A new type of chitosan hydrogel sorbent generated by an.pdf

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A new type of chitosan hydrogel sorbent generated by anionic surfactant gelation

Sudipta Chatterjee, Tania Chatterjee, Seung H. Woo *

Department of Chemical Engineering, Hanbat National University, San 16-1, Deokmyeong-Dong, Yuseong-Gu, Daejeon 305-719, Republic of Korea

a r t i c l e i n f o

Article history:

Received 24 October 2009

Received in revised form 19 December 2009Accepted 21 December 2009

Available online 2 February 2010

Keywords:

Adsorption

Chitosan

Hydrogel beads

Sodium dodecyl sulfate

Surfactant

a b s t r a c t

A new type of chitosan hydrogel beads (CSB) with a coreshell membrane structure was generated by

sodium dodecyl sulfate (SDS) gelation process. CSB exhibited higher mechanical strength and acid stabil-

ity than chitosan hydrogel beads (CB) formed by alkali gelation. The effect of SDS concentration variationduring gelation on the adsorption capacity of CSB for congo red (CR) as a model anionic dye showed that

CSB formed by 4 g l1 SDS gelation had the highest adsorption capacity. The maximum adsorption capac-

ity of CSB (208.3 mg g1) obtained from the Sips model was found slightly higher than that of CB

(200.0 mg g1). Membrane materials of CSB obtained after squeezing core water from the beads showed

approximately 25 times higher volumetric adsorption capacity than CB.

2009 Elsevier Ltd. All rights reserved.

1. Introduction

The effluents discharged from textile industry contain a large

variety of dyes and it is estimated that around 1015% of the dyesare lost in the effluent during the dyeing processes (Crini, 2006;

dos Santos et al., 2007). The discharge of dye containing effluents

to the receiving water bodies retards photosynthesis by aquatic

plants and phytoplanktons due to abnormal colouration of water

(Robinson et al., 2001). Furthermore, some dyes in the effluents

are toxic, carcinogenic or mutagenic to human beings (Crini,

2006). Azo dyes represent about 50% of all dyes and more than

53% of these commonly azo dyes are known to be highly resistant

to biological degradation process (Manu and Chaudhari, 2002).

Congo red (CR) is one of important azo dyes and it mainly occurs

in the effluents discharged from textile, paper, printing, leather

industries, etc. CR is metabolized to benzidine, a known human

carcinogen.

Various techniques such as coagulation/flocculation (Hasaniet al., 2009), activated carbon adsorption (Kadirvelu et al., 2003),

oxidation (Malik and Saha, 2003), ozonation (Selcuk, 2005), elec-

trochemical oxidation (Radha et al., 2009), membrane separation

(Chiu et al., 2009), biological degradation (Gopinath et al., 2009),

etc., have been applied for the treatment of dye containing efflu-

ents and most of the techniques are reported as expensive and

not environment friendly (Crini, 2006). Activated carbon is the

most widely used adsorbent for dye removal, but it is too expen-

sive and there is difficulty in the regeneration process ( Kadirvelu

et al., 2003). Various low-cost adsorbents such as coir pith acti-

vated carbon (Namasivayam and Kavitha, 2002), fungal and algal

biomasses (Khalaf, 2008), bacterial biomass (Vijayaraghavan

et al., 2008), neem leaf powder (Bhattacharrya and Sharma,2004), activated desert plant (Bestani et al., 2008), palm kernel

seed coat (Oladoja and Akinlabi, 2009), etc., have been used for

the removal of dye from wastewater. However, low-adsorption

capacities of some of these adsorbents for dyes initiate further

search for new adsorbents.

Chitosan (CS) is a natural heteropolymer of glucosamine and

N-acetyl glucosamine residues, and obtained by alkaline deacety-

lation of chitin (a polymer made up of N-acetyl glucosamine

residues), the next most abundant natural polysaccharide after

cellulose (Chung and Chen, 2008; Crini and Badot, 2008).

Recently, CS hydrogel beads have generated great interest for

removal of environmentally hazardous chemicals due to their bio-

degradability, low-cost, and multiple functional groups (Crini and

Badot, 2008; Chatterjee et al., 2009a,b). CS hydrogel beads aremore extensively used than flake and powder forms of this poly-

mer because of their high surface area and porosity (Varma et al.,

2004). CS hydrogel beads have shown surprisingly high adsorp-

tion capacities for numerous dyes and heavy metals, as compared

to various adsorbents surveyed in recent review papers (Crini,

2006; Guibal, 2004; Gupta and Suhas, 2009). Nevertheless, CS

hydrogel beads formed by conventional physical or alkali gelation

face serious impediments to commercial application, such as low-

mechanical strength, low-acid stability, and a large material vol-

ume. Different methods like chemical cross-linking (Chiou et al.,

2004), carboxy alkyl substitution (Cestari et al., 2004), carbon

nanotubes impregnation (Chatterjee et al., 2009c), etc., can

0960-8524/$ - see front matter 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2009.12.089

* Corresponding author. Tel.: +82 42 821 1537; fax: +82 42 821 1593.

E-mail address:[email protected](S.H. Woo).

Bioresource Technology 101 (2010) 38533858

Contents lists available at ScienceDirect

Bioresource Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o r t e c h
http://dx.doi.org/10.1016/j.biortech.2009.12.089mailto:[email protected]://www.sciencedirect.com/science/journal/09608524http://www.elsevier.com/locate/biortechhttp://www.elsevier.com/locate/biortechhttp://www.sciencedirect.com/science/journal/09608524mailto:[email protected]://dx.doi.org/10.1016/j.biortech.2009.12.089


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improve mechanical stability of CS hydrogel beads, but still do

not yield enough strength for use in actual situations. Moreover,

sometimes these methods cause a significant decrease in adsorp-

tion capacity (Crini and Badot, 2008).

Recently, the study on interactions between polymeric materi-

als and anionic surfactants has been a subject of fundamental re-

search (Thongngam and McClements, 2005; Trabelsi et al., 2006).

According to literature survey, fabrication of CS hydrogel beadsby anionic surfactant gelation and its application in the adsorption

research field have not been reported to date. In this study, a new

type of CS hydrogel beads (CSB) was generated by anionic surfac-

tant gelation process using sodium dodecyl sulfate (SDS). A de-

tailed study of the mechanical properties of these materials

together with its adsorption performance for CR as a model anionic

dye was investigated.

2. Methods

2.1. Materials

CS (>85% deacetylation), SDS, and CR were purchased from Sig-

ma Chemical Co., USA. All other analytical grade chemicals werepurchased from Sigma Chemical Co., USA.

2.2. Surfactant and alkali gelation

Formation of chitosan hydrogel beads by SDS gelation (CSB) in-

volved dropwise (drop volume 20 ll) addition of CS solution

(1 wt.% CS in 2 vol.% acetic acid) into SDS solution of various con-

centrations between 1 and 50 g l1 through a T-1000-B pipet tip,

Axygen scientific, USA. The subsequent beads formation in the

same SDS solution depletes the amount of SDS. In order to attain

the same amount of SDS in the beads with subsequent bead forma-

tion in the solution, maximum twenty hydrogel beads were formed

in 10 ml SDS solution of desired concentration and beads were ta-

ken from the same SDS solution after 3 h. CS hydrogel beadsformed by alkali gelation (CB) involved dropwise addition of CS

(1 wt.%) in acetic acid solution (2 vol.%) to alkali mixture

(H2O:MeOH:NaOH = 4:5:1, w/w). As-prepared beads were exten-

sively washed with deionized water and preserved in aqueous

environment for future use.

2.3. Structure analysis

Optical micrographs of CB, and CSB by 4, 10, 20 and 50 g l1 SDS

gelation were taken using Nikon Microscope Eclipse 80i, Japan. Ele-

mental analyses of CB, and CSB formed with various SDS concen-

trations (5, 10, 20 and 50 g l1) were performed using Elemental

analyzer (EA1108, Fisons). Infrared (IR) spectra of CB and CSB

formed with various SDS concentrations (5, 10, 20 and 50 g l1

)were characterized using a FTIR Spectrophotometer (Nicolet

6700, Thermal) with KBr pellet.

2.4. Mechanical stability

The response of the CB and CSB to ultrasonication gives an in-

sight into the mechanical stability of the beads and it was deter-

mined by measuring weight loss after ultrasonication of 1 g wet

beads in 100 ml deionized water using 750 W ultrasonic processor

(VC 750, Sonics) with a high power sonic tip operated at 20 kHz

frequency and under various power amplitudes (a) 21%, (b) 25%,

(c) 30%, and (d) 35% for 10 min. The beads obtained after ultrason-

ication were collected using 1 mm sieve and percentage dry weight

loss of beads was measured from the weight difference of thebeads before and after ultrasonication.

2.5. Acid stability

Acid stability of gel particles was characterized by determining

the mass loss due to gel dissolution in acidic solution. The swelling

experiment of beads in acid solution was performed by adding 1 g

wet beads of CB and CSB in 50 ml deionized water of various pH

levels (pH 27) and the beads were allowed to swell for 6 h at

30

C in shaking condition. The percentage dry weight loss of thebeads was determined from the difference of wet weight of the

hydrogel beads before and after swelling.

2.6. Adsorption study

The adsorption capacity of CSB formed by 4 g l1 SDS gelation

was compared with CB for adsorption of CR from 100 mg l1 aque-

ous solution. Here CR was selected as a model anionic dye. Mem-

brane materials of the CSB (CSM) were obtained after squeezing

core water from the beads and the adsorption performance of

CSM was also evaluated in this study. The batch adsorption exper-

iments were performed in glass vials (20 ml) containing 10 ml CR

solution of desired concentration and 0.2 g wet adsorbent materi-

als at pH 5 and 30 C under shaking condition (150 rpm) for 24 h.The performance of CSB formed in various SDS solutions from 2

to 50 g l1 was studied for adsorption of 100 mg l1 CR solution.

Equilibrium isotherm studies were carried out at a fixed tempera-

ture (30 C) using CB and CSB formed by 4 g l1 SDS gelation as

adsorbent materials, and different initial concentrations of CR

(101000 mg l1) were prepared from a stock solution

(1000 mg l1). The kinetics experiments were performed to deter-

mine equilibrium time for adsorption of CR (100 mg l1) onto CB

and CSB, and different time intervals up to 960 min were used

for this study. The amount of CR in solution before and after

adsorption was analyzed at its absorption maximum (kmax,

497 nm) using a DR5000 spectrophotometer (HACH, USA). All the

experiments were conducted in triplicate. The amounts of CR ad-

sorbed by the adsorbent materials were calculated using the fol-lowing equation:

q C0 Ceq V

W 1

where q (mg g1) is the amount of CR adsorbed by the adsorbent

materials, C0 and Ceq (mg l1) are the initial and equilibrium li-

quid-phase concentration of CR, respectively,V(l) is the initial vol-

ume of dye solution, and W (g) is the dry weight of adsorbent

materials.

2.7. Adsorption isotherm models

The non-linear forms of the Langmuir, Freundlich and Sips iso-

therm models were used to analyze the equilibrium isotherm dataand these models were evaluated by the non-linear coefficients of

determination (R2) and a non-linear Chi-square test (v2). The

expression of the Langmuir model is given as:

qe qmKLCe1 KLCe

2

whereCeis the equilibrium concentration of CR (mg l1) in the solu-

tion,qe is the equilibrium CR concentration (mg g1) on the adsor-

bent, and qm (mg g1) and KL (l mg

1) are Langmuir constants

related to the adsorption capacity and energy of adsorption,

respectively.

The expression of the Freundlich model is:

qe KFC1ne 3

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KFis the Freundlich constant related to the sorbent capacity of sor-

bent andn is an empirical parameter representing the heterogene-

ity of site energies.

Sips model is a combination of Langmuir and Freundlich models

and it is expressed as:

qe qmaxKeqC

ne

1 KeqCne

4

Keq (l mg1) represents the equilibrium constant of Sips equa-

tion and qmax (mg g1) is the maximum adsorption capacity. Sips

isotherm model is characterized by the heterogeneity factor, n.

2.8. Desorption studies

Desorption studies were carried out with CR loaded beads ob-

tained from an adsorption system with 10 ml of CR solution

(100 mg l1), and 0.2 g wet weight of beads (CB and CSB). After

adsorption for 24 h at pH 5, the beads were separated by filtration

and CR concentration in the filtrate was measured spectrophoto-

metrically. The beads were washed gently with deionized water

to remove unadsorbed CR molecules. After washing, beads were

transferred into 10 ml of deionized water adjusted to pH 1013and CR desorbed from the beads to the solution was measured

after 24 h.

3. Results and discussion

3.1. Formation of CS hydrogel beads by alkali and SDS gelation

Formation of CB involves neutralisation of each droplet of CS

solution in alkali solution and this process generates a physical

hydrogel bead that contains only water and CS in the free amine

form. The neutralisation of NH3 sites into NH2 leads to the disap-

pearance of ionic repulsions between polymer chains, and the

physical hydrogel bead is formed by physical cross-linking of poly-

mer chains involving hydrogen bonds and hydrophobic interac-tions (Ladet et al., 2008). Physical hydrogel formation of CS

simply involves the process of hydrophobic/hydrophilic balance

(Montembault et al., 2005).

Formation of CSB begins when drops of CS solution are added to

SDS solution (250 g l1). The mixing between the two solutions is

not instantaneous because CS solution droplets are viscous. The

oppositely charged surfactant (SDS) and polyelectrolyte (CS) come

into contact with one another by means of counter-diffusion across

the surfactant/polyelectrolyte solution interface. Unlike the deep

penetration of small OH ion during alkali gelation into the CS

droplet, complex formation occurs only at the interface due to

the large size of the surfactant molecule, and a gel capsule is

formed around the drop. This effect results in shrinkage of the

polyelectrolyte drop, and hydrogel beads are thus formed by asso-ciative phase separation (Lapitsky and Kaler, 2004). Such a network

is stabilised by a combination of electrostatic, iondipole, and

hydrophobic interactions (Thongngam and McClements, 2004).

After the first soft membrane layer is rapidly formed, surfactant

molecules are still able to penetrate through the layer, and a sec-

ond membrane layer is formed by contact with chitosan molecules

that are diffused to the inner surface. Ultimately, a shell membrane

composed of thin layers is formed.

3.2. Structure of hydrogel beads

Optical microscope images of hydrogel beads (figure not

shown) illustrate that CB consist purely of CS molecules, whereas

CSB formed by 4 g l1

SDS gelation consist of a sparsely gelled coreencapsulated by a dense shell, indicating a coreshell structure.

The images of CSB at different stages of gelation (figure not shown)

clearly indicate that SDS complexation continues in SDS solution

even after bead formation, and structural organisation of the beads

changes with time after formation in the same solution. Cross-sec-

tions of CSB exhibit a multi-membrane structure. As SDS concen-

tration is increased in the gelling solution, stronger and denser

hydrogel beads are formed. Additionally, shrinkage is observed

from osmotic action of the shell membrane, by which more water

molecules in the shell are released at high concentrations of SDS in

the gelling solution.

The results of elemental analysis of CSB formed by various SDSconcentrations are listed inTable 1. The sulfur (S) content of CSB is

close to the stoichiometric molar ratio, but this value slightly in-

creases with an increase in SDS concentration in the gelling solu-

tion. The determination of SDS content of CSB is purely based on

S (%) obtained by elemental analysis because the amount of S in

CSB is solely contributed by SDS molecules. Thereby, the increase

in SDS concentration during gelation increases SDS content in

CSB (Table 2).

FTIR spectra of CB (figure not shown) show characteristic peaks

assignment of CB: 3442 cm1 (wide peak of OH stretching over-

lapped with NH stretching), 2878 cm1 (CH stretching),

1651 cm1 (amide II band, NH bending and C@O stretching of

acetyl groups), 1382 cm1 (OH bending and CN stretching) and

1071 cm1

(bridge COC stretching and CO stretching). Charac-teristic peaks obtained for CSB (figure not shown) with various

SDS concentrations during gelation (5, 10, 20, 50 g l1) are:

3441 cm1 (wide peak of OH stretching overlapped with NH

stretching), 2923 and 2853 cm1 (CH stretching), 1635 cm1

(amide II band, NH bending and C@O stretching of acetyl groups),

1467 cm1 (asymmetric CH bending of CH2 group), 1379 cm1

(OH bending and CN stretching) and 1061 cm1 (bridge COC

stretching and CO stretching). The appearance of new spectral

Table 1

Elemental analysis of CSBs with various concentrations of SDS.

Element (%) SDS concentration (g l1)

5 10 20 50

N 3.36 0.03 3.40 0.02 3.41 0.03 3.37 0.01

C 47.52 0.31 47.50 0.34 47.42 0.08 48.14 1.98

H 8.46 0.07 8.46 0.11 8.38 0.05 8.49 0.30

S 6.14 0.32 6.52 0.16 6.71 0.04 6.77 0.01

Data represents average of three replicates with standard deviations.

SDS (g l-1

)

0 5 10 15 20 25

Dryweightloss(

%)

0

20

40

60

80

100

120

CB (21%)

CB (25%)

CB (30%)

CB (35%)CSB (21%)

CSB (25%)

CSB (30%)

CSB (35%)

Fig. 1. Mechanical stability test of CB and CSB formed at various SDS concentrations

(5, 10 and 20 g l

1). The value in the parenthesis of the legend represents poweramplitude during ultrasonic operation.

S. Chatterjee et al. / Bioresource Technology 101 (2010) 38533858 3855


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unity (n= 1.02), indicating that adsorption onto CSB is homoge-neous. The close similarity between maximum adsorption capacity

values obtained from Langmuir (208.1 mg g1) and Sips

(208.3 mg g1) isotherm models for CSB beads indicated homoge-

neous adsorption process. The maximum adsorption capacity of

CSB (208.3 mg g1) and CB (200.0 mg g1) obtained from the Sips

isotherm model was similar, whereas maximum adsorption capac-

ity of CSB (208.1 mg g1) obtained from the Langmuir isotherm

model was higher than that of CB (179.2 mg g1). Thereby,

mechanically improved CSB exhibited similar (Sips isotherm) or

higher (Langmuir isotherm) maximum adsorption capacity than

CB.

The comparison of maximum adsorption capacity of CSB

(208.3 mg g1) with that of other adsorbents used for adsorption

of CR such as 6.70 mg g1

of activated carbon prepared from coirpith (Namasivayam and Kavitha, 2002), 41.20 mg g1 of neem leaf

powder (Bhattacharrya and Sharma, 2004), 66.23 mg g1 of palm

kernel seed coat (Oladoja and Akinlabi, 2009), and 330.62 mg g1

of N,O-carboxymethyl CS (Wang and Wang, 2008) indicated that

CSB could be used as an effective adsorbent for adsorption of CR

from aqueous solutions. Moreover, adsorption performance of this

sorbent could be further improved by surface modification or

impregnation with various chemicals and materials as CR adsorp-

tion capacity increased by cetyl trimethyl ammonium bromide

impregnation (Chatterjee et al., 2010) or carbon nanotubes impreg-

nation (Chatterjee et al., 2009d).

3.8. Kinetic study

Experimental kinetic data for adsorption of CR onto CB and CSB

from a 100 mg l1 solution have been illustrated inFig. 3and equi-

librium adsorption time for both adsorption systems was 420 min.

Two simplified kinetic models including pseudo-first-order and

pseudo-second-order equations, and intra-particle diffusion mod-

el, were used in this study.

The non-linear form of the pseudo-first-order rate equation is

given as:

qt qe1 ek1t 5

whereqeandqtare the amounts of CR adsorbed (mg g1) at equilib-

rium and at a predetermined time (t), respectively, andk1(min1) is

the rate constant of this equation. The constants, k1 and qe values

obtained from this rate model are given in Table 5.

The non-linear form of pseudo-second-order rate equation isexpressed as:

qt q2ek2t

1 qek2t and h k2q

2

e 6

where hrepresents the initial adsorption rate (mg g1 min1) andk2(g mg1 min1) is the pseudo-second-order rate constant. The val-

ues ofqe,k2and h obtained from rate model are presented inTable

5.

The correlation coefficient (R2) values of the pseudo-first-order

equation were 0.998 and 0.994 for CB and CSB, respectively. For the

pseudo-second-order model, the correlation coefficient (R2) values

were 0.988 and 0.991 for CB and CSB, respectively. TheR2 values of

both rate models for each adsorption system indicated that CRadsorption onto CB and CSB could be better explained by pseu-

do-first-order rate model than pseudo-second-order rate model.

As shown inTable 5, the qe values of CB (83.34 mg g1) and CSB

(116.92 mg g1) obtained from pseudo-first-order rate model were

in better agreement with qe (exp) value of CB (83.19 mg g1) and

CSB (115.90 mg g1), respectively, than qe values of CB

(96.59 mg g1) and CSB (140.15 mg g1) obtained from pseudo-

second-order rate model.

Ce(mg l

-1)

0 200 400 600 800 1000

qe

(m

gg-1)

-50

0

50

100

150

200

250

Experimental data (CB)

Langmuir non-linear (CB)Freundlich non-linear (CB)Sips non-linear (CB)Experimental data (CSB)Langmuir non-linear (CSB)Freundlich non-linear fit (CSB)Sips non-linear fit (CSB)

4 g l-1SDS gelation,

pH 5, 300C

Fig. 2. Plot ofqe vs. Ce for adsorption of CR onto CB and CSB formed by 4 g l1 SDS

gelation; pH 5 and 30 C.

Table 4

Constants for equilibrium isotherm models with error analysis values.

Langmuir isotherm modelAdsorbent KL (l mg

1) qm (mg g1) Error analysis

R2 v2

CB 0.026 179.2 0.980 12.86

CSB 0.046 208.1 0.997 1.60

Freundlich isotherm model

Adsorbent KF(l g1) 1/n Error analysis

R2 v2

CB 26.91 0.291 0.938 23.00

CSB 39.17 0.262 0.893 51.09

Sips isotherm model

Adsorbent qmax (mg g1) Keq (l mg

1) n Error analysis

R2 v2

CB 200.0 0.054 0.72 0.993 2.69

CSB 208.3 0.044 1.02 0.997 1.70

t (min)

0 200 400 600 800 1000 1200

qt

(mgg-1)

0

20

40

60

80

100

120

Experimental data (CB)

Pseudo-first-order (CB)Pseudo-second-order (CB)Intra particle diffusion (CB)Experimental data (CSB)Pseudo-first-order (CSB)Pseudo-second-order (CSB)

Intra particle diffusion (CSB)

4 g l-1

SDS gelation

C0= 100 mg l

-1, pH 5

Fig. 3. Plot ofq tvs. tfor adsorption of CR onto CB and CSB formed by 4 g l

1 SDSgelation; initial CR concentration, 100 mg l1; pH 5.

S. Chatterjee et al. / Bioresource Technology 101 (2010) 38533858 3857


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The intra-particle diffusion equation is given as:

qt kpt0:5 7

kpis the intra-particle diffusion rate constant (mg g1 min0.5) and

the values ofkpfor CB and CSB were 4.96 and 5.76 mg g1 min0.5,

respectively (Table 5). The correlation coefficients (R2) values for CB

(0.947) and CSB (0.953) indicated that intra-particle diffusion has a

significant role in initial stage of adsorption in the study.

3.9. Desorption study

Desorption studies help to understand the mechanism of

adsorption and also help in the recovery of CB and CSB. The results

indicated that CSB exhibited less increase in desorption (from16.18% 0.89 to 25.06% 1.72) than CB (from 25.92% 1.01 to

36.84% 2.060) with pH change from 10 to 13. CB showed very

low-desorption for CR with pH change because of strong bond for-

mation between CR and CS molecules and involvement of some

interactions other than electrostatic interactions. Moreover, the

less desorption for CSB than CB with pH change suggests strong

hydrophobic interactions between CSB and CR molecules.

4. Conclusions

CS hydrogel bead formed by SDS gelation (CSB) produced dense

coreshell membrane structure, and it showed higher mechanical

strength and acid stability than conventional CS hydrogel bead

formed by alkali gelation (CB). CSB formed by 4 g l

1 SDS gelationexhibited slightly higher adsorption capacity than CB for congo red

(CR). Membrane materials of CSB (CSM) generated by removing

core water had approximately 25 times higher volumetric adsorp-

tion capacity than CB for CR. Thus, generation of CSM from CSB

could enhance the technical and commercial importance of con-

ventional CB in the field of wastewater treatment by solving its

major limitations.

Acknowledgement

This research was supported by Basic Science Research Program

through the National Research Foundation of Korea (NRF) funded

by the Ministry of Education, Science and Technology (grant num-

ber 2009-0079636).

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Table 5

Constants of different rate models for CB and CSB a.

Adsorbent qe (exp) Pseudo-first-order equation Pseudo-second-order equation Intra-particle diffusion

(mg g1) qe (cal) (mg g1) k1 (min

1) qe (cal) (mg g1) k2 (g mg

1 min1) h(mg g1 min1) kp (mg g1 min0.5)

CB 83.19 83.34 0.010 96.59 1.24 104 1.16 4.96

CSB 115.90 116.92 0.007 140.15 5.61 105 1.10 5.76

a Initial CR concentration was 100 mg l1.

3858 S. Chatterjee et al. / Bioresource Technology 101 (2010) 38533858

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