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Colloids and Surfaces B: Biointerfaces 91 (2012) 250– 257

Contents lists available at SciVerse ScienceDirect

Colloids and Surfaces B: Biointerfaces

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

emoval of alizarin red from water environment using magnetic chitosan withlizarin Red as imprinted molecules

ulu Fana, Ying Zhangb, Xiangjun Lia, Chuannan Luoa,c,∗, Fuguang Lua, Huamin Qiua

College of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, ChinaDepartment of Chemical Engineering, Dalian University of Technology, Dalian, 116024, ChinaKey Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China

r t i c l e i n f o

rticle history:eceived 1 September 2011eceived in revised form 27 October 2011ccepted 5 November 2011vailable online 15 November 2011

a b s t r a c t

A novel, chitosan coating on the surface of magnetite (Fe3O4) (MIMC) was successfully synthesized usingalizarin red (AR) as a template for adsorption and removal of AR from aqueous solutions. Characteriza-tion of the obtained MIMC was achieved by FTIR spectra, SEM micrographs and XRD. Batch adsorptionexperiments were performed to investigate the adsorption conditions, selectivity and reusability. Theresults showed that the maximum adsorption capacity was 40.12 mg/g, observed at pH 3 and tempera-ture 30 ◦C. Equilibrium adsorption was achieved within 50 min. The kinetic data, obtained at the optimum

eywords:hitosanagnetite

angmuirdsorption

pH 3, could be fitted with a pseudo-second-order equation. Adsorption process could be well describedby Langmuir adsorption isotherms and the maximum adsorption capacity was calculated as 43.08 mg/g.The selectivity coefficient of AR and other dyes onto MIMC indicated an overall preference for AR, whichwas much higher than non-imprinted magnetic chitosan beads. Moreover, the sorbent represented high

abilit

lizarin redemplate

stability and good repeat

. Introduction

Dyes and pigments represent one of the problematic groups,hich are emitted in to wastewaters from various industrial

ranches, mainly from the dye manufacturing, textile finishing andlso from food coloring, cosmetics, paper and carpet industries1,2]. Discharge of dye effluents into the natural streams is toxic tohe aquatic lives. Color affects the nature of water and inhibits theunlight penetration into the stream and reduces photosyntheticctivity [3,4]. It is well known that wastewaters containing dyesre very difficult to treat, because these chemicals are recalcitrantolecules resistant to traditional aerobic digestion [5]. Adsorption

f dyes onto a sorbent can be an effective low cost method of coloremoval.

Nowadays, great interests are focused on low cost sorbentsor water treatment. The use of low cost sorbents has become anlternative to expensive methods such as membrane filtration, ionxchange or carbon adsorption [6,7]. A sorbent can be assumed aslow cost” if it requires little or none processing, or if it is con-idered as a by-product or waste material that could be obtained

n abundance [8]. Recently, numerous approaches have beentudied for the development of cheaper and more effective adsor-ents containing polysaccharides [9]. Chitosan exhibits a higher

∗ Corresponding author. Fax: +86 53182765491.E-mail addresses: chm luocn@ujn.edu.cn (C. Luo), fanlu1949@126.com (F. Lu).

927-7765/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfb.2011.11.014

y.© 2011 Elsevier B.V. All rights reserved.

adsorption capacity and faster adsorption rate of anionic dye pol-lutants than many conventional adsorbents due to the presenceof large amounts of amino group (–NH2) [10]. In acidic solution,the amino groups of chitosan are easily protonated and can bindanionic dye anions. Chitosan is efficient and easily regenerablerelative to other adsorbent materials. The use of chitosan resinsfor the removal of dyes from aqueous solutions was reported byseveral authors [8,11–15]. In addition, magnetic fluids have thecapability to treat large amounts of wastewater within a short timeand can be conveniently separated from wastewater; at the sametime, they could be tailored by using functionalized polymers, novelmolecules, or inorganic materials to impart surface reactivity [16].Coating chitosan with magnetic fluids is a new method to expandfunction of the chitosan, and the method has been reported that itcan improve the surface area for adsorption and reduce the requireddosage for the adsorption of dyes [17–19]. They had succeededthe preparation of sorbents with high adsorption capacity for theremoval of dyes, but without achieving any selectivity.

Molecular imprinting technique (MIT) is a type of synthe-sized material with specific recognition ability for the templatemolecules [20,21]. As for chitosan-based MIT, till now, many studieshave been reported, with a wide range of compounds as templates,such as metal ions [22], protein [23] and amino acid [24]. But, work

about dyes as templates has been reported rarely. The molecularimprinting technique based on chitosan is of interest in studieson the selective removal of dyes from aqueous solutions [25,26].In comparison with the common absorbents, the MIT improves

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

St

aHfpns

(wwdsTwrti

2

2

w(CcGAlp

2

rfldwMw

by plotting a calibration curve for AR over a range of concentra-

cheme 1. Synthesis route of MIMC and their application for removal of AR withhe help of an external magnetic field.

bsorbents’ high reusability, selectivity and lower consumption.owever, the selective adsorbents were difficult to be separated

rom waste water. Thus, MIT based on magnetic chitosan is a greatotential adsorbent. In this work, AR imprinted magnetic chitosananoparticles based on MIT were first synthesized and applied inelective removing AR from aqueous solution.

In this work, chitosan coating on the surface of magnetiteFe3O4), which was using AR as imprinted molecules (MIMC)as successfully synthesized, and applied for removing AR fromastewater. The resulting functional material is easily separatedue to the magnetism. Furthermore, high removal efficiency andelectivity in adsorbing AR were achieved by applying the MIMC.he initial pH effect, kinetics, equilibrium, desorption and reuseere also examined for better comparison of the experimental

esults. This information will be useful for further applications inhe treatment of practical waste effluents. The preparation of MIMCs schematically illustrated in Scheme 1.

. Materials and methods

.1. Materials

Chitosan (degree of deacetylation 92.2% and MW5.0 × 105 Da)as purchased from Shandong Hecreat marine bio-tech Co., Ltd.

Qingdao, China). Alizarin red was supplied by Shanghai Reagentorp. (Shanghai, China). FeCl3·6H2O and FeCl2·4H2O were pur-hased from Damao Chemical Agent Company (Tianjin, China).lutaradehyde, epichlorohydrin and 3% acetic solution wereldrich products. All other reagents used in this study were ana-

ytical grade, and distilled or double distilled water was used in thereparation of all solutions.

.2. Preparation of magnetic particles

250 mL 1.5 mol/L ammonia solution was added in a four-neckounded bottom flask and a N2 purge gas connected to the reactionask.1.7 g of FeCl3·6H2O, 0.63 g of FeCl2·4H2O and 25 mL of doubleistilled water were added dropwise to ammonia solution, which

as purged with nitrogen and stirred in a water bath at 95 ◦C for 2 h.agnetic particles for use in the preparation of magnetic chitosanas obtained by magnetic separation [27].

iointerfaces 91 (2012) 250– 257 251

2.3. Preparation of magnetic chitosan

0.5 g chitosan flake was dissolved in a 30 mL 1.5% of acetic solu-tion. 0.2 g magnetic particles were added in the chitosan solutionin a four-neck rounded bottom flask. After ultrasonic dispersion,3.0 mL liquid paraffin and Span-80 were added in the solution. Thesolution’s pH was adjusted to maintain a level of 8.0–9.0 by adding25% (v/v) ammonium hydroxide solution during the reaction. Afterabove steps, 1.5 mL of pure glutaraldehyde was added into reac-tion flask to mix with the solution and stirred at 60 ◦C for 1.5 h.The precipitate was washed with petroleum ether, ethanol and dis-tilled water in turn until pH was about 7. The precipitate was thendried in a vacuum oven at 50 ◦C. The obtained product was magneticchitosan.

2.4. Preparation of molecularly imprinted and non-imprintedmagnetic chitosan

The molecularly imprinted magnetic chitosan (MIMC) was pre-pared as follows: 50 mL 0.5 mol/L AR solution was poured into250 mL three-neck flask. After that, 2 g magnetic chitosan wasadded. The mixture was stirred for 2 h, and then 5 mL of epichloro-hydrin solution was added to the above solution and mechanicallystirred for another 1 h. At the end of this period the resulted prod-uct was collected, washed with 0.1 mol/L NaOH and dried in anoven at 60 ◦C for 24 h. To prepare the desired adsorbent for ARsolution separation from dilute aqueous solutions, the templateAR molecules were leached out by stirring 1 g of MIMC particlesin 200 mL of 0.1 M NaOH solution for 24 h at 200 rpm and 30 ◦C.This step was repeated for 3 times to ensure maximum extractionof imprint molecule which would avoid its leaching in subsequentadsorption and extraction experiments.

Non-imprinted magnetic chitosan (NIMC) was prepared by thesame procedure in the absence of template AR molecules andtreated in the same manner.

2.5. Adsorption studies

All batch experiments were performed on a thermostatedshaker (THZ-98A) with a shaking of 150 rpm. The effects of thetemperature on dye removal were carried out in the 20 mL of AR(100 mg/L, pH 3.0) with 0.1 g of adsorbent at different temperature(30 ◦C, 40 ◦C, 50 ◦C) for 50 min. The influence of pH on AR removalwas studied by adjusting AR solutions (100 mg/L) to different pHvalues (1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 and 8.0) using a pH meter(DELTA-320) and agitating 20 mL of AR solution with 0.1 g of adsor-bent at 30 ◦C for 50 min. The effect of temperature on AR removalwas carried out in the 20 mL of AR solution (100 mg/L, pH 3.0) with0.1 g of adsorbent for 50 min.

For kinetic study, 100 mg/L AR solution (20 mL, pH 3.0) were agi-tated with 0.1 g of adsorbent at 30 ◦C for predetermined intervalsof time. Batch equilibrium adsorption experiments were carriedout by agitating 20 mL various concentrations of AR solution atpH 3.0 with 0.1 g of adsorbent at 30 ◦C until equilibrium wasestablished.

The samples were withdrawn from the shaker at predeterminedtime intervals and the dye solutions were separated from the adsor-bent by magnetic separation. The absorbencies of samples weremeasured using a UV–vis spectrophotometer (Specord 200). Thenthe concentrations of the samples were determined by using linearregression equation (A = 0.126 + 0.00404 × Ce, R2 = 0.9981) obtained

tions. The amounts of AR adsorbed onto samples were calculatedby subtracting the final solution concentration from the initial con-centration of AR solution.

2 es B: Biointerfaces 91 (2012) 250– 257

l

Q

wii

2

tdst

K

oM

2

aItewciwl7

2

tmomaAC

2

ttdta

3

3

Fa

Fig. 1. Scanning electron microscope of MIMC.

52 L. Fan et al. / Colloids and Surfac

The amount of AR adsorbed per unit mass of MIMC was calcu-ated from the following equation:

= (C0 − Ce)VW

, E = (C0 − Ce)C0

× 100%

here C0 and Ce are the initial and equilibrium concentrations of ARn milligrams per liter, respectively, V is the volume of AR solution,n liters, and W is the weight of the adsorbent used, in grams.

.6. Selective determination

The selectivity of MIMC and NIMC for AR over other dyes solu-ions were evaluated from the selectivity coefficient K, which wasetermined by incubating 0.1 g of beads with each individual dyesolutions present in 50 mL of distilled water under identical condi-ions.

The selectivity coefficient is defined as:

1 = Q1

Q2, K2 = Q1

Q3

Q1 (adsorption capacity of AR on MIMC), Q2 (adsorption capacityf AR on NIMC) and Q3 (adsorption capacity of dyes solutions onIMC).

.7. Desorption and regeneration studies

The desorption study is very important since the regeneration ofdsorbent decides the economic success of the adsorption process.n this study, several solvents/solutions were tried to regeneratehe biosorbents. 0.1 mol/L NaOH aqueous solution was found to beffective in desorbing AR from the loaded adsorbents. The beadsas regenerated using 0.1 mol/L NaOH aqueous solution, the pro-

edure was repeated for many times until AR could not be detectedn the filtrate. Then, MIMC was washed thoroughly with distilled

ater to a neutral pH. The regenerated MIMC was reused in the fol-owing adsorption experiments and the procedure was repeated for

times by using the same MIMC.

.8. Characterization of the samples

Microscopic observation of magnetic particles, magnetic chi-osan and dried MIMC was carried out by using a scanning electron

icroscope (S-2500, Japan Hitachi). FTIR spectra were measuredn a Nicolet, Magna 550 spectrometer. The magnetic chitosan wasixed with KBr and pressed to a pellet for measurement. Wide

ngle X-ray diffraction (WAXRD) patterns were recorded by a D8DVANCE X-ray diffraction spectrometer (Bruker, German) with au K� target at a scan rate of 0.02◦ 2� s−1 from 10◦ to 80◦.

.9. Replication of batch experiment

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

. Results and discussion

.1. Characterization of MIMC

The morphology of MIMC was observed by SEM. As shown inig. 1, the well shaped particles with diameter about 30 nm werechieved. Majority of the particles were spherical, which indicated

Fig. 2. IR spectra of chitosan (A), and MIMC (B).

MIMC had large surface area and large number of effective imprint-ing sites could exist in the surface to rebind the template moleculesin aqueous media.

Infrared spectra of chitosan and MIMC samples are shown inFig. 2. Curve A in Fig. 2 shows the IR spectrum of the chitosan. Themajor peaks for chitosan in Fig. 2A can be assigned as follows: theadsorption band around 3420 cm−1, revealing the stretching vibra-tion of N–H groups bonded with O–H groups in chitosan, and at1661 cm−1 confirms the N–H scissoring from the primary amine,due to the free amino groups in the crosslinked chitosan. The bandaround 1065 cm−1 is attributed to the combined effects of C–Nstretching vibrations of primary amines and the C–O stretchingvibrations from the primary alcohol of chitosan. The new peak ofMIMC in Fig. 2B is displayed near 580 cm−1 (characteristic peak ofFe3O4), which demonstrates that a layer of chitosan was formed onthe surface of magnetite particles.

XRD patterns of pure Fe3O4 and MIMC are shown in Fig. 3,indicating the existence of iron oxide particles (Fe3O4), which hasmagnetic properties and can be used for the magnetic separation.The XRD analysis results of pure Fe3O4 and MIMC were mostly coin-

cident. Six characteristic peaks for Fe3O4 (2� = 30.1, 35.5, 43.3, 53.4,57.2 and 62.5), marked by their indices ((2 2 0), (3 1 1), (4 0 0), (4 2 2),(5 1 1), and (4 4 0)), were observed in both samples.

L. Fan et al. / Colloids and Surfaces B: Biointerfaces 91 (2012) 250– 257 253

Fig. 3. XRD pattern of Fe3O4 (A) and MIMC (B).

8642

10

20

30

40MIMCNIMC

Qe/

mg.

g-1

pH

Ft

3

toApawdtoasco

wadw

D

d

R

1008060402000

5

10

15

20

25

30

35

40

100 mg/L50 mg/L

Qe/

mg.

g-1

t/min

1008060402000

1

2

3

4

5 100 mg/L 50 mg/L

t/Qe

t/min

A

B

ig. 4. Effect of pH on the adsorption capacity (initial concentration, 100 mg/L;emperature, 303 K; contact time, 50 min).

.2. Effect of pH value on adsorption

The pH of the aqueous solution, the most important parame-er on adsorption studies, strongly affects the adsorption propertyf beads for AR. Fig. 4 shows the effect of pH on the sorption ofR on the prepared absorbents. The dye uptake was increased asH decreased. The maximum adsorption values for AR onto MIMCnd NIMC were 39.5 mg/g and 17.6 mg/g at pH 3, respectively, fromhich the imprinting effect was greatly observed. The observedecrease in the uptake values at low pH (<pH 3) was attributed tohe decrease in AR dissociation which led to a lower concentrationf the anionic dye species available to interact with the MIMC’sctive sites. Above the optimum pH values, the MIMC displayed aharp decrease in the uptake value as pH increased. This behaviorould be explained on the basis of the lower extent of protonationf amino groups at high pH.

The mechanisms of the adsorption process of AR on the MIMCere due to be the ionic interactions of the colored dye with the

mino groups of the MIMC. In aqueous solution, the AR was firstissolved and the sulfonate groups of AR (D–SO3Na) dissociate andere converted to anionic dye ions.

–SO3Na ↔ D–SO3− + Na+

The amino groups of MIMC were protonated under acidic con-

itions according to the following reaction:

–NH2 + H+ ↔ R–NH3+

Fig. 5. (A) Effect of contact time on AR adsorption by MIMC; (B) pseudo-second-order kinetics for adsorption of AR (pH 3, temperature: 303 K).

In addition, under acidic conditions (pH < 3), the sulfonategroups (D–SO3

−) combined with H+, which decreased the adsorp-tion capacity of AR, according to the following reaction:

D–SO3− + H+ ↔ D–SO3H

As a result, the sorption processed proceeds through elec-trostatic interaction between the two counterions (R–NH3

+ andD–SO3

−) [28]:

R–NH3+ + D–SO3

− ↔ R–NH3+· · ·SO3-D

At pH 3, most of –NH2 groups were protonated, which werefavorable for the adsorpion of AR. However, at high pH, the num-ber of protonated –NH2 groups were decrease and more –OH wereavailable to compete with the anionic sulfonic groups, therefore theadsorption capacity for the AR decreases at high pH.

3.3. Adsorption kinetics

The effect of the contact time for MIMC on the adsorption capac-ity for AR is described in Fig. 5. Obviously, the adsorbent showed agood performance in adsorption during the first 40 min. The timerequired to achieve the adsorption equilibrium was only 50 min.There was no significant change from 1 h to 3 h.

The adsorption kinetics of AR onto MIMC are investigated

with two kinetic models, namely the Lagergren pseudo-first-orderand pseudo-second-order model. The Lagergren rate equation isone of the most widely used adsorption rate equations for the

2 es B: Biointerfaces 91 (2012) 250– 257

ak

l

wee

utfbpibw

w

a

watsmtfM(orc

aartITas

3

tauT

wQQm

1008060402000.0

0.5

1.0

1.5

2.0

2.5

Ce/Q

e

Ce/mg.L-1

5.04.54.03.53.02.52.0

2.6

2.8

3.0

3.2

3.4

3.6

3.8

lnQ

e

lnCe

A

B

54 L. Fan et al. / Colloids and Surfac

dsorption of solute from a liquid solution. The pseudo-first-orderinetic model can be expressed by the following equation [29]:

n(Qe − Qt) = ln Qe − K1t

here Qe and Qt refer to the amount of AR adsorbed (mg/g) atquilibrium and at any time, t (min), respectively, and K1 is thequilibrium rate constant of pseudo-first-order sorption (1/min).

The slope and intercept of the plot of log (Qe − Qt) versus t aresed to determine the first-order rate constant, K1. It was found thathe correlation coefficient (R2) had low value (<97%) for adsorbentsor AR concentrations studied and a very large difference existedetween Q (experimental) and Q (calculated), indicating a poorseudo-first-order fit to the experimental data. The inapplicabil-

ty of the pseudo-first-order model to describe the kinetics of ARy adsorption using adsorbents was also observed in some previousorks [30,31].

The another kinetic model is pseudo-second-order model,hich is expressed by [32]:

dQt

dt= K2(Qe − Qt)

2

Rearranging the variables gives,

dQt

(Qe − Qt)2

= K2dt

Integrating this equation for the boundary conditions t = 0 to t = tnd Q = 0 to Q = Qt, gives:

t

Qt= 1

(K2Q 2e )

+ t

Qe

here K2 is the equilibrium rate constant of pseudo-second-orderdsorption (g mg−1 min−1). The slope and intercept of the plot of/Qt versus t were used to calculate the second-order rate con-tant, K2 (Fig. 5B). The corresponding kinetic parameters from bothodels are listed in Table 1. The correlation coefficient (R2) for

he pseudo-second-order adsorption model has high value (>99%)or adsorbent. The calculated equilibrium adsorption capacity by

IMC is 43.08 mg/g, which is consistent with the experimental data40.12 mg/g) [33]. These facts suggested that the pseudo-second-rder adsorption mechanism was predominant, and that the overallate of the AR adsorption process appeared to be controlled by thehemisorption process [34].

In addition, the optimum contact time for adsorption of ARppeared to be 50 min. This could be attributed to the large surfacerea, the sufficient exposure of active sites and the high surfaceeactivity of the MIMC. The sorption of AR was rapid during the ini-ial stages of the sorption process, followed by a gradual process.n latter stages, however, the rate of AR adsorption became slower.he AR had to first encounter the boundary layer effect and thendsorb on the surface, and finally they had to diffuse into the poroustructure of the adsorbent which took a longer time.

.4. Evaluation of adsorption isotherm models

The equilibrium adsorption isotherm is fundamental to describehe interactive behavior between the solution and the adsorbentnd is important in designing an adsorption system. The widelysed Langmuir model has been found to fit the process successfully.he equation can be expressed as:

Ce

Qe= 1

(KLQ0)+ Ce

Q0

here Ce is the equilibrium concentration of AR in solution (mg/L),e is the adsorbed value of AR at equilibrium concentration (mg/g),0 the maximum adsorption capacity (mg/g), and KL is the Lang-uir binding constant, which is related to the energy of adsorption.

Fig. 6. (A) The linear dependence of Ce/Q on Ce; (B) the linear dependence of ln Qe

on ln Ce (pH, 3; temperature, 303 K; contact time, 50 min).

Plotting Ce/Qe against Ce gives a straight line with slope and inter-cept equal to 1/Q0 and 1/(KLQ0), respectively. It is described inFig. 6A.

By calculating, the results are as follows:

Ce

Qe= 0.023Ce + 0.3823, (R2 = 0.9925),

Q0 = 43.48 mg g−1, KL = 0.06 L mg−1

The value of Q0 obtained from Langmuir curves was mainly con-sistent with that experimentally obtained (40.12 mg/g), indicatingthat the adsorption process was mainly monolayer. The complex-ing adsorption mechanism for AR may give controlled monolayeradsorption.

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 = 1.885 + 0.4249 ln Ce, KF = 6.532,

1n

= 0.4249, R2 = 0.878

L. Fan et al. / Colloids and Surfaces B: Biointerfaces 91 (2012) 250– 257 255

Table 1Adsorption kinetic parameters of AR onto MIMC.

Initial conc. C0 (mmol/mL) Pseudo-first-order R2 Pseudo-second-order Qe,exp (mg/g) R2

K1 (min−1) Qe,cal (mg/g) Qe,cal (mg/g) K2 (g/(mg min))

24 20.84 0.0032 18.8 0.99425 43.08 0.0022 40.12 0.998

rARgAs

ib

R

afswo

wa

Frt

Table 2Thermodynamic parameters at different temperatures.

T (K) �G (kJ mol−1) �H (kJ mol−1) �S (J mol K−1)

303 −6.604 −16.48 −32.6

50 0.0316 13.26 0.8100 0.00308 21.14 0.9

The Langmuir and Freundlich adsorption constants and the cor-esponding correlation coefficients were gotten. The adsorption ofR was well fitted to the Langmuir isotherm model with the higher2 (0.99). It indicated the adsorption took place at specific homo-eneous sites within the adsorbent forming monolayer coverage ofR at the surface of the absorbent. The Freundlich constant 1/n wasmaller than 1, indicating a favorable process.

Furthermore, the essential characteristics of the Langmuirsotherm can be described by a separation factor, which is definedy the following equation:

L = 1(1 + KLCe)

The value of RL indicates the shape of the Langmuir isothermnd the nature of the adsorption process. It is considered to be aavorable process when the value is within the range 0–1. In thetudy, the value of RL calculated for the initial concentrations of ARas 0.16. Since the result is within the range of 0–1, the adsorption

f AR onto the adsorbent appears to be a favorable process.The observed decrease in both values of 1/T and ln(Qe/Ce)

ith elevated temperature indicates the exothermic nature of thedsorption process, which was shown in Fig. 7A. The values of

0.003300.003250.003200.003150.00310

2.2

2.3

2.4

2.5

2.6

2.7

lnQ

e/C

e

1/T

R2=0.963

86420

75

80

85

90

95

E/%

n/time

A

B

ig. 7. (A) Van’t Hoff plots for the uptake of AR dyes on the MIMC (A); (B) effect ofecycling adsorbents on AR adsorption (B) (pH, 3; initial concentration, 100 mg/L;emperature, 303 K; contact time, 50 min).

313 −6.278323 −5.952

ln(Qe/Ce) at different temperatures were treated according to Van’tHoff equation:

ln(

Qe

Ce

)= − �H

(RT)+ �S

R,

R is the universal gas constant (8.314 J/mol K) and T is the abso-lute temperature (in Kelvin). Plotting ln(Qe/Ce) against 1/T gives astraight line with slope and intercept equal to −�H/R and �S/R,respectively.

The negative value of �H (Table 2) shows exothermic nature ofadsorption process. Gibbs free energy of adsorption (�G) is calcu-lated from the following relation:

�G = �H − T�S

The negative value of �G (Table 2) indicated that the adsorptionreaction was spontaneous. The observed decrease in negative val-ues of �G with increasing temperature implied that the adsorptionbecame less favorable at higher temperatures.

3.5. Evaluation of the selective adsorption

For the purpose of evaluating the selectivity of the adsorbent, theselective adsorption studies were carried out under the optimumconditions. The results are shown in Table 3. Based on the resultsshown in Table 3, it can be seen that the adsorption capacity ofMIMC for AR was 3 times greater than that of NIMC. NIMC couldeasily adsorb other dyes as well as AR, it demonstrated that thespecific recognition cavities for AR created in MIMC unlike NIMC,which were developed by AR-imprinting. In the case of MIMC, thecavities created after removal of the template were complementaryto the imprint AR in size, shape and coordination geometries. It isevident that MIMC has a strong ability to selectively adsorb AR frommixed dyes in aqueous solution.

3.6. Effect of recycling adsorbents on AR adsorption

From practical application of view, reuse is a crucial factor for theadvanced adsorbent [35–37]. Such adsorbents have higher adsorp-tion capability as well as better desorption property which willreduce the overall cost of the adsorbents.

To evaluate the possibility of regeneration and reusabilityof MIMC as an adsorbent, the desorption experiments wereperformed. Desorption of AR from MIMC was demonstratedusing three different eluents, namely 0.01 mol/L NaOH, 0.1 mol/LNaOH, and 0.5 mol/L NaOH. It was found that the quantita-

tive desorption efficiencies using them were 85.3%, 93.5% and87.2%, respectively. The reusability was checked by following theadsorption–desorption process for three eluents, the 0.1 mol/LNaOH was the optimum eluent.

256 L. Fan et al. / Colloids and Surfaces B: Biointerfaces 91 (2012) 250– 257

Table 3Selective determination.

Interfering ions Adsorption capacity of AR (mg/g) K1 Adsorption capacity of different acid dyes (mg/g) K2

Q1 Q2 Q3 Q4

MIMC NIMC MIMC NIMC

Acid orange 7 36.89 12.13 3.04 12.28 19.65 3.002.563.122.59

rFsrutbtidab

4

ntipmpornicfi

A

S

R

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Acid orange 10 38.44 15.03

Methyl blue 37.26 11.93

Remazol black 5 35.64 13.78

The effect of recycling times on the adsorption process wasepeated 7 times, and the results are shown in Fig. 7B. It is shown inig. 7B that the uptake capacity of AR on the adsorbent decreasedlowly with increasing cycle numbers. The percentage adsorptionemained steady at about 90% in the first five cycles, and then theptake capacity of AR decreased. At the sixth regeneration cycle,he adsorption remained at 75%. These results show that the adsor-ents can be recycled for AR adsorption with 0.1 mol/L NaOH, andhe adsorbent can be reused. This could be ascribed to the fact that,n the basic solution, the positively charged amino groups wereeprotonated and the electrostatic interaction between chitosannd dye molecules became much weaker. Therefore, the MIMC cane reused for fifth dye adsorption.

. Conclusions

In the present investigation, the templated magnetic chitosananoparticles were prepared using the imprinting technique withhe AR as a template and evaluated as sorbents for AR. The max-mum adsorption capacity of MIMC for AR was 40.12 mg/g atH 3.0 and 30 ◦C. Adsorption of AR onto MIMC fitted the Lang-uir adsorption isotherms. The kinetics of adsorption followed a

seudo-second-order rate equation. An overall selectivity for ARbserved shows that MIMC can be used effectively to remove andecover AR from aqueous solutions. Furthermore, the templatedanoparticles could be regenerated through the desorption of AR

n 0.1 M NaOH solution and could be reused to adsorb AR. MIMCan be easily separated from aqueous solution by external magneticeld.

cknowledgment

This work was supported by the Shandong Provincial Naturalcience Foundation (Y2008B53).

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