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Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 5158

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l homepage: www.elsevier .com/ locate /colsur fa

pH dependence and thermodynamics ofHg(II) adsorption onto

chitosan-poly(vinyl alcohol) hydrogel adsorbent

Xiaohuan Wang a,1, Ruzhong Sun b,, Chuanyi Wang a,

a Key Laboratory of Functional Materials andDevices for Special Environments of CAS, Xinjiang TechnicalInstitute of Physics & Chemistryof CAS, 40-1

South Beijing Road, Urumqi 830011, PR Chinab College of Chemistryand Pharmacy Engineering, Nanyang NormalUniversity, 1638 WolongRoad, Nanyang 473061, PR China

h i g h l i g h t s

CTS-PVA hydrogel adsorbent showed

superior adsorption properties for

Hg(II) ions. pH influence and theromodynamics

of Hg(II) adsorption on the hydrogel

adsorbent was studied. Functional groups responsible for

Hg(II) adsorption changed with the

pH ofsolutions. The binding force between Hg(II) and

functional groups was strengthened

at high temperatures. Results obtained in this study may

provide a scientific and engineering

basis for Hg(II) removal.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:

Received 2 June 2013

Received in revised form 25 August 2013

Accepted 29 August 2013

Available online 6 September 2013

Keywords:

pH dependence

Thermodynamics

Chitosan/poly(vinyl alcohol) hydrogel

adsorbent

Hg(II)

Adsorption

a b s t r a c t

The chitosan/poly(vinyl alcohol) (CTS-PVA) hydrogel adsorbent with three-dimensional network struc

ture showed superior adsorption properties for Hg(II) ions. The pH influence study showed Hg(II

adsorption on the hydrogel adsorbent is strongly pH-dependent. The adsorption capacity in pH 2.0

solution (200.20 mg/g) is higher than that in pH 11.00 solution (140.27 mg/g), which indicated that Hg(II

adsorption on the hydrogel adsorbent was not only by electrostatic interactions. FT-IRspectral analysi

before and after Hg(II) adsorption represented that the functional groups responsible for Hg(II) adsorp

tion changed with the pH of solutions. Thermodynamic studies revealed that Hg(II) adsorption on th

hydrogel adsorbent is a favorable, spontaneous, and endothermic chemisorption process. The bindin

force between Hg(II) ions and functional groups was strengthened at high temperatures, which mad

the adsorption more favorable at high temperatures. The adsorption process fitted well by the Langmui

and the Freundlich isotherm models. The Langmuir maximum adsorption capacity increased from 697.7

to 950.62 mg/g with increasing temperature from 20to 60 C. This study will contribute to an in-deptunderstanding ofadsorption phenomena, and provide a scientific and engineering basis for the practica

application ofthe CTS-PVA hydrogel adsorbent.

2013 Elsevier B.V. All rights reserved

Corresponding author. Tel.: +86 377 63525056. Corresponding author. Tel.: +86 991 3835879; fax: +86 991 3838957.

E-mail addresses: wxh0377@ms.xjb.ac.cn(X. Wang), nysrzh@163.com (R. Sun),

cywang0991@163.com (C. Wang).1 Tel.: +86991 3835879; fax: +86991 3838957.

1. Introduction

Allmercury compoundsare known to be highlytoxic chemicals

Inorganic mercury has been reported to produce harmful effect

in culture medium at 5g/L. It exists in two ionic states: Hg(Iand Hg(II). Hg(II) or mercuric salts, are much more common i

the environment than Hg(I) or mercurous salts [1]. Hg(II) can b

0927-7757/$ see front matter 2013 Elsevier B.V. All rights reserved.

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52 X.Wang et al. / Colloids and Surfaces A: Physicochem.Eng. Aspects 441 (2014) 5158

methylated by reducing bacteria in anoxic habitats and trans-

formed into methylmercury (MeHg+ orMe2Hg). So, it is considered

as the most toxic form of mercury [2]. Recently, great efforts have

been made to develop methods that can effectively remove Hg(II)

ions from wastewater, andat thesame time, recover itscompounds

in a more concentrated form to avoid the second pollution after

removing them from the water [3]. The use of adsorbents pos-

sessing selectivity toward Hg(II) ions makes good contributions

to achieving this target. Polymer adsorbents containing ligandssuch as nitrogen-containing functional groupsare often used in the

selective removal of Hg(II) from aqueous solutions [46].

Chitosan (CTS), a copolymer that is primarily composed

of(14) linked 2-amino-2-deoxy-d-glucopyranose units, andresidual 2-acetamido-2-deoxy-d-glucopyranose units, is a biopoly-

mer of the most widely studies on heavy metal removal. It shows

outstanding adsorption capacity for Hg(II) ions ranging from 430

to 1127mg/g especially in pH close to neutral, due to the presence

of large number of functional groups (acetamido, primary amino

and/or hydroxyl groups) with high chemical reactivity in its chem-

ical structure [5,7,8]. However, the protonation of amino groups

results in CTS dissolution in acidic solutions, which limits CTS to be

used as an adsorbent in acidic media. In addition, the amine groups

of CTS do not have good adsorption selectivity for different metal

ions [9]. All of these determine CTS is not a satisfying adsorbent for

the selective removal of Hg(II) ions from wastewater [10].

Poly(vinyl alcohol) (PVA), a semicrystalline hydrophilic poly-

mer, is usually used to blend with CTS to obtain a variety of

materials with good mechanical and chemical properties, such as

hydrogels [11,12], blend foams [13], blend/composite membranes

or films [14], blend beads [15,16], etc. The addition of PVA can

improve the mechanical property and reduce the brittleness of the

dried sample. Meanwhile, hydroxyl groups in PVA polymer struc-

ture may contribute to the adsorption for heavy metal ions. These

materials have been widely studied in the removal of heavy metal

ions such as lead, copper, silver and cadmium ions from water

or wastewater [11,12]. However, little attention has been paid to

investigating their adsorption characteristics for mercury ions.

Our previous studies showed that the CTS-PVA hydrogel adsor-bent prepared by a glutaraldehyde cross-linking in combination

with an alternate freeze-thawed process demonstrated superior

adsorption properties for Hg(II) ions [17]. The hydrogel adsor-

bent contains NH2, NHCOCH3 and C N groups as well as OH

groups. It can selectively adsorb Hg(II) ions from multi-component

solutions with high efficiency. The CTS-PVA hydrogel adsorbent

containing 30wt.% PVA showed moderate mechanical property,

excellent adsorption properties, and the most important is, it had

no leaching in solutions. So, it was thereby selected as an objective

adsorbent for typical adsorption experiments in the present work.

The present work focused on the pH dependence and adsorption

mechanisms of the CTS-PVA hydrogel adsorbent for Hg(II) ions in

differentpH solutions,as well as the detailed adsorption thermody-

namics. This study will contribute to an in-depth understanding ofadsorption phenomena and open up an effective way for mercury

removal from water.

2. Experimental

2.1. Materials

CTS (industrial grade, the degree of deacetylation was 75%,

and the average molecular weight was 3105 g/mol) was pur-

chased from Zhejiang Golden-Shell Biochemical Co. Ltd. (Zhejiang,

China). PVA(industrialgrade, the degree of hydrolysis was99% and

the average degree of polymerization was 1700) was provided by

Lanzhou Xinxibu Vinylon Company Ltd (Gansu, China). Glutaralde-

hyde with a concentration of 25%, mercuric acetate and other

chemicalswere of analyticalgrade andcommerciallyobtainedfrom

Tianjin Kermel Chemical Reagent Co., Ltd (Tianjin, China). Aqueous

solutions were all prepared with Millipore water (18.25 M/cm).

2.2. Preparation

The CTS-PVA hydrogel adsorbent with a three-dimensional net-

work structure waspreparedaccording to our previous report[17].

Its schematic network structure and the digital photo of the dried

samplewere shown in Fig.1. The sampleusedfor adsorption exper-

iments was milled and sieved through an 80-mesh screen.

2.3. Adsorption experiments

The adsorption experiments were carried out by adding certain

amount of the driedsampleinto a simulatedwastewater containing

Hg(II) ions at a desirable concentration and pH value, and then the

mixture was shaken in a thermostatic shaker bath at an appropri-

ate temperature until the adsorptiondesorption equilibrium was

established. The pH of solutions was adjusted by the dilute acetic

acid or sodium hydroxide solution and measured by a pH meter

(Mettler Toledo 320).Forinvestigating theeffectof theinitial pH (pH0) of solutions on

adsorption, a pH range from 2.00 to 11.00 was selected, and a con-

centrationof 85.56mg/L wasselected as the initial concentration of

Hg(II) solution to avoid precipitation of Hg(II) ions. For equilibrium

adsorption experiments at different temperatures (20, 30, 40, 50

and 60C), Hg(II) solutions with a concentration range from about

500mg/L to 2500mg/L were used, and the mixture was shaken in

a thermostatic shaker bath for 24h to ensure the equilibrium to be

established.

The concentration of mercury in solutions was determined by

an atomic fluorescencespectrophotometer (AF-640,Beijing Beifen-

gruili Analytical Instrument Co., China). The adsorption capacity of

the adsorbent sample for Hg(II) ions at a given time tor at equilib-

rium can be derived using the following equation:

q =(C0 C) V

m , (A.1)

where q is the amountof Hg(II) adsorbed at time tor at equilibrium

(mg/g), C0 is the initial Hg(II) concentration (mg/L), Cis the Hg(II)

concentration at time tor at equilibrium (mg/L), m is the mass of

the adsorbent used (g) and Vis the volume of Hg(II) solution used

(L).

2.4. Characterization

2.4.1. The determination of the isoelectric point (pI)

Theisoelectricpoint(pI)of theCTS-PVA hydrogel adsorbentwasdetermined by the solid addition method [18]. 0.1mol/L NaCl solu-

tion was used as electrolytic solution in this study. The pH value

of the solution was adjusted with 0.1 mol/L NaOH or 0.1 mol/L HCl

solutions to cover a range from 2 to 12 in approx 2pH unit incre-

ments. To 25mLNaCl solutions with the desired initial pH value

(pH0), 0.1000 g CTS-PVA hydrogel adsorbent samples were added.

Then theconical flasks were securely cappedimmediately. The sus-

pensions were manually shaken andallowed to equilibrate for48 h

with intermittent manual shaking at room temperature. The final

pH value (pHf) of each supernatant fluid was determined again.

By plotting the difference between the pH0and the pHf(i.e., pH,which equals pH0minus pHf) versus pH0, a curve can be obtained.

The pH value which is corresponding to pH= 0 in the resulting

curve is the pI of the sample.

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Fig. 1. Schematic structure(A) and digital photo (B)of theCTS-PVA hydrogel adsorbent.

2.4.2. Fourier transform infrared spectroscopy (FTIR)

The FTIR spectra of the CTS-PVA hydrogel adsorbent before and

after Hg(II) adsorption were recorded using a Fourier transform

infrared spectrometer (FTS-165, BIO-RAD, USA). All the sampleswere prepared as potassium bromide tablets, and the range of the

scanning wavenumbers was 5004000cm1.

2.4.3. Surface area analysis

The surface area of the CTS-PVA hydrogel adsorbent were ana-

lyzed by a nitrogen adsorptiondesorption method at 77K using

a surface area analyzer (Micromeritics, ASAP 2020). The pretreat-

ment conditions are 105 C and vacuum for 3h. The surface area

was calculated by the BrunauerEmmertTeller (BET) equation.

3. Results and discussion

3.1. pH dependence and adsorption mechanisms of the hydrogel

adsorbent for Hg(II) ions

3.1.1. Effect of the pH0of solution on adsorption

The determination of the isoelectric point (pI) of an adsorbent is

necessary for further elucidating the adsorption mechanism. So, a

preliminary test of pI wasdetermined by thesolid addition method

[18]. Result showed that the pI of the sample was 7.85. Therefore,

in the solution of pH value below 7.85, the particle surface of the

hydrogel adsorbent is positively charged. Otherwise, the surface is

negatively charged [18].

The effect of the pH0 of solution on Hg(II) adsorption was

shown in Fig. 2. The pH-dependent curve showed two peaks

and a minimum, which revealed the strong pH-dependence ofHg(II) adsorption on the hydrogel adsorbent. Previous study about

lead (II) adsorption on CTS-PVA hydrogel bead also showed a

similar phenomena [12]. The adsorption capacity in pH 2.00

solution (200.20mg/g) is higher than that in pH 11.00 solution

(140.27mg/g), whichindicatedthat Hg(II) adsorption on the hydro-

gel adsorbent was not only by electrostatic interactions, because

that, the positively charged surface of the adsorbent in pH 2.00

solution was not as favorable as the negatively charged surface

in pH 11.00 solution for the adsorption of Hg(II) cations. The high

adsorption capacity of the adsorbent in pH 2.00 solution also indi-

cated that there must be more than one mechanismresponsiblefor

Hg(II) adsorption on the hydrogel adsorbent. Our previous study

has revealed that both chelation and ion exchange contributed to

Hg(II) adsorption on the CTS-PVA hydrogel adsorbent [17].

3.1.2. Analysis of adsorption mechanisms under different pH

conditions

In order to further illustrate the nature of Hg(II) adsorption o

the hydrogel adsorbent under different pH conditions, FT-IR spectra of the dried sample before and after adsorption in different pH

solution were compared.

Firstly, we compared FT-IR spectra of the hydrogel adsorben

before and after adsorption in pH 2.00 acetic acid and mercuri

acetate solutions, respectively (Fig. 3). It was found that, com

pared with the FT-IR spectrum of the unloaded sample (Fig. 3a)

the FT-IR spectrum of the sample after adsorption in pH 2.00 aceti

acid solution (Fig. 3b) showed several obvious spectral changes

The characteristic peak of the N H stretching vibration situate

at about 3372cm1 obviously shifted to the higher wavenum

ber (3403 cm1). Meanwhile, the characteristic peaksof the C O

stretching vibration (shifted from 1651 to 1635cm1), the N H

deformation vibration (shifted from 1598 to 1557cm1) and

the C N stretching vibration ( shifted from 1420 to 1384 cm

1

strongly shifted to the lower wavenumbers. These changes may b

caused by the binding of NH2 and NHCOCH3 groups with pro

tons to form complexes (Eqs. (B.1) and (B.2)), and thereby leading

the surface of the sample to be positively charged [12].

R NH2 +H+ R NH3

+ (B.1

Fig. 2. pH0 effect on the adsorption of the CTS-PVA hydrogel adsorbent for Hg(I

ions. Adsorption experimentsC0 : 85.56mg/L; sample dose: 0.0100g/50mL; th

range ofpH0: 2.0011.00; temperature: 30C; contact time: 24h.

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Fig. 3. FT-IR spectra of the unloaded CTS-PVA hydrogel adsorbent (a), the sample

after being dipped in pH 2.00 acetic acid solution (b) and the sample after Hg(II)

adsorption in pH 2.00 mercuric acetate solution (c), respectively.

NH CCH3

O

+ H+ CH3C

O

NH2+

R

R

(B.2)

Compared with FT-IR spectra of the unloaded sample (Fig. 3a)

and the sample after adsorption in pH 2.00 acetic acid solution

(Fig. 3b), the FT-IR spectrum of the adsorbent after adsorption

in pH 2.00 mercuric acetate solution (Fig. 3c) showed several

new changes. The characteristic peaks of the saccharide structure

stronglyshifted to the lowerwavenumbers.Meanwhile, the charac-

teristic peak of the C H stretching vibration shifted tothe higher

wavenumbers (2935 cm1).These indicated thatfreependant OH

groups in the polymer structure should interact with Hg(II) ions in

pH 2.00 mercuric acetate solution. The possible chemical reaction

was given as follows:

R OH + Hg2+ (R OH)Hg2+ or (R OH)2Hg2+ (B.3)

Despite that, several other spectral changes were observed inFig, 3c when compared with Fig. 3a. The characteristic peak corre-

sponding to the C O and C N stretching vibration shifted from

1651cm1 to 1641cm1, which is not as obvious as that observed

in Fig.3b. Thismaybeindicatethe interaction of NHCOCH3groups

and C N groups with Hg(II) ions, because that the C N group is a

milder basic ligand than NH2 or OH groups and it can interact

with a verysoft acidsuch asHg(II) ions. The reaction between C N

groups and Hg(II) ions has been confirmed by our previous study

[17] and other related researches [19]. It was given as follows:

RCH N R' + (CH3COO)2Hg RCH HgOOCCH3

R'

N

(B.4)

The characteristic peak of the N H deformation vibration in

Fig.3c nearly disappeared completely when compared withFig. 3b.

This may be due to the reaction between NHCOCH3 groups and

Hg(II) ions, which was given as follows:

R NH CCH3+(CH3COO)2Hg CH3C

O

N

R

HgOOCCH3orCH3C N Hg N CCH3R

O OO

R (B.5)

Secondly, we compared FT-IR spectra of the hydrogel adsorbent

before and after adsorption in different pH mercuric acetate solu-

tions (shown in Fig. 4). Itcan be seen that, compared with the FT-IR

spectrum after adsorption in pH 2.00 mercuric acetate solution

Fig. 4. FT-IR spectra of the unloaded CTS-PVA hydrogel adsorbent (a) and samples

after Hg(II)adsorptionin differentpH solutions(b: pH 2.00; c: pH 5.00; d: pH 7.00;

e: pH9.00; f: pH11.00).

(Fig. 4b), the FT-IR spectrum after adsorption in pH 5.00 mercuric

acetate solution (Fig. 4c) showed several more obvious changes.

Except for the obvious changes of the characteristic peaks of thesaccharide structure, C N groups and NHCOCH3 groups, the

characteristic peaks of the N H stretching vibration obviously

shifted to the higher wavenumber (from 3398 to 3428 cm1).

Meanwhile, the characteristic peaks of the C H stretching

vibration near 2935 cm1 and the C H symmetrical deformation

vibration at 1417cm1 and 1381cm1 evidently shifted to the

lower wavenumbers. These indicated that free pendant NH2groups may also interact with Hg(II) ions when the sample was

dipped in pH 5.00 mercuric acetate solution. The possible chemical

reaction was given as follows:

2R NH2 +Hg2+ (R NH2)2Hg

2+ (B.6)

The FT-IR spectra after Hg(II) adsorption in pH 7.00 and 9.00

mercuric acetate solutions were very similar (Fig. 4d and e). Com-

pared with the FT-IR spectrum of the unloaded sample (Fig. 4a),

the obvious shifts of the FT-IR spectra after Hg(II) adsorption in

pH 7.00 and 9.00 mercuric acetate solutions mainly concentrated

on the characteristic peaks of the N H stretching vibration, the

C O stretching vibration, the N H deformation vibration and

the C N stretching vibration.These indicated NH2, NHCOCH3,

and C N groups may allparticipatein Hg(II)adsorption under such

pH conditions.

Compared with Fig. 4a, the FT-IR spectrum after Hg(II) adsorp-

tion in pH 11.00 (Fig. 4f) only showed an obvious shift of the

characteristic peak of the N H stretching vibration in NH2groups. This implied NH2 groups may be the main functional

groups responsible for Hg(II) adsorption in pH 11.00 mercuric

acetate solutions. According to the research of Li and Bai [12], OH

ions can be adsorbed onto the surface of the CTS-PVA hydrogeladsorbent through hydrogen bonds when the pH of solutions is

higher than its pI, and thereby lead to the surface of the adsorbent

negatively charged (Eq. (B.7)) [12].

R NH2 +OH R NH2. . .OH

(B.7)

So, in solutions which pH value is higher than the pI of the

adsorbent, the negative charged surface of the adsorbent will

facilitate Hg(II) ions being adsorbing by the electrostatic interac-

tion.

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Table 1

Parameters associated with Hg(II) adsorption on the CTS-PVA hydrogel adsorbent at different temperatures. (T: K; qm,exp: mg/g;KL: L/g; aL: L/mg;qm,cal: mg/g; S:m2/g; G

kJ/mol; H: kJ/mol; S: kJ/(mol K);KF:L/mg.).

T qm,exp The Langmuir model S RL G H S The Freundlich model

KL aL qm,cal R2 KF n R2

293 697.70 7.0215 0.0092 763.36 0.9973 87.056 0.16300.0429 4.748 94.5606 0.2925 0.9979

303 723.87 10.8378 0.0141 769.23 0.9979 87.726 0.11280.0284 6.003 134.227 0.2492 0.9970

313 741.31 15.6397 0.0202 775.19 0.9984 88.405 0.08160.0200 7.156 48.183 0.179 173.1929 0.2174 0.9972

323 837.25 41.4079 0.0484 854.70 0.9987 97.473 0.03570.0084 9.999 307.7797 0.1532 0.9972

333 950.62 71.1238 0.0754 943.40 0.9976 107.590 0.02320.0054 11.806 401.7723 0.1319 0.9892

3.2. Adsorption thermodynamics

3.2.1. Adsorption isotherms

The adsorption isotherms of Hg(II) adsorption on the CTS-PVA

hydrogel adsorbent at different temperature were presented in

Fig. 5. The isotherm shapes are consistent with the favorable

adsorption equilibrium patterns proposed by Weber et al. [20].

This suggested the adsorption process of Hg(II) adsorption on the

hydrogel adsorbent should be a favorable process. Such anticipa-

tionwas also confirmed by the equilibrium parameterRLcalculated

in the following section. The increase of the adsorption capacity

with increasing temperature indicated that the adsorption processof the CTS-PVA hydrogel adsorbentfor Hg(II) ionswas endothermic.

3.2.2. Adsorption isotherm analysis

The analysis of isothermdata is veryimportant for developingan

equation which canaccurately representthe results andbe used for

design purposes. The adsorption data obtained in this study were

analyzed by the well-known and widely applied isotherm models,

namely, the Langmuir and the Freundlich isotherm models.

The Langmuir model. The Langmuir model is perhaps the most

straightforward non-linear isotherm model. It is predicated on

the assumptions that the energy of sorption for each molecule is

the same and independent of surface coverage. And that sorption

occurs only on localizedsites and involves no interactions between

adsorbed molecules [20]. The Langmuir model is usually expressedas follows [21]:

qe =x

m =

KLCe(1+ aLCe)

, (A.2)

wherex is theamount of Hg(II) ions adsorbed (mg),m is theamount

of adsorbent used (g),Ce(mg/L) andqe(mg/g) are the liquid phase

Fig. 5. Adsorption isotherms of Hg(II) adsorption on the CTS-PVA hydrogel

adsorbent at different temperatures. Adsorption experimentsthe range of C0:

02500 mol/L; sample dose: 0.0500 g/25mL; pH0: 5.50; the range of temperature:

2060 C; contact time: 24h.

concentration and solid phase concentration of Hg(II) ions at equi

librium, respectively.

At low surface coverage, the Langmuir isotherm reduces to

linear relationship. The most common linear form of the Langmui

model is formulated as:

Ceqe

=1

KL+ (

aLKL

)Ce, (A.3

where KL(L/g) andaL(L/mg) are the Langmuir isotherm constants

respectively, and aLrelates to the energy of adsorption. When Ce/q

is plotted against Ce, a straight line will be obtained. The value ofK

can be obtained from the intercept which is 1/KL, and the value oaL can be obtained from the slope which is aL/KL. The maximum

adsorption capacity of the adsorbent, qm,cal, i.e., the equilibrium

monolayer capacity or saturation capacity, is numerically equal t

KL/aL. The Langmuir parameters of Hg(II) adsorption on the CTS

PVA hydrogel adsorbent at different temperatures were listed i

Table 1.

From Table 1, it can be seen that the linear correlation

coefficients (R2) at different temperatures are all close to 1. Thi

indicatedthat the adsorption process fitted well with the Langmui

model. So, it can be considered that Hg(II) ions were adsorbed with

a monolayer on the particle surface of the adsorbent. The Langmui

maximum adsorption capacity (qm,cal) increased from 697.70 to

950.62mg/g with the temperature of solutions increasing from 2

to 60C, which reflected the endothermic nature of the adsorption

process again. Compared with other adsorbents (Listed in Table 2

[2229], the Langmuir maximum adsorption capacity of the CTS

PVA hydrogel adsorbent are quite high. This indicated the CTS-PVA

hydrogel adsorbent is a superior adsorbent that can be used for th

removal of Hg(II) from aqueous solutions. The value ofaLincreased

from0.0092L/mg to 0.0754 L/mgwith increasingtemperature from

20 to 60 C, which indicated the binding force between Hg(II) ion

Table 2

A comparison of themaximumadsorption capacityof theadsorbents forHg(II) ion

Adsorbent Maximum adsorption

capacity (mg/g)

Source

Chitosan adsorbent (which is

crosslinked with glutaraldehyde)

145 (25C) [22]

Modified magnetic chitosan

adsorbents (which is crosslinked with

glutaraldehyde and functionalized

with magnetic nanoparticles (Fe3O4))

152 (25C) [22]

The polyaniline/attapulgite (PANI/ATP)

composite

800 (25C) [23]

A chitosanthioglyceraldehyde Schiffs

base cross-linked magnetic resin

(CSTG)

982 [24]

The cross-linked magnetic

chitosan-phenylthiourea (CSTU) resin

1353 [25]

The chitosanECH matrix 621.83 [26]

The polyaniline/humic acidcomposite 671 [27]

The PPyRGO composite 980 [28]

The ethylenediamine-modified

magnetic crosslinking chitosan

microspheres (EMCR)

539.59 [29]

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Fig. 6. Plot ofRLagainst C0at different temperatures. Adsorption experimentsthe

range ofC0: 02500mol/L; sample dose: 0.0500g/25mL; pH0: 5.50; the range of

temperature: 2060C; contact time: 24h.

and functional groups of the hydrogel adsorbent was strengthened

at a higher temperature. This further substantiated the endother-

mic nature of the adsorption process.

The dimensionless constant separation factor or equilibrium

parameter, RL, is another factor that can express the essential fea-

tures of the Langmuir isotherm. It is defined by the following

relationship [30]:

RL =1

1+ (KL/qm)C0 . (A.4)

For favorable adsorption process, the value of RL should be

ranged from 0 to 1. If the value of R L is beyond 1, it implies that

the adsorption process is unfavorable. The value of RLof Hg(II)

adsorption on the CTS-PVA hydrogel adsorbent changed with C0was shown in Fig. 6, and the values of R L at different temper-

atures were given in Table 1. Values of RL were in the range of

01, which indicatedthe adsorption process of the hydrogel adsor-

bent for Hg(II) ions is favorable again. Values of RLdecreased with

the increase of the temperature suggested the adsorption is more

favorable at high temperatures.

The Freundlich model. The Freundlich model is an empirical

equation and perhaps the most widely used nonlinear sorption

equilibrium model. This model applies to adsorption onto hetero-

geneous surfaces with a uniform energydistribution and reversible

adsorption. Moreover, this model is not restricted to the formation

of the monolayer. Thats to say, the amount of adsorbate adsorbed

on the adsorbent will increase in case of increasing the adsorbate

concentration in the solution.The Freundlichmodel has the generalform as follows [31]:

qe = KFCne , (A.5)

whereKFis the Freundlichconstantwhich relates to sorption capac-

ity(L/mg),n is the heterogeneity factor whichrelatesto the sorption

intensity. KFand n are empirical constants which is dependent on

several environmental factors. The value ofn ranges from 0 to 1,

andindicates thedegree of non-linearity between thesolutioncon-

centration and the adsorption. If the value ofn is equal to 1, the

adsorption is linear. If the value is below 1, the adsorption process

is chemical. If the value is above 1, the adsorption is a favorable

physical process. The more heterogeneous the surface, the closer

the value ofn is to 0 [12,32].

For determination of these empirically derived constants, the

Freundlich model is usually expressed the logarithmic form as fol-

lows:

log(qe) = n log(Ce) + log KF. (A.6)

KFand n can be determined from the slope and intercept of the

linear plot of log(qe) versus log(Ce). The Freundlich parameters of

Hg(II) adsorption on the CTS-PVA hydrogel adsorbent at different

temperatures were listed in Table 1.From Table 1, it can be seen that the linear correlation

coefficients (R2) at different temperatures are close to 1, which

indicated that the Freundlich model can also be used to describe

the adsorption process of the CTS-PVA hydrogel adsorbent for

Hg(II) ions. The values ofn decreased from 0.2925 to 0.1318 with

increasing temperature from 20 to 60C. This suggested that the

adsorption process of Hg(II) ions on the hydrogel adsorbent is

chemical, and the surface of the adsorbent is more heterogeneous

at high temperatures.

3.3. The specific surface area of the hydrogel adsorbent toward

Hg(II) ions binding

The Langmuir monolayer saturation capacity (qm,cal, mg/g) cal-culated from the Langmuir equation (Eq. (A.3)), i.e., the ultimate

adsorption capacity at high concentrations, can be used to esti-

mate the specific surface area (S, m2/g) of the CTS-PVA hydrogel

adsorbenttoward Hg(II) binding, usingthe following equation[33]:

S =qm,calNA

1000M , (A.7)

where N is Avogadro constant, 6.021023 mol1, A is the cross-

sectional area of metal ion (m2), M is the molar weight of

Hg(II) ions, 200.59g/mol. According to the radius of Hg(II) ion

(1.101010 m), the cross-sectional area of Hg(II) ion was cal-

culated to be 3.801020 m2. The specific surface areas of the

hydrogel adsorbenttowardHg(II) binding at differenttemperatures

were calculated and listed in Table 1.From Table 1, it can be seen that the specific surface area of

the hydrogel adsorbent toward Hg(II) ions binding increased with

increasingtemperature.This indicatedthat Hg(II) adsorptionon the

hydrogel adsorbent is chemisorption. The BET specific surface area

of the sample was determined to be 14.724m2/g, which is much

smaller than the binding specific surface area calculated. This fur-

ther confirmed the chemisorption nature of the adsorption process.

3.4. Thermodynamic parameters

Withthe helpof equilibrium dataobtainedat different tempera-

tures, thermodynamicparameters such as Gibbs freeenergy change

(G, J/mol), enthalpy change (H, J/mol) and entropy change (S,

J/(mol K)) of the adsorption process of the CTS-PVA hydrogel adsor-bent for Hg(II) ions can be determined by Gibbs equation and Vant

Hoff equation listed as follows:

G = RT ln KL, (A.8)

ln KL =H

(RT) +

S

R , (A.9)

where KLis the equilibrium constant obtained from the Langmuir

model (L/g),Tis the absolute temperature (K), R is the universalgas

constant (8.314J/(mol K)). The values ofHand Scan be deter-

mined from the slope and the intercept of the plot of ln(KL) versus

1/T. The plotand thermodynamic parametersof the adsorption pro-

cess of the hydrogel adsorbent for Hg(II) ions were shown in Fig. 7

and Table 1, respectively.

5/25/2018 hidrogel

7/8

X. Wang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 5158 5

Fig. 7. The plot of ln(KL) versus1/T.

The linear correlation coefficient (R2) obtained from Fig. 7 was

0.9807. It is very close to 1. Such a good linear relationship made

the calculation of the values ofHand Saccording to Eq. (A.9)

possible.The values ofG are all negative at all temperatures. This indi-

cated that the adsorption process was spontaneous. The reduced

values ofG with increasing the temperature suggested the spon-taneous nature is improved at higher temperature. The positive

value ofHsuggested the adsorption process was an endothermicprocess. The positive value ofSindicated the entropy of the sys-

temincreased after adsorption, that is to say, therandomness at the

solidliquid interface increased. This unusual phenomenon may be

owing to the fact that the desolvation disturbs the structure of the

reaction medium and promotes the disorganization of the system

during the formation process of complex. It was also observed by

Weber et al. [20] and Guerra et al. [34].

4. Conclusions

Hg(II) adsorption on the CTS-PVA hydrogel adsorbent is a favor-

able, spontaneous, and endothermic chemisorption process. The

pH of solution had a great effect on Hg(II) adsorption on the hydro-

gel adsorbent. The adsorption mechanisms and functional groups

responsible for Hg(II) adsorption changed with the pH of solutions.

In lower pH solutions, chelation between functional groups and

Hg(II)ionswas the mainmechanism.Free pendant OHgroupsand

C N g roups a s w ell a s NHCOCH3groupswere themain functional

groups responsible for Hg(II) adsorption. When pH of solution was

close to thepI ofthe hydrogel adsorbent,freependant OH, NH2and NHCOCH3groups aswell asC N groupsallinvolved inHg(II)

adsorption. While in solutions which pH was much higher than the

pI of the hydrogel adsorbent, electrostatic interaction played animportant role. Both chelation and electrostatic interaction made

contributions to Hg(II) adsorption, and free pendant NH2groups

became the main functional groups responsible for Hg(II) adsorp-

tion. The binding force between Hg(II) ions and functional groups

was strengthened at higher temperature, and thereby the adsorp-

tion was more favorable at high temperature. Hg(II) adsorption on

thehydrogeladsorbent canbe well explainedby both theLangmuir

and the Freundlich isotherm models.

Acknowledgements

This work is financial supported by the Western Light Pro-

gram of the Chinese Academe of Sciences (XBBS201116), the

National Natural Science Foundation of China (21107133), and the

One Hundred Talents program of Chinese Academy of Science

(1029471301).

References

[1] D.W. Boening, Ecological effects, transport, and fate of mercury: a generareview, Chemosphere 40 (2000) 13351351.

[2] I. Wagner-Dobler, Pilotplant for bioremediation of mercury-containingindustrial wastewater, Appl. Microbiol. Biotechnol. 62 (2003) 124133.

[3] N. Li, R.B. Bai, C.K. Liu, Enhanced and selective adsorption of mercury ions ochitosanbeads graftedwith polyacrylamide viasurface-initiatedatom transferadical polymerization, Langmuir 21 (2005) 1178011787.

[4] S. Kagaya, H. Miyazaki, M. Ito, K. Tohda, T. Kanbara, Selective removal of mercury(II) from wastewater using polythioamides, J. Hazard. Mater. 175 (201011131115.

[5] P. Miretzky, A. Fernandez Cirelli, Hg(II) removal from water by chitosan anchitosan derivatives:A review, J. Hazard. Mater. 167(2009) 1023.

[6] H.B. Sonmez, B.F. Senkal, N. Bicak, Poly(acrylamide) grafts on spherical beapolymers for extremely selectiveremovalof mercuric ions fromaqueoussolutions,J. Polym.Sci Part A: Polym.Chem.40 (2002)30683078.

[7] A. Bhatnagar, M. Sillanpaa, Applications of chitin- and chitosan-derivativefor the detoxification of water and wastewater a short review, Adv. ColloiInterfaceSci. 152 (2009) 2638.

[8] G.Crini,Recentdevelopments inpolysaccharide-basedmaterialsusedas adsorbents in wastewatertreatment, Prog. Polym. Sci. 30 (2005)3870.

[9] E. Guibal, Interactions of metal ions with chitosan-based sorbents: a reviewSep. Purif. Technol. 38 (2004)4374.

[10] G. Crini, P.-M. Badot, Application of chitosan, a natural aminopolysaccharide, for dye removal from aqueous solutions by adsorption processes usinb atch s tudie s: a re view of r ecent liter ature , Pr og . Po lym. Sci. 33 (20 08399447.

[11] T. Wang, M. Turhan, S. Gunasekaran, Selected properties of pH-sensitivebiodegradable chitosanpoly(vinyl alcohol) hydrogel, Polym. Int. 53 (2004911918.

[12] L. Jin,R.B. Bai,Mechanismsof leadadsorption on chitosan/PVAhydrogel beadsLangmuir 18 (2002) 97659770.

[13] X. Wang, Y.S. Chung, W.S. Lyoo, B.G. Min, Preparation and properties of chitosan/poly(vinyl alcohol) blend foams for copper adsorption, Polym. Int. 5(2006) 12301235.

[14] H.A.Shawky,Synthesis of ion-imprintingchitosan/PVA crosslinked membranfor selectiveremoval of Ag(I), J. Appl. Polym.Sci. 114 (2009)26082615.

[15] M. Kumar, B.P. Tripathi, V.K. Shahi, Crosslinked chitosan/polyvinyl alcohoblend beads for removal and recovery of Cd(II) from wastewater, J. HazardMater. 172 (2009)10411048.

[16] W.S.W. Ngah, A. Kamari, Y.Koay, Equilibriumand kineticsstudiesof adsorptioof copper(II) on chitosan and chitosan/PVA beads, Int. J. Biol. Macromol. 3

(2004) 155161.[17] X. Wang, W. Deng, Y. Xie, C. Wang, Selective removal of mercury ions using

chitosanpoly(vinyl alcohol) hydrogel adsorbent with three-dimensional network structure, Chem. Eng. J. 228 (2013) 232242.

[18] L.S. Balistrieri, J.W. Murray, The surface-chemistry of goethite (alpha-FeOOHin majorion seawater, Am.J. Sci. 281 (1981) 788806.

[19] R.S. Vieira, M.L.M. Oliveira, E. Guibal, E. Rodriguez-Castellon, M.M. BeppuCopper, mercury and chromium adsorption on natural and crosslinked chtosan films: an XPS investigation of mechanism, Colloids Surf. A 374 (2011108114.

[20] W.J. Weber, P.M. McGinley, L.E. Katz, Sorption phenomena in subsurface systems concepts,models and effects on contaminant fateand transport, WateRes. 25 (1991) 499528.

[21] I. Langmuir, The constitution and fundamental properties of solids and liquidparti solids, J. Am. Chem. Soc. 38(1916) 22212295.

[22] G.Z. Kyzas, E.A. Deliyanni, Mercury(II) removal with modified magnetic chtosan adsorbents, Molecules18 (2013) 61936214.

[23] H.Cui,Y. Qian,Q. Li,Q. Zhang,J. Zhai,Adsorptionof aqueous Hg(II)bya polyanline/attapulgite composite, Chem. Eng. J. 211212 (2012) 216223.

[24] M. Monier, Adsorption of Hg2+, Cu2+ andZn2+ ionsfrom aqueous solutionusinformaldehydecross-linked modifiedchitosan-thioglyceraldehydeschiffs baseInt. J. Biol. Macromol. 50 (2012) 773781.

[25] M. Monier, D.A. Abdel-Latif, Preparation of cross-linked magnetic chitosanphenylthiourea resin for adsorption of Hg(II), Cd(II) and Zn(II) ions fromaqueous solutions, J. Hazard. Mater. 209210(2012) 240249.

[26] R.B. Rabelo, R.S. Vieira, F.M.T. Luna, E. Guibal, M.M. Beppu, Adsorption ocopper(II) and mercury(II) ions onto chemically-modified chitosan membranes equilibrium and kinetic properties, Adsorpt. Sci. Technol. 30 (2012122.

[27] Q. Li, L. Sun, Y. Zhang, Y. Qian, J. Zhai, Characteristics of equilibrium, kineticstudiesfor adsorptionof Hg(II) andCr(VI)by polyaniline/humicacid compositDesalination 266 (2011) 188194.

[28] V. Chandra, K.S. Kim, Highly selective adsorption of Hg2+ by a polypyrrolereduced graphene oxide composite, Chem. Commun. 47 (201139423944.

[29] L. Zhou, Z. Liu, J. Liu, Q. Huang, Adsorption of Hg(II) from aqueous solutioby ethylenediamine-modified magnetic crosslinking chitosan microsphere

Desalination 258 (2010) 4147.

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