Chemical Engineering Journal 210 (2012) 590–596

Contents lists available at SciVerse ScienceDirect

Chemical Engineering Journal

journal homepage: www.elsevier .com/locate /ce j

Removal of nickel(II) ions by histidine modified chitosan beads

Ahmet Eser, V. Nüket Tirtom, Tülin Aydemir ⇑, Seda Becerik, Ays�e DinçerCelal Bayar University, Faculty of Arts and Sciences, Department of Chemistry, 45140 Manisa, Turkey

h i g h l i g h t s

" Chitosan was functionalized with histidine for better nickel adsorption." Morphology of the sorbent were discussed using FTIR, TGA and SEM analysis." The incorporation of chelating groups can increase the adsorption capacity." Langmuir and Freundlich isotherms were used to fit the equilibrium adsorption data.

a r t i c l e i n f o

Article history:Received 4 June 2012Received in revised form 31 August 2012Accepted 10 September 2012Available online 20 September 2012

Keywords:Ni(II) removalAdsorptionWaste-water treatmentKinetic parametersModification

1385-8947/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.cej.2012.09.020

⇑ Corresponding author. Tel.: +90 2362013176; faxE-mail addresses: ahmet.eser@cbu.edu.tr (A. Ese

Aydemir).

a b s t r a c t

In order to increase the nickel adsorption capacity of raw chitosan beads (CB), they were chemically mod-ified with histidine (HIS–ECH–CB) by using crosslinking agent, epichlorohydrine (ECH). The nature andmorphology of the sorbent were characterized using FTIR, TGA and SEM analysis. For optimization ofadsorption conditions, sorption experiments were performed by varying contact time, pH, temperatureand initial nickel concentration. Based on the adsorption experiment, the HIS–ECH–CB showed the signif-icant adsorption capacity of 55.6 mg/g under the optimal adsorption condition. Nickel adsorption iso-therms data were fitted to Freundlich isotherm. Thermodynamic parameters namely DG�, DH� and DS�of the Ni(II) adsorption process were calculated. The negative values of Gibbs free energy of adsorption(DG�) indicated the spontaneity of the adsorption of Ni(II) ions on the histidine modified chitosan.Desorption of Ni(II) ions from HIS–ECH–CB could be done rapidly by using 0.1 M HCl, HNO3 and EDTAsolutions and the beads could be used again to adsorb Ni(II) ions.

� 2012 Elsevier B.V. All rights reserved.

1. Introduction

Ni(II) and its various compounds are extensively being used invarious industries such as metal plating facilities, mining opera-tions, fertilizer industries, tanneries, batteries, paper industriesand pesticides, and wastewaters are directly or indirectly dis-charged into the environment, especially in developing countries.Removal of Ni(II) from industrial effluents has a primary impor-tance because contamination of wastewater causes very serioushealth and environmental problems. Excessive accumulation ofnickel might bring about serious lung and kidney problems [1,2].Metals can be separated from other toxic pollutants, because theyundergo chemically transformations. Also they are nonbiodegrad-able, and have great environmental, economic, and public healthimpacts [3,4]. Most methods which have been used to reduce me-tal concentration from industrial waste are chemical precipitation,ion exchange, membrane filtration, electrolytic methods, reverseosmosis, solvent extraction, and adsorption [5,6]. Some of these

ll rights reserved.

: +90 2362412158.r), aydemirt@yahoo.com (T.

methods are limited by high operational cost and/or may also beinefficient in the removal of some toxic metal ions, mainly at tracelevel concentrations [6,8]. Adsorption techniques which have beenused for metal ions removal from aquatic environment is the mostfrequently applied technique owing to its advantages such as vari-ety of adsorbent materials and high efficiency at a relatively lowcost. For an effective adsorption capacity, sorbents have a greatimportance. Biopolymers are part of a class of biosorbents usedin pollutant removal from aquatic environments, and chitosan,which is the second most abundant biopolymer in nature, can beemphasized among them [9]. From the chemical point of view,chitosan is a poly (2-amine-2-deoxy-d-glucose), obtained throughchitin, poly(N-acetyl-D-glucosamine) deacetylation in alkalinemedium. This polymer is soluble in dilute organic acid solutions,such as acetic, propionic, formic and lactic acid. Chitosan has excel-lent properties for the adsorption of metal ions, principally due tothe presence of amino groups (ANH2) in the polymer matrix, whichcan interact with metal ions in solution chelation and complexa-tion reactions. The high content of amino groups also makes possi-ble many chemical modifications in polymer with the purpose ofimproving its features as an adsorbent, such as selectivity andadsorption capacity [10]. Therefore cross-linking process can

A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596 591

enhance the resistance of chitosan against acids and chemicals[11,12]. Chemical cross-linking can change the crystalline natureof chitosan and enhance the resistance of chitosan against acid, al-kali and chemicals. Some of commonly used cross-linking agentsare epichlorohydrine (ECH) glutaraldehyde, and ethylene glycoldiglycidyl ether [13,14]. Histidine is known to be a fundamentalbinding site of proteins and oligopeptides for metal ions. In theselarge molecules metal ions, in most cases, are coordinated exclu-sively by the side chain donor groups of various amino acids,including histidine. In the present study, chitosan was functional-ized with histidine in order to better the chelation properties ofchitosan. Histidine presents nitrogen groups as amino and imidaz-ole functionalities where nickel binding may occur [16]. Influenceof contact time, initial pH, temperature and initial concentration ofNi(II) ions were studied. To predict the nature of the adsorptionprocess, the non-linear Langmuir and Freundlich isotherms wereused to fit the equilibrium adsorption data.

2. Experimental

2.1. Reagents and solutions

Nickel sulfate hexahydrate and glacial acetic acid (analytical de-gree) were provided by Merck. Epichlorohydrin (ECH) wasprovided by Fluka. Chitosan of commercial degree with 85%deacetylation and histidine aminoacid were provided by Sigma.All other reagents used in this study were analytical grade.

2.2. Instrumentation

The batch experiments were carried out in a Labart SH-5 withcontrolled agitation. Atomic absorption spectrophotometer SpectraAA 220 FS Varian, equipped with a flame atomizer and hollow cath-ode lamps of studied metals, was used for nickel determination.

2.3. Preparation of CB

CB was obtained using a method adapted from Zeng and Ruc-kenstein [17]. Chitosan was dissolved in acetic acid (2% v/v) solu-tion producing 2.5% (w/v) solution. The viscous solution was leftovernight before adding drop wise into a sodium triphosphate(TPP) (pH was adjusted to 8.2 by 0.1 N HCl) solution. This is to en-sure that the acetic acid within the chitosan gel is neutralized andto coagulate the chitosan gel to spherical uniform gel beads. Beadswere stirred 4 h for hardening and then the beads were filtered andwashed with distilled water. Finally, CB was dried at 40 �C for 12 h,and stored in a desiccator for further adsorption experiment.

2.4. Preparation of ECH–CB

The crosslinking of CB by epichlorohydrin was carried out as de-scribed by Bueno et al. [15]: 5 mL of epichlorohydrin, 50 mL of2.0 M NaOH and 0.266 g of sodium borohydride (NaBH4) wereadded to CB in an erlenmeyer flask. The solution was kept understirring at room temperature (25 �C) for 15 min. After the process,more NaOH and epichlorohydrin were added following a constantvolumetric proportion of 2:1 and the final solution kept under stir-ring for 16 h. After this procedure, the beads were washed withultrapure water until reaching neutral pH, indicating that excessof epichlorohydrin was removed.

2.5. Preparation of HIS–ECH–CB

The immobilization of histidine was performed using similarprocedure that described previously [16]. After washing with

1.5 M sodium carbonate (Na2CO3) solution, the beads were placedin a recipient and 10% (w/v) solution of histidine in 1.5 M Na2CO3

solution added. The mixture was kept under agitation at 60 �Cfor 24 h. After this time, beads were washed until excess of non-immobilized histidine was washed out.

2.6. Characterization of CB and HIS–ECH–CB

Fourier transform infrared (FTIR) analysis was accomplished ona Perkin Elmer spectrum BX scanning from 4000 cm�1 to 400 cm�1

at room temperature. CB, ECH–CB and HIS–ECH–CB were mixedwith KBr and pressed to plates for measurements. The weight losstemperatures of the CB and HIS–ECH–CB were determined with aMettler Toledo TGA analyzer (TGA/SDTA851e). The surface mor-phology of the beads was examined under scanning electronmicroscopy (SEM) (XL30-SFEG, FEI/Philips).

2.7. Adsorption studies

The sorption experiments were performed by batch equilibra-tion method. Stock solution of nickel containing 1000 mg/L wasprepared and this was used for sorption experiments. Batch sorp-tion experiments in duplicate were carried out by mixing 0.1 g ofsorbent with 25 ml of 1000 mg/L as initial nickel concentration.The contents were shaken thoroughly using a thermostated shakerrotating at a speed of 160 rpm. The solution was then filtered andthe residual nickel concentration was measured using atomicabsorption spectrophotometer. pH measurements were carriedout with Hanna instruments with pH electrode.

The effect of agitation period was conducted at room tempera-ture and under the stirring rate of 160 rpm with 0.1 g of adsorbent.The effect of pH on the adsorption of Ni(II) ions was studied in a pHrange of 4–9. The pH of the initial 25 mL solution of 1000 mg/L wasadjusted to the required pH value using appropriate buffers. Forthis purpose, the following buffer solutions were used, 0.1 M aceticacid/sodium acetate (pH 4.0–5.0), citric acid/sodium citrate (pH6.0), and 0.1 M Tris–HCl solution (pH 7.0–9.0). The influence of dif-ferent temperature was conducted in a range of 298–313 K underthe optimum agitation period and pH. Different concentration ofnickel solution from the range of 25–1000 mg/L was studied underthe optimum pH, temperature and agitation period as has beendetermined from the previous step.

The amount of metal ion adsorbed was calculated according tothe following equations:

qe ¼ðC0 � CeÞ � V

mð1Þ

where qe is the amount (mg g�1) of metal ions adsorbed by theHIS–ECH–CB beads, Co and Ce are the metal concentrations(mg L�1) in the solution initially and after adsorption, respec-tively, V the volume (L) of the solution and m is the mass (g) ofadsorbent used.

2.8. Desorption studies

For desorption studies, 0.1 g of sorbent was loaded with 25 mLof 1000 mg/L Ni(II) solution. The agitation rate was fixed at160 rpm for all sorbents. Ni(II) loaded sorbents were collectedgently washed with distilled water to remove any unadsorbedNi(II). The amount of Ni(II) adsorbed per g of sorbents was deter-mined by measuring the residual nickel concentration. The sor-bents were agitated with 25 mL of 0.1 M EDTA, HCl and HNO3

solutions and the amount of desorbed Ni(II) was determined asbefore.

The percentage of metal ion desorbed was calculated accordingto the following equations:

592 A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596

D ¼ Amount of metal ions desorbedAmount of metal ions adsorbed

� 100 ð2Þ

3. Results and discussion

3.1. Characterization of CB and HIS–ECH–CB

FTIR spectra, depicted in Fig. 1, shows the changes observed inchitosan structures when natural beads were crosslinked with epi-chlorohydrin and functionalized with histidine. Since epichlorohy-drin tends to bond to chitosan using their hydroxyl groups, thefinal structure does not present different groups from the pristineone, although the intensity of some peaks varies. The IR spectrumof chitosan exhibits an adsorption band from 3600 to 3200 cm�1

due to OAH and NAH stretching vibration; at around 2850 cm�1

assigned to ACH stretching vibrations in ACH and ACH2. The pickat around 1600 cm�1 is due to amino group bending vibrations inANH2. 1150 cm�1 is due to CAOAC in the pyranose ring. In thespectrum of ECH–CB, the definition of a peak near 1030 cm�1 isattributed to the stretch of CAO bond, formed in the crosslinkingprocess, which tends to form crosslinks. In the spectrum for HIS–ECH–CB, the linkage of histidine to ECH–CB system is supportedby the increase in intensity at 1342 cm�1, attributed to NAH vibra-tion and 1627 cm�1, attributed to N@C bonds [18]. Compared theFT-IRspectrun of Ni(II) ions loaded ECH–HIS–ECH–CB with pristineECH–HIS–ECH–CB, some differences can be observed. For instance,

Fig. 1. FTIR spectrum of CB, CB crosslinked with

the instensity of peak around 3400 cm�1 was reduced after Ni(II)ions adsorption, suggesting the participation of AOH and NH2 informing complexes with Ni(II) ions.

SEM images of CB, HIS–ECH–CB and nickel adsorbed HIS–ECH–CB are shown in Fig. 2a, b and c respectively. The surface change inthe SEM images of CB indicate the structural changes in the sorbentbefore and after nickel treatment. HIS–ECH–CB have a tighterstructure than HIS–ECH–CB and also has not a crack unlike chito-san bead (Fig. 2a and b). Fig. 2c shows that there is a mass transferof nickel ions onto the nickel-sorbed HIS–ECH–CB. The results fromTGA are presented in Fig. 3a–c. The natural CB and HIS–ECH–CBlost more weight at higher temperatures than nickel sorbed HIS–ECH–CB. The crosslinking processes usually turn the polymericalmatrices more resistant to degradation when compared to the for-mer polymer. Fig. 3c shows that the Ni(II) ions were really uptakenby the HIS–ECH–CB, probably via chitosan–histidine–nickel com-plex formation that shows degradation with new peak, beforethe final degradation of polymer at about 250 �C.

3.2. Effect of agitation period

Agitation period is the amount of time required for an adsorp-tion process to become constant and reaching to equilibrium. Theadsorption capacity of HIS–ECH–CB was determined by varyingthe contact time in the range of 2–24 h. It is shown in Fig. 4 thatthere was a rapid uptake within the first 4 h. Meanwhile forHIS–ECH–CB the adsorption equilibrium was attained at 24 h.

ECH, HIS–CB and Ni(II) adsorbed HIS–CB.

Fig. 2. SEM images of (a) CB, (b) HIS–CB and (c) nickel sorbed HIS–CB.

A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596 593

Therefore, 24 h of contact time was chosen as the optimum contacttime for the HIS–ECH–CB.

3.3. Effect of initial pH on nickel(II) adsorption

The removal of ion from aqueous solution was highly depen-dent on pH of the solution and in many cases it altered the surfacecharge of the sorbent. Therefore, the sorption capacity of theHIS–ECH–CB were performed at different pH levels in the rangeof 4.0–9.0 (0.1 M acetic acid/sodium acetate (pH 4.0–5.0)), citricacid/sodium citrate (pH 6.0), and 0.1 M Tris–HCl solution (pH7.0–9.0). It is obvious from Fig. 5 that maximum sorption capacitywas observed at pH 5.0. So, optimum pH was chosen 5.0 forHIS–ECH–CB. Similar result was found by Vijaya et al. [19]. At pHvalues higher than 7.0, precipitation of Ni(II) ions as Ni(OH)2 occurssimultaneously and could lead to inaccurate interpretation ofadsorption. At lower pH than 5.0, the adsorption capacity of HIS–ECH–CB was low because of the protonation of the amino groupsin the lower pH region. This reduces the number of binding sitesavailable for the adsorption of Ni(II) ions. Moreover, the proton-ation of amino groups induced an electrostatic repulsion of Ni(II)cations.

3.4. Effect of temperature on nickel(II) adsorption

To evaluate the thermodynamic parameters of Ni(II) adsorptionon the beads under study, the adsorption experiments were per-formed at four different temperatures (298, 303, 308 and 313 K).25 mL of the Ni(II) solution with a concentration of 1000 mg/Lwas allowed to equilibrate with 0.1 g of bead. The equilibrium con-stant for the adsorption process, KC, calculated with Eq. (3) [20],was evaluated at 298, 308 and 318 K for metal cation (Table 1):

KC ¼Xe

Ci � Xeð3Þ

where Xe is the concentration of solute adsorbed on the resin atequilibrium, mmol/L; Ci the initial ion concentration, mmol/L. Tocalculate the free energy of the adsorption (DG�), the followingEq. (4) was employed:

DG� ¼ �RT ln KC ð4Þ

The Eq. (5), allows to evaluate the standard enthalpy (DH�) andenthropy (DS�) of the adsorption by plotting lnKC vs. 1/T.

ln KC ¼DS�

R� DH�

RTð5Þ

where R (8.314 J/mol K) is the gas constant. The values of theslope �DH�/R and the intercept DS�/R from Fig. 6 give DH�andDS� for the adsorption of Ni2+ ions on the bead. The values ofthe thermodynamic parameters (DG�, DH�, DS�) are presented inTable 1. As presented in Table 1, the negative values of DG� forall ions under all conditions indicate the spontaneous nature ofthe adsorption. The negative DH� means a chemical exothermicprocess and support the chemisorption is the rate-determiningstep. The adsorption of Ni(II) on HIS–ECH–CB was demonstratedto be exothermic, with a negative entropy change that partiallyretarded adsorption.

3.5. Effect of initial Ni(II) ions concentration

In a batch adsorption process, the initial metal ions concentra-tion of the solution provides the necessary driving force to over-come the mass transfer resistance of metals between the solutionand solid phases. The effect of initial Ni(II) ions concentration onadsorption capacity was studied in the range of 25–1000 mg/L.These experiments were performed at pH 5.0 and 24 h agitationperiod with an adsorbent dosage of 0.1 g. Obtained data are plot-ted that it is shown in Fig. 7. We found that when initial Ni(II)ions concentration increased from 25 to 1000 mg/L, the uptakecapacity of HIS–ECH–CB for Ni(II) ions increased from 2.94 to55.6 mg/g. This could be explained by the following three rea-sons. First of all, a higher Ni(II) ion as concentration led to morebindings ites on the surface of HIS–ECH–CB compared with alower initial Ni(II) ions concentration at the same dosage ofadsorbent. Secondly, a higher initial Ni(II) ions concentration in-creased driving force to overcome the mass transfer resistance ofNi(II) ions between the aqueous and solid phases resulting inhigher chance of collision between the Ni(II) ions and the HIS–ECH–CB. Lastly, the increasing uptake capacity of HIS–ECH–CBfor Ni(II) ions with increasing initial Ni(II) ions concentrationmay also be because of a more intensity interaction betweenthe Ni(II) ions and HIS–ECH–CB.

3.6. Effect of common ions in the medium

The adsorption capacity of the HIS–ECH–CB in the presence ofother common ions which are normally present in water viz., Cl�,SO2�

4 , NO�3 and HCO�3 ions were investigated with a fixed initialconcentration of 50 mg/L of these ions by keeping 1000 mg/L asinitial Ni(II) concentration under the optimum conditions. Effectof co-ions have a moderate effect on adsorption capacity. Theadsorption capacity of HIS–ECH–CB was 45 mg/g in the presence

Fig. 3. TGA curves of (a) HIS–CB and (b) nickel sorbed HIS–CB.

594 A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596

of common ions while it was 55.6 mg/g in the absence of commonions for the adsorption of Ni(II).

3.7. Sorption isotherm models

The two most commonly used isotherms, namely Freundlichand Langmuir isotherms have been adopted to describe theadsorption characteristics of HIS–ECH–CB. The linearizations

according to the Freundlich and Langmuir models of adsorptionisotherms and isotherm were examined.

3.7.1. Freundlich isothermThe linear form of Freundlich isotherm [21] is written as the fol-

lowing equation:

log qe ¼ log kF þ1n� log Ce ð6Þ

Fig. 4. Effect of contact time on the adsorption capacity of HIS–CB at 303 K.

Fig. 5. Effect of pH on the adsorption capacity of HIS–CB at 303 K.

Fig. 6. Plot of lnKC as a function of reciprocal of temperature (1/T) for theadsorption of Ni(II) by HIS–CB.

Fig. 7. Effect of initial Ni(II) ions concentration on adsorption capacity of HIS–CB.

A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596 595

where qe is the amount of nickel adsorbed per unit weight of thesorbent (mg/g), Ce the equilibrium concentration of nickel in solu-tion (mg/L), kF (mg/g), a measure of adsorption capacity, and 1/n,the adsorption intensity, were calculated from the slope and inter-cept of the plot logqe vs. logCe (shown in Fig. 8) and the values arelisted in Table 2a. The values of 1/n lying between 0 and 1 confirmthe favorable conditions for adsorption. The R values for the modi-fied sorbents are high indicating the applicability of Freundlichisotherm.

Fig. 8. Adsorption isotherm of nickel(II) ions on HIS–CB, linearized according toLangmuir equations.

Table 2aFreundlich isotherm constants.

Freundlich isotherm

1/n n kF (mg/g) R

0.446 2.24 5.84 0.9984

3.7.2. Langmuir isothermLangmuir isotherm [22] model is expressed in the form of fol-

lowing equation:

Ce

qe¼ 1

Q �bþ Ce

Q �ð7Þ

where Q� is the amount of adsorbate at complete monolayer cover-age (mg/g), which gives the maximum sorption capacity of sorbentand b (L/mg) is the Langmuir isotherm constant that relates to theenergy of adsorption calculated from the slope and intercept ofthe plot Ce/qe vs. Ce (shown in Fig. 9) and the values are shown inTable 2b. The essential characteristics of the Langmuir isotherm

Table 1Thermodynamic parameters for the adsorption of Ni2+ on the histidine modified chitosan bead.

M2+ KC �DG� (kJ/mol) DH� (kJ/mol) DS� (J/mol K)

298 K 303 K 308 K 313 K 298 K 303 K 308 K 313 K

Ni2+ 6.69 6.59 4.77 3.41 4.78 4.73 3.99 3.17 �0.172 �519.8

Fig. 9. Adsorption isotherm of nickel(II) ions on HIS–CB, linearized according toFreundlich equations.

Table 2bLangmuir isotherm constants.

Langmuir isotherm

Q� (mg/g) b (L/mg) RL R

140.8 0.0011 0.476 0.9754

Fig. 10. Nickel(II) desorption capacity of HIS–CB in different solutions.

596 A. Eser et al. / Chemical Engineering Journal 210 (2012) 590–596

can be expressed in terms of the dimensionless constant separationfactor or equilibrium parameter RL [23].

RL ¼1

1þ bCoð8Þ

where Co is the initial Ni(II) concentration for adsorption study wasdetermined as 1000 mg/L. The RL value was calculated and is listedin Table 2b. The RL value lying between 0 and 1 indicated that theconditions were favorable for adsorption. The higher R value of Fre-undlich over Langmuir isotherm indicated the suitability of Freund-lich isotherm than the Langmuir isotherm.

3.8. Desorption studies

Desorption studies will help to elucidate the nature of adsorp-tion process and to recover the Ni(II) from sorbents. Moreover, italso will help to regenerate the sorbents so that it can be usedagain to adsorb metal ions, and develop the successful sorptionprocess [14]. Desorption experiments were performed at 25 �C byusing 0.1 M HCl, 0.1 M HNO3 and 0.1 M EDTA solutions. Percentagedesorptions of Ni(II) from the sorbent is shown in Fig. 10. It can beseen from the results that capacity of HCl, HNO3 and EDTA solu-tions is close to each other in terms of percentage of desorption.

4. Conclusions

The present investigation shows that the incorporation of che-lating groups can increase the adsorption capacity of CB for Ni(II).The pH of the medium has an influence on the sorption of Ni(II)onto HIS–ECH–CB and a maximum sorption capacity was observedat pH 5.0. The sorption data follows Freundlich isotherm. The nat-ure of sorption process is spontaneous. Also, maximum desorptionof Ni(II) was observed 0.1 M EDTA solution. It can be concludedthat HIS–ECH–CB are an effective adsorbent for the adsorption ofNi(II) ions.

References

[1] J.P.K. Wong, Y.S. Wong, N.F.Y. Tam, Nickel biosorption by two chlorella species,C. Vulgaries (a commercial species) and C. Miniata (a local isolate), Bioresour.Technol. 73 (2000) 133–137.

[2] C.E. Borba, R. Guirardello, E.A. Silva, M.T. Veit, C.R.G. Tavares, Removal ofnickel(II) ions from aqueous solution by biosorption in a fixed bed column:experimental and theoretical breakthrough curves, Biochem. Eng. J. 30 (2006)184–191.

[3] V.K. Gupta, S. Sharma, Removal of cadmium and zinc from aqueous solutionsusing red mud, Ind. Eng. Chem. Res. 42 (2003) 6619.

[4] W.S.W. Ngah, S.A. Ghani, A. Kamari, Adsorption behaviour of Fe(II) and Fe(III)ions in aqueous solution on chitosan and cross-linked chitosan beads,Bioresour. Technol. 96 (2005) 443.

[5] M.C. Basso, E.G. Cerrella, A.L. Cukierman, Activated carbons developed from arapidly renewable biosource for removal of cadmium(II) and nickel(II) ionsfrom dilute aqueous solutions, Ind. Eng. Chem. Res. 41 (2002) 180.

[6] M. Prasad, S. Saxena, Sorption mechanism of some divalent metal ions ontolow-cost mineral adsorbent, Ind. Eng. Chem. Res. 43 (2004) 1512.

[7] J.R. Evans, W.G. Davids, J.D. MacRae, A. Amirbahman, Kinetics of cadmiumuptake by chitosan-based crab shells, Water Res. 36 (2002) 3219.

[8] Z. Reddad, C. Gerente, Y. Andres, P. Cloirec, Adsorbtion of several metal ionsonto a low cost biosorbent: kinetic and equilibrium studies, Environ. Sci.Technol. 36 (2002) 2067.

[9] A.J. Varma, S.V. Deshpande, J.F. Kennedy, Metal complexation by chitosan andits derivatives: a review, Carbohydr. Polym. 55 (2004) 77.

[10] P. Chassary, T. Vincent, E. Guibal, Metal anion sorption on chitosan andderivative materials: a strategy for polymer modification and optimum use,React. Funct. Polym. 60 (2004) 137.

[11] K.C. Justi, V.T. Fávere, M.C.M. Laranjeira, A. Neves, R.A. Peralta, Kinetics andequilibrium adsorption of Cu(II), Cd(II), and Ni(II) ions by chitosanfunctionalized with 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol, J. Colloid Interface Sci. 291 (2005) 369–374.

[12] A.H. Chen, S.C. Liu, C.Y. Chen, C.Y. Chen, Comparative adsorption of Cu(II),Zn(II), and Pb(II) ions in aqueous solution on the crosslinked chitosan withepichlorohydrin, J. Hazard. Mater. 154 (2008) 184–191.

[13] S.T. Lee, F.L. Mi, Y.J. Shen, S.S. Shyu, Equilibrium and kinetic studies ofcopper(II) ion uptake by chitosan–tripolyphosphate chelating resin, Polymer42 (2001) 1879.

[14] W.S.W. Ngah, C.S. Endud, R. Mayanar, Removal of copper(II) ions from aqueoussolution onto chitosan and cross-linked chitosan beads, React. Funct. Polym.50 (2002) 181–190.

[15] S.M.A. Bueno, K. Haupy, M.A. Vijayalakshmi, In vitro removal of human IgG bypseudobiospecific affinity membrane filtration on a large scale. A preliminaryreport, Int. J. Artif. Organs 18 (1995) 392.

[16] M.M. Beppua, E.J. Arruda, R.S. Vieira, N.N. Santos, Adsorption of Cu(II) onporous chitosan membranes functionalized with histidine, J. Membr. Sci. 240(2004) 227–235.

[17] E. Ruckenstein, X. Zeng, Control of pore sizes in macroporous chitosan andchitin membranes, Ind. Eng. Chem. Res. 35 (1996) 4169.

[18] M.L. Duarte, M.C. Ferreira, M.R. Marvão, in: M.G. Peter, A. Domard, R.A.A.Muzzarelli (Eds.), A Statistical Evaluation of IR Spectroscopic Methods toDetermine Degree of Acetylation of Chitin and Chitosan, University ofPotsdam, 2000, p. 367.

[19] Y. Vijaya, S.R. Popuri, V.M. Boddu, A. Krishnaiah, Modified chitosan andcalcium alginate biopolymer sorbents for removal of nickel(II) throughadsorption, Carbohydr. Polym. 72 (2008) 261–271.

[20] M.V. Dinu, E.S. Dragan, Evaluation of Cu+2, Co+2 and Ni+2 ions removal fromaqueous solution using a novel chitosan/clinoptilolite composite: Kinetics andisotherms, Chem. Eng. J. 160 (2010) 157–163.

[21] H.M.F. Freundlich, Uber die adsorption in lösungen, Zeitschrift fürPhysikalische Chemie 57A (1906) 385–470.

[22] I. Langmuir, The constitution and fundamental properties of solids and liquids,J. Amer. Chem. Soc. 38 (1916) 2221–2295.

[23] T.W. Weber, R.K. Chakravorti, Pore and solid diffusion models for fixed bedadsorbents, AIChE 20 (1974) 228–238.