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Colloids and Surfaces B: Biointerfaces 88 (2011) 574– 581

Contents lists available at ScienceDirect

Colloids and Surfaces B: Biointerfaces

j our na l ho me p age: www.elsev ier .com/ locate /co lsur fb

reparation of magnetic modified chitosan and adsorption of Zn2+ from aqueousolutions

ulu Fan, Chuannan Luo ∗, Zhen Lv, Fuguang Lu, Huamin Qiuollege of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, China

r t i c l e i n f o

rticle history:eceived 4 March 2011eceived in revised form 10 July 2011ccepted 15 July 2011vailable online 3 August 2011

a b s t r a c t

The performance of a cross-linked magnetic modified chitosan (CMMC), which has been coated withmagnetic fluids and cross-linked with glutaraldehyde, has been investigated for the adsorption of Zn2+

from aqueous solutions. The CMMC with a diameter range of 20–50 nm was prepared. The effects of pHand the contact time for the adsorption have been discussed, and the optimal adsorption conditions forthe adsorption of Zn2+ have been obtained. The research results showed that CMMC was highly efficient

2+

eywords:agnetic modified chitosanlutaraldehydedsorptionn2+

for fast adsorption of Zn within the first 25 min, and adsorption equilibrium could be achieved in 30 min.Equilibrium studies showed that the data of Zn2+ adsorption followed the Langmuir model. The maximumadsorption capacity for Zn2+ was estimated to be 32.16 mg/g with a Langmuir adsorption equilibriumconstant of 0.01 L/mg at 298 K, which demonstrated that the CMMC had obvious efficient adsorption ofZn2+. The CMMC was stable and easily recovered. Moreover, the adsorption rate was about 90% of theinitial saturation adsorption capacity after being used five times.

. Introduction

Heavy metal contamination of various water resources haseen given great concern because of the toxic effect to humaneings, animals and plants in the environment. The major sourcef heavy metal pollutants is industry, including mining, metal plat-ng, electric device manufacturing, etc. Zinc, abundant in municipal

astewater, is one of the heavy metals which are harmful to humanealth, though micro-quantities of zinc are essential for humans’odies. The symptoms of zinc poisoning are mainly anemia, arrestf growth and sudden death [1–3].

In order to minimize the adverse effects of zinc in the environ-ent, it is desirable to find ways to capture it. Several technologies

ave been developed for the removal of zinc from industrialastewater, such as chemical precipitation, ion exchange, coagula-

ion, electrolysis, reverse osmosis processes and adsorption [4]. Butome technological problems such as time-consuming, instabilitynd being difficult to be separated, exist especially when applied toiluted metal solutions. At present, adsorption techniques appearso be a feasible option technically and economically [5], so thereas been increased interest in the use of other adsorbent materials,

articularly low-cost adsorbents [6].

Chitosan has been reported to be a suitable biopolymer for theemoval of metal ions from aqueous solution [7–9], since the amino

∗ Corresponding author. Tel.: +86 53182765491.E-mail address: fanlu1949@126.com (L. Fan).

927-7765/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfb.2011.07.038

© 2011 Elsevier B.V. All rights reserved.

and hydroxyl groups present on chitosan can act as chelation sites.It is noteworthy that metal adsorption involves different mech-anisms (chelation versus electrostatic attraction), depending onsolution composition, pH, and speciation of the metal ions [6].

Most of the chitosan-based adsorbents are submicron tomicron-sized and need large internal porosities to ensure ade-quate surface area for adsorption. However, the diffusion limitationwithin the particles leads to the decrease in the adsorption rate andavailable capacity [10–12]. Compared to the traditional micron-sized supports used in separation process, nano-sized adsorbentsdisplay quite good performance due to high specific surface areaand the absence of internal diffusion resistance [13,14]. The nano-adsorbents cannot be separated easily from aqueous solution byfiltration or centrifugation. The application of magnetic adsorbenttechnology to solve environmental problems has received consid-erable attention in recent years [15–18]. Magnetic nano-adsorbentscan be manipulated by an external magnetic field to facilitate phaseseparation [19,20,12]. The excellent adsorption characteristics ofmagnetic chitosan for heavy metals can be attributed to (1) highhydrophilicity due to large number of hydroxyl groups of glu-cose units, (2) presence of a large number of functional groups(acetamido, primary amino, so that it can absorb heavy metal ions inwastewater treatment and/or hydroxyl groups), (3) high chemicalreactivity of these groups and (4) flexible structure of the polymer

chain [21].

In present work, the magnetic cross-linking chitosan nanopar-ticles were prepared by binding modified chitosan on the surfaceof magnetic (Fe3O4). In addition, this paper studies the potential

L. Fan et al. / Colloids and Surfaces B: Biointerfaces 88 (2011) 574– 581 575

O

OH

OH

NH2

O

n

+ CHOCH3OH

O

OH

OH

N

O

n

+

CH

ClCH2 CHCH

O

NaOH

O

O

OH

N

O

n

+

CH

CHCH

O

SC(NH2)2 O

O

OH

N

O

n

+

CH

CH2

CHHO CH2 NH NH2

SHCl

O

O

OH

NH2

O

CH2

CHHO CH2 NH NH2

S

e form

oiaissmic

2

2

inwCsw

2

rs1d

n

Scheme 1. Schematic depiction of th

f CMMC for adsorption of Zn2+ from aqueous solution, includ-ng pH value of the solution and the adsorption contact time. Thedsorption process has then been optimized. The Zn2+ adsorptionsotherm has been measured and discussed. The method improvedpace orderliness of molecular and increased chitosan molecule’sites with metal ions. The high content of amine groups in chitosanakes it possible to chemically modify with the purpose of improv-

ng its features as an adsorbent, such as selectivity and adsorptionapacity.

. Experimental

.1. Materials

Thiourea-modified chitosan (Scheme 1), which was synthesizedn the Laboratoire 204 of College of Chemistry and Chemical Engi-eering, University of Jinan. FeCl3·6H2O, FeCl2·4H2O and Zn(NO3)2ere purchased from Damao Chemical Agent Company (Tijin,hina). Glutaraldehyde was Aldrich. All other reagents used in thistudy were analytical grade, and distilled or double distilled wateras used in the preparation of all solutions.

.2. Preparation of magnetic particles

250 mL 1.5 mol/L ammonia solution was added in a four-neck

ounded bottom flask, with a dropper, a thermometer, a magnetictirrer, and a N2 purge gas was connected to the reaction flask..7312 g of FeCl3·6H2O, 0.6268 g of FeCl2·4H2O and 25 mL of doubleistilled water were added dropwise to ammonia solution, which

ation of thiourea–chitosan particles.

were purged with nitrogen and stirred in a water bath at 95 ◦C for2 h. Magnetic particles used in the modified chitosan coating wereobtained by magnetic separation [7].

2.3. Preparation of magnetic modified chitosan

0.5 g modified chitosan flake was dissolved in a 50 mL 3% ofacetic solution to give a final concentration of 1.5% (w/v). 0.2 g mag-netic particles were added into the modified chitosan solution in afour-neck rounded bottom flask. After ultrasonic dispersion, 3.0 mLliquid paraffin and Span-80 were added in the solution. The pH wasadjusted to 8.0–9.0 by adding 25% (v/v) ammonium hydroxide solu-tion during the reaction. Then, 2.0 mL of pure glutaraldehyde wasadded into reaction flask to mix with the solution and stirred at60 ◦C for 2 h. The precipitates were washed with petroleum ether,ethanol and distilled water in turn until pH was about 7. The pre-cipitates were then dried at 50 ◦C. The obtained products weremagnetic modified chitosan.

2.4. Adsorption experiments

Batch adsorption experiments were carried out by using theCMMC as the adsorbent. A conical flask containing 50 mL of Zn2+

solutions with initial concentrations of 1300 mg/L and CMMC(0.3 g/mL) was shaken in a SHA-C shaker (Changzhou, China) with

a speed of 100 rpm until the system reached equilibrium. Equilib-rium was considered to be achieved when two consecutive Zn2+

concentrations in solution that were measured over a time periodof 30 min between samples showed no significant difference in

5 es B: B

cod0bse

Q

wZs

wwa

2

ucamwwaItewpdas

2

ccTCc

76 L. Fan et al. / Colloids and Surfac

oncentration. The pH range from 2.0 to 6.0 was got by 0.1 mol/L HClr 0.1 mol/L NaOH. Three replicates were used for each adsorptionatum, and variation among these replicates found to be less than.5%. The adsorption amount and adsorption rate were calculatedased on the difference in the Zn2+ concentration in the aqueousolution before and after adsorption, according to the followingquation:

= (C0 − Ce)V

W, E = (C0 − Ce)

C0× 100%

here C0 and Ce are the initial and equilibrium concentrations ofn2+ in milligrams per liter, respectively, V is the volume of Zn2+

olution, in liters, and W is the weight of the CMMC used, in grams.50 mL of Zn2+solution with initial concentrations of 1300 mg/L

as studied for adsorption process, and 50 mL of Zn2+ solutionsith initial concentrations from 200 to 1700 mg/L were studied for

dsorption kinetics in our experiments.

.5. Desorption experiments and reuse

For desorption studies, 0.2 g of CMMC was loaded with Zn2+

sing 100 mL (1300 mg/L) metal ion solution at 25 ◦C, pH 5.0 andontact time of 30 min. Metal ion-loaded CMMC was collected,nd gently washed with distilled water to remove any unabsorbedetal ions. The final concentration of Zn2+ in the aqueous phaseas determined. The desorption ratio of metal ions from CMMCas calculated from the amount of metal ions adsorbed on CMMC

nd the final concentration of metal ions in the desorption medium.n this study, several solvents/solutions were tried to regeneratehe biosorbents. 0.1 mol/L HCl aqueous solution was found to beffective in desorbing Zn2+ from the loaded adsorbents. The beadsere regenerated using 0.1 mol/L HCl aqueous solution, and therocedure was repeated for many times until Zn2+ could not beetected in the filtrate. To test the reusability of the beads, thisdsorption–desorption cycle was repeated six times by using theame affinity adsorbents.

.6. The uptake behavior of Zn2+ from binary mixtures

The relative higher uptake of Zn2+ at pH 2.0 was taken as an indi-ation of its selective separation from other metal ions. The initial

oncentration of all metal ions in the mixture was 1300 mg/L [13].he uptake behavior of Zn2+ from binary mixtures with Cu2+, Pb2+,d2+ and Hg2+ was studied at pH 2.0 and some other adsorptiononditions as the study of pH in Section 2.4.

Fig. 1. The SEM images of magnetic particles (

iointerfaces 88 (2011) 574– 581

2.7. Characterization of the samples

The geometries of the magnetic particles and magnetic chitosanmicrospheres were observed by using a scanning electron micro-scope (S-4800, Hitachi Ins). The dimension and morphology ofCMMC were observed by transmission electron microscopy (TEM)(Hitachi, H-800). FTIR spectra were measured by a Nicolet, Magna550 spectrometer. The magnetic chitosan was mixed with KBr andpressed to be a pellet for measurement. The concentration of theamine active sites in the obtained resins was estimated by using thevolumetric method. Metal ions were analyzed by atomic absorptionspectrometry (Kejie, AA4520).

2.8. Replication of batch experiment

Each batch adsorption experiment above was conducted twiceto obtain reproductive results with error <5%. In the case of devia-tion larger than 5%, more tests were carried out. The experimentaldata could be reproduced with an accuracy greater than 95%. Allthe data of batch adsorption experiments listed in Section 3 are theaverage values of two tests.

3. Results and discussion

3.1. Characterization of magnetic particles and magneticmodified chitosan

Fig. 1 shows the SEM micrograph of magnetic particles and mag-netic modified chitosan. The SEM analysis of the products providesinformation on the size and morphology of them. It can be seen fromFig. 1 that the magnetic particles with a diameter of about 30 nmwere observed and had a particle shape. The SEM image of magneticmodified chitosan (Fig. 1B) shows that the final products exhibitedaggregation as a result of surface modification by the attachmentof modified chitosan. Magnetic modified chitosan had a sphericalshape.

These findings (Fig. 2) show that the modified chitosan wasimmobilized on the surface of Fe3O4 particles with good distri-bution. The construction of the magnetic modified chitosan wascore–shell. In addition, the surface of the adsorbents had lots oftiny interspaces structure. It was attributed to reactions occurring

on the particle surface, and the heavy metals in the solution couldbe adsorbed easily by the adsorbents.

Infrared spectra of magnetite particles and magnetic modi-fied chitosan samples are shown in Fig. 3. Curve A in Fig. 3

A), and magnetic modified chitosan (B).

L. Fan et al. / Colloids and Surfaces B: B

Ft

saspfs1nhpus

3

oScaditar

ig. 2. Transmission electron micrograph of immobilizing the modified chitosan onhe surface of magnetic nanoparticles.

hows the IR spectrum of the magnetic particles. The peaks atbout 3400 cm−1, 1600 cm−1 and 580 cm−l are ascribed to an O Htretching vibration and characteristic peaks of Fe3O4. The majoreaks for magnetic modified chitosan in Fig. 3B can be assigned asollows: 580 cm−1 (characteristic peak of Fe3O4), 3420 cm−1 (O Htretching vibration), 1661 cm−1 (N H deformation vibration), and065 cm−1 (C N stretching vibration). The IR spectrum of the mag-etic modified chitosan demonstrated that the modified chitosanad cross-linked with magnetic particles successfully because theireaks were similar. Because of the presence of magnetic particles,sing an external magnetic field, the CMMC could be facile and fasteparated from aqueous solution during the experiments.

.2. Effect of pH on the adsorption process

The effect of pH on the adsorption process has been investigatedver the range from 2.0 to 5.0, and the results are shown in Fig. 4A.electing an optimum pH is very important for the adsorption pro-ess, since pH affects not only the surface charge of adsorbent, butlso the degree of ionization and the speciation of the adsorbateuring the reaction. As indicated in Fig. 4A, the maximum capac-

ty of Zn2+ absorption occurred at pH 5.0. This was attributed tohe presence of free lone pair of electrons on nitrogen atoms suit-ble for coordination with the metal ion to give the correspondingesin–metal complex. The slight decrease of the uptake in the acidic

400030002000100000

10

20

30

40

50

60

T/%

λ/ cm-1

A

Fig. 3. IR spectra of magnetite particles (A)

iointerfaces 88 (2011) 574– 581 577

media may be attributed to the protonation of the lone pair of nitro-gen that hinders the complex formation. The uptake of Zn2+ beyondthe natural pH (pH > 5) was attributed to the formation of metalhydroxide species such as soluble Zn2+ and/or insoluble precipitateof Zn(OH)2.

The relatively higher uptake of Zn2+ at pH 5 may be due to thepresence of HCl in the medium which resulted in the formation ofanion complex such as ZnCl3−. This anion was able to exchangethrough the Cl−, which was electrostatically attached to CMMCaccording to the following reaction [22]:

R–NH2 + H+ → R–NH3+, Zn2+ + Cl− → ZnCl3−

R–NH3+ + ZnCl3− → R–NH3

+ ZnCl3−

In addition, the –CH2COO− groups were free from the protona-tion [23]:

2R–CH2COO− + Zn2+ → (R–CH2COO−)2 Zn2+

Thus, pH of 5.0 was selected as the optimum pH value of Zn2+

solution for the following adsorption experiment.

3.3. Effect of initial concentration of Zn2+

As shown in Fig. 4B, the adsorption capacity of the metal ionsincreased with increasing initial concentration of Zn2+. The max-imum adsorption capacity occurred at 1300 mg/L. The maximumadsorption capacity was 32.16 mg/g. Above 1300 mg/L, the adsorp-tion capacity of Zn2+ began to be stable and showed a slightdecrease.

3.4. Effect of contact time on Zn2+ adsorption

Equilibrium time is another important parameter to heavy met-als wastewater treatment process. The effect of the contact time foradsorbent on the adsorption capacity for Zn2+ is described in Fig. 5A.Obviously, adsorbent showed a good performance in adsorptionduring the first 25 min. The time required to achieve the adsorp-tion equilibrium was only 30 min, implying that equilibrium wasreached. There was no significant change from 1 h to 24 h. The con-tact time of 30 min was found to be sufficient to reach equilibrium,so it was selected in further experiments. Such a fast adsorption ratewas attributed to the functional groups on adsorbent. The main rea-son was that adsorbents had large surface areas that could supplya large number of activity points for heavy metal ions absorption.In latter stages, however, the adsorption capacity of Zn2+ became

slower. It was attributed to the great decrease of the bonding siteson the surface of adsorbent and the aggregation between particu-lates. The surface of the former had many NH2 groups that couldcoordinate with Zn2+, but the surface of the latter ones only had

40003000200010000

40

50

60

70

λ/ cm-1

T/%

B

, and magnetic modified chitosan (B).

578 L. Fan et al. / Colloids and Surfaces B: Biointerfaces 88 (2011) 574– 581

654325

10

15

20

25

30

Q/m

g.g-1

pH15001000500

15

20

25

30

Q/m

g.g-1

Ce/mg.L-1

A B

on ad

taf

3

aut

w(caewI

stta

Fig. 4. Effects of pH (A) and initial concentration (B)

OH, which had poor complexing ability with metal ions. In addi-ion, the aggregation between particulates decreased the surfacereas that could supply a large number of activity sites ( NH2, OH)or the absorption of heavy metal ions.

.5. Adsorption isotherms

Fig. 5B shows the adsorption isotherms of Zn2+ on adsorbentt different temperatures. The adsorption curves indicate that theptake of Zn2+ decreased as the temperature increased. The adsorp-ion data were plotted according to Langmuir equation:

Ce

Q= 1

KLQ0+ Ce

Q0

here Ce is the equilibrium concentration of metal ions in solutionmg/L), Q is the adsorbed value of metal ions at equilibrium con-entration (mg/g), Q0 is the maximum adsorption capacity (mg/g),nd KL is the Langmuir binding constant, which is related to thenergy of adsorption. Plotting Ce/Q against Ce gives a straight lineith slope and intercept equal to 1/Q0 and 1/(KLQ0), respectively.

t is described in Fig. 6A.By calculating, the results are as follows:

Ce

Q= 0.0304Ce + 3.92909, Q0 = 32.89 mg/g,

KL = 0.01 L/mg, R2 = 0.9996

The value of Q0 obtained from Langmuir curves is mainly con-

istent with that experimentally obtained (32.16 mg/g), indicatinghat the adsorption process was mainly monolayer. The chela-ion adsorption mechanism of Zn2+ may give controlled monolayerdsorption.

2001501005015

20

25

30

Q/m

g.g-1

t/min

12

-1

A B

Fig. 5. Effects of contact time (A) and temperature (B) on

sorption of Zn2+ on removal efficiency by adsorbent.

Freundlich isotherm is an empirical equation based on adsorp-tion on a heterogeneous surface. The equation is commonlyrepresented by:

ln Qe = ln KF +(

1n

)ln Ce

KF (mg/g (L/mg)1/n) and n are the Freundlich constants charac-teristics of the system, indicating the adsorption capacity and theadsorption intensity, respectively. If the value of 1/n is lower than 1,it indicates a normal Langmuir isotherm; otherwise, it is indicativeof cooperative adsorption. It is described in Fig. 6B.

By calculating, the results are as follows:

ln Qe = 1.429 + 0.2859 ln Ce, KF = 4.174,

1n

= 0.2886, R2 = 0.963

The Langmuir and Freundlich adsorption constants and the cor-responding correlation coefficients were got. The adsorption of Zn2+

was well fitted to the Langmuir isotherm model with the higher R2

(0.999). It indicated the adsorption took place at specific homoge-neous sites within the adsorbent forming monolayer coverage ofZn2+ at the surface of the sorbent. The Freundlich constant 1/n issmaller than 1, indicating a favorable process.

Furthermore, the essential characteristics of the Langmuirisotherm can be described by a separation factor, which is definedby the following equation [24,25]:

RL = 1

(1 + KLCe)

The value of RL indicates the shape of the Langmuir isothermand the nature of the adsorption process. It is considered to be afavorable process when the value is within the range 0–1. In our

33032031030024

26

28

30

Q/m

g.g

T/K

adsorption of Zn2+ on removal efficiency by CMMC.

L. Fan et al. / Colloids and Surfaces B: Biointerfaces 88 (2011) 574– 581 579

2000150010005000

10

20

30

40

50

60

Ce/Q

(g.L

-1)

Ce/(mg.L-1 )

7.57.06.56.05.55.04.52.5

3.0

3.5

lnQ

e

lnCe

3.53.43.33.23.13.0-4.1

-4.0

-3.9

-3.8

-3.7

-3.6

-3.5

ln(Q

/Ce)

/L.g

-1

103T -1/K-1

A

B

C

Fig. 6. The linear dependence of C /Q on C (A), Freundlich isotherm plots for thea

sio

waw

l

Rtwi

l

0

5

10

15

20

25

30

35

Acetic acid(0.5%) HNO3(0.1 mol/L)HCl(0.1 mol/L)

g Adsorptiong Desorption

Qe/m

g.g-1

654321075

80

85

90

E/%

n/times

A

B

shown in Fig. 7B that the uptake capacity of Zn2+ on the adsorbents

e e

dsorption of Zn2+(B), and Van’t Hoff plots for the adsorption of Zn2+ (C).

tudy, the value of RL calculated for the initial concentrations of Zn2+

s 0.07. Since the result is within the range of 0–1, the adsorptionf Zn2+ onto adsorbent appears to be a favorable process.

The observed decrease in both values of 1/T and ln(Q/Ce)ith elevated temperature indicates the exothermic nature of the

dsorption process. The values of ln(Q/Ce) at different temperaturesere treated according to Van’t Hoff equation [26]:

n(

Q

Ce

)= − �H

(RT)+ �S

R

is the universal gas constant (8.314 J/mol K) and T is the absoluteemperature (in K). Plotting ln(Q/Ce) against 1/T gives a straight lineith slope and intercept equal to −�H/R and �S/R, respectively. It

s described in Fig. 6C.By calculating, the results are as follows:

n(

Q

Ce

)= 663

T− 6.002(R2 = 0.9821), �H = −5.51 kJ/mol

Fig. 7. The desorption of Zn2+ from Zn-loaded CMMC in three eluent buffers (A) andeffect of recycling adsorbents on Zn2+ adsorption (B).

The negative value of �H shows exothermic nature of adsorp-tion process. Gibbs free energy of adsorption (�G at 298 K) wascalculated from the following relation:

�G = �H − T�S, �G = −20.38 kJ/mol

The negative value of �G indicates that the adsorption reactionis spontaneous [27].

3.6. Desorption experiments and reuse

From practical point of view, repeated availability is a crucial fac-tor for an advanced adsorbent [28–30]. Such adsorbent has higheradsorption capability as well as better desorption property whichwill reduce the overall cost for the adsorbent.

To evaluate the possibility of regeneration and reusability ofCMMC as an adsorbent, the desorption experiments were per-formed. Desorption of Zn2+ from CMMC was demonstrated usingthree different eluent buffers, namely 0.1 mol/L HCl, 0.1 mol/LHNO3 and 0.5% acetic acid. It was found that the quantitative des-orption efficiencies using HCl, HNO3 and acetic acid were 97.2, 82.1and 70%, respectively. The reusability was checked by following theadsorption–desorption process for three eluent buffers, which areshown in Fig. 7A. The 0.1 mol/L HCl was the optimum eluent buffer.It is worth mentioning that, in all samples, no residual adsorbentswere observed during experimentation, as evidenced by the factthat we did not detect any Fe in the concentrated resulting wastew-ater after treating with HCl. This is another important characteristicof magnetic separation techniques.

The effect of recycling times on the adsorption process wasrepeated 6 times (n = 6), and the results are shown in Fig. 7B. It is

decreased slowly with increasing cycle number. The percentageadsorption remained steady at about 90% in the first five cycles,and then the uptake capacity of Zn2+ decreased. In Zn2+ solution,

580 L. Fan et al. / Colloids and Surfaces B: B

Table 1The uptake behavior of Zn2+ from binary mixtures.

Interfering ions Adsorption capacityof Zn2+ Q1/mg/g

Adsorption capacity ofdifferent ion Q2/mg/g

K (selectivecoefficient)

Cd2+ 29.97 12.21 2.37Hg2+ 28.75 3.35 8.58Pb2+ 29.62 2.53 11.71Cu2+ 29.07 2.97 9.79

Table 2Maximum adsorption capacities for the adsorption of Zn2+onto various chitosanadsorbents.

Adsorbent Adsorption capacity (mg/g) Reference

Natural chitosan membranes 9.5 This workNatural chitosan spheres 10.21 [28]

Ztwcowohcsactfimict

3

sitT

K

Qe

4

CZtaowc(Zowu

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

Carboxymethyl chitosan 20.4 [29]Ulva fasciata sp. 13.5 [30]CMMC 32.16 This work

n2+ was grabbed by OH groups and NH2 groups of modified chi-osan. If the nanocomposites are separated at this stage, metal ionsill be removed from solution. However, under acidic condition, H+

an cause the protonation of amino groups, which means that partf sites occupied by metal ions may be replaced by H+. After beingashed with deionized water to neutralize, the absorption capacity

f the CMMC can be reconditioned. Thus, the recycled CMMC hadigh capacity for Zn2+ removal in each cycle. These results indi-ated no appreciable loss in activity over at least five cycles. At theixth regeneration cycle, the adsorption remained at 75%. The prob-ble mechanism of the regeneration may be that in the first fiveycles, both electrostatic and complex reaction occurred betweenhe hydrochloric acid solution and the metal ions; however, afterve cycles, only electrostatic interaction prevailed. The probableechanism was that some OH groups and NH2 groups of mod-

fied chitosan decreased, which led to the situation that modifiedhitosan had poor complexing ability with metal ions, and the elec-rostatic interaction of Zn2+ prevailed.

.7. The uptake behavior of Zn2+ from binary mixtures

The results of selective determination are shown in Table 1. Ithows that in the presence of interfering ions, the adsorption capac-ty of Zn2+ remained steady at about 30 mg/g. These results showhat the adsorbents had high selectivity and adsorption for Zn2+.he selective coefficient equation is given by

= Q1

Q2

1 (adsorption capacity of Zn2+), Q2 (adsorption capacity of differ-nt ions).

. Conclusions

Adsorption of Zn2+ from aqueous solutions was studied usingMMC. The following conclusions were drawn: the adsorption ofn2+ by CMMC was found to be dependent upon the pH. In addi-ion, more than 90% of Zn2+ was adsorbed within the first 25 min,nd the time required to achieve the adsorption equilibrium wasnly 30 min. Equilibrium data at different temperatures were fittedell with Langmuir isotherms, indicating that the adsorption pro-

ess was mainly monolayer. Compared to the unmodified chitosanTable 2), CMMC showed greatly improved uptake properties of

n2+ due to the higher concentration of active sites on the surfacef CMMC. Feasible improvements in the uptake properties alongith the magnetic properties encourage efforts for CMMC to besed in water and wastewater treatment.

[

[

iointerfaces 88 (2011) 574– 581

Acknowledgments

This work was supported by the Shandong Provincial NaturalScience Foundation (Y2008B53) and Shandong Provincial Key Sub-ject (Laboratory) Research Foundation (XTD0705).

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