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Colloids and Surfaces A: Physicochem. Eng. Aspects 461 (2014) 151–157

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l h om epage: www.elsev ier .com/ locate /co lsur fa

nfluence of dissolved oxygen on Fe(II) and Fe(III) sorption ontohitosan

na Gyliene ∗, Rima Binkiene, Mykolas Baranauskas, Genrik Mordas, Kristina Plauskaite,idmantas Ulevicius

enter for Physical Sciences and Technology, A. Gostauto 9, LT-01108 Vilnius, Lithuania

i g h l i g h t s

Of all the iron ions only Fe(III) aresorbed by chitosan. Fe(II) removalfrom solutions proceeds after its oxi-dation to Fe(III).The dissolved oxygen and increasingvalues of pH favour the conversion ofFe(II) ions into Fe(III).Iron ion removal from solutions pro-ceeds due to the formation of bondsbetween the –OH groups of chitosanand Fe(III) ions.

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

r t i c l e i n f o

rticle history:eceived 6 May 2014eceived in revised form 20 July 2014ccepted 21 July 2014

a b s t r a c t

The Fe(II) and Fe(III) ions uptake by chitosan is distinguished by rapid sorption kinetics in comparisonwith that of other heavy metals such as Cu(II) and Ni(II).

The correlation between the kinetics of dissolved oxygen and Fe(II) ions sorption by chitosan points tothe different sorption mechanisms for Fe(II) and Fe(III). The consumption of dissolved oxygen corresponds

vailable online 30 July 2014

eywords:hitosanorption

to the sorbed Fe(II) quantities indicating its conversion to Fe(III). Only Fe(III) is sorbed by chitosan. Thesorption proceeds by the interaction of these ions with –OH groups of chitosan.

© 2014 Published by Elsevier B.V.

ron ionsissolved oxygen

. Introduction

In recent years chitosan has been very intensively inves-igated due to its unique properties such as biocompatibility,iorenewability and biodegradability. Chitosan, poly(1→4)-2-mino-2deoxy-d-glucopyranose is a deacetylated derivative ofatural polymer chitin. The functional groups such as amino,

ydroxyl, acetamide present in the chitosan chain determine itsorption properties.

∗ Corresponding author. Tel.: +370 5 2729127; fax: +370 5 2649774.E-mail addresses: gyliene@ktl.mii.lt, onagyliene@gmail.com (O. Gyliene).

ttp://dx.doi.org/10.1016/j.colsurfa.2014.07.027927-7757/© 2014 Published by Elsevier B.V.

The main reason of the limited use of chitosan as a sorbent inpractice is its low sorption rate in comparison with that of syntheticion exchangers [1–5]. The intrinsic physical structure of chitosandetermines a slow diffusion inside chitosan particles and, as a con-sequence, a slow sorption rate. In order to increase the availablesites for sorption different means have been proposed: a decreasein particle size, an increase in porosity, reduction in crystallinity,deposition on inert materials (sand, glass particles), etc. It has beenshown [6–9] that the granulation of chitosan to microsize alsohas an insignificant effect on sorption kinetics. The sorption rate

and capacity remarkably increase only when the nanosize chitosanmaterial (nanoparticles and nanofibres) is used [10–12].

Chitosan usually is characterized by the deacetylation degree(DD) and molecular weight (MW), which in main are determined by

1 Physic

totoro

R

icoca

tneoimTg

tpbtiit

sto

2

2

ttftopwp

wwipamhia

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r

Ni(II).The unusual course of Fe(III) sorption could be due to the affinity

of Fe(III) to the –OH groups of chitosan. In this case the micropre-cipitation of the insoluble Fe(III) compounds onto the surface of

52 O. Gyliene et al. / Colloids and Surfaces A:

he number of functional groups in the chitosan chain. The presencef amino groups determines the complexation of transition metals,herefore, the hazardous heavy metals ions are selectively sorbednto chitosan; meanwhile innocuous metal ions (K, Na, Ca, Mg, etc.)emain in the solution [13–15]. However, the amine groups (–NH2)f chitosan react easily with H+ according to the equation:

NH2 + H+ ↔ RNH3+ (1)

The protonation constant of this reaction equals to ∼6.3. Thus,n the case of the sorption of transition metals in acidic solutions aompetition between the coordination reactions and protonationf amino groups proceeds. At pH∼3 the amino groups are almostompletely protonated. Therefore, the transition metal sorption incidic solutions is very weak.

On the other hand, the protonation of amino groups capacitateshe sorption of substances possessing a negative charge, such asitrate, fluoride, metal oxyanions (arsenate, molybdate, vanadate,tc.), anions of organic acid (citrate, tartrate) [16–18]. The sorptionf complicated organic compounds such as dyes, pharmaceut-cals, etc is stipulated by the complex electrostatic, donor–acceptor,

olecular interactions between the sorbent and sorbate [19,20].he role of –OH group in the sorption process is much less investi-ated.

However, a major part of the works done in this field concernshe kinetic parameters and sorption capacity of chitosan for variousollutants. The detailed interactions between the sorbate and sor-ent are investigated to a much less degree. It could be suspectedhat some types of the interactions are not sufficiently conceptual-zed as it is in the case of Fe(II) and Fe(III) sorption [21,22]. Chitosanntensively sorbs both iron ions despite a weak interaction betweenhe chitosan–NH2 and –OH groups with Fe(II).

Our investigations have also shown the capability of chitosan toorb oxygen from solutions. This work was done with the purposeo determine the influence of the presence of oxygen in solutionsnto the sorption peculiarities of Fe(II) and Fe(III) onto chitosan.

. Experimental

.1. Sorption experiments

Chitosan flakes with the deacetylation degree of about 80% andhe molecular weight of 2,50,000 and powder with the deacetyla-ion degree of 75% and the molecular weight of 24,50,000 producedrom crab shells (“Sonat”, Russia) were used for experiments. Chi-osan after keeping for 1 day in distilled water for swelling was putn a glass filter for water removal. When the experiments wereerformed in acidic solutions, chitosan was treated and adjustedith an H2SO4 solution until a desirable pH value was reached. Sorepared it was used for sorption experiments.

All the experiments were carried out under batch conditionsith solutions containing CuSO4, NiSO4, Fe2(SO4)3 or FeSO4. pHas adjusted with an H2SO4 solution. Adsorption was performed

n tightly closed 100 ml vessels at room temperature (20 ± 2 ◦C) byouring the metal ions containing solutions onto 0.1–1 g of chitosannd occasional mixing. In the case of Fe(III) sorption the experi-ents were carried out no longer as 15 min especially at pH values

igher 2.7 due to possible precipitation of insoluble Fe(OH)3. Exper-ments were performed 3–5 times achieving standard errors 3–5%t a confidence of 95%.

The sorbed quantities of Cu(II), Ni(II) and Fe(II) were determined

rom the changes in their concentrations in solutions using chem-cal analysis.

Cu(II) concentrations in solutions were determined photomet-ically at � = 440 nm using diethyldithiocarbamate as an indicator.

ochem. Eng. Aspects 461 (2014) 151–157

Ni(II) concentrations were determined photometrically at� = 490 nm using dimethylglyoxime as an indicator.

Fe(II) in solutions was determined using o-nitrophenantroline[23] which enables determination Fe(II) in the concentrationrange 0.01 to 0.1 mg L−1 with an accuracy of 0.001 mg L−1.O-nitrophenantroline makes the colored complex with Fe(II) stablewith the maximal absorption at � = 490 nm meanwhile the com-plex with Fe(III) is weak and colorless. Fe(III) in solutions wasdetermined after its reduction to Fe(II) with hydroxylamine anddetermination of the total amount of Fe(II) and Fe(III).

2.2. Oxygen sorption from solutions

For determination of dissolved oxygen concentration in thesolutions, chitosan was put into a 330 ml vessel fully filled withdistilled water and tightly plugged with an electrode sensitive tooxygen concentrations up to 0.01 mgO2 L−1. It was registered bymeans of an oxymeterOxi level 2.

2.3. FT-IR investigations

The infrared spectra of chitosan were recorded in KBr pellets ona Fourier transformation infrared spectrometer (Hartman & Braun,Canada) with 2 cm−1 scale resolutions. The spectra were recordedin the wave number region between 4000 and 500.

3. Results and discussion

In order to clarify possible interactions between chitosan andFe(II) and Fe(III) during the sorption process the kinetic compara-tive studies of sorption metal ions forming stable amino complexessuch as Cu(II) and Ni(II), weak amino complexes such as Fe(II) andnot forming amino complexes such as Fe(III) were performed. Themeasurement of residual metal ions concentrations in solutionsgave some unexpected results (Fig. 1). The most rapid adsorptionproceeds in the case of Fe(III) ions. Fe(II) ions are sorbed some-what slower. The slowest sorption is in the case of Ni(II). UsuallyCu(II) forms more stable amino complexes as compared to Ni(II),therefore the Cu(II) sorption rate is somewhat higher than that of

Fig. 1. Heavy metal ion uptake by chitosan flakes from their 1 mmol L−1 solutionsat pH 3. Load 10 g·L−1.

O. Gyliene et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 461 (2014) 151–157 153

F ′ ′

flF

conMctpc

shWiedpaccsf

t

FfltE

ig. 2. pH influence on Fe(III) (1and 1 ) and Fe(II) (2 and 2 ) sorption on chitosanakes (1 and 2) and chitosan powder (1′ and 2′). Equilibrium time 15 min. Initiale(II) or Fe(III) concentrations 100 mg L−1. Load 1 g L−1.

hitosan is possible. The surprising thing is that the sorption kineticf Fe(II) resembles that of Fe(III) (Fig. 1). At pH∼3 Fe(II) ions formeither stable amino complexes nor insoluble hydroxo compounds.oreover, the colour of the sorbent during Fe(II) sorption rapidly

hanges to red-brown, which is also characteristic of Fe(III) sorp-ion. It could be suspected that a rapid conversion of Fe(II) to Fe(III)roceeds in the bulk of solution or even directly onto the surface ofhitosan.

Experiments performed under equilibrium conditions witholutions containing Fe(III) or Fe(II) ions indicated that pH valuesave a decisive influence on the uptake of iron ions by chitosan.ith increase in pH the sorbed quantities of Fe(III) ions sharply

ncrease; meanwhile the influence of pH on Fe(II) sorption is mod-rate (Fig. 2). The sorbed amounts of iron ions onto chitosan alsoepend on the form of chitosan. The sorption ability of chitosanowder is much higher than that of chitosan flakes. Taking intoccount that the deacetylation degree and molecular weight of bothhitosan forms are close, the reason of such an effect probably is aonsiderably larger surface area of powder in comparison with theurface area of flakes and as a result a much higher value of the

unctional groups available for sorption.

The sorption ability of chitosan also depends on the concen-ration of metal ions in the solution (Fig. 3). When the initial

ig. 3. Influence of Fe(II) concentration on its sorption peculiarities onto chitosanakes (1, 2) under equilibrium conditions and pH changes (1′ , 2′): 1 and 1′ in dis-illed water solutions; 2 and 2′ in solutions containing 20 g L−1 Na2SO4. Initial pH 2.quilibrium time 24 h. Load of chitosan 1 g L−1.

Fig. 4. Isotherm of Fe(II) removal by chitosan flakes from distilled water and solu-tions containing 20 g L−1 Na2SO4. Initial pH 2. Load of chitosan 1 g L−1.

concentrations of Fe(II) are low (up to 10 mg L−1), the sorbed quan-tities of iron ions are also low. The changes in pH also proceed withsorption. However, they increase from the initial pH 2 to pH 6–7 atFe(II) concentration ∼30 mg L−1 and only to pH ∼3 at Fe(II) concen-trations 100–150 mg L−1. This significant increase in pH values atlow sorbed quantities hardly could be explained by the protonationof amino groups of chitosan with release of OH− groups from water.It should be taken into account that before sorption chitosan wastreated with H2SO4 until a constant value pH 2 of chitosan suspen-sion was reached. The peculiarity of Fe ion sorption from solutionis that after sorption of about 1 mmol g−1 of iron ions the limit ofsorption is reached; a further increase in Fe(II) concentration doesnot increase the sorption capacity of chitosan. The margin of pHchange is also reached. Such sorption is unusual for heavy metalswhen the sorbed metal quantities correspond to the quantity ofavailable amino groups.

Unexpected results were obtained when the ionic strength ofsolutions was increased. The addition of sodium sulphate to solu-tions containing Fe(II) ions caused an increase in both the sorptionrate and sorption ability of chitosan (Figs. 3 and 4). Usually anincrease in ionic strength causes a decrease in sorption ability forpollutants when they are removed due to electrostatic or donor-acceptor interactions. Thus, this effect of background electrolyteindicates, that the mechanism of iron ion sorption onto chitosansubstantially differs from that of other heavy metal sorption.

The sorption peculiarities were evaluated by testing the exper-imental data according to the Langmuir (Fig. 4) and Freundlichisotherms. The Langmuir isotherm describes the sorption in thecase of monolayer coverage

qe = KaqmCe

1 + KaCe,

Where Ka is the Langmuir constant, qm is the maximum sorp-tion corresponding to the monolayer coverage, and Ce and qe arethe equilibrium concentrations of adsorbate in the solution and inthe sorbent, respectively. In the linear form this equation could bepresented as

Ce 1 Ce

qe=

Kaqm+

qm.

The plotting Ce/qe versus Ce enables to determine Ka and qm.

154 O. Gyliene et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 461 (2014) 151–157

Table 1Parameters of the Langmuir and Freundlich equations for ligand sorption onto chi-tosan under the conditions of Fig. 4.

Langmuir equation Freundlich equation

Ka (L mg−1) qm R2 KF (L g−1) 1/n R2

q

l

cts

siwAf

ipc(tre

Fts∼c

ssp

e

Fc

the decrease in Fe(II) concentration in solutions; meanwhile Fe(III)concentration after a sharp decrease at the initial stage remains

Curve 1 166 40 0.9555 302 −3.3 0.912Curve 2 201 44 0.991 123 −1.04 0.647

The equilibrium data were tested for the Freundlich model.

e = KFCe1/n

Its linearization enables to determine the constants KF and 1/n.

og (qe) = log (KF) + 1n

log (Ce) ,

According to the adsorption theory the constant KF indicates thehitosan sorption capacity when the concentration of adsorbate inhe solution is equal to 1 mol L−1. The coefficient 1/n represents theorption intensity and adsorbent heterogeneity.

The parameters calculated applying these two models are pre-ented in Table 1. Higher values of the regression coefficients R2

n the case of Langmuir model indicate that the sorption proceedsith formation of a monolayer of sorbate on the chitosan surface.

sound explanation in this case could be that only the surfaceunctional groups of chitosan participate in sorption.

For better understanding of the sorption mechanism of ironons the measurements of dissolved oxygen concentrations wereerformed. A somewhat higher sorption rate is observed onto ahitosan powder (Fig. 5, curve 1) as compared to that onto flakesFig. 5, curve 2). Despite a slow sorption of oxygen onto chitosanhe dissolved oxygen from water after certain time is completelyemoved. Moreover, chitosan flakes are capable of sorbing somextra quantities of oxygen (Fig. 5, 3) from a new portion of water.

The sorption kinetics of oxygen correlates with the kinetics ofe (II) ion removal from the solution (Fig. 6A) It should be notedhat FeSO4 salts always contain some Fe(III). Analysis of preparedolutions showed that the Fe(III) content was about 9 mg L−1in1 mmol L−1 FeSO4. In closed vessels these concentrations did not

hange with time.Remarkably, that Fe(III) sorption (Fig. 6B) is faster than Fe(II)

orption onto chitosan. Moreover, in this case any changes in dis-

olved oxygen concentration do not proceed during the sorptionrocess.

Simultaneous measurements of dissolved oxygen in the pres-nce of chitosan in Na2SO4 solutions, when only oxygen sorption

ig. 5. Oxygen sorption onto chitosan powder (1) and flakes (2); second sorption ofhitosan powder (3) Load of chitosan 3 g L−1.

Fig. 6. Dissolved oxygen concentration and residual total Fe ions concentrationsduring Fe(II) (A) and Fe(III) (B) sorption by chitosan at the initial pH 2,7 and a chitosanload of 3 g L−1.

onto chitosan proceeds, and in FeSO4 solutions (Fig. 7), whenFe(II) sorption proceeds in addition to oxygen sorption, showeda more rapid decrease in dissolved oxygen concentration in thecase of FeSO4, solutions. Remarkably, its decrease correlates with

nearly constant ∼3 mg L−1 during the whole sorption time and laterafter some days. It could be supposed that the equilibrium Fe(III)

Fig. 7. Dissolved oxygen concentrations (1, 2) during sorption in Na2SO4 (1) andFeSO4 solutions (2) and residual Fe(II) (3) and Fe(III) (4) concentrations during sorp-tion by chitosan at pH 2,7 and a chitosan load of 1 g L−1.

O. Gyliene et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 461 (2014) 151–157 155

Table 2Summation of the results of Fe(II) and Fe(III) sorption onto chitosan.

Initial sorption conditions Conditions after 6 h sorption

Load, (g L−1) Fe ion concentration(mg L−1)

pH Residual Fe ionconcentration (mg L−1)

O2 consumption(mg L−1)

pH Ratio between sorbedFeII) andO2 consumption, mol:mol

3.5 Fe(II) 102 3 69 4.2 5.5 0.59:0.273.5 Fe(II) 55 3 28 3.3 5.5 0.48:0.21

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the saccharide ring. Usually, the peak at 1560 cm is assigned to–N–H deformation vibration indicating the presence of free aminogroups in chitosan.

700 1200 1700 2200 2700 3200 3700

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1

2

3

1 Fe(II)55 3.2 30

1 Fe(III)60 3 2

1 Fe(III)60 2.7 10

oncentrations in the bulk of the solution and onto the surface iseached. The Fe(II) ion sorption process proceeds with a remark-ble increase in pH. The reason could be Fe (II) oxidation to Fe (III)y dissolved oxygen according to the equation

Fe2+ + 0.5O2 + 2H+ = 2Fe3+ + H2O. (2)

However, in closed vessels without a chitosan load any changesn the concentrations of iron ions and dissolved oxygen as well asn pH values do not proceed. Significant changes take place onlyn the case when chitosan is present in the solution. Evidentlyhitosan enhances the decrease in oxygen concentration in FeSO4olutions. Possibly, chitosan acts as a catalyst in this reaction [24].t could be assumed that the sorbed oxygen onto the chitosan sur-ace interacts with Fe(II) forming insoluble Fe(III) compounds. Thisssumption is supported by the correlation between the concen-rations of removed dissolved oxygen and Fe(II) ions. There alsoxists a possibility of the catalytic effect of chitosan in the reactionf Fe(II) conversion to Fe(III) in the bulk of solution and the formede(III) is rapidly sorbed by chitosan.

The results of the sorption of Fe(II) under equilibrium condi-ions presented in Table 2 show a basic difference between Fe(II)nd Fe(III) sorption. Fe(II) sorption is related to the consumptionf dissolved oxygen, but, more importantly with the ratio close to.5 mol of oxygen to 1 mol of sorbed Fe(II). Taking into account thatxygen is capable of giving 2 electrons in the redox reaction, it cane anticipated that in the sorption process Fe(II) is completely oxi-ized to Fe(III). In the case of Fe(III) sorption any changes in theoncentration of dissolved oxygen do not proceed.

The values of pH also can vary in both directions. In the case ofe(II) sorption it increases; meanwhile in the case of Fe(III) sorp-ion it decreases. Reaction (2) could be the reason of pH increase inhe case of Fe(II) sorption, while solely Fe(III) precipitation could behe reason of the decrease in pH values in the case of Fe(III) sorp-ion onto the chitosan surface; meanwhile sulphate ions remainn the solution. Despite the set constant initial amount of chitosanefore its application for sorption, the amino groups of chitosanlso could have some influence on the pH changes during sorption.he release of H+ ions from chitosan during sorption is also pos-ible. The results presented suggest that Fe(III) is only sorbed byhitosan, Fe(II) sorption proceeds only after its oxidation to Fe(III).

In order to evaluate possible chemical interactions, kineticeasurements were carried out, as well. The reaction order was

alculated according to the pseudo first order equation [25]

n(qe − qt) = ln qe − k1t

nd the pseudo-second order equation [27]

t

qt= 1

k2q2e

+ t

qe,

where qe is the amount of iron ions or oxygen sorbed onto chi-

osan under equilibrium conditions, mg g−1, qt is the amount ofigand sorbed onto chitosan at time t, mg g−1, k1 is the rate con-tant of pseudo first order reaction, h−1, and k2 is the rate constantf pseudo-second order reaction, g mg−1 h−1.

3.2 4.7 0.44:0.20 2.7 –0 2.4 –

The pseudo-first order equation indicates that the sorption ratedepends only on sorbate concentration. The calculations accordingto this kinetic equation showed that the plots are far from linearand the process is more complicated.

The application of a pseudo-second order model provides amuch better correlation of the experimental data in comparisonwith a pseudo-first order model (Table 3). The pseudo-second ratemodel fits over the whole time interval. The model is based onthe assumption that chemical sorption involving valency forcesthrough sharing or exchange of the electrons between the sorbentand the sorbate may be the rate limiting step. In our case it couldbe interactions of oxygen or Fe(III) with the functional groups ofchitosan or the interaction of sorbed oxygen with Fe(II) ions.

A better fit of the sorption kinetic to the pseudo-second ordermodel than to the first one also indicates the complexity of thesorption process of Fe ions onto chitosan.

Fig. 8 displays FT-IR spectra of initial chitosan powder (spec-trum 1), after the sorption of Fe(II) ions (spectrum 2) and afterthe sorption of Cu(II) (spectrum 3). Chitosan powder demon-strates the –OH broad stretching with a maximum at 3432 cm−1,the amide I bands at 1632 cm−1 with a shoulder in the range of1566–1546 cm−1, which could be assigned to the amide II band,the C–H stretching band at 2878 cm−1, the bridge oxygen stretch-ing band at 1156 cm−1, and the C–O stretching bands in the regionof 1070–1120 cm−1 characteristic of –C–O stretching vibrations in

−1

Wavenumbe r, cm-1

Fig. 8. IR absorbance spectra of chitosan powder (1), after sorption of Fe(II) (2) andCu(II) (3).

156 O. Gyliene et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 461 (2014) 151–157

Table 3The rate constants and correlation coefficients in kinetic experiments.

Figure and Curve mark Pseudo-first orderreaction parameters

Pseudo-second orderreaction parameters

k1 (h−1) R2 k2 (mg−1 h−1) R2

Fig. 1 Cu(II) 117 0.739 1.5 0.928Ni(II) 96 0.598 1.9 0.905Fe(II) 113 0.598 0.23 0.983Fe(III) 147 0.684 0.07 0.989

Fig. 5 Curve 1 0.038 0.853 0.25 0.936Curve 2 0.040 0.899 0.13 0.956Curve 3 0.041 0.636 0.14 0.996

Fig. 6A Curve Fe (total) 25 0.625 0.005 0.958Curve O2 1.9 0.835 0.51 0.888

Fig. 6B Curve Fe 33 0.858 0.26 0.883Curve O2 ∼0 0.020 – –

Fig. 7 Curve 1 0.013 0.596 0.12 0.982Curve 2 0.09 0.877 0.42 0.925

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In the case when Fe(II) is sorbed, the shoulder in the region566–1546 cm−1 disappears and a new distinct peak appears at

wavenumber of 1535 cm−1; meanwhile the peak at 1632 cm−1 isot influenced. The emergence of this peak could be connected to aigh basicity of amide oxygen which should have a strong affinityo Fe(III) ions. A strong effect of Fe(II) on the chitosan spectrum isbserved also at wavenumbers of 2800 to 3432 cm−1. In this regione(II) diminishes the absorption intensity and shifts the last peako more positive values (3444 cm−1) indicating strong interactionsetween the –OH groups and Fe(II) ions. Besides, the changes in thebsorption bands in the region 1200–900 cm−1 also show possiblenteractions of the hydroxyl groups of chitosan with iron ions afterorption.

After Cu(II) sorption the peak at 3432 cm−1 weakens and themide bands 1632 cm−1 and shoulder 1566–1546 cm−1 move toore positive values 1636 cm−1 and 1580–1570 cm−1, respec-

ively, indicating the Cu(II) interactions both with the amine groupsnd –OH group. The involvement of both –NH2 and –OH groups inhe case of the Ni(II) sorption process was convincingly shown byhe authors of paper [26].

The data presented on the Fe(II) and Fe(III) sorption evidentlyhow that Fe(II) and Fe(III) sorption onto chitosan is influenced byissolved oxygen and the presence of oxygen containing groups

n chitosan and considerably differs from the other heavy metalorption.

. Conclusions

Comparative studies of Cu(II), Ni(II), Fe(II) and Fe(III) sorptionnto chitosan have shown a difference in the sorption of heavyetals and iron ions from the solution.The correlation between the kinetics of dissolved oxygen and

e(II) ions sorption by chitosan points to the different sorptionechanisms for Fe(II) and Fe(III). It could be suspected that Fe(II) is

xidized by dissolved oxygen to Fe(III), then its sorption proceedsy the interaction of these ions with the –OH groups of chitosan.

cknowledgment

This work was partly supported by the European Social Fundgency under EUREKA project E!5808 BIOSOEX No. VP1-3.1-SMM-6-V-01-003.

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