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Chemical Engineering Journal 168 (2011) 286–292

Contents lists available at ScienceDirect

Chemical Engineering Journal

journa l homepage: www.e lsev ier .com/ locate /ce j

reparation and characterization of magnetic chitosan nanoparticles and itspplication for Cu(II) removal

hen Yuwei, Wang Jianlong ∗

aboratory of Environmental Technology, INET, Tsinghua University, Beijing 100084, PR China

r t i c l e i n f o

rticle history:eceived 28 November 2010eceived in revised form 3 January 2011ccepted 4 January 2011

a b s t r a c t

The magnetic chitosan nanoparticles were prepared by a simple one-step in situ co-precipitation methodand characterized by means of X-ray diffraction (XRD), transmission electron microscope (TEM), FourierTransform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and energy dispersive X-ray spectrometer (EDS). The sorption performance of the nanoparticles for removing Cu(II) from aqueous

eywords:hitosanagnetic chitosan nanoparticle

iosorbentsotherm

solution was investigated. The experimental results showed that the particles were super-paramagnetic,with the saturation magnetization of about 36 emu/g and the size was in the range of 8–40 nm. The EDSimages confirmed the presence of Cu(II) on the surface of magnetic chitosan nanoparticles. The maximumsorption capacity was calculated to be 35.5 mg/g using the Langmuir isotherm model. The mechanism ofCu(II) sorption onto the magnetic chitosan nanoparticles was tentatively proposed.

opperiosorption

. Introduction

Toxic heavy metal pollution is one of the most significant envi-onmental problems due to their hazards to human being andcological systems. The treatment methods used for removingetal ions from aqueous solution include physical, chemical and

iological technologies. Biosorption, defined as to remove vari-us pollutants from aqueous solution by biological material suchs fungi, yeast, algae, etc., has received increasing attention inecent years, because it has several advantages in comparison withhysical and chemical methods, such as membrane separation, ionxchange and chemical precipitation [1]. Chitosan is produced from-deacetylation of chitin, a major component of crustacean shellsnd fungal biomass and it is readily available from seafood process-ng wastes. Chitosan, because of its high amino content, has beenound to possess good sorption capacity for many heavy metal ionshrough complexation with the amine groups. It has been widelysed as biosorbent for removing various metal ions from wastew-ter [2,3].

Magnetic separation technique has some advantages, such asigh efficiency, cost-effectiveness. Magnetic carriers are usually

omposed of the magnetic cores to ensure a strong magneticesponse and a polymeric shell to provide favorable functionalroups and features for various applications [4–6].

∗ Corresponding author. Tel.: +86 10 62784843; fax: +86 10 62771150.E-mail address: wangjl@tsinghua.edu.cn (W. Jianlong).

385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.cej.2011.01.006

© 2011 Elsevier B.V. All rights reserved.

Compared to the traditional micro-sized magnetic supportsused in separation process, nano-sized magnetic carriers possessquite a good performance due to higher specific surface area andlower internal diffusion resistance [7,8]. In addition, magnetite(Fe3O4) has been widely used as magnetic material due to theirexcellent magnetic properties, chemical stability and biocompati-bility. Therefore magnetic chitosan nanoparticles are a promisingbiosorbent for removing heavy metals. This material has not onlystrong metal chelating capability due to presence of the amine andhydroxyl groups in chitosan chain, but also the feature of nano-materials. In addition, due to magnetic properties, it can easily beseparated from the sorption system by using magnetic field.

Copper is one of the most common pollutants in indus-trial effluents. Several industries, for example, dyeing, paper,petroleum, copper/brass plating and copper–ammonium rayon,discharge Cu(II)-containing wastewater. In the copper-cleaning,plating and metal-processing industries, Cu(II) concentration wasabout 100–120 mg l−1 [9]. It has been a major concern because ofits toxicity to aquatic life, human beings and the environment.

Low-cost biosorbents may be an alternative material forwastewater treatment [10–14]. It would be of great interest todevelop a novel biosorbent with a large sorption surface area, lessdiffusion resistance, higher specific sorption capacity and fast sep-aration for large volumes of solution.

Recently, many researches have reported the preparation ofthe magnetic chitosan/Fe3O4 composites and their applications forremoving metal ions. However, to our knowledge, there have been afew reports on preparation, characterization and adsorption prop-erties of magnetic nanosized chitosan composite adsorbent. For the

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C. Yuwei, W. Jianlong / Chemical E

reparation of magnetic chitosan beads, most of the researcherspplied two-step method, and the size of the particles was mostlyn micrometer scale.

In this paper, a novel magnetic chitosan nanoparticles was pre-ared through a simple one-step in situ co-precipitation method.heir performance was characterized, and the sorption property foremoving Cu(II) from aqueous solution was investigated.

. Materials and methods

.1. Chemicals and materials

Chitosan flakes (85% deacetylated) used in the experimentsere purchased from Sinopharm Chemical Reagent Co., Ltd., Shang-ai, China. FeSO4·7H2O (≥99.0%), FeCl3·6H2O (≥99.0%), CH3COOH≥99.5%) were purchased from Beijing Modern East Fine Chemi-al Ltd. NaOH (≥96.0%) was supplied by Beijing Chemical Works.u(NO3)2·3H2O (99.0–102.0%) was supplied by Sinopharm Chemi-al Reagent Ltd.

.2. Synthesis of chitosan–magnetite nanocomposites

Magnetic chitosan nanoparticles were prepared by chemicalo-precipitation of Fe2+ and Fe3+ ions by NaOH in the presencef chitosan, followed by hydrothermal treatment [15]. We modi-ed this method. Briefly, 2 g chitosan was dissolved into 100 mL 2%H3COOH solution, FeSO4 and FeCl3 were dissolved in 1:2 (molaratio), then the resulting solution was chemically precipitated at0 ◦C by adding 30% NaOH dropwise with constant stirring underhe protection of argon. The suspension was heated to 90 ◦C andept for 1 h under continuous stirring and separated by centrifug-ng several times in water and then in ethanol. The particles werenally dried in vacuum at 70 ◦C.

.3. Characterization methods

Powder X-ray diffraction (XRD) patterns were obtained at roomemperature by D/max-TTR III, Japan, using CuK� radiation inhe range of 2� = 10–90◦. The magnetic property was measuredn a vibrating sample magnetometer (VSM) (730T, Lakeshoper,merica) at room temperature. The dimension and morphologyf magnetic chitosan nanoparticles were observed by transmis-ion electron microscopy (TEM) (JEM-200CX, FEI, USA). Fourierransform infrared spectroscopy (FTIR) spectra of magnetic chi-osan nanoparticles before and after adsorbed Cu(II) were recordedsing FTIR (Spectrum GX, Perkin-Elmer) connected with a com-uter. Samples were prepared in KBr disks. The scanning rangeas 400–4000 cm−1. The presence of Cu(II) ions on the surface ofagnetic chitosan nanoparticles was detected by energy dispersive-ray spectrometer (EDS).

.4. Adsorption experiments

The adsorption experiments were carried out by mixing 20 mgorbent with 15 mL Cu(II) solution of 100 mg/L. The initial pH wasdjusted to 5.0 using 0.1N HCl and 0.1N NaOH. The sorption experi-ent was performed at 150 rpm and 298.15 K for 8 h. Samples were

ollected at fixed intervals (5, 10, 20, 30 min, 1, 1.5, 2, 3, 4, 6, 8 h), andltrated with 0.22 �m filter film, then used for analyzing Cu(II) con-entration by atomic absorption spectrometric method with flame

tomization (AAS 6 Vario).

Equilibrium studies were carried out by mixing 20 mg sor-ent with 15 mL solution containing different initial concentrationf Cu(II) (25–250 mg/L), the resulting mixture was shaken at50 rpm and different temperatures (288.15, 293.15, 298.15,

ring Journal 168 (2011) 286–292 287

303.15, 308.15 K) for 4 h, under optimum pH condition (pH = 5.0).All experiments were conducted three times.

The adsorbed amount of Cu(II) per unit weight of magnetic chi-tosan nanoparticles at time t, qt (mg/L) was calculated from themass balance equation as:

qt = (C0 − Ct)Vm

where C0 and Ct (mg/L) are the initial Cu(II) concentration and theCu(II) concentrations at any time t, respectively; V is the volumeof the Cu(II) solution; and m is the mass of the magnetic chitosannanoparticles.

2.5. Desorption experiments

For desorption studies, 20 mg of magnetic chitosan nanopar-ticles (m) was loaded with Cu(II) using 15 mL (C0 = 100 mg/L)(V1 = 15 mL) at pH 5.0 and contact time of 4 h. The agitation ratewas fixed as 150 rpm. The amount of Cu(II) adsorbed by magneticchitosan nanoparticles were determined using the supernatantCu(II) concentration (C1). The magnetic chitosan nanoparticlesloaded Cu(II) were then agitated with 15 mL (V2 = 15 mL) EDTA(0.02 M–0.1 M). The final concentration of Cu(II) ions (C2) in theaqueous phase was determined by means of an atomic absorp-tion spectrophotometer. The desorption ratio (R) of metal ions frommagnetic chitosan nanoparticles was calculated from the amountof metal ions adsorbed on nanoparticles and the final concentra-tion of metal ions in the desorption medium. To test the reusabilityof the beads, this adsorption–desorption cycle was repeated fourtimes using the same affinity adsorbent.

The desorption ratio was calculated by:

R(%) = (C2V2/m)((C0 − C1)V1/m)

× 100% = C2

C0 − C1× 100%

3. Results and discussion

3.1. Preparation of magnetic chitosan nanoparticles

For the preparation of magnetic chitosan beads, two-stepmethod was widely used. The first step is to synthesize Fe3O4 par-ticles, and the second one is to bind them with chitosan. Thereare two binding methods: verse-phase suspension cross-linkingmethod [16–18], and precipitation method [6,19,20]. The size ofthe particles was mostly in micrometer scale. Comparing withthe verse-phase suspension cross-linking method, the precipita-tion method is quite simple and facile to be carried out, especiallyin post-treatment [21]. In the present study, a simple one-stepin situ co-precipitation method was developed and used to syn-thesize magnetic chitosan nanoparticles. Because chitosan couldprecipitate under alkaline condition, when NaOH is added to theacidic solution containing chitosan, Fe(II) and Fe(III) ions, magnetiteparticles are formed during precipitation of chitosan, leading tothe formation of chitosan–magnetite particles. Moreover, NaOH isadded to the solution dropwise with constant stirring, the formedchitosan–magnetite particles are in nanometer size.

3.2. Characterization of magnetic chitosan nanoparticles

3.2.1. XRD analysis

XRD patterns of pure Fe3O4 and magnetic chitosan nanopar-

ticles are shown in Fig. 1, indicating the existence of iron oxideparticles (Fe3O4), which has magnetic properties and can be usedfor the magnetic separation. The XRD analysis results of pure Fe3O4and magnetic chitosan nanoparticles were mostly coincident. Six

288 C. Yuwei, W. Jianlong / Chemical Engineering Journal 168 (2011) 286–292

100806040200

Inte

nsity

/cps

(Fe3 O4 )

(CMNs)

c6

3

tsaslctTr

3

orcF

3

o

2θ/ o

Fig. 1. XRD pattern of Fe3O4 and magnetic chitosan nanoparticles.

haracteristic peaks for Fe3O4 (2� = 30.1, 35.5, 43.3, 53.4, 57.2 and2.5) [17] were observed in both samples.

.2.2. Magnetic propertiesThe magnetic performance of the magnetic chitosan nanopar-

icles prepared in this study was determined using VSM, Fig. 2howed their typical magnetization loop. There was no remanencend coercivity, suggesting that magnetic chitosan nanoparticles areuperparamagnetic [22]. The saturation magnetization was calcu-ated to be about 36 emu/g. This value was higher than that of otherhitosan based Fe3O4 beads. They reported the saturation magne-ization was about 17.6 emu/g and 16.3 emu/g respectively [18,23].herefore, the magnetic chitosan nanoparticles can be easily sepa-ated with the help of the external magnetic field.

.2.3. TEMThe TEM image of the magnetic chitosan nanoparticles was

bserved. Fig. 3 showed that the size of the particles was in theange of 8 nm–40 nm. Moreover, TEM images also showed differentontrasts of chitosan–Fe3O4: the dark areas present for crystallinee3O4 while the bright ones are associated with chitosan.

.2.4. FTIR analysisTo confirm the existence of the surface coating, FTIR spectra

f the pure Fe3O4, chitosan and magnetic chitosan nanoparticles

20000100000-10000-20000

-40

-30

-20

-10

0

10

20

30

40

mag

netiz

atio

n/(e

mg/

g)

magnetic field/(Oe)

Fig. 2. Magnetic hysteresis curves of magnteic chitosan nanoparticles.

Fig. 3. TEM images of magnteic chitosan nanoparticles.

were examined and shown in Fig. 4. For pure Fe3O4, the peakat 580 cm−1corresponds to Fe–O group; for chitosan, the peakat 3436 cm−1 is attributed to O–H stretching vibration, and C–Hstretching vibration of the polymer backbone is manifested throughpeaks at 2919 and 2874 cm−1. The characteristic biosorption peakof primary amine (–NH2) appears at 3436 and 1655 cm−1. Thebiosorption bands around 1075 and 1030 cm−1 display the stretchvibration of C–O bond. The IR spectra indicated that chitosan andFe3O4 are both presented in magnetic chitosan nanoparticles, andthe Fe3O4 magnetic nanoparticles were coated by the chitosan.

TEM and IR results are important because they evidenced thesuccessful coating of Fe3O4 nanoparticles by chitosan. Chitosan onthe surface of the magnetic nanoparticles is available for coordi-nating with heavy metal ions, making those ions removed fromaqueous solution.

3.2.5. EDS analysis before and after Cu(II) biosorptionThe EDS spectra of magnetic chitosan nanoparticles showed the

peak of C, O, N and Fe, which were three major constituents of

40080012001600200024002800320036004000

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1063890

580

899

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15991655

2874

3436

1628

1064

CS

CMNs

trans

mitt

ance

/ %

wavenumbers/cm -1

Fe3O4580

Fig. 4. FTIR spectra of Fe3O4, chitosan and magnteic chitosan nanoparticles.

C. Yuwei, W. Jianlong / Chemical Engineering Journal 168 (2011) 286–292 289

1086420

NFe

FeFe

O

C

Energy (Kev)

a

1086420

N CuFe

FeFe

O

C

b

Fb

cFceCam

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Energy (Kev)

ig. 5. EDS spectra of magnteic chitosan nanoparticles before (a) and after (b) Cu(II)iosorption.

hitosan and magnetite, confirming the existence of chitosan ande3O4 (Fig. 5(a)). The EDS spectra of magnetic chitosan nanoparti-les after Cu(II) sorption presented a new peak, corresponding to Culement (Fig. 5(b)). The EDS spectra provided a direct evidence foru(II) adsorbed on magnetic chitosan nanoparticles. Other studieslso use EDS analysis to give a direct detection of the presence ofetals on the adsorbents [24,25].

.3. Equilibrium isotherm

Fig. 6 showed the isotherms of Cu(II) adsorption onto magnetichitosan nanoparticles at different temperatures. It can be seen thathe sorption capacity increased with increasing temperature, indi-ating that the adsorption reaction is endothermic. This is similar tohe results obtained by using magnetic Cu(II) ion impregnated com-osite adsorbent [26,27]. In general, the adsorption process takeslace by two consequent processes, namely, diffusion and complex-tion. The increase in the adsorption capacity was not only due tohe increase of the diffusion rate of Cu(II) onto the sorbent surface,ut also due to the increase of the rate of complexation with theunctional groups present in the adsorbent [26].

The equilibrium isotherm equations could be used to describehe experimental sorption data and provide some insight intohe sorption mechanism, the surface properties and the affin-ty between sorbent and sorbate [28]. In this study, differentinds of isotherms, including the Langmuir, the Freundlich, theedlich–Peterson (R–P) [29], the Slips [30], the Toth, and the

ubini–Radushkevich (D–R) [31] isotherms were applied to model

he experimental results. The forms of these isotherms are listed inable 1.

The Langmuir isotherm model is representative of monolayerorption occurring on energetically uniform surface on which

Fig. 6. Equilibrium adsorption isotherms for Cu(II)-magnetic nanoparticles systemat different temperatures.

the adsorbed molecules are not interactive. Accordingly, equi-librium is attained once the monolayer is completely saturated.The Freundlich model describes the sorption on an energeticallyheterogeneous surface on which the adsorbed molecules are inter-active and the amount of solute adsorbed increases infinitely withincrease in the concentration. The Redlich–Peterson (R–P) equa-tion contains three parameters and incorporates the features ofthe Langmuir and the Freundlich isotherms. Derived from poten-tial theory, the Toth equation is used in heterogeneous systems,which assumes a quasi-Gaussian energy distribution, i.e. most siteshave a sorption energy lower than the peak of maximum sorp-tion energy. Dubinin–Radushkevich (D–R) isotherm model wereapplied to determine the sorption type (physical or chemical sorp-tion), which is more general than the Langmuir model because itdoes not require homogenous sorption sites or constant sorptionpotential.

For the Langmuir isotherm, qe and Ce are the amount adsorbed(mg/g) and the sorbate concentration on solution (mg/L), both atequilibrium; kL (L/mg) is the Langmuir constant related to theenergy of sorption; and qm (mg/g) is the maximum sorption capac-ity for monolayer formation on sorbent. In the R–P equation, kRP,˛RP, ˇ are the R–P parameters, ˇ lies between 0 and 1. For ˇ = 1,the R–P equation becomes to the Langmuir form. When kRP and˛RP are much greater than unity, the equation can transform tothe Freundlich form. For the D–R model The constant k gives themean free energy E (kJ/mol) of sorption per molecule of the sorbatewhen it is transferred to the surface of the solid from infinity in thesolution and can be computed using the relationship:

E = 1

(2k)1/2

E was the mean sorption energy. This parameter gives informa-tion about chemical or physical sorption. The magnitude of E isbetween 8 and 16 kJ/mol, the process follows chemical sorption,while for the values of E < 8 kJ/mol, the process is of a physicalnature.

The parameters of the Langmuir, the Freundlich and the D–R

models could be obtained by linear regression analysis. For theother equations, the model parameters were estimated by non-linear regression. The computed constants were shown in Table 2.It can be noted that the R–P model describes the sorption bet-ter than other isotherms (Fig. 7). In fact, the values of ˇ were

290 C. Yuwei, W. Jianlong / Chemical Engineering Journal 168 (2011) 286–292

Table 1The forms of different isotherms.

Model Equation Linear form

Langmuir q = qmkLCe1+kLCe

Ceqe

= 1kLqm

+ Ceqm

Freundlich qe = kFCe1/n ln qe = ln kF + 1

n ln Ce

Redlich–Peterson (R–P) qe = kRPCe

1+˛RPCeˇ

(Ceqe

= 1kRP

+ ˛RPCeˇ

kRP

)

Slips (or Langmuir–Freundlich) qe = kSCe1/b

1+˛SCe1/b

Toth qe = ktCe

(˛t+Ce)1/t

Dubinin–Radushkevich (D–R) qe = qmexp( − kε2) ln qe = ln qm − kε2ε = RT ln(

1 + 1Ce

)

Table 2Equilibrium parameters for Cu(II) biosorption.

Model Temperature (K)

288.15 293.15 298.15 303.15 308.15

Langmuirqm (mg/g) 29.6 30.2 33.7 33.8 35.5kL (L/mg) 0.0229 0.0235 0.0196 0.0213 0.0201R2 0.9799 0.9788 0.9826 0.9810 0.9890

FreundlichkF (mg/g) 2.54 2.66 2.53 2.59 2.64n 2.26 2.28 2.17 2.16 2.15R2 0.9540 0.9506 0.9612 0.9492 0.9616

Sips (or Langmuir–Freundlich)kS (Lbmg1−b/g) 0.582 0.700 0.956 0.676 0.873˛S (L/mg)b 0.0192 0.0222 0.0252 0.0195 0.0230b 0.976 1.02 1.15 0.995 1.08R2 0.9614 0.9589 0.9681 0.9641 0.9779

Tothkt (mg/g) 41.6 43.8 46.1 49.3 52.2˛t 55.6 54.7 61.2 58.6 61.1t 0.952 0.947 0.954 0.945 0.943R2 0.9628 0.9600 0.9660 0.9650 0.9774

Redlich–PetersonkRP (l/g) 0.505 0.543 0.653 0.575 0.674˛RP × 10−3 (l/g)� 4.25 5.55 18.4 5.85 15.0ˇ 1.25 1.21 1.01 1.19 1.04R2 0.9839 0.9817 0.9826 0.9835 0.9891

Dubini–Radushkevich

caam

Fd

qm (mg/g) 74.7 76.0K × 10−3 (mol2/kJ2) 5.5 5.3E (kJ/mol) 9.53 9.71R2 0.9698 0.9674

loser to unity than 0, implying that the isotherm was morepproaching the Langmuir than the Freundlich model, which canlso be confirmed by that the regression coefficients of the Lang-uir model was higher with respect to the Freundlich model.

250200150100500

2

4

6

8

10

T=288.15°C T=293.15°C T=298.15°C T=303.15°C T=308.15°C

Ce/

qe/(g

/L)

Ce/(mg/L)

ig. 7. R–P plot for the adsorption of Cu(II) on magnetic chitosan nanoparticles atifferent temperatures.

84.9 88.5 91.15.4 5.2 5.19.62 9.81 9.900.9742 0.9665 0.9763

Hence, the monolayer coverage process of heavy metal on mag-netic chitosan nanoparticles was approved by the best fit ofequilibrium data in both the R–P and the Langmuir isothermexpressions.

In the Freundlich model, the n values in the range of 1–10 indi-cated that the sorption process was favorable.

The maximum sorption capacity calculated from the Lang-muir isotherm was 29.6–35.5 mg/g, depending on the temperature.These were close to the experimental values, suggesting that thesurface of the sorbent was homogeneous. However, the maximumsorption capacity derived from the D–R model was quite different.This may attributed to the different assumptions considered in theformulation of the isotherms. The differences were also reportedin other papers [28]. The value of E at different temperatures wasfound to be 9.51–9.90 kJ/mol, indicating that the process is chemicalsorption.

For the equilibrium study, Ng et al. [32] reported the sorptionequilibrium on chitosan for the removal of Cu(II). Based on fittingthe data with the Langmuir adsorption isotherm, they found an

adsorption capacity of 2.0834 mg of Cu(II)/g of chitosan. Zhou et al.[17] studied the adsorption of Cu(II) by thiourea-modified magneticchitosan microspheres (TMCS). They reported that the Langmuirisotherm correlated better than the Freundlich isotherms, sug-gesting a monolayer adsorption. They calculated the maximum

C. Yuwei, W. Jianlong / Chemical Enginee

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30

40

50

60

70

80

90

100

580

824

890

1062

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580

1063

28633352

after CS/Fe3 O4

CS/Fe3 O4

trans

mitt

ance

/ %

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15931637

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ai

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tmsem3o

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[

[

[12] E. Guibal, Interactions of metal ions with chitosan-based sorbents: a review,

ig. 8. FTIR spectra of magnteic chitosan nanoparticles before and after Cu(II)iosorption.

dsorption capacity of 66.7 mg/g when Cu(II) concentration wasn the range of 25–350 mg/L.

Chang et al. [33] studied the removal of Cu(II) usingonodisperse chitosan-bound Fe3O4 magnetic nanoparticles. The

dsorption data obeyed the Langmuir equation with a maximumdsorption capacity of 21.5 mg/g and the adsorption equilibriumonstant of 0.0165 L/mg at 300 K. Huang et al. [6] investigated theerformance of cross-linked magnetic chitosan and its adsorptionharacteristics for copper(II) removal from aqueous solution. Theyoncluded that the Langmuir isotherm was better compared withhe Freundlich isotherm. And the sorption capacity of Cu(II) was8.13 mg/g at pH 6.0.

Based on the above analysis, for many studies, the Langmuir andhe Freundlich were used to fit the experiment data and the Lang-

uir isotherm correlated better than the Freundlich model. In ourtudy, six different kinds of isotherms were applied to describe thequilibrium and gave the important information. Also, the maxi-um sorption capacity obtained from the Langmuir isotherm was

5.5 mg/g. This result is comparable with the adsorption capacityf the other similar sorbents reported in literature.

.4. FTIR analysis after Cu(II) adsorption

FTIR analysis was carried out mainly to identify functionalroups capable of adsorbing metal ions [28]. Fig. 8 showed the FTIRpectra of magnetic chitosan nanoparticles and Cu-loaded mag-etic chitosan nanoparticles. The peak at 1637 cm−1 correspondingo the vibration of NH2 in amine shifts from 1637 to 1627 cm−1,ndicating that NH2 took part in adsorption. It is also observed that,fter Cu(II) sorption, there is a new band at 1317 cm−1, which ishe characteristic peak of the association of the magnetic chitosananoparticles and Cu(II). The peak at 1317 cm−1 was due to C–Ntretching vibration [24]. In other words, Cu(II) adsorption wasound to affect the bonds with N atom. So it is reasonable to assumehat the nitrogen atom should be the main sites for Cu(II) sorptiony magnetic chitosan. Also, the peak at 3352 cm−1 correspondingo the stretching vibration of OH-group shifts from 3352 cm−1 to234 cm−1 after Cu(II) sorption, indicating that –OH group also takeart in sorption. This conclusion was consistent with other studies.i and Bai [34] used FTIR spectra to show that the binding of lead

ons to nitrogen atom in chitosan and oxygen atom in –OH group

ay contribute to lead adsorption on chitosan/PVA beads. Othertudies also found that –OH and –NH2 was involved in adsorptionrocess [24,35].

[

[

ring Journal 168 (2011) 286–292 291

3.5. Regeneration of magnetic chitosan nanoparticles

Generally, the adsorbed metal ions can be desorbed and con-centrated by eluant. However, acids such as HCl and HNO3 mayreact with Fe3O4, which is the magnetic component of magneticchitosan nanoparticles. Ethylendiamine tetraacetic acid (EDTA) isknown as a very strong chelating agent for many heavy metal ionsand was proposed to replace the active groups on magnetic chi-tosan nanoparticles and preferentially complex with metal ions.Consequently, EDTA was chosen as the eluant for metal ions. At aconcentration of 0.02 M EDTA and with the contact time of 3 h, it ispossible to desorb 90% of Cu(II) ions adsorbed on magnetic chitosannanoparticles into the solution. Increasing EDTA concentration to0.1 M resulted in 96% desorption of Cu(II). And the adsorptioncapacity of the nanoparticles could still be maintained more than90% after four cycles.

4. Conclusions

In this study, a novel magnetic chitosan nano-biosorbent wasprepared, characterized and used for the removal of Cu(II) fromaqueous solution. The particles size varied from 8 nm to 40 nm,with superparamagnetic property. The equilibrium data could bedescribed by the Dubini–Radushkevich (D–R) and the Langmuirisotherms. The maximum sorption capacity for Cu(II) was calcu-lated to be 35.5 mg/g from the Langmuir isotherm. More than90% Cu(II) ions adsorbed could be eluated from magnetic chitosannanoparticles using 0.02–0.1 M EDTA. FTIR analysis suggested that–NH2 and –OH were involved in the removal mechanism of Cu(II).

Acknowledgements

The authors are grateful to the precious comments and carefulcorrection made by anonymous reviewers. The authors also wouldlike to thank the financial support provided the National NaturalScience Foundation of China (Grant No. 50830302).

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