-linked chitosan beads was explored
for vanadate and molybdate sorption [32]. Uptake capacities of
402.5 mg/g for vanadate and 763 mg/g for molybdate were obtained.
The sorption into beads (763 mg molybdate/g) was better than into
flakes (329.7 mg molybdate/g). Authors reported that both anions
(molybdate and vanadate) showed similar sorption behavior which
waslikely due tothe similarities in the chemistryof these ions.A pHof
approximately 3 was favorable for the sorption of these metal anions,
which was consistent with (i) the electrostatic attraction between the
protonated amine sitesandthe strongly anionicmetal speciesand,(ii)
the appearance of polynuclearhydrolyzed metal speciesin the3.0–3.5
pH range. Sorption kinetics were mainly controlled by intraparticle
diffusion for beads, while for flakes the controlling mechanisms were
both external and intraparticle diffusions.
The adsorption of sulfate (SO4
also been evaluated by Moret and Rubio [33] on chitin-based material
high, 150 mg SO4
molybdate ions in the presence of sulfate ions, but reaction required
longer equilibration time (60 min for 92% removal). Practical examples
of removal of these anions were studied in actual mining effluents,
attainingvalues of the order of 71% SO4
flotation mill effluent and 80% sulfate removal from a coal AMD-acid
mine drainage (Mo free). The regeneration of the adsorbent material
was possible through the anions desorption in alkaline medium.
Arsenic in natural waters is a worldwide problem. Arsenic toxicity,
its health hazards, and the treatment techniques are well known and
have been widely reported. Extensive research is being conducted to
control/minimize the arsenic contamination in drinking water.
Dambies et al. [34] investigated the sorption of As(V) on molybdate-
impregnated chitosan gel beads. The sorption capacity of raw chitosan
for As(V) was increased by impregnation with molybdate. The
optimum pH for arsenic uptake was ca. pH 3. The As(V) sorption
capacity, over molybdenum loading, was ca. 160 mg/g. The exhausted
sorbent was regenerated by phosphoric acid desorption. Three
sorption/desorptioncycleswereconductedwithonlya smalldecrease
in sorption capacity.
Chitosan powder derived from shrimp shells, was converted into
bead form and used to remove As(III) and As(V) from water in both
batch and continuous operations [35]. The optimal pH value for As(III)
and As(V) removal was ca. 5. Adsorption capacities of 1.83 and
1.94 mg As/g bead for As(III) and As(V), respectively, were reported.
The sorption of As(V) onto chitosan flakes has been studied by
Kwok et al. [36]. Authors selected 96 h contact time to ensure that
equilibrium has been achieved over the whole concentration
spectrum. The rate of desorption of arsenate from chitosan increased
with the increase of the initial pH from 3.50 to 4.50. The capacity of
the arsenate ion on chitosan was governed by the protonation
reaction of chitosan and an increase of pH led to a decrease of the
protonated groups on chitosan which were available for sorption of
arsenate ion and influenced the speciation of arsenate ions in the
aqueous phase. The dominant arsenate ions were in the form of
from the aqueous phase might be due to the adsorption of arsenate
ions to the protonated amine group on chitosan. A novel pseudo-first
order reversible model, incorporating the effect of changing pH profile
throughout the adsorption and desorption cycle, was newly devel-
oped to describe the sorption and the desorption in the batch kinetic
systems of As(V) and chitosan simultaneously. The pH value of the
−) on chitosan flakes depends on the cross-linking. It
2−) and molybdate (MoO4
−) ions has
2−/g with DD=25%. Chitin also proved to adsorb
2−and 85% MoO4
−from a Cu–Mo
−. It was believed that the removal mechanism of arsenate ions
adsorption and desorption reaction of arsenate and chitosan could be
predicted from the pH against time profile. The adsorption capacities
were reported from 1331 µg arsenate/g chitosan at initial pH 5.5 to
14,160 µg arsenate/g chitosan at initial pH 3.5.
A study on the removal of arsenic from groundwater using iron–
chitosancomposites wasconducted [37]. Removalof As(III)andarsenic
(V) was studied through adsorption at pH 7.0 under equilibrium and
dynamic conditions. The monolayer adsorption capacity from the
Langmuir model for iron chitosan flakes (ICF) (22.47±0.56 mg/g for
As(V) and 16.15±0.32 mg/g for As(III)) was found to be considerably
higher than that obtained for iron chitosan granules (ICB) (2.24±
0.04 mg/g for As(V); 2.32±0.05 mg/g for As(III)). Anions including
sulfate, phosphate and silicate at the levels present in groundwater did
not cause serious interference in the adsorption behavior of arsenate/
arsenite. The column regeneration studies were carried out for two
sorption–desorption cycles for both As(III) and As(V) using ICF and ICB
as sorbents. One hundred and forty-seven bed volumes of As(III) and
112 bed volumes of As(V) spiked groundwater were treated in column
experiments using ICB, reducing arsenic concentration from 500 to
<10 μg/L.Theeluentusedfortheregenerationof thespentsorbentwas
0.1 M NaOH. The adsorbent was also successfully applied for the
removal of total inorganic arsenic down to <10 μg/L from arsenic
contaminated groundwater samples.
Chromium, another important metal, has many industrial applica-
tions such as in textile, electroplating, leather tanning and metallurgy
industries,and therefore,the wastes generated by these industries are
rich in hexavalent Cr(VI)or trivalentCr(III)forms ofchromium.Cr(VI)
is more toxic than Cr(III) and has therefore, lead greater environ-
mental concern. Chromium is potentially toxic to humans as it is
considered a carcinogen. The adsorption of Cr(VI) on chitosan flakes
was investigated against the process parameters such as pH,
adsorbent dose and initial Cr(VI) concentration by Aydın and Aksoy
[38]. The effects of these factors were studied in the ranges 1.5–9.5,
1.8–24.2 g/L and 15–95 mg/L, respectively. Maximum removal was
attained from a solution as concentrated as 30 mg/L at pH 3 with an
adsorbent dosage of 13 g/L. The adsorption capacity of chitosan flakes
wasdetermined as22.09 mg/gat thesespecified conditions. However,
the adsorption capacity was recorded as high as 102 mg/g for 100 mg/
L initial Cr(VI) concentration. Pseudo-second-order kinetic model
exhibited the highest correlation with data. The results showed that
both monolayer adsorption and intraparticle diffusion mechanisms
limited the rate of Cr(VI) adsorption.
The ability of cross-linked and non-cross-linked chitosan as an
adsorbent for Cr(VI) removal from aqueous solution has been
demonstrated [39]. Cr(VI) adsorption behavior could be described
of 10 to 1000 mg/L Cr(VI). The maximum adsorption capacity for both
types of chitosan was found to be 78 mg/g for the non-cross-linked
chitosan and 50 mg/g for the cross-linked chitosan for the Cr(VI)
removal. The optimum pH for maximum Cr(VI) removal was 5.
To achieve enhanced removal of Cr(VI), perlite beads were coated
with chitosan by drop-wise addition of a liquid slurry containing
chitosan and perlite to an alkaline bath [40]. The adsorption capacity of
chitosan-coated perlite was found to be 104 mg/g of adsorbent from a
solution containing 5000 mg/L of Cr(VI). On the basis of chitosan, the
capacity was 452 mg/g of chitosan. It was reported by the authors that
thiscapacitywasconsiderablyhigher thanthatof chitosaninitsnatural
and modified forms, which was in the range of 11.3 to 78 mg/g of
chitosan. The beads loaded with chromium were regenerated with
sodium hydroxide solution of different concentrations.
Boddu et al. [41] prepared a composite chitosan biosorbent by
coating chitosan, onto nonporous ceramic alumina. Batch and
continuous column sorption experiments with this sorbent were
carried out at 25 °C to evaluate Cr(VI) adsorption from synthetic and
actual chrome plating wastewater samples. Experimental equilibrium
data were fitted to Langmuir and Freundlich models. The maximum
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capacity for Cr(VI) obtained from the Langmuir model was 154 mg/g.
The adsorption capacities reported in this study on the twice-coated
biosorbent was considerably higher than those previously reported
values in literature, indicating that the chitosan in the composite
biosorbent has greater adsorption capacity than unsupported chit-
osan and the coating process significantly improved the adsorption
capacity of chitosan. This improvement was attributed to the
increased surface area and facilitation of transport of chromium ions
to the binding sites on chitosan.
Quaternary ammonium salt of chitosan (QCS) was synthesized via
reaction of a quaternary trimethyl ammonium, glycidyl chloride [42]
and examined for Cr(VI) removal. The sorption capacity was found to
be pH dependent. The optimum pH range for adsorption was found to
be 3.5–4.5, at which Cr(VI) existed frequently as the most easily
adsorbed species, HCrO4
was 30.2 mg/g, while at pH 4.5 the capacity was 68.3 mg/g. The
kinetics of Cr(VI) on the cross-linked quaternary chitosan salt (QCS)
were found to follow second-order rate mechanism. Cr(VI) ions were
eluted from cross-linked QCS by treatment with a 1 mol/L solution of
NaCl/NaOH to give a chromium efficiency of more than 95%.
Chromium removal onto cross-linked chitosan wasstudied by Rojas
et al. [43] as a function of pH, particle size, adsorbent dose, chromium
concentration and chromium oxidation state. The optimum adsorption
pH was 4.0, while chromium(VI) was partially reduced in the range
pH≤3.0. The chitosan potential for chromium(III) removal was found
lower (6 mg/g), while higher uptake was observed for chromium(VI)
(215 mg/g). This high capacity was explained due to the large
stoichiometry of protonated amine sites in the acidic range of pH.
Three cross-linked chitosan-derivatives were used as sorbents for
the removal of Cr(VI) from aqueous solutions [25]: (i) Ch, without
grafting; (ii) Ch-g-Aam, grafted with acrylamide; and (iii) Ch-g-Aa,
grafted with acrylic acid. Ch-g-Aam material presented the highest
sorption capacity for Cr(VI) removal (935 mg/g at pH 4) among the
studied and cited chitosan materials. The FTIR spectra of Cr(VI)-loaded
and non-loaded sorbents were also shown to elucidate the mechanism
of Cr(VI) sorption onto the prepared chitosan sorbents. The peaks of
amino groups of Cr(VI)-loaded chitosan sorbents presented shifts with
respect to non-loaded ones (Ch, 1665–1669 cm−1; Ch-g-Aam, 1672–
1679 cm−1; Ch-g-Aa, 1726–1731 cm−1), suggesting the electrostatic
interaction between HCrO4
two new peaks were observed in FTIR spectra of Cr(VI)-loaded sorbents
which attributed to Cr–O and Cr=O bonds of chromate anions,
confirming the sorption of Cr(VI) onto the chitosan-derivatives at 789
and910 cm−1,781and924 cm−1,779and907 cm−1forνCr–OandνCr=O,
respectively, in the case of Ch, Ch-g-Aam and Ch-g-Aa. The regeneration
experiments, without significant loss in sorption capacity.
Chitosan–Fe(0) nanoparticles (chitosan–Fe(0)) were prepared using
non-toxic and biodegradable chitosan as a stabilizer and batch
experiments were conducted to evaluate the influences of initial Cr(VI)
chitosan–Fe(0) [44]. The authors suggested that the overall disappear-
ance of Cr(VI) might include both physical adsorption of Cr(VI) onto the
chitosan–Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III).
Characterization with high-resolution X-ray photoelectron spectrosco-
Fe(III) were the predominant species on the surface of chitosan–Fe(0).
Chitosan also inhibited the formation of Fe(III)–Cr(III) precipitation due
that chitosan–Fe(0) hasthe potential to become an effective agent for in
situ subsurface environmental remediation.
A novel aminated chitosan adsorbent with higher adsorption
ability for metal cations and metal anions was prepared [45]. Through
cross-linking amination reaction, the content of amidocyanogen of
aminated chitosan adsorbent was enhanced four times than that of
chitosan cross-linked adsorbent. The adsorption ability of the novel
−. The Cr(VI) adsorption capacity at pH 9.0
−and amino groups of chitosan.Furthermore,
aminated chitosan adsorbent for nickel citrate and Cr(VI) was
enhanced remarkably. When the initial concentration of metallic ion
was 1000 mg/L, the adsorption capacity of the novel aminated
chitosan adsorbent for nickel citrate and Cr(VI) was up to 30.2 mg/g
and 28.7 mg/g, respectively.
Rhenate sorption on chitin and chitosan has been studied by Kim
et al. [46] as an analogue of radioactive pertechnate anion. The
mechanism was described by ion-pair formation in the diffuse double
layer between NH3
amount of sorbed rhenate decreased with the increase in pH from 3 to
6.5, indicating a lowering of the sorption capacity of chitosan. At pH 3, a
large number of amine groups were in protonated form and could
interact with the negatively charged perrhenate anion via electrostatic
interactions. At higher pH, the amount of protonated amine groups
decreaseddrastically,limitingthesorptionofrhenate. Withtheincrease
in the ionic strength from 0.01 to 0.1 M, rhenate sorption on chitosan
decreased by 90%. The sorption capacity of chitin and chitosan for
rhenate adsorption was also compared. pH 3 was found favorable for
adsorption on chitin, however, pH 4.1 was found more favorable in case
of chitosan. Even under these conditions, the percentage of rhenate
sorbed on chitin was much smaller than the percentage of rhenate
sorbed on the chitosan. The main difference between the two organic
polymers was that, for chitin, the majority of NH2 groups were
acetylated, so that the amount of protonated amine groups was smaller
by far, than in chitosan for the similar experimental conditions.
Consequently, chitin had a much smaller surface charge. Thus, a smaller
that the sorption of perrhenate occurred only when a large number of
protonated amine groups were present on the organic molecule.
Acid-washed Ucides shells (AWUS) showed good adsorption
potential for anionic gold-cyanide (Au(CN)2
chromate (CrO4
biosorption uptakes by AWUS were up to 0.17 mmol Au/g AWUS (pH
3.4), 0.15 mmol Se/g (pH 3.0), 0.54 mmol Cr/g (pH 2.0) and
0.79 mmol V/g (pH 2.5). An increased ionic strength (IS) suppressed
the primary anion uptake as chloride ions competed for biosorbent
Chitosan-derivatives have also been explored for the removal and
recovery of precious metals. The adsorption of gold (Au(III)) ions onto
chitosan and N-carboxymethyl chitosan (NCMC) has been investigat-
ed [48]. The percentage adsorption increased first with the rise in pH
andthenreacheda maximumat aboutpH4.0and6.0,for chitosanand
NCMC, respectively. It decreased sharply with a further increase in
equilibrium pH. The uptake of Au3+on chitosan and NCMC were
30.95 mg/g of chitosan and 33.90 mg/g of NCMC. The Au3+ions were
readily removed from chitosan and NCMC by treatment with an
aqueous EDTA solution. Based on the desorption studies, it was
concluded that ion exchange was the controlling mechanism.
Chitosan-derivatives were found very efficient for removing gold
from dilute acidic solutions [49]. Maximum uptake capacity reached
600 mg/g (ca. 3 mmol/g). The speciation of gold (under chloride and
hydroxide–chloride forms) appeared to be a predominant parameter
influencing uptake. In acidic solutions, chitosan was protonated and
protonated amine groups were available for thesorption of anionic gold
species. The optimum pH range was pH 2–3 for glutaraldehyde cross-
linked chitosan, but the sorption capacity strongly decreased with
increasing pH. Rubeanic acid grafting decreased the influence of pH on
gold sorption. Sulfur grafting increased the polymer chelating sites that
involved in ion-pair formation. Sorption kinetics was influenced by pH
and the type of chitosan-derivatives. The grafting of sulfur compounds
and the hexamethylene diisocyanate cross-linking enhanced sorption
kinetics probably due to the presence of highly reactive chelating sites
and better diffusion properties.
+surface group and rhenate anions in solution. The
−), selenate (SeO4
3−) at low pH [47]. Equilibrium
2−) and vanadate (VO4
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Chitosan was also examined for the removal of soluble silver from
industrial waste streams [50]. Stirred-batch and column methods
were used to remove free (hydrated) silver ion as well as the
ammonia, thiocyanate, thiosulfate, and cyanide complexes of silver
in simulated wastewater at an initial concentration of 50 mg/L and in
a pH range of 2–10. In the case of the free silver ion, Ag+, and in
However, the anions, Ag(SCN)3
pH 2, and Ag(CN)2
examined in these experiments. The calculated silver ion capacity in a
flow-through column at pH 6 was reported ca. 42 mg/g.
The chitosan microparticles were prepared using the inverse phase
results showed that the maximum adsorption capacity was found at pH
The adsorption reaction followed the pseudo-second-order kinetics,
indicating the main adsorption mechanism of chemical adsorption. The
isotherm adsorption equilibrium was well described by Langmuir iso-
thermswiththemaximumadsorptioncapacityof129.9 mg/gforPt(IV)
and112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and
without loss of the adsorption capacity up to at least 5 cycles and the
desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H2SO4
eluent was used. The results also showed that the pre-concentration
factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the
recovery was found to be more than 97% for both precious metal ions.
Chitosan-derivatives have also been explored for the removal of
some radionuclides from water. Chitosan benzoyl thiourea derivative
has been synthesized and used successfully for the removal of the
hazardous60Co and152+154Eu radionuclides from aqueous solutions
by Metwally et al. [52]. The maximum adsorption capacities for Co(II)
and Eu(III) were 29.47 (mg/g) and 34.54 (mg/g), respectively. It was
found that uptake% of Eu(III) and Co(II) reached its maximum values
of 75.0% and 98.0% at pH 3.5 and 8.0, respectively, at 10−5M ion
Adsorption of uranium(VI) from aqueous solution onto cross-linked
chitosan (CCTS) was investigated in a batch system by Wang et al. [53].
The maximum Langmuirmonolayercapacity was foundtobe 72.6 mg/g.
contact time, pH, and initial uranium(VI) concentration. Kinetic studies
showed that the adsorption followed a pseudo-second-order kinetic
ions with chitosan should refer to the excellent comprehensive reviews
published elsewhere [5–7]. A summary of adsorption capacities of
chitin- and chitosan-derivatives for different metal ions and radio-
nuclides has been presented in Table 1.
It is evident from the vast literature survey that chitin-, chitosan-
and its derivatives have been proven very promising biosorbents for
the removal of metal ions from water and wastewater. The mechanism
of metal adsorption on chitin- and chitosan-derivatives has been
proposed to occur via electrostatic interactions in acidic media (ion
exchange), metal chelation (coordination) and due to the formation of
ion pairs [5–7]. Several parameters influencethis reaction such as, ionic
charge of the adsorbent, solution pH and the chemistry of the metal ion
(ionic charge, ability to be hydrolyzed and to form polynuclear species)
2−and Ag(S2O3)2
−was not bound to any significant extent at any pH
3−, were bound only at
2.2. Chitin- and chitosan-derivatives for dyes removal
Dyes are important water pollutants which are generally present
in the effluents of textile, leather, paper and dye manufacturing
industries. The worldwide high level of production and extensive use
of dyes generates colored wastewaters which cause water pollution.
The colored dye effluents are generally considered to be highly toxic
to the aquatic biota and affect the symbiotic process by disturbing the
natural equilibrium through reduced photosynthetic activity due to
the coloration of water in streams. Some dyes are reported to cause
allergy, dermatitis, skin irritation, and cancer in humans. Thus, the
removal of dyes from effluents before they are mixed up with
unpolluted natural water bodies is important. Various studies on
chitin and chitosan for dyes removal from water and wastewater have
been conducted in recent years [53–66]. These studies demonstrated
that chitosan-based biosorbents are efficient materials and have an
extremely high affinity for many classes of dyes.
Table 1
Adsorption capacities of chitin and chitosan-derivatives for various metal ions and
radionuclides removal from water.
S. no.Adsorbent AdsorbateAdsorption
Chitosan flakes
Cu, Zn, As,
and Cr
14.0 mg/g
5.93 mg/g
815.0 mg/g
222.0 mg/g
164.0 mg/g
75.0 mg/g
1.8–2.2 mmol/g
137, 108, 58,
and 124 mg/g
2.26 mmol/g
188–518 mg/g
196.07 mg/g
114.94 mg/g
72.0 mg/g
Aminated chitosan beads
Porous-Magnetic Chitosan beads
Chitosan coated on perlite
Chitosan coated on perlite
Chitosan obtained from
silkworm chrysalides (ChSC)
Chitosan obtained from
silkworm chrysalides (ChSC)
Carboxylgrafted chitosan
Amido-grafted chitosan
Chitosan coated on to polyvinyl
chloride (PVC) beads
Chitosan coated on to polyvinyl
chloride (PVC) beads
14.Cu(II)87.0 mg/g [24]
318.0 mg/g
935.0 mg/g
120.5 mg/g
18.Cu(II) 87.9 mg/g[27]
45.45 mg/g
ca. 400–
450 mg/g
402.5 mg/g
21. Glutaraldehyde cross-linked
chitosan beads
Glutaraldehyde cross-linked
chitosan beads
chitosan gel beads
Chitosan beads
Chitosan beads
Chitosan flakes
763.0 mg/g[32]
23.As(V)ca. 160.0 mg/g[34]
1.83 mg/g
1.94 mg/g
14,160 µg/g
102.0 mg/g
78.0 mg/g
50.0 mg/g
154.0 mg/g
27.Chitosan flakesCr(VI)[38]
Non-cross-linked chitosan
Cross-linked chitosan
Chitosan coated onto nonporous
ceramic alumina
Quaternary ammonium salt of
chitosan (QCS)
Cross-linked chitosan
Cross-linked chitosan
Aminated chitosan
Aminated chitosan
Chitosan particles
N-carboxymethyl chitosan
Chitosan benzoyl thiourea
Chitosan benzoyl thiourea
Cross-linked chitosan
31.Cr(VI)30.2–68.3 mg/g[42]
6.0 mg/g
215.0 mg/g
30.2 mg/g
28.7 mg/g
90 mg/g
30.95 mg/g
33.90 mg/g
42.0 mg/g
29.47 mg/g
41.Eu(III)34.54 mg/g [52]
42.U(VI)72.6 mg/g[53]
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Wu et al. [58] examined the suitability of chitosan for the removal
of reactive dyes. A comparison of the maximum adsorption capacity
for reactive red 222 (RR222) by chitosan flakes and beads showed
uptake capacities of 293 mg/g for flakes and 1103 mg/g for beads
which was explained by the fact that the beads possessed a greater
surface area than the flakes.
The abilities of removal of three reactive dyes (RR222, RB222, and
RY145) and of immobilization of tyrosinase using flake-type and
highly swollen bead-type of chitosans at 30 °C have also been
investigated [59]. The capacity of dye adsorption using swollen
chitosan beads was about five times, up to 1653 g/kg, as compared to
chitosan flakes. The adsorption process could be best described by the
pseudo-second-order equation, indicating the controlling nature of
chemisorption (chemical reaction). The highly swollen chitosan beads
applied in this work, showed promising potential for enzyme
immobilization and color removal.
The adsorption of reactive dye (reactive red 189) from aqueous
solutions on cross-linked chitosan beads was studied in a batch
system[60]. The equilibriumisotherms at different particlesizes (2.3–
2.5, 2.5–2.7 and 3.5–3.8 mm) and the kinetics of adsorption with
respect to the initial dye concentration (4,320, 5,760 and 7,286 g/m3),
temperature (30, 40 and 50 °C), pH (1.0, 3.0, 6.0 and 9.0), and cross-
linking ratio (cross-linking agent/chitosan weight ratio: 0.2, 0.5, 0.7
and 1.0) were investigated. The maximum monolayer adsorption
capacities obtained from the Langmuir model were very large, (1936,
1686 and 1642 mg/g) for small, medium and large particle sizes,
respectively, at pH 3.0 and 30 °C, for the cross-linking ratio of 0.2. The
initial dye concentration and the pH of aqueous solutions significantly
affected the adsorption capacity of dye RR189 on the cross-linked
chitosan. However, the adsorption of the dye on chitosan was slightly
influenced by the temperature and the epichlorohydrin (ECH)/
chitosan weight ratio. It was suggested that the rate-limiting step
may be the chemical adsorption but not the mass transport.
A batch system wasalso applied to study the adsorption of reactive
dye (reactive red 189) from aqueous solutions by cross-linked
chitosan beads [61]. The ionic cross-linking reagent sodium tripoly-
phosphate was used to obtain rigid chitosan beads. To stabilize
chitosan in acid solutions, chemical cross-linking reagent epichloro-
hydrin (ECH), glutaraldehyde and ethylene glycol diglycidyl ether
were used andECH showedthehighest adsorptiveremoval of the dye.
The Langmuir model agreed well with experimental data and its
calculated maximum monolayer adsorption capacity was found to be
1802–1840 g/kg at pH 3.0, and 30 °C. The electrostatic interactions
between the dye and chitosan beads governed the adsorption
mechanism. The desorption data showed that the removal percent
of dye from the cross-linked chitosan beads was 63% in NaOH
solutions at pH 10.0 and 30 °C. It was observed that the desorbed
chitosan beads could be reused to adsorb the dye and to reach the
same capacity as that before desorption.
Chiou et al. [62] examined the adsorption of four reactive dyes,
three acid dyes and one direct dye onto cross-linked chitosan beads.
The adsorption capacity values ranged from 1911 to 2488 mg/g at pH
3–4. The authors reported that the adsorption conforms to Langmuir
isotherm model and pseudo-second-order kinetic model. In addition,
adsorption capacity appeared to increase with the decreasing pH of
solution. The adsorption capacities of the cross-linked chitosan beads
were much higher than those of chitin for anionic dyes. It showed that
the major adsorption site of chitosan is an amine group, –NH2, which
is easily protonated to form –NH3
electrostatic interaction between the –NH3
anions was used to explain the high adsorption capacity of anionic
dyes onto chemically cross-linked chitosan beads.
Kinetics of the adsorption of reactive dyes by chitin was studied by
Akkaya et al. [63]. The effect of initial concentration, temperature,
shaking rate and pH on the adsorption of reactive yellow 2 (RY2) and
reactive black 5 (RB5) using chitin was investigated. The authors
+in acidic solutions. The strong
+of chitosan and dye
reported that RY2 and RB5 are significantly adsorbed on chitin. The
adsorption capacities were found ca. 38 mg/g for RY2 at 293 K, while
65 mg/g for RY5 at 333 K. It was suggested by the authors that the
adsorption kinetics was controlled by surface diffusion as the BET
surface area of chitin used in this study was very low. At particularly
lower temperatures, surface diffusion was more dominant.
The treatment of synthetic reactive dye wastewater (SRDW) by
adsorption process was studied using chitin modified by sodium
hypochlorite and original chitin in batch experiments [64]. Maximum
dye adsorption by chitin increased from 133 mg/g to 167 mg/g with
rise in temperatures from 30 to 60 °C. For modified chitin, the capacity
decreasedfrom124 mg/gto 59 mg/gwhenthetemperatureincreased
from 30 °C to 60 °C, respectively. The authors suggested that although
modified chitin had lower adsorption capacity as compared to chitin,
elution of the dye from modified chitin was easier than chitin.
Therefore, modified chitin could be suitable in a column system for
dye pre-concentration as well as wastewater minimization. In
addition, the column study showed that modified chitin could be
used for more than four cycles of adsorption and eluted by distilled
water. The main mechanism of dye adsorption onto modified chitin
was physical adsorption, while the chemical adsorption was respon-
sible in chitin.
Adsorption of reactive orange 16 by quaternary chitosan salt (QCS)
was used as a model to demonstrate the removal of reactive dyesfrom
textile effluents by Rosa et al. [65]. The adsorption experiments were
conducted at different pH values and initial dye concentrations. The
maximum adsorption capacity determined was 1060 mg of reactive
dye/g of adsorbent, corresponding to 75% occupation of the
adsorption sites. The results indicated that the adsorption process
was not dependent on solution pH, since the most probable
mechanism for adsorption was the interaction of the polymer
quaternary ammonium groups with the dye sulfonate groups.
The adsorption of Remazol black 13 dye onto chitosan in aqueous
solutions was investigated [66]. Experiments were carried out as a
function of contact time, initial dye concentration (100–300 mg/L),
particle size (0.177, 0.384, 1.651 mm), pH (6.7–9.0), and temperature
(30–60 °C). The maximum adsorption capacity (qm) was found to be
91.47–130.0 mg/g. The amino group nature of the chitosan provided
reasonable dye removal capability. The kinetics of reactive dye
adsorption followed the pseudo-first and second-order rate expres-
sion which demonstrates that intraparticle diffusion plays a signifi-
cant role in the adsorption mechanism. The authors also provided
scanning electron microscopy (SEM) images to show that the dye was
densely and homogeneously adhered to the surface of the carrier, as a
result of either natural entrapment in to the porous chitosan material,
due to physical adsorption by electrostatic forces or covalent binding
between the cellular chitosan and the carrier.
Chitosan was cross-linked using glutaraldehyde in the presence of
through thereaction with tetraethylenepentaminefollowedbyglycidyl
trimethylammonium chloride, to produce chitosan/amino resin (R1)
and chitosan bearing both amine and quaternary ammonium chloride
moieties (R2), respectively. The uptake of reactive black 5 (RB5) from
aqueous solutions using R1 and R2 resins was studied using batch and
column methods. The resins showed high affinity for the adsorption of
RB5 and an uptake value of 0.63 and 0.78 mmol/g was reported for
resins R1 and R2, respectively at 25 °C. The resin was regenerated
effectively using NH4OH/NH4Cl buffer (pH 10).
Chitosan was modified to possess the ability to adsorb cationic
dyes from water by Chao et al. [68]. Four kinds of phenol derivatives:
4-hydroxybenzoic acid (BA), 3,4-dihydroxybenzoic acid (DBA), 3,4-
dihydroxyphenyl-acetic acid (PA), and hydrocaffeic acid (CA), were
used individually as substrates of tyrosinase to graft onto chitosan.
These modified chitosans were used in experiments for uptake of the
cationic dyes, crystal violet (CV) and bismarck brown Y (BB). The
optimum adsorptive uptake for CV and BB occurred at pH 7 and 9,
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respectively at 30 °C. Langmuir type adsorption was found to occur
and the maximum adsorption capacities for both dyes were increased
with the following order: CTS–CA>CTS–PA>CTS–DBA>CTS–BA.
Chitosan-derivatives, by grafting poly (acrylic acid) and poly
(acrylamide) through persulfate induced free radical initiated
polymerization processes and covalent cross-linking of the prepared
materials, were prepared and evaluated as biosorbents for Remacryl
Red TGL (a basic dye) removal [69]. It was found that the grafting
modifications greatly enhanced the adsorption performance of the
biosorbents. Kinetic studies also revealed a significant improvement
of sorption rates by the modifications. The amount of adsorbed values
derived from the Langmuir model at 298 K were 0.479, 0.727, and
1.068 mmol/g (204.22, 309.82, and 510.74 mg/g) for three forms of
chitosan, respectively.
Chitosan beads were synthesized for the removal of a cationic dye,
malachite green (MG), from aqueous solution [70]. The monolayer
adsorption capacities were found to be 93.55 mg/g at 303 K;
74.83 mg/g at 313 K; 82.17 mg/g at 323 K, respectively. The kinetic
experiments confirm that sorption process obeys the pseudo-second-
order kinetic model. The temperature strongly influenced the
adsorption process. The adsorption of malachite green increased
from 18.80% to 99.38% with an increase in pH of the solution from 2.1
to 11.0. Beyond pH 8, the dye adsorption remained almost constant.
Batch adsorption experiments were carried out for the removal of
methylene blue (MB), a cationic dye, from its aqueous solution using
chitosan-g-poly(acrylic acid)/montmorillonite (CTS-g-PAA/MMT) nano-
composites as adsorbent [71]. The adsorption behaviors of the nano-
composite showed that the adsorption kinetics and isotherms were in
good agreement with pseudo-second-order equation and the Langmuir
equation, respectively, and the maximum adsorption capacity was
1859 mg/g for CTS-g-PAA/MMT with wt.% of 30% and weight ratio of
7.2:1. The desorption studies revealed that the nanocomposite provided
the potential for regeneration and reuse after MB dye adsorption.
The adsorption using chitosan-based adsorbent for the removal of
basic blue 3 (BB 3) from aqueous solutions was studied [72]. This
(themaximumadsorption capacity was166.5 mg/g), dependingon the
process, involving adsorption on the external surface, diffusion into the
bulk and electrostatic interactions. It was explained by the authors that
sulfonate groups contributed to the sorption mechanism through
electrostatic interactions between SO3
are known as strong cation exchangers) and the cationic sites of BB 3.
Addition of NaCl enhanced the performance of the adsorbent.
N-benzyl mono- and disulfonate derivatives of chitosan were used
for the removal of dyes from aqueous solution [73]. The effectiveness
of these materials in adsorbing basic blue 9 (BB 9) has been studied as
a function of agitation time, initial concentration and solution salinity.
Experimental results confirmed the strong cation exchanger character
of the sulfonated derivatives and showed that disulfonate derivatives
of chitosan exhibited higher sorption capacities toward cationic dye
than the monosulfonic one. Sorption of BB 9 reached equilibrium
within 20–40 min and the maximum adsorption onto disulfonate
derivative was 121.9 mg/g at pH=3.
Chitosan intercalated montmorillonite (Chi-MMT) was prepared
by dispersing sodium montmorillonite (Na+-MMT) into chitosan
solution at 60 °C for 24 h and was examined for three basic dyes viz.
basic blue 9 (BB9), basic blue 66 (BB66) and basic yellow 1 (BY1) [74].
The Chi-MMT showed the highest adsorption capacity in the range of
46–49 mg/g, when the initial dye concentration was 500 mg/L, being
equivalent to 92–99 wt.% of dye removal. The adsorption capacities of
Chi-MMT for all basic dyes increased with an increase of initial dye
concentration. An increase of adsorption capability of Chi-MMT was
attributed to the existence of intercalate-chitosan. It could enlarge the
pore structure of Chi-MMT, facilitating the penetration of macromo-
lecular dyes, and also electrostatically interact with the applied dyes.
−groups of the sorbent (which
The ability of chitosan as an adsorbent for the removal of acid
dyestuff, namely, acid green 25, acid orange 10, acid orange 12, acid
red 18, and acid red 73, from aqueous solution has been studied [75].
The monolayer adsorption capacities were determined to be 645.1,
922.9, 973.3, 693.2, and 728.2 mg of dye/g chitosan for acid green 25,
acid orange 10, acid orange 12, acid red 18, and acid red 73,
respectively. The differences in adsorption capacities might be due to
the effect of molecular size and the number of sulfonate groups of
each dye. The results demonstrated that monovalent and/or smaller
dyemoleculeshadsuperioradsorptioncapacitiesdueto anincreasein
the dye/chitosan ratio in the system. The smaller dye molecules were
able to penetrate deeper into the internal pore structure of the
chitosan particles. Electrostatic attractions governed the possible acid
dye adsorption mechanism onto chitosan.
The efficacy of chitosan in the form of hydrobeads to removecongo
red, an anionic dye, from water has been examined [76]. It was
reported that chitosan beads is a good adsorbent for the removal of
congo red from its aqueous solution and 1 g of chitosan in the form of
hydrobeads can remove ca. 93 mg of the dye at pH 6.0. The reason for
higher adsorption of congo red on prepared chitosan in this study was
explained due to the fact that chitosan being polycationic in nature
attracted congo red, an anionic dye, and thus increased dye
adsorption. Sodium chloride and sodium dodecyl sulfate (SDS) were
found to inhibit the adsorption process. Authors reported that
physical forces as well as ionic interaction were responsible for
binding of congo red with chitosan.
The adsorption performance of chitosan (CS) beads impregnated
with triton X-100 (TX-100) as a nonionic surfactant and sodium
dodecyl sulfate (SDS) as an anionic surfactant was investigated for the
removal of anionic dye, congo red (CR), from aqueous solution by
Chatterjee et al. [77]. The Sips maximum adsorption capacity in dry
weight of the CS/TX-100 beads was 378.79 mg/g and 318.47 mg/g for
the CS/SDS beads, higher than the 223.25 mg/g of the CS beads.
Modification of CS beads by impregnation with nonionic surfactant, or
even anionic surfactant, at low concentrations was found to enhance
adsorption of anionic dye. It was suggested by the authors that
adsorption of CR onto impregnated beads involved some hydrophobic
interactions between CR and surfactant molecules (TX-100 and SDS)
impregnated in the beads.
The adsorption of eosin Y, as a model anionic dye, from aqueous
solution using chitosan nanoparticles prepared by the ionic gelation
between chitosan and tripolyphosphate was examined by Du et al.
[78]. The adsorption capacity was found to be 3.333 g/g. The
adsorption process was endothermic in nature with an enthalpy
change (ΔH) of 16.7 kJ/mol at 20–50 °C. The optimum pH value for
eosin Y removal was found to be 2–6. The dye was desorbed from the
chitosan nanoparticles by increasing the pH of the solution. The
desorption percentage was about 60% within 60 min at pH 11.0,
whereas 98.5% of the dye could be eluted at pH 12 in 150 min.
The capabilities of chitosan and chitosan–EGDE (ethylene glycol
diglycidyl ether) beads for removing acid red 37 (AR 37) and acid blue
25 (AB 25) from aqueous solution have also been investigated [79].
Chitosan beads were cross-linked with EGDE to enhance its chemical
resistance and mechanical strength. It was shown that the adsorption
capacities of chitosan for both acid dyes were comparatively higher
than those of chitosan–EGDE. The desorption study revealed that after
three cycles of adsorption and desorption by NaOH and HCl, both
adsorbents retained their promising adsorption abilities. FTIR analysis
proved that the adsorption of acid dyes onto chitosan-based
adsorbents was physical adsorption.
The performance of nanochitosan (with particle size range from
0.0663 μm to 1.763 μm) as an adsorbent to remove acid dyes from
aqueous solution has been explored by the researchers [80]. The
monolayer adsorption capacities were determined to be 1.77, 4.33,
1.37 and 2.13 mmol/g nanochitosan for acid orange 10, acid orange
12, acid red 18 and acid red 73, respectively. The differences in
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capacities might be due to the differences in the particle size of dye
molecules and the number of sulfonate groups on each dye molecule.
The results have demonstrated that monovalent and smaller dye
molecular sizes have superior capacities due to the increase in dye/
chitosan surface ratio in the system and deeper penetration of dye
molecules into the internal pore structure of nanochitosan. The
mechanism of the adsorptionprocessof acid dye on nanochitosan was
proposed to be the ionic interactions of the colored dye ions with the
amino groups on the chitosan.
Poly(methylmethacrylate) grafted chitosan was found to be an
efficient adsorbent for the removal of three anionic azo dyes (Procion
Yellow MX, Remazol Brilliant Violet and Reactive Blue H5G) over a
wide pH range of 4–10 and maximum at pH 7 [81]. The adsorption
capacity for yellow, violet and blue dyes was 250, 357 and 178 mg/g,
respectively. The kinetic study results suggested that adsorption
kinetics of the dye molecules were not diffusion controlled, but
chemisorption was the main sorption mechanism. The anionic dye,
bearing sulfonic groups, is electrostatically attracted by protonated
amine groups of the chitosan, thus, neutralized the anionic charges of
dyes that can bind together. The removal of the dye reached a
maximum at pH 4 with the complete neutralization of the anionic
charges. However, with increasing pH, deprotonation at amino group
took place that resulted in poor interaction between the dye and the
biopolymer and therefore, the decrease in adsorption. On the other
hand, at much acidic pH (pH<4), protonation took place at the
nitrogenand carbonylgroups presentin the dyeswhich decreasedthe
adsorption due to electrostatic repulsion between the same charges.
However, in chitosan-graftpoly(methylmethacrylate) (Ch-g-PMMA),
the dangling ester groups at the grafted chitosan appeared to be
mainly responsible for the adsorption and not the amino groups as
was also evident by IR spectrum of dye loaded adsorbent. Further,
other than electrostatic interaction some interaction in the form of
conformational affects might also be operative. The sensitivity to pH
after pH 4 was not seen in the graft copolymer because the major
binding took place at PMMA grafts and only a very small amount of
NH2were available for binding after grafting.
Several other workers also examined the potential of chitosan and
its derivatives for different types of dyes removal from water [82–88].
A summary of adsorption capacities of chitin- and chitosan-deriva-
tives for different dyes has been presented in Table 2.
Readers interested in a detailed discussion of the interaction of
dyes with chitosan and its derivatives should refer to an excellent
comprehensive review by Crini and Badot [8]. It is evident from the
recent literature survey that chitin- and especially chitosan and its
derivatives have been found promising adsorbents for dyes removal.
Various classes of dyes have been studied so far and all these studies
suggest that chitosan shows higher potential for various dyes.
However, it is necessary to continue the identification of the most
promising types of chitosan to achieve higher sorption capacities. The
mechanism of dye adsorption on chitin- and chitosan-derivatives
needs further detailed investigation as different mechanisms have
beenproposedby differentresearchers[8], suchassurfaceadsorption,
chemisorption, diffusion and adsorption–complexation. Further re-
search is needed to gain a better understanding of adsorption
mechanism of dye adsorption on chitin- and chitosan-derivatives.
Such studies would provide a better understanding of adsorption
phenomenon involve in the uptake of a given dye [8].
2.3. Chitin- and chitosan-derivatives for phenols removal
Among the various aqueous pollutants generally present in
wastewaters, phenol and substituted phenols are considered as
priority pollutants. Phenols cause unpleasant taste and odor of
drinking water and can exert negative effects on different biological
processes. The ubiquitous nature of phenols, their toxicity even in
trace amounts and the stricter environmental regulations make it
necessary to develop processes for the removal of phenols from
wastewaters. Chitin- and chitosan-derivatives have also been inves-
tigated for phenol and substituted phenols removal from water and
Table 2
Adsorption capacities of chitin and chitosan-derivatives for various dyes removal from
S. no. AdsorbentAdsorbate Adsorption
Chitosan flakes
Chitosan beads
chitosan beads
Reactive red 222
Reactive red 222
Reactive red 189
293.0 mg/g
1103.0 mg/g
1936 mg/g
1840 g/kg
1911 –
2488 mg/g
4.Reactive red 189 [61]
5. Cross-linked
chitosan beads
Four reactive dyes,
three acid dyes
and one direct dye
Reactive yellow 2
Reactive black 5
Synthetic reactive
dye wastewater
Synthetic reactive
dye wastewater
Reactive orange 16
38.0 mg/g
65.0 mg/g
133–167 mg/g
9. Chitin modified
by sodium hypochlorite
Quaternary chitosan
salt (QCS)
59–124 mg/g [64]
10. 1060.0 mg/g[65]
11.Remazol black 13 91.47–
130.0 mg/g
0.63 mmol/g
0.78 mmol/g
Chitosan/amino resin
Chitosan bearing both
amine and quaternary
ammonium chloride
Powdered cross-linked
chitosan grafted with
acrylic acid
Chitosan bead
Reactive black 5
Reactive black 5
Remacryl Red TGL 204.2–
510.7 mg/g
15. Malachite green 74.83–
93.55 mg/g
1859.0 mg/g
poly(acrylic acid)/
Disulfonate derivatives
of chitosan
grafted chitosan
grafted chitosan
grafted chitosan
Methylene blue [71]
17. Basic blue 3166.5 mg/g[72]
18. Basic blue 9121.9 mg/g [73]
Acid green 25
Acid orange 10
Acid orange 12
Acid red 18
Acid red 73
Congo red
Eosin Y
645.1 mg/g
922.9 mg/g
973.3 mg/g
693.2 mg/g
728.2 mg/g
93.0 mg/g
3.33 g/g
Acid orange 10
Acid orange 12
Acid red 18
Acid red 73
Procion Yellow MX
1.77 mmol/g
4.33 mmol/g
1.37 mmol/g
2.13 mmol/g
250.0 mg/g
31.Remazol Brilliant
Reactive Blue
Indigo carmine
357.0 mg/g[81]
178.0 mg/g[81]
1334.0 mg/g
34.ChitosanIndigo carmine
35.Cross-linked chitosan
Cross-linked chitosan
Chitosan grafted with
amide groups
Chitosan grafted with
carboxyl groups
Metanil yellow[87]
36.Reactive blue 15722.0 mg/g[87]
37.Remazol Yellow
Gelb 3RS
Basic yellow 37
1211.0 mg/g[88]
38.595.0 mg/g[88]
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wastewater. The equilibrium and kinetics of chlorophenols sorption
by chitosan, polyD-glucosamine, were studied under simulated
groundwater conditions [89]. Comparison between two types of
chitosan, flakes and highly swollen beads, demonstrated that the
maximum pentachlorophenol (PCP) uptake capacities depend on the
specific surface area of the particles. Out of the five kinds of
chlorophenols, i.e. 2,4,6-trichlorophenol (2,4,6-TCP), 3,4-dichloro-
phenol (3,4-DCP), 2,3-dichlorophenol (2,3-DCP), 2,6-dichlorophenol
(2,6-DCP) and 3-monochlorophenol (3-MCP), flake-type chitosan
exhibitedmaximumsorptionefficiency forTCP,followedby DCPs,and
finally MCP (the three kinds of DCP, with the same elemental
compositions, were sorbed equally).
The adsorption of phenol onto chitin was studied as a function of
initial pH, temperature and initial phenol concentration [90]. The pH
primarily affected the degree of ionization of the phenol and the
surface properties of chitin. The functional groups of chitin will be
protonated at low-pH values and resulted in a stronger attraction for
negatively charged ions in the adsorption medium. Phenol being
weakly acidic would be partially ionized in solution. These ions would
be negatively charged and would be directly attracted due to
electrostatic forces by the protonated amino groups of the chitin. As
the pH increased, the overall surface charge of the chitin became
negative and adsorption decreased. The equilibrium uptake of phenol
by chitin was also affected by temperature which was attributed to
the enlargement of pore size or creation of some new active sites on
the adsorbent surface due to bond rupture. The highest phenol
adsorption capacity was determined as 21.5 mg/g for 300 mg/L initial
phenol concentration at pH 1.0 and 40 °C.
The application of magnetite-immobilized chitin for pentachlorophe-
nol (PCP) removal was demonstrated by Pang et al. [91]. For chitin
ratio at 1:2, initial pH 6, 25 °C, 200 rpm and 60 min in batch system. The
immobilization efficiency (IE) was 99.4% and immobilization capacity
(IC) was 2.0 mg chitin/mg magnetite. High initial pH (pH>11) and
temperature (>30 °C) lowered the IE and IC. For PCP (10 mg/L) adsorp-
tion,theoptimizedconditionswere:1500 mg/Limmobilizedchitin,initial
pH 6, 25 °C, 200 rpm and 60 min in batch system. The removal efficiency
(RE) was 57.9% and removal capacity (RC) was 5.4 mg/g. The adsorption
ability of immobilized chitin decreased with pH and increased with
temperature. However, increasing the amount of immobilized chitin
(24,000 mg/L) increased the RE up to 92%.
Beads of chitosan–sodium alginate were prepared from chitosan
and sodium alginate (an anionic polysaccharide) [92]. These beads
were treated with CaCl2in order to improve the stability as well as the
sorption capacity of the biosorbent. It was reported that the percent
removal of phenol and o-chlorophenol increased rapidly with
increase in the dose of chitosan–calcium (CS/Ca) alginate blended
beads due to the greater availability of binding sites of the biosorbent.
The maximum Langmuir monolayer capacity was reported as
108.69 mg/g for phenol and 97.08 mg/g for o-chlorophenol. Based
on the thermodynamic values, the adsorption processes was
associated with chemical ion-exchange mechanism. The fixed bed
columns of CS/Ca alginate beads saturated with phenol or chlor-
ophenol was regenerated by passing 0.1 M NaOH solution as an eluent
at a fixed flow rate of 1 mL/min. Further, results from the limited
number of column adsorption–desorption cycle indicated that the
adsorption capacity of the CS/Ca alginate beads decreased in the
second and third adsorption–desorption cycles.
β-cyclodextrin (CS–CD), and a cross-linked β-cyclodextrin polymer
(EPI–CD) were prepared asadsorbents to remove phenol, p-nitrophenol
and p-chlorophenol from aqueous solution [93]. It was found that the
adsorption capacity of phenols onto chitosan was very small (1.98–
2.58 mg/g). However, functional chitosan chemically modified by β-CD
or salicylaldehyde exhibits much better adsorption ability for phenols.
CS–CD (20.56–179.73 mg/g) and EPI–CD (41.11–131.50 mg/g) exhibit
outstanding adsorption efficiency for these phenols. The adsorption
ability of CS–CD was better than EPI–CD. CS–SA presented good
adsorption ability for phenols. The adsorption of phenols onto EPI–CD,
CS–CD and CS–SA was predominated by hydrophobic interaction,
hydrogen bonding and π–π interaction, respectively. The low temper-
ature was found favorable for the adsorption of phenols. Ethanol was
removed from the adsorbent. The regenerated adsorbent could adsorb
could be reused six times.
Laccase from Coriolus versicolor was immobilized on chitosan using
glutaraldehyde as a cross-linking agent [94]. After immobilization,
laccase retained 52.2% of its original activity and was used to study 2,4-
dichlorophenol (2,4-DCP) removal from aqueous solutions. Favorable
cross-linking of laccase with chitosan occurred using 5% glutaraldehyde
for 8 h. The ratio of laccase to cross-linked chitosan was 20 mg/g after
6 h of reaction. The recovery of immobilized laccase activity was 52.2%.
The optimum pH for immobilized laccase was 4.5, which was less than
the optimum pH for the free enzyme (5.0). The immobilized enzyme
also demonstrated greater stability at room temperature over time.
When used to remove 2,4-DCP from wastewater, the optimum condi-
tions for the immobilized enzyme were a pH of 5.5 and a temperature
rangeof35–45 °C.Theimmobilizedenzymeretainedremovalefficiency
above 50% for up to six usages.
Chitosan–abrus precatorius (CS/Ab) blended beads were used as
adsorbent for the removal of phenolic compounds from aqueous
solution [95]. The maximum monolayer adsorption capacity of phenol,
2-chlorophenol and 4-chlorophenol on to the (CS/Ab) beads was found
to be 156 mg/g, 204 mg/g and 278 mg/g, respectively. A summary of
adsorption capacities of chitin- and chitosan-derivatives for different
phenols is presented in Table 3.
As compared to metal ions and dyes, there are comparatively less
reports available, demonstrating the usefulness of chitin- and chitosan
and its derivatives for the removal of phenols. Most of these studies are
limited only to chloro- or nitro-phenols. Additionally, chitin-, chitosan
and its derivatives show low affinity for phenols removal and there is a
strong need to conduct extensive research to enhance the removal
efficiencies/adsorption capacities of these biosorbents for different
phenols after appropriate treatment. Furthermore, the mechanism of
phenols adsorption on chitin- and chitosan-derivatives also needs to be
studied in detail as most of the articles focused only on the adsorption
potential (adsorption capacity) of chitin- and chitosan-derivatives for
phenols removal and little efforts have been made to elucidate the
sorption mechanism.
2.4. Chitin- and chitosan-derivatives for anions removal
and various inorganic anions have been found in potentially harmful
pollutants from drinking water supplies is an emerging issue. In recent
years, chitin- and chitosan-derivatives have been successfully utilized for
some anions removal from water. The adsorption of nitrate by chitosan
hydrobeads was examined by Chatterjee and Woo [96]. The maximum
adsorptioncapacitywas92.1 mg/gat30 °C.Intraparticlediffusionplayed
significant role at the initial stage of the adsorption process. Nitrate
which was explained due to the fact that a decrease in the pH of the
solution resulted in more protons being available to protonate the
chitosan amine group. This resulted in an enhancement of nitrate
adsorption by chitosan beads due to increased electrostatic interactions
between negatively charged nitrate group and positively charged amine
group. Above pH 6.4, an appreciable amount of nitrate adsorption by
nitrate from the loaded beads was accomplished by increasing the pH of
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the solution to the alkaline range, and a desorption ratio of 87% was
achieved around pH 12.0.
The adsorption of nitrate onto chitosan beads modified by cross-
linking with epichlorohydrin (ECH) and surface conditioning with
sodium bisulfate was investigated by Chatterjee et al. [97]. The
maximumadsorptioncapacitywas foundat a cross-linking ratio of 0.4
and conditioning concentration of 0.1 mM NaHSO4. The maximum
adsorption capacity was 104.0 mg/g for the conditioned cross-linked
chitosan beads at pH 5, while it was 90.7 mg/g for normal chitosan
beads. The nitrate adsorption was found strongly pH dependent, and
the maximum nitrate removal was found at pH 3. The high adsorption
capacities in acidic solutions (pH 3–5) were due to the strong
electrostatic interactions between its adsorption sites and nitrate.
The applicability of neodymium-modified chitosan as adsorbents
for the removal of excess fluoride ions from water was studied by Yao
et al. [98]. The effect of various physico-chemical parameters such as
temperature (283–323 K), pH (5–9), adsorbent dose (0.2–2.0 g/L),
particle size (0.10–0.50 mm) and the presence of co-anions (NO3
and SO4
equilibrium sorption was 11.4–22.3 mg/g. The sorption process was
found to be complex, and both the boundary of liquid film and
intraparticle diffusion contributed to the rate-determining step. The
used adsorbents could be regenerated in 24 h by 4 g/L of sodium
A novel adsorbent namely magnesia/chitosan (MgOC) composite
was prepared to remove fluoride from drinking water by Sundaram et
al. [99]. The maximum Langmuir monolayer capacity was found ca.
11 mg/g. The mechanism of fluoride removal of both MgO and MgOC
composite was mainly governed by adsorption. The higher defluor-
idation capacity (DC) of MgOC composite might be attributed to the
fact that chitosan also contributed in the enhancement of DC by
removing fluoride through hydrogen bonding. It was suggested that
MgOC composite being biocompatible, biodegradable, cost effective,
shaped into any desired form which possesses higher defluoridation
capacity with minimum contact time, can be used as a promising
sorbent for fluoride removal.
The metal-binding property of chitosan was used to incorporate
titanium (Ti) metal and applied as an adsorbent for fluoride adsorption
by Jagtap et al. [100]. Ti loading was varied from 5 to 50 wt.%. It was
observed that an increase in titanium loading from 5 to 15% improved
−, Cl−
2−) on removal of fluoride ions were studied. The maximum
fluoride removal from 61 to 89%. A 15% Ti loading was optimum as it
showed the highest fluoride removal and reduces the fluoride level to
permissible limits. Further increasing titanium loading showed a
be7.2 mg/g.ThefluorideuptakewasmaximumatpH7anddecreasedin
acidic andalkaline pH. Thepresence ofco-existinganions has a negative
effecton fluoride adsorption. The adsorbentwas found to have very fast
kineticsinthefirst30 minandthentheratesloweddownasequilibrium
was approached. A comparison of fluoride removal in simulated and
field water shows a high adsorption capacity in simulated water.
Protonated chitosan beads (PCB) were examined for fluoride
removal by Viswanathan et al. [101]. Sorption process was found to be
independent of pH and altered in the presence of other co-existing
anions. The maximum Langmuir monolayer capacity was found in the
range of 4.72–7.32 mg/g. The sorption process followed pseudo-
second-order and intraparticle diffusion kinetic models. The adsorp-
tion mechanism was explained on the basis of FTIR analysis, where a
slight widening of –NH2stretching band in FTIR spectra of the fluoride
sorbed PCB was observed which confirmed the presence of hydrogen
bonding between protonated amine (NH3
that the PCB removed fluoride by means of hydrogen bonding which
was due to electrostatic interactions between positively charged
surface and negatively charged fluoride ions. 0.1 M HCl was identified
as the best eluent. Field trial results indicated that PCB could be
employed as a best sorbent for fluoride removal.
The same researchers also prepared multifunctional chitosan beads
after chemical modification by introducing multifunctional groups, viz.,
order to utilize both amine and hydroxyl groups for fluoride removal
[102].Theprotonatedcum carboxylatedchitosanbeads(PCCB)showed
a maximum DC of 1800 mg F−/kg, whereas, raw chitosan beads
displayed only 52 mg F−/kg adsorption capacity. The mechanism of
fluoride removal by PCCB was explained by H-bonding.
The fluoride adsorption potential of novel nano-hydroxyapatite/
chitin (n-HApCh) composite was explored by Sundaram et al. [103].
The effect of pH, interfering anions and contact time were examined.
n-HApCh composite possesses higher defluoridation capacity (DC) of
2840 mg F−/kg than nano-hydroxyapatite (n-HAp) which showed a
DC of 1296 mg F−/kg. The enhancement in DC of n-HApCh composite
over n-HAp was explained due to biosorption by chitin, adsorption by
physical forces and fluoride ion entrapped in fibrilliar capillaries and
spaces of polysaccharide networkof the chitin moiety. Recently, Xie et
al. [104] investigated the removal of perchlorate from aqueous
solution by protonated cross-linked chitosan. The maximum
+) and fluoride, suggesting
+and COOH groups by means of protonation and carboxylation in
Table 3
Adsorption capacities of chitin and chitosan-derivatives for various phenols removal
from water.
AdsorbentAdsorbate Adsorption
Magnetite-immobilized chitin
Beads of chitosan–
sodium alginate
Beads of chitosan–
sodium alginate
21.5 mg/g
5.4 mg/g
108.6 mg/g
4. o-chlorophenol 97.0 mg/g[92]
p-nitrophenol and
p-nitrophenol and
p-nitrophenol and
2.5 mg/g
6.Functional chitosan, chemically
modified by β-cyclodextrin
Functional chitosan, chemically
modified by cross-linked
β-cyclodextrin polymer
Chitosan–abrus precatorius
Chitosan–abrus precatorius
Chitosan–abrus precatorius
179.7 mg/g
131.5 mg/g
8. Phenol156.0 mg/g[95]
9. 2-chlorophenol 204.0 mg/g[95]
10.4-chlorophenol278.0 mg/
Table 4
Adsorption capacities of chitosan-derivatives for different anions removal.
S. no. Adsorbent AdsorbateAdsorption
Chitosan hydrobeads
Chitosan beads modified
by cross-linking with
epichlorohydrin (ECH)
and surface conditioning
with sodium bisulfate
(MgOC) composite
Protonated chitosan
beads (PCB)
chitin (n-HApCh)
Protonated cross-linked chitosan
92.1 mg/g
104.0 mg/g
3.Fluoride11.4–22.3 mg/g[98]
4.Fluoride11.0 mg/g[99]
5.Fluoride7.2 mg/g[100]
6.Fluoride4.7–7.3 mg/g[101]
7.Fluoride2840.0 mg/kg[103]
8.Perchlorate45.45 mg/g[104]
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monolayer adsorption capacity was found to be 45.45 mg/g. The
presence of other anions inhibited the perchlorate adsorption. The
adsorbent was well regenerated by sodium hydroxide solution with
pH12 andreusedfor about15 cycles.Electrostatic attractionaswellas
physical forces was suggested as the main driven forces for
perchlorate adsorption. A summary of adsorption capacities of chitin-
and chitosan-derivatives for different anions is provided in Table 4.
Recent studies have shown that chitosan and its derivatives can be
successfully applied for the removal of anions (especially fluoride and
nitrate). However, as mentioned previously, it is necessary to
continue identification of the most promising types of chitosan for
anions removal. Additionally, mechanistic studies with anions need to
be performed in detail to propose the binding mechanism. There is, as
yet, little information in the literature on this topic, which needs to be
explored more in detail.
2.5. Chitin- and chitosan-derivatives for miscellaneous pollutants removal
Two types of chitosan microparticles (CMs) and their silver-
complex CMs (SCMs) were prepared using different cross-linking
agents, i.e.glutaraldehyde and epichlorohydrin, in order to investigate
the adsorption and release behaviors of a typical pesticide, methyl
parathion (MP) [105]. The maximumadsorption capacities of Ag(I) on
glutaraldehyde-cross-linked CM (CM # 1) and epichlorohydrin-cross-
linked CM (CM # 2) were found to be 140 mmol/g and 290 mmol/g,
and those of MP on SCM # 1 and SCM # 2 were 180 mmol/g and
60 mmol/g,respectively. It wasalsoconfirmedthatSCM # 1has better
absorptivity for MP than SCM # 2, in spite of its lower adsorption
capacity of Ag(I). The ratios of MP/Ag adsorbed on the SCMs are 1.3
and 0.2 for SCM # 1 and SCM # 2, respectively.
The removal of two fungicides, 4,4′-iso-Propylidene diphenol
(BPA), and diphenylolpropane 4,4′-dioxyaceticacid (BPAc) has been
investigated by Şişmanoğlu, [106]. The Langmuir maximum mono-
layer coverage was reported to be 4.30×10−3mol/g for BPA and
2.62×10−3mol/g for BPAc. The pseudo-first-order model and
intraparticle diffusion were used to describe the adsorption behavior
of BPA and BPAc onto chitin.
The ability of chitin and chitosan to adsorb humic acid has been
studied [107]. The adsorption capacities of humic acid at room
temperature (27 °C) were 27.30 mg/g for chitin and 28.88 mg/g for
chitosan. It was suggested that chitin and chitosan can be utilized to
remove humic acid.
Chitosan was successfully coated on PET granules through a dip
and phase inversion process and the coated granules were examined
for the performance and mechanism of humic acid removal through a
series of batch adsorption tests [108]. Chitosan-coated granules were
found to have positive zeta potential values at pH<6.6, mainly due to
the protonation of the amino groups in chitosan. Adsorption of humic
acid onto chitosan-coated granules was pH dependent and significant
amounts of humic acid could be adsorbed under acidic and neutral pH
conditions. The adsorption process involved a two-step process:
protonation of the amino groups in chitosan, followed by attachment
of humic acid onto the protonated amino sites on the surface. Under
low-pH conditions, the adsorption process was transport-controlled,
but under high-pH conditions, both transport and attachment played
an important role in humic acid adsorption onto chitosan-coated
granules. While chitosan has been widely studied for metal removal
from aqueous solution, it is also possible to extend the application of
chitosan as an adsorbent to remove charged organic compound such
as humic acid from water and wastewater.
The effects of pH and ionic strength on the adsorption capacity for
fulvic acid (FA) by chitosan hydrogel beads were examined [109]. The
maximum adsorption capacity of FA on chitosan hydrogel beads was
1.67 mg/g at pH 6.0. FTIR along with XPS analyses revealed that the
aminegroupsonthe beadswereinvolvedin thesorptionofFA andthe
organic complex between the protonated amino groups and FA was
formed after FA uptake. Electrostatic interaction and surface com-
plexation were found to be involved in the complex sorption of FA on
the chitosan hydrogel beads.
Chitin and chitosan have also been examined for the removal of
endocrine disrupting chemicals, estrone (E1) and 17β-estradiol (E2)
fromwater[110]. It wasreportedthatit took about 1 and2 days for E1
to achieve the equilibration onto chitin and chitosan, respectively. The
limited adsorption capacity was observed by chitin and chitosan for
estrogenic compounds. The authors reported that chitin was slightly
more effective than chitosan in adsorbing E1, suggesting that the
process is primarily adsorption rather than ion exchange in nature.
The feasibility of chitosan, with different molecular weights, to
simultaneously remove various pollutants from the discharge of an eel
culture pond was evaluated [111]. Experimental results indicated that
chitosan with high molecular weight was best in removing turbidity,
suspended solids, and biological and chemical oxygen demand (BOD
and COD). In contrast, chitosan of low molecular weight excelled at
removing NH3and PO4
high molecular weight did well at eliminating suspended solids of
various particle sizes relative to chitosan with low molecular weight.
The best removal percentage achieved by chitosan for removing
turbidity, suspended solids, BOD, COD, NH3, PO4
87.7%, 62.6%, 52.3%, 62.8%, 91.8%, 99.1%, and 99.998% removal,
respectively. When chitosan with a high molecular weight was added
at 12 mg/L, the quality of treated wastewater successfully complied
with government discharge standards.
3−from wastewater. Additionally, chitosan with
3−, and bacteria was
3. Conclusions and future perspectives
This review focuses on the recent developments related to
detoxification of water and wastewater using chitin- and chitosan-
derivatives and reports the main advances published over the last 10–
15 years. It should be noted that the maximum adsorption capacities
reported in this paper provide some idea of sorbent effectiveness for
The use of chitin-, chitosan and its derivatives for removing various
pollutants from water and wastewater presents many attractive
features such as the outstanding adsorption capacity, especially for
metal ions and dyes, and thefactthat these materials are low cost, non-
toxic and biocompatible. However, their potential for other pollutants,
e.g. phenols, anions, pesticides, humic substances needs extensive
research. Although the amount of available literature data for chitin/
chitosanapplicationinwaterandwastewatertreatmentis increasingat
a tremendous pace, there are still several gaps which need to be filled.
Some of the important issues can be summarized below:
(1) Selection and identification of an appropriate form of chitin/
chitosan is one of the key issues to achieve the maximum
removal/adsorption of specific type of pollutant depending
upon the adsorbent–adsorbate characteristics.
(2) The conditions for the production of chitosan loaded with high
amino groups on its surface need to be optimized, which conse-
quently would increase the maximum removal of pollutants.
(3) Cost factor should not be ignored. Low production cost with
higher removal efficiency would make the process economical
and efficient.
(4) Mechanistic studies withorganicpollutants(phenolsanddyes)
and inorganic anions need to be performed in detail to propose
a correct binding mechanism of these pollutants with chitin-
and chitosan-derivatives.
(5) Regeneration studies need to be performed in detail with the
pollutants-laden adsorbent (chitin- and chitosan-derivatives)
to recover the metals as well as adsorbent. It will enhance the
economic feasibility of the process.
(6) The potential of chitin/chitosan-derivatives under multi-com-
ponent pollutants needs to be assessed. This would make a
A. Bhatnagar, M. Sillanpää / Advances in Colloid and Interface Science 152 (2009) 26–38
Page 14
Author's personal copy
significant impact on the potential commercial application of
chitosan to industrial systems.
(7) Thereisscarcedataavailablefortheadsorptionofmetalionsinthe
presence of phenols, dye and other contaminants and vice-versa.
Therefore, more research should be conducted in this direction.
(8) It is further suggested that the research should not limit to only
lab scale batch studies, but pilot-plant studies should also be
conducted utilizing chitin- and chitosan-derivatives to check
their feasibility on commercial scale.
(9) The effectiveness of the treatment depends not only on the
properties of the adsorbent and adsorbate, but also on various
environmental conditions and variables used for the adsorption
process e.g., pH, ionic strength, temperature, existence of
competing organic or inorganic compounds in solution, initial
adsorbent concentration, contact time and speed of rotation etc.
These parameters should be taken into account while examining
the potential of chitin/chitosan-derivatives.
(10) The development in the field of adsorption process using chitin/
chitosan-derivatives essentially requires further investigation of
testing these materials with real industrial effluents.
If it is possible to develop such adsorbents having all the above-
mentionedcharacteristics, then these adsorbentsmay offer significant
advantagesover currently available commercially expensive activated
carbons and, in addition contribute to an overall waste minimization
The authors are grateful to the European Commission (Brussels)
for the Marie Curie Research Fellowship for Transfer of Knowledge
(No. MTKD-CT-2006-042637).
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