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Hydrogels as a Potential Chromatographic System:Absorption, Speciation, and Separation of ChromiumSpecies from Aqueous MediaOzgur Ozay a , Nahit Aktas b & Nurettin Sahiner a ca Chemistry Department , Faculty of Sciences and Arts, Canakkale Onsekiz Mart University ,Canakkale, Turkeyb Chemical Engineering Department , Faculty of Engineering, Yuzuncu Yil University , Van,Turkeyc Nanoscience and Technology Research and Application Center (NANORAC) , Canakkale,TurkeyAccepted author version posted online: 27 May 2011.Published online: 08 Jun 2011.

To cite this article: Ozgur Ozay , Nahit Aktas & Nurettin Sahiner (2011) Hydrogels as a Potential Chromatographic System:Absorption, Speciation, and Separation of Chromium Species from Aqueous Media, Separation Science and Technology, 46:9,1450-1461, DOI: 10.1080/01496395.2011.560918

To link to this article: http://dx.doi.org/10.1080/01496395.2011.560918

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Hydrogels as a Potential Chromatographic System:Absorption, Speciation, and Separation of ChromiumSpecies from Aqueous Media

Ozgur Ozay,1 Nahit Aktas,2 and Nurettin Sahiner1,31Chemistry Department, Faculty of Sciences and Arts, Canakkale Onsekiz Mart University,Canakkale, Turkey2Chemical Engineering Department, Faculty of Engineering, Yuzuncu Yil University, Van, Turkey3Nanoscience and Technology Research and Application Center (NANORAC), Canakkale, Turkey

Hydrogels with highly charged forms and amphiphilic character,based on an anionic monomer 2-acrylamido-2-methyl-1-propansulfonic acid sodium salt (AMPSNa) and a cationicmonomer 3-acrylamidopropyltrimethylammoniumchloride (APT-MACl), were synthesized via a photo-polymerization techniqueand investigated for potential use in the separation of chromium spe-cies with different oxidation states. They were used for three mainpurposes. First, a single chromium species was successfully removedfrom an aqueous medium in the presence of other forms using theappropriate design and synthesis of the hydrogels. Secondly, thecopolymerized p(AMPSNa-co-APTMACl) hydrogels were used toremove two chromium species simultaneously from an aqueousmedium. Lastly, in addition to speciation of the chromium species,their separation and removal by an externally applied magnetic fieldusing magnetically responsive hydrogels was demonstrated.

Keywords chromium species separation; hydrogel; magnetic-composite; removal; speciation

INTRODUCTION

In nature, chromium is found in two stable forms, namelychromium (III) and chromium (VI) (1). Of these, hexavalentchromium is highly toxic, carcinogenic, and damages mostbiological systems (2). The other form, trivalent chromium,can be found in trace amounts in organisms including plantsand animals. Cr (VI), the more potent form of chromium,has a high oxidation potential (3). Although there are afew beneficial industrial applications of chromium such asin the textile, tanning (4), and chrome steel industries (5),they all in one way or another pollute the environment bygenerating waste containing forms of chromium. Chro-mium, as well as being one of the most abundant naturally

occurring elements, can diffuse through rocks, soil, volcanicdust, and gases into the environment causing serious threatto living species (6). The determination and removal of chro-mium (VI) species in different chemical structures such asHCrO�

4 ; Cr2O2�7 and CrO2�

4 ;, (7) from waste waters andfrom environmental samples is more difficult compared toother types of toxic metals (8). By using modern instrumen-tal techniques (9) such as inductively coupled plasma-atomicemission spectrometry (ICP-AES), inductively coupledplasma-mass spectrometry (ICP-MS), electro-thermalatomic absorption spectrometry (ETAAS), and flameatomic absorption spectrometry (FAAS), only the totalamount of chromium can be determined. To determineamounts of chromium and its derivatives ion chromato-graphy (IC) should be used (10). In the spectrophotometricdetermination and separation of chromium (III) and chro-mium (VI) species, complex-forming substances must beused (1,11). For the derivation and separation of the twochromium forms, methods such as ion-exchange, solventextraction, co-precipitation, electrochemical separation,selective volatilization and liquid-liquid extraction (1,12–15), as well as cloud point extraction, and solid phase extrac-tion (SPE) (16,17) are generally utilized. The removal ofchromium species in any form from aqueous media is anextremely important issue and a very difficult task. To deter-mine the source of pollution is exceptionally important forthe prevention of such pollution and in taking measures toassuage environmental concerns. For chrome removal bio-mass, clay, activated carbon (18), ion-exchange resins, andmembrane technologies (4) are generally employed.

Hydrogels and hydrogel composites were recentlyemployed as compelling materials for the removal of metalion species (19,20). Hydrogels, also known as smartmaterials, are cross-linked, water-insoluble networks ofhydrophilic polymers. Due to the hydrophilic groups suchas �OH, �COOH, NH2, �CONH2, and �SO3H in theirpolymeric chains, they can absorb water up to hundreds

Received 12 October 2010; accepted 3 February 2011.Address correspondence to Nurettin Sahiner, Chemistry

Department, Faculty of Sciences and Arts, Canakkale OnsekizMart University, Terzioglu Campus, Canakkale 17020, Turkey.Tel.: þ90-2862180010-2041; Fax: þ90-2862181948. E-mail:sahiner71@gmail.com

Separation Science and Technology, 46: 1450–1461, 2011

Copyright # Taylor & Francis Group, LLC

ISSN: 0149-6395 print=1520-5754 online

DOI: 10.1080/01496395.2011.560918

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of times their dry mass. Additionally, hydrogels canrespond to the changes in their environment by swelling,shrinking, color changing (complexing with metal ions orother species), bending and actuating (moving under anexternal force), and so on. Many environmental stimulisuch as pH, ionic strength, and temperature, as well asmagnetic and electrical fields (19–23) can provoke thesechanges. All these features in addition to their low fabri-cation cost make them a unique material for variousenvironmental applications. Although hydrogels have beenreported for their absorption potential for different metalions in the literature (19,20,22,24,25) very few studies existon the separation of troublesome metal species, of whichchromium is an example (26,27). Moreover, there are noreports on simultaneous absorption of both types of chro-mium species (III and VI) using a single adsorbent orabsorbent. Intelligent polymeric hydrogels can be designedfor multipurposes such as the separation and removal of allchromium species. Hence, in this study copolymerichydrogels bearing anionic (2-acrylamido-2-methyl-1-pro-pansulfonic acid sodium salt) and cationic (3-acrylamido-propyltrimethylammoniumchloride) moieties in variousformulations were synthesized and used for the simul-taneous separation and removal of chromium species.Previously, it was reported that chromium (III) can beremoved from aqueous medium by a magnetically functio-nalized anionic hydrogel (19,20). In this study, in additionto anionic parts, a hydrogel having cationic moiety (posi-tively charged functional groups) can be used for theabsorption of Cr (VI) concurrently. The separation ofchromium was achieved by the speciation of a chromiumion mixture through the use of individual hydrogels as asingle homopolymeric structure and later by desorptionstudies in an acidic medium. Furthermore, p(AMPSNa-co-APTMACl) copolymeric hydrogels were employed for sim-ultaneous absorption of Cr (III) and Cr (VI). Finally, itwas demonstrated that composite hydrogels with a ren-dered magnetic property can be used to convenientlyremove chromium species from the aqueous media with ahigher absorption capacity than bare hydrogels. The pre-pared chromium solution, at various concentrations of spe-cies (5–50 ppm), can be separated up to 98% effectively byusing multiple absorption-desorption cycles employingp(AMPSNa-co-APTMACl) copolymeric hydrogels.

EXPERIMENTAL

Materials

2-acrylamido-2-methyl-1-propansulfonic acid sodiumsalt (50%) and 3-acrylamidopropyltrimethylammoni-umchloride (75wt%) were used as monomers, andN,N0-methylenebisacrylamide (MBA) as crosslinker,2,20-azobis(2-methylpropionamidine) dihydrochloride wasused as a UV initiator; all were purchased from Aldrich,

Merck, and Acros Chemical Companies. CrCl3 � 6H2O(Merck), K2Cr2O7, K2CrO4 (Sigma), FeSO4 � 7H2O, FeCl3(Aldrich), and sodium hydroxide (Fluka) were used as themetal ion sources for the absorption and the magnetic com-posite hydrogel synthesis. All the reagents were of analyticalgrade or highest purity available, and were used withoutfurther purification. 18.2MX � cm (Millipore Direct-Q3UV) distilled water was used throughout the synthesis andabsorption experiments. The pH measurements were carriedout using a Sartorius Documeter pH meter.

Preparation of the Hydrogels and the CompositeHydrogels

Cross-linked p(AMPSNa), p(APTMACl), andp(AMPSNa-co-APTMACl) hydrogels were prepared in acylindrical rod shape via photo-polymerization in the pres-ence of a UV initiator through irradiation of their aqueoussolution. A typical hydrogel synthesis procedure is asfollows: 0.5mol% of MBA based on total monomeramount was dissolved=mixed in water containing themonomers. To this solution, 1ml of the initiator solution,and 2,20-azobis(2-methylpropionamidine) dihydrochloride(typically 0.5mol% with respect to monomer amount dis-solved in water) was added. The mixture was vortexedand transferred to a plastic straw with a 0.5 cm inner diam-eter. The precursor solution was irradiated in a photo reac-tor (LUZCHEM, 420 nm, Canada) for 3 hours. Theobtained hydrogels were in cylindrical rod form and werecut to the preferred size, approximately 0.5 cm long andwere cleaned by immersing the hydrogel pieces in distilledwater for 3 days with the wash water replenished every8 h to remove the species which did not react (monomers,initiator, cross-linker). After the cleaning procedure, thehydrogels were dried in an oven (40�C) until they reacheda constant weight and were kept in sealed containers forthe preparation of the magnetic particles, as well as forthe absorption and separation experiments.

In order to obtain magnetic composite hydrogels, barehydrogels were loaded to their maximum capacity withmetal ions. The magnetic ferrite particles were preparedinside hydrogels by modifying the reported procedure(19,23). The magnetic particles were prepared in two steps.First, the hydrogels were placed in a mixture of 0.5M Fe(II) and 1M Fe (III) ion aqueous solution (250ml, Fe(II): Fe (III) mole ratio is 1:2) for 24 h for loading of theseions. Second, the hydrogels were soaked in DI water toremove the unbound and=or the physisorbed metal ionsfor another 12 h. After cleaning, the iron ion (Fe (II) andFe (III)) loaded hydrogels were transferred into 0.5M alka-line solution (sodium hydroxide) (250ml) and the reactionproceeded for 12 h in a shaking water bath at ambient tem-perature. Finally, the hydrogels were cleaned by washingwith distilled water and were dried in a vacuum oven at40�C.

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Characterization and Swelling Behavior ofHydrogels and Composite Hydrogels

In order to determine the thermal behavior of the hydro-gels and the composite hydrogels, thermogravimetricanalysis (TGA) was carried out (SII TG=DTA 6300) witha heating range of 50–1100�C under N2 flow (100ml=min) with 10�C=min heating rate using about 4mg of sam-ple. The FT-IR spectra of the hydrogels were obtained(Perkin Elmer Spectrum 100) using the ATR apparatuswith 4 cm�1 resolution between 4000–650 cm�1. To deter-mine the carbon and sulfur amounts in the hydrogels,elemental analysis was carried out with an elementalanalyzer instrument (Leco SC-144 DR). The swellingexperiments for the hydrogels were carried out at roomtemperature in different media (deionized (DI), tap andsea water). The seawater was obtained off the coast ofCanakkale from the Dardanelles Strait in Turkey.Pre-weighed hydrogels were immersed in any of the afore-mentioned types of water and the mass increase wasrecorded by weighing the soaked hydrogels at certain timeintervals after blot drying with filter paper to remove theexcess water on their surfaces. Swelling characterizationwas also studied as a function of pH between 2–12 byadjusting the pH of the solutions with 0.1M HCl and0.1M NaOH. The hydrogels were kept for 24 h in differentacidic and basic solutions to determine the effect of pH ofthe medium on the swelling behavior of the gels.

The mass percent swelling was determined using thefollowing expression:

% S ¼ ðMt �M0ÞM0

� ��100 ð1Þ

where M0 and Mt are the initial mass and the mass at dif-ferent time-intervals, respectively. All the experiments werecarried out in triplicate and the average values are reportedin the data.

Absorption and Simultaneous Absorption of ChromiumSpecies Studies

Chromium species were removed in two ways from theaqueous solution using anionic and cationic hydrogels.First the absorption of chromium species from singlespecies media was studied using p(AMPSNa) andp(APTMACl) prepared as homopolymeric hydrogels. Herep(AMPSNa), due to its negative charge, exhibits a selectiveabsorption tendency for Cr (III), and p(APTMACl), due toits positive charge, exhibits a selective absorption affinityfor Cr (VI). Second not only Cr (III) but also Cr (VI)species were simultaneously removed from the mixedmedia using p(AMPSNa-co-APTMACl) hydrogels thatwere prepared as a copolymer in different ratios (2:1,1:1, 1:2). Additionally, the magnetically functionalized

p(AMPSNa-co-APTMACl) hydrogels were used to removemetal ion species from aqueous media.

For the absorption studies, 2000 ppm solutions contain-ing a single species of each of the chromium species wereprepared. The solutions containing a mixture of the chro-mium species were prepared by mixing these solutions indifferent ratios. The concentrations of these solutions weredetermined by ICP-AES. Desorption studies were per-formed on the chromium-absorbed hydrogel using 50ml0.5M HCl. All the absorption, desorption, and separationexperiments were repeated thrice as illustrated in the corre-sponding graphs with standard deviation and error bars.

The absorption experiments were performed employing0.2 g hydrogel and 50ml solution at room temperature. Theanionic hydrogel was only used for the absorption of Cr(III) and the cationic hydrogel was used for the absorptionof Cr2O

2�7 and CrO2�

4 as Cr (VI) species.In order to determine the effect of the concentration of

the chromium species on the absorption process, approxi-mately 0.2 g of hydrogels were used with seven differentmetal ion concentrations in the range of 50–1500 ppm with50ml volume of each solution. The absorption studies wereperformed in a water bath shaker at room temperature for24 h. Transient studies of absorption of the chromium spe-cies were carried out using 0.2 g hydrogel as the absorbentand 1000 ppm (50ml) solution in a water bath shaker atambient temperature. The time dependent absorption ofCr (III) with p(AMPSNa) hydrogel and the two Cr (VI)forms, Cr2O

2�7 and CrO2�

4 , with p(APTMACl) were stud-ied. Additionally, the time dependent simultaneous absorp-tion isotherm of Cr (III) and Cr (VI) species were studiedusing the p(AMPSNa-co-APTMACl) (1:1) hydrogel underthe same conditions (0.2 g hydrogel, 1000 ppm, 50ml). Twodifferent species containing solutions were used for simul-taneous absorption. In the first solution mixture,1000 ppm of chromium species Cr (III)þCr2O

2�7 , and in

the second solution mixture, 1000 ppm solution of Cr(III)þCrO2�

4 was used. The time dependent absorptionisotherm of both Cr2O

2�7 and CrO2�

4 species was thusformed. An equilibrium absorption study was also carriedout using magnetically functionalized p(AMPSNa) andp(AMPSNa-co-APTMACl) hydrogels with 0.2 g hydrogelweights in a solution of 500 ppm (50ml) concentrationfor 24 hours. The maximum equilibrium absorptionamounts of bare and magnetic hydrogels were determined.In order to determine the effect of the amount of hydrogelduring the absorption process, three different hydrogelamounts (0.1, 0.2, and 0.3 g) were used with the 50 ppm(50ml) solution.

Speciation, Separation and Determination ofChromium Species with ICP-AES

Homopolymer p(AMPSNa) and p(APTMACl) hydro-gels were used for the speciation and the acid treated

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desorption (separation) of chromium species as well as thequantification of each species using ICP-AES. Presumably,the electrostatic interaction of the Cr (III) and Cr (VI) spe-cies in the solution with the appropriate functional groupsin the structure of the homopolymer hydrogels enables theseparation of these two chromium species from each other.However, it is necessary that p(APTMACl) hydrogelshould not absorb any Cr (III) and by the same token,p(AMPSNa) hydrogel should not absorb any Cr (VI). Inthese absorption studies, 0.3 g of each hydrogel was used.The desorption studies were carried out in 4� 50ml0.5M HCl solutions. Initially, the p(APTMACl) hydrogeland then the p(AMPSNa) hydrogel was used for theabsorption of 50 ppm 50ml Cr (III). Following this pro-cedure, a 0.3 g mixture of anionic and cationic hydrogelswere used to separate Cr (III) and Cr (VI) mixtures of vari-ous concentrations (ranging between 100 ppm Cr (III)þ100 ppm Cr (VI) and 1 ppm Cr (III)þ 1 ppm Cr (VI)) fromeach other at room temperature in a shaking water bath.The chromium species, which were absorbed into the anio-nic and cationic hydrogels, were desorbed by using 50ml0.5M HCl (with 4 treatments) and the separation and puri-fication ratios with respect to the initial amounts weredetermined.

In another experiment, 0.3 g of anionic and cationichydrogel mixture was put through consecutive absorption-desorption processes in order to illustrate the reusability ofthe hydrogels as well as to compare the purification ratiosto the initial concentrations.

Speciation and separation of chromium using anionicand cationic hydrogels were carried out as follows: A100ml mixture of chromium species whose concentrationwas pre-determined by ICP-AES was divided in two equalparts of 50ml. In one batch, 0.3 g of dry anionic hydrogelwas added to separate only Cr (III) and in the other batch0.3 g of dry cationic hydrogel was added to enable Cr (VI)absorption. The mixtures were kept at ambient tempera-ture in a shaking water bath for 24 hours. Following thisprocedure, the hydrogels were left in 2� 100ml of purewater for the removal of unbound species and the chro-mium species were separated through desorption in 0.5MHCl (4� 50ml). The extent of separation was determinedusing ICP-AES. The results were confirmed using IC. Thisprocedure was repeated four times in order to maximize thespeciation, purification, and the separation ratios of thechromium species.

ICP-AES, IC Measurements and Calculations

The Cr (III) measurements were carried out usingICP-AES (Varian Liberty II AX Sequential) and the Cr(VI) measurements (for Cr2O

2�7 � CrO2�

4 species) were doneusing Ion Chromatograph system (IC) (Shimadzu, Japan)in the absorption, desorption, and separation studies.Additionally, the Cr (VI) amounts were also measured by

IC to verify ICP-AES measurements. In order to determinethe Cr (III) amount in the Cr (III) and Cr (VI) mixture sol-ution, initially the total amount of Cr in the solution wasmeasured using ICP-AES. The amount of Cr (VI) wasdetermined using IC. The amount of Cr (III) in the solutionwas calculated as follows:

Total Cr ðppmÞ ¼ Cr ðIIIÞ ðppmÞ þ Cr ðVIÞ ðppmÞ ð2Þ

All instrumental measurements regarding the chromiumspecies were carried out in triplicate and the mean values ofthe measurements with standard deviations were plotted.The specifications of the ICP-AES and the IC instrumentswhich were used in this study are given as supportinginformation in a table.

In the chromium ion absorption studies, the maximummetal ion concentration absorbed per unit mass of thehydrogel, qe (mg=g) was calculated using the followingequation:

qe ¼ ðC0 � CeÞV=W ð3Þ

where C0 and Ce are the initial and the equilibrium metalion concentrations (mg=L), V is the volume of the metalion solution, and W is the weight (in grams) of the hydro-gels or the magnetic hydrogels that were used.

RESULTS AND DISCUSSION

Characterization of Hydrogels andMagnetic-Hydrogels

To confirm the hydrogel chemical structure and theircopolymeric forms, FT-IR spectra of each hydrogel weretaken and are illustrated in Fig. 1(a). The strong peaks(1) and (2) in Fig. 1(a) observed at 1181 cm�1 and1040 cm�1, belong to the S-O stretching vibrations in thechemical structure of p(AMPSNa). The investigation ofthe FT-IR spectrum of the synthesized hydrogels as shownin Fig. 1 (1, 2, and 3) displays peaks at 3428 cm�1 and3321 cm�1 belonging to the stretching vibrations of N-Hfor amide groups in the structure of the anionic andcationic monomers. In addition, the peaks observed at1542 cm�1 and at 1298 cm�1 in the spectrum belong tothe N-H bending and C-N stretching vibrations, respect-ively for both the p(APTMACl), p(AMPSNa-co-APTMACl) hydrogels and the cross-linker. The evaluationof the peaks belonging to the p(APTMACl) hydrogel at3367 cm�1 and 3257 cm�1 belong to the N-H stretchingvibration of the amide group. The peaks at 1639 cm�1,1552 cm�1 and 1265 cm�1 in p(AMPSNa) belong toC=O stretching, N-H bending, and C-S stretching,respectively. The peak at 1480 cm�1 in the spectrumbelongs to a characteristic C-N stretching for the positivelycharged, nitrogen-containing groups. In the spectrum ofthe p(AMPSNa-co-APTMACl) (1:1) hydrogel, the N-H

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vibration belonging to the amide group of the cationicmonomer is observed at 3367 cm�1 and 3257 cm�1, whereasthe strong peaks of the S-O stretching vibrations of theanionic monomer were observed at 1181 cm�1 and1040 cm�1. In light of the individual peaks carrying thecharacteristics of both monomers belonging to the copoly-mer, the hydrogels appeared to have formed with their cor-responding monomers.

Additionally, the elemental analysis results confirmthe formation of copolymeric hydrogels. The results ofthe % carbon and sulfur analysis of the hydrogels were35.45% C, 13.08% S for p(AMPSNa), 46.63% C, 7.28% Sfor p(AMPSNa-co-APTMACl) (1:1), and 48.60% C, 0%S for p(APTMACl), respectively. According to theseresults, 47% AMPSNa, connected with 53% APTMAClduring polymerization and crosslinking to form thep(AMPSNa-co-APTMACl) (1:1) hydrogel. The small dif-ferences between the calculated and the measured valuesin the homopolymer hydrogels may be due to the differencein their reactivity. Although both monomers are acryla-mide derivatives they have different functional groups.

To render a magnetic property in hydrogels for potentialdirected application (guiding the absorbent) in toxic metalion removal upon completion of their tasks (removing tar-get ions), the hydrogels were made magnetically-responsiveby synthesizing magnetic ferrite (Fe3O4) in situ by theabsorption of ferrite particle-forming metal ions followedby their reduction inside p(AMPSNa-co-APTMACl)hydrogels as reported in the literature (19,20). The TGthermogram of the bare p(AMPSNa-co-APTMACl) (1:1)and the magnetic p(AMPSNa-co-APTMACl) (1:1) hydro-gels, that can potentially be used in the simultaneousabsorption of chromium species and then be confiscatedunder externally applied magnetic field from the absorp-tion medium, were used to determine the magnetic particlecontent of the composite hydrogel. From the TGA asshown in Fig. 1(b), the total amount of magnetic particlesformed in-situ constituted 7.2 weight % of the gel bodymass. As both hydrogels were heated to over 1100�C, thedifference between two samples as demonstrated inFig. 1(b) should be due to the magnetic component ofthe composite materials. The incorporation of inorganicmaterials such as magnetic particles caused the structureto become thermally more stable and this effect is clearlyvisible between 600–800�C.

Swelling Studies

The feasibility in terms of stimuli sensitivity (pH, ionicstrength, magnetic field, and so on) and the usability ofhydrogels in aqueous media in environmental applicationsare closely related to their swelling abilities. Hydrogels thatcan easily swell in all kinds of aqueous media may absorbmetal ions from an aqueous environment readily owing totheir appropriate functional groups. Therefore, time-dependent swelling experiments for the p(AMPSNa),p(APTMACl), and p(AMPSNa-co-APTMACl) (1:1)hydrogels produced were carried out and their correspond-ing graphs are illustrated in Fig. 2(a). As seen in Fig. 2(a),the anionic and the cationic hydrogels attain theirmaximum swelling capacity in 240 minutes and they imbibewater approximately 9000% by mass. The copolymer con-taining both the anionic and the cationic groups reachesequilibrium in more or less the same time and swells upto 1300% by mass. As all the monomers used are acidicand basic in character, the hydrogels produced from themare pH responsive. Therefore, a graph for pH vs %S valuesof all the hydrogels was constructed and is shown inFig. 2(b). Figure 2(b) illustrates that the copolymer hydro-gel swells less in both acidic and basic media in comparisonto the ionic hydrogels. The anionic and cationic hydrogelsshow typical pH swelling behavior, that is the anionicp(AMPSNa) hydrogel swells more in basic media(pH> 7) whereas the cationic p(APTMACl) hydrogelswells more in acidic media (pH< 7) and vice versa as theykeep charged forms. At about pH 6–8, there is a big change

FIG. 1. (a) FT-IR spectra of hydrogels and (b) TGA thermograms of

bare and magnetic p(AMPSNa-co-APTMACl) (1:1).

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in their swelling behaviors as it is the transient intervalbetween acid and base. The examination of the swellingcharacteristics of the synthesized hydrogels in differentmedia (tap water, seawater) resulted in very differentdegrees of swelling and confirms that the swelling abilityof the hydrogels differs drastically based on the medium.As can be seen in Fig. 2(c), the p(AMPSNa), p(APT-MACl), and p(AMPSNa-co-APTMACl) (1:1) hydrogelsmay swell up to 1350, 4120, and 390% by mass, respect-ively, in seawater. The reason for lesser swelling degreesin tap water and seawater is due to the presence of

dissolved anions and cations in these media. The hydrogelsthat were synthesized within the scope of this study well aslittle as 390% under salty (seawater) conditions and as highas 9000% in DI water.

Individual and Simultaneous Absorption Studies onChromium Species using Hydrogels

It is possible to remove chromium species either indi-vidually or simultaneously from an aqueous medium byusing p(AMPSNa), p(APTMACl), and p(AMPSNa-co-APTMACl) hydrogels. P(AMPSNa) contains an anionicfunctional group whereas p(APTMACl) contains a catio-nic functional group. Therefore, p(AMPSNa) was assumedto have a higher tendency to attract Cr (III) while p(APT-MACl) is presumed to have higher selectivity towards Cr(VI). The p(AMPSNa-co-APTMACl) hydrogels that weresynthesized using both these monomers has the ability toabsorb both chromium species simultaneously as demon-strated in Fig. 3. As can be seen from the figure, the aque-ous solutions of Cr (III) and Cr (VI) have different colorsand can be found in the same aqueous environments. Asdepicted, copolymeric p(AMPSNa-co-APTMACl) hydro-gels with the magnetic responsive ability prepared as pre-viously mentioned can be used to remove both speciessimultaneously. This is a great achievement, relevant to

FIG. 2. (a) The swelling behavior of p(AMPSNa), p(APTMACl) and

p(AMPSNa-co-APTMACl) hydrogels in DI water, (b) Swelling of hydro-

gels as a function of pH (pH is adjusted with 0.1M HCl and 0.1M

NaOH), (c) Swelling characterization of p(AMPSNa), p(AMPSNa-co-

APTMACl) (1:1), p(APTMACl) in DI, tap and sea waters. (Color figure

available online)

FIG. 3. Digital camera images of simultaneous absorption of Cr (III)

and Cr (VI) with magnetic p(AMPSNa-co-APTMACl) (1:1) hydrogels

[mixture: 25 ppm Cr (III)þ 25 ppm Cr (VI) (50ml), 0.5 g hydrogel].

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the cleaning of industrial wastes from dye manufacturing,the leather industry, and metallurgy.

In order to determine the effect of initial concentrationof the chromium species on their absorption from an aque-ous medium using the synthesized hydrogels with anionicand cationic nature, seven different metal ion concentra-tions in the range of 50–1500 ppm each with 50ml volumewere used with 0.2 g hydrogels as absorbent and the resultsare listed in Table 1. The Langmuir and the Freundlich iso-therms were applied for the chromium ion absorptions.The following equation was used for the Langmuirisotherm calculations (28).

Ce=qe ¼ ðCe=qmaxÞ þ 1=qmaxKL ð4Þ

where Ce is the equilibrium concentration of the metal ions(mg=L), qe is the amount of the metal ions adsorbed (mg=g), qmax is the maximum adsorption capacity of the metalions (mg=g). In order to determine the nature of the

TABLE 1Langmuir and Freundlich constants in the removal of chromium species from aqueous media by p(AMPSNa),

p(APTMACl), p(AMPSNa-co-APTMACl) hydrogels

�Chromiumspecies

Langmuir isotherm constants Freundlich isotherm constants

Hydrogels qm (mg=g) R2 n R2

Cr3þ p(AMPSNa) 59.63 0.9999 4.796 0.8351p(AMPSNa-co-APTMACI) (1:1) 33.12 0.9932 2.430 0.7828

Cr2O2�7 p(APTMACI) 158.8 0.9998 3.759 0.9569

p(AMPSNa-co-APTMACI) (1:1) 78.46 0.9762 1.470 0.9623CrO2�

4 p(APTMACI) 72.01 0.9992 3.360 0.9608p(AMPSNa-co-APTMACI) (1:1) 42.22 0.9954 1.799 0.9631

�[Chromium ions concentration: 50, 100, 250, 500, 750, 1000, 1500 ppm; 50ml, 0.2 g hydrogel].

FIG. 4. (a) The absorption of p(AMPSNa-co-APTMACl) (1:1) hydro-

gels for chromium species with various concentration, qe versus Ce, (b)

Langmuir isotherm, and (c) Freundlich isotherm (50, 100, 250, 500, 750,

1000, 1500 ppm chromium solution, 0.2 g hydrogel, 50ml.).

FIG. 5. (a) The absorption isotherms of p(AMPSNa) for Cr (III) and

p(APTMACl) for Cr2O2�7 and CrO2�

4 as Cr (VI), (b) The simultaneous

absorption isotherms of p(AMPS-c-APTMACl) (1:1) hydrogels for Cr

(III) and Cr (VI) (1000 ppm chromium solutions (50ml), 0.2 g hydrogel).

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absorption, the Freundlich isotherms were also widelyused (29).

log qe ¼ logKf þ 1=n logCe ð5Þ

where qe (mg=g) is the adsorption capacity at equilibrium,Ce (mg=L) is the equilibrium concentration of the metalsalts in solution, Kf and n are the physical constants incor-porating the factors affecting the adsorption processes suchas the adsorption capacity and the intensity of adsorption.As can be seen from Table 1, the absorption studies yieldedthe result that the hydrogels fitted best to the Langmuirisotherms.

Looking into the Ce� qe plot belonging to the simul-taneous absorption of the chromium species by p(AMPSNa-co-APTMACl) (1:1) hydrogels as shown in Fig. 4(a), themaximum absorption capacities for Cr2O

2�7 ;CrO2�

4 andCr3þ were determined as 73.80, 34.71, and 30.75mg=g,respectively. The initial solution concentrations to attainthe maximum absorption capacity were 1000, 750, and500 ppm, respectively. For the calculation of Langmuir iso-

therms Ce=qe vs Ce was plotted and a linear relation wasobtained, implying monolayer coverage as shown inFig. 4(b). Similar results were also obtained from theFreundlich absorption isotherm (Fig. 4(c)). The isothermsfor the individual absorption studies with the p(AMPSNa)and p(APTMACl) hydrogels are shown in Fig. 5(a) and theisotherms from the simultaneous absorption studies usingthe p(AMPSNa-co-APTMACl) (1:1) hydrogels are shownin Fig. 5(b). As seen in the figures, the single absorptionand the simultaneous absorption of the chromium specieswas completed in approximately 400 minutes. The mainpurpose of the investigation was to determine the effectof the amount of the absorbing material on the absorptionprocess and to enable the removal of up to 100% of thechromium species from the aqueous solution using thesynthesized hydrogel systems. Thus, it was important todetermine the amount of the hydrogel that provides suf-ficient separation, for example, of at least 99% of bothchromium species. As illustrated in Fig. 6, the use of0.3 g of hydrogel enables 99.9% removal of the chromiumspecies from the aqueous medium. As a result of this,0.3 g of hydrogel was used in the separation and the specia-tion processes.

The Effect of Magnetic Hydrogels on theAbsorption Process

In order to determine the effect of the magnetic hydro-gels on the absorption process, copolymers of p(AMPSNa)in varying ratios were magnetically functionalized. Sincethe p(APTMACl) hydrogel could not absorb the iron ionsthat are essential for in situ magnetic particle preparation,the cationic hydrogel cannot be prepared in this way toprovide a magnetic property. Small increases in the absorp-tion capacity of magnetic hydrogels have been previouslyreported (19). Table 2 summarizes the comparison of theabsorption capacity of bare and magnetic hydrogel pre-pared at different mole ratios for different chromiumspecies. As expected, as the content of p(AMPSNa)decreased in the copolymeric hydrogels, the Cr (III)

FIG. 6. The effect of the amount of absorbent on the removal of

chromium species with p(AMPSNa) and p(APTMACl) hydrogels (Initial

concentration 50 ppm, 50ml).

TABLE 2The comparison of metal ion absorption capacity of bare and magnetic p(AMPSNa) based hydrogels

Hydrogelp(AMPSNa)

p(AMPSNa-co-APTMACI) (2:1)

p(AMPSNa-co-APTMACI) (1:1)

p(AMPSNa-co-APTMACI) (1:2) p(APTMACI)

�ChromiumSpecies Barea Magnetica Barea Magnetica Barea Magnetica Barea Magnetica Barea Magnetica

Cr3þ 58.52 63.44 44.22 46.58 30.20 34.51 16.54 17.92 – N.SCr2O

2�7 - 3.94 29.49 22.57 49.75 50.62 91.33 93.88 116.66 N.S

CrO2�4 - 4.38 15.84 17.07 26.50 28.88 52.60 53.12 64.04 N.S

�Concentration: 500 ppm (50ml), Absorbent: 0.2 g hydrogel.amg=g dry gel, N.S. Not synthesized.

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absorption capacity also decreased. On the other hand, asthe cationic character of p(AMPSNa-co-APTMACl)hydrogel was increased the absorption tendency for Cr(VI) species increased. Additionally, as shown in Table 3,the bare p(AMPSNa) gel did not absorb any Cr (VI)whereas the magnetic composite of the hydrogel absorbs3.94mg=g Cr (VI). The absorption capacity of all the mag-netic copolymeric hydrogel composites was somewhathigher than bare hydrogels regardless of chromium species.The reason for this increase in the absorption capacitymight be due to some affinity of the magnetic nano-

particles for chromium species as depicted in Fig. 7. Thisprovides extra efficiency in the removal of the same specieswith different oxidation states in the same environment asshown in Fig. 3, in addition to the advantage that magneti-cally functionalized hydrogels can be easily removed fromthe aqueous medium with an external magnetic field.

Speciation, Separation, and Determination of ChromiumSpecies with ICP-AES

The main aim of this study was to separate Cr (III) andCr (VI) species by absorption using separate anionic and

TABLE 3The separation % of Cr (III) and Cr (VI) by different hydrogels at different concentrations of mixtures

Solution matrixb

Solution mixture of Cra Cr (III) Cr (VI)b Hydrogelc Absorptionb (%) Recoveryb,d,e (%)

50 ppm (III) 2.5 – p(APTMACl) – N.D.(��)50 ppm (VI) – 2.5 p(AMPSNa) – N.D.(��)100 ppm (III)þ 100 ppm (VI) 5 5 p(AMPSNa) 60.80� 3.8 58.24� 2.9100 ppm (III)þ 100 ppm (VI) 5 5 p(APTMACl) 68.65� 3.1 66.48� 2.050 ppm (III)þ 50 ppm (VI) 2.5 2.5 p(AMPSNa) 80.43� 2.4 80.04� 2.250 ppm (III)þ 50 ppm (VI) 2.5 2.5 p(APTMACl) 83.27� 1.8 82.44� 2.350 ppm (III)þ 5 ppm (VI) 2.5 0.25 p(AMPSNa) 98.40� 1.0 98.21� 1.750 ppm (III)þ 5 ppm (VI) 2.5 0.25 p(APTMACl) 91.35� 2.1 90.53� 2.250 ppm (III)þ 1 ppm (VI) 2.5 0.05 p(AMPSNa) 98.10� 1.4 98.00� 1.450 ppm (III)þ 1 ppm (VI) 2.5 0.05 p(APTMACl) 92.12� 2.5 90.25� 2.310 ppm (III)þ 10 ppm (VI) 0.5 0.5 p(AMPSNa) 88.02� 3.1 87.06� 3.610 ppm (III)þ 10 ppm (VI) 0.5 0.5 p(APTMACl) 90.39� 1.9 88.41� 2.95 ppm (III)þ 50 ppm (VI) 0.25 2.5 p(AMPSNa) 87.16� 3.1 86.22� 2.65 ppm (III)þ 50 ppm (VI) 0.25 2.5 p(APTMACl) 97.78� 1.8 97.20� 1.95 ppm (III)þ 5 ppm (VI) 0.25 0.25 p(AMPSNa) 89.45� 3.9 89.25� 3.45 ppm (III)þ 5 ppm (VI) 0.25 0.25 p(APTMACl) 91.02� 3.0 90.45� 2.35 ppm (III)þ 1 ppm (VI) 0.25 0.05 p(AMPSNa) 89.85� 2.6 87.08� 2.55 ppm (III)þ 1 ppm (VI) 0.25 0.05 p(APTMACl) 86.77� 4.6 86.17� 3.81 ppm (III)þ 50 ppm (VI) 0.05 2.5 p(AMPSNa) 89.15� 2.8 88.25� 2.51 ppm (III)þ 50 ppm (VI) 0.05 2.5 p(APTMACl) 98.67� 0.7 98.08� 0.61 ppm (III)þ 5 ppm (VI) 0.05 0.25 p(AMPSNa) 86.68� 5.7 85.45� 4.71 ppm (III)þ 5 ppm (VI) 0.05 0.25 p(APTMACl) 88.72� 5.3 88.06� 4.11 ppm (III)þ 1 ppm (VI) 0.05 0.05 p(AMPSNa) 81.12� 4.1 80.18� 3.81 ppm (III)þ 1 ppm (VI) 0.05 0.05 p(APTMACl) 78.44� 5.9 78.32� 4.250 ppm (III)þ 5 ppm (VI) (�) 2.5 0.25 p(AMPSNa) 97.68� 1.1 97.11� 1.250 ppm (III)þ 5 ppm (VI) (�) 2.5 0.25 p(APTMACl) 86.82� 3.2 86.26� 2.75 ppm (III)þ 50 ppm (VI) (�) 0.05 0.25 p(AMPSNa) 88.89� 2.0 88.81� 1.15 ppm (III)þ 50 ppm (VI) (�) 0.05 0.25 p(APTMACl) 95.63� 1.3 94.45� 1.8

a50ml.bDetected by ICP-AES, confirmed by IC.cFor 0.3 g hydrogel.d0.5M HCl (50ml� 4).eaccording to initial concentration.(�) Cr (VI) prepared from K2CrO4.(��) Washed with DI water (2� 50ml) (before desorption).N.D. Not detected.

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cationic hydrogels and to determine the amounts of bothchromium species by ICP-AES and IC measurements.For this reason a total volume of 100ml mixture of chro-mium species was divided in two equal parts, 50ml each.To one batch, 0.3 g of dry p(AMPSNa) hydrogel wasadded to separate only Cr (III), and to the other batch0.3 g of dry p(APTMACl) hydrogel was added for Cr(VI) adsorption. The hydrogels were desorbed in an acidicmedium and the amounts of the separated chromium spe-cies were determined via ICP-AES and the procedure isdepicted in Fig. 8. Table 3 summarizes all of the resultsof the speciation and separation experiments. As seen inTable 3, the p(AMPSNa) hydrogels do not absorb Cr(VI) and the p(APTMACl) hydrogels do not absorb Cr

FIG. 8. (a) The removal of Cr (VI) from the mixture of Cr (III) and Cr

(VI) by p(APTMACl) hydrogel, (b) The removal of Cr (III) from the mix-

ture of Cr (III) and Cr (VI) by p(AMPSNa) hydrogel. (c) The separation

of Cr (VI) by p(APTMACl) hydrogel and (d) The separation of Cr (III) by

p(AMPSNa) hydrogel. (Initial concentration 50 ppm 50ml with 0.3 g

hydrogels).

TABLE 4The % separation values of Cr (III) and Cr (VI) by consecutive four absorption–desorption cycles in a row by different

hydrogels at various concentrations of their mixtures

(�) Solution mixture of Cra,b �Hydrogelc1. Absorptiond

(%)2. Absorptiond

(%)3. Absorptiond

(%)4. Absorptiond

(%)Recoveryd,e

(%)

100 ppm (III)þ 100 ppm (VI) p(AMPSNa) 60.80� 3.8 28.54� 2.2 4.88� 0.9 3.22� 1.4 96.28� 2.7100 ppm (III)þ 100 ppm (VI) p(APTMACl) 68.65� 3.1 21.12� 1.9 5.52� 0.8 2.73� 1.1 97.65� 2.250 ppm (III)þ 50 ppm (VI) p(AMPSNa) 80.43� 2.4 12.44� 1.5 3.10� 1.1 1.10� 0.5 96.15� 3.450 ppm (III)þ 50 ppm (VI) p(APTMACl) 83.27� 1.8 8.45� 1.8 4.87� 1.4 1.85� 1.0 98.02� 1.710 ppm (III)þ 10 ppm (VI) p(AMPSNa) 88.02� 3.1 7.12� 0.9 2.80� 1.0 1.32� 1.2 98.31� 1.310 ppm (III)þ 10 ppm (VI) p(APTMACl) 90.39� 1.9 5.25� 1.1 2.88� 0.7 – 98.18� 1.15 ppm (III)þ 5 ppm (VI) p(AMPSNa) 89.45� 3.9 4.88� 1.3 4.19� 1.6 – 97.25� 1.85 ppm (III)þ 5 ppm (VI) p(APTMACl) 91.02� 3.0 6.12� 1.7 2.05� 1.1 – 98.48� 0.81 ppm (III)þ 1 ppm (VI) p(AMPSNa) 81.12� 4.1 7.28� 2.1 4.63� 1.3 3.62� 2.1 94.26� 2.71 ppm (III)þ 1 ppm (VI) p(APTMACl) 78.44� 5.9 9.41� 3.0 6.70� 2.0 2.05� 1.7 95.72� 2.8

a50ml.bDetected by ICP-AES, confirmed by IC.cFor 0.3 g hydrogel.dAccording to initial concentration.e0.5M HCl (50ml� 4).�Same hydrogel was employed in all absorbtion cycle.(�) Cr (VI) prepared from K2Cr2O7 and Cr (III) from CrCl3.

FIG. 7. The schematic representation of simultaneous absorption of dif-

ferent chromium species by magnetic p(AMPSNa-co-APTMACl) (1:1)

hydrogel from aqueous environments.

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(III). In the chromium solutions at different concentra-tions, even following the first absorption, the chromiumspecies were separated from each other by 58.24% withrespect to their initial concentrations using the appropriatehydrogels, thus making speciation possible. As the concen-tration of the chromium species decreased, a separation ofup to 98.21% with respect to the initial concentration wasachieved as demonstrated for the 50 ppm (III)þ 5 ppm(VI) mixture in Table 3. If the same hydrogels were putthrough four consecutive absorption-desorption cycles inthe same solution for separation and purification, the chro-mium species would be separated in ratios ranging between95.72–98.48% with respect to their initial concentrations asshown in Table 4. Therefore, it is possible to remove all ofone type of chromium species from aqueous environmentsbearing in mind that copolymeric hydrogels with magneticproperties would provide even better results. The magneticcomposites were not studied, as magnetic ferrite alsoabsorbs both forms of chromium (Cr (III) and Cr (VI)).Hydrogels are unique materials that may be designed fora determined source of pollution and are a powerful toolfor the separation of any form of chromium in environ-mental applications. These hydrogel systems even deter-mine the form of species as an alternative to ICP-AESand give the total amount of chromium.

CONCLUSION

Hydrogels with anionic and cationic characteristics forspecific environmental applications were synthesized usingredox polymerization. The anionic hydrogel displays selec-tive behavior for Cr (III), whereas the cationic hydrogel hasselectivity for Cr (VI). Additionally in the copolymericform, owing to the presence of the anionic groups in thecopolymer, these hydrogels could also be magneticallydesigned which also provides an increase in their absorp-tion capacity. The magnetic hydrogels with increasedabsorption capacity can be easily removed from the sol-ution medium through the use of an external magneticfield. It was demonstrated that chromium species with dif-ferent oxidation forms can be separated using theabsorption-desorption abilities of both hydrogels to avoidtedium. Even with these simple hydrogel systems, a separ-ation of up to 98% would be achievable for a bothersomechromium species. Therefore, p(AMPSNa) and p(APT-MACl) and its copolymeric hydrogels are suitable for theseparation of chromium species and for their removal, aswell as their use in the quantification of each chromiumspecies using AAS, GFAAS or ICP-AES and IC.

ACKNOWLEDGEMENTS

This work is supported by Canakkale Onsekiz MartUniversity (COMU BAP 2010=186). Also, N. Sahinergreatly appreciated the financial support by the

Turkish Academy of Science under the 2008-TUBAGEBIP Program.

REFERENCES

1. Karosi, R.; Andruch, V.; Posta, J.; Balogh, J. (2006) Separation of

chromium (VI) using complexation and its determination with

GFAAS. Microchem. J., 82 (1): 61.

2. Hu, J.; Chen, G.; Lo, I.M.C. (2005) Removal and recovery of Cr(VI)

from wastewater by maghemite nanoparticles. Water Res., 39 (18):

4528.

3. Zhu, X.; Hu, B.; Jiang, Z.; Li, M. (2005) Cloud point extraction for

speciation of chromium in water samples by electrothermal atomic

absorbtion spectrometry. Water Res., 39 (4): 589.

4. Zaroual, Z.; Chaair, H.; Essadki, A.H.; El Ass, K.; Azzi, M. (2009)

Optimizing the removal of trivalent chromium by electrocoagulation

using experimental design. Chem. Eng. J., 148 (2–3): 488.

5. Sedumedi, N.N.; Mandiwana, K.L.; Ngobeni, P.; Panichev, N. (2009)

Speciation of Cr(VI) in environmental samples in the vicinity of the

ferrochrome smelter. J. Hazard. Mater., 172 (2–3): 1686.

6. Monasterio, R.P.; Altamirano, J.C.; Martinez, L.D.; Wuilloud, R.G.

(2009) A novel fiber-packed column for on-line preconcentration and

speciation analysis of chromium in drinking water with flame atomic

absorption spectroscopy. Talanta, 77 (4): 1290.

7. Kumbasar, R.A. (2010) Studies on extraction of chromium (VI) from

acidic solutions containing various metal ions by emulsion liquid

membrane using Alamine 336 as extractant. J. Hazard. Mater., 178

(1–3): 875.

8. Liu, J.; Zhang, W.; Ren, Z., Ma, J. (2009) The separation and concen-

tration of Cr(VI) from acidic dilute solution using hollow fiber

renewal liquid membrane. Ind. Eng. Chem. Res., 48 (9): 4500.

9. He, Q.; Chang, X.; Zheng, H.; Jiang, N.; Wang, X. (2008) Determi-

nation of chromium (III) and total chromium in natural waters using

a surface ion-imprinted silica gel as selective adsorbent. Int. J. Environ.

Anal. Chem., 88 (6): 373.

10. Hagendorfer, H.; Goessler, W. (2008) Separation of chromium (III)

and chromium (VI) by ion chromatography and an inductively

coupled plasma mass spectrometer as element-selective detector.

Talanta, 76 (3): 656.

11. Hosseini, M.S.; Bandegharaei, A.H.; Raisi, H.; Belador, F. (2009)

Sorption of Cr(VI) by Amberlite XAD-7 resin impregnated with

brilliant gren and its determination by quercetin as a selective spectro-

photometric reagent. J. Hazard. Mater., 169 (1–3): 52.

12. Sahu, S.K.; Meshram, P.; Pandey, B.D.; Kumar, V.; Mankhand, T.R.

(2009) Removal of chromium (III) by cation exchange resin, Indion

790 for tannery waste treatment. Hydrometallurgy, 99 (3–4): 170.

13. Li, H.; Li, Z.; Liu, T.; Xiao, X.; Peng, Z.; Deng, L. (2008) A novel

technology for biosorption and recovery hexavalent chromium in

wastewater by bio-functional magnetic beads. Bioresour. Technol.,

99 (14): 6271.

14. Martendal, E.; Maltez, H.F.; Carasek, E. (2009) Speciation of Cr(III)

and Cr(VI) in environmental samples determined by selective separ-

ation and preconcentration on silica gel chemically modified with

niobium (V) oxide. J. Hazard. Mater., 161 (1): 450.

15. Hosseini, M.S.; Belador, F. (2009) Cr(III)=Cr(VI) speciation determi-

nation of chromium in water samples by luminescence quenching of

quercetin. J. Hazard. Mater., 165 (1–3): 1062.

16. Sun, Z.; Liang, P. (2008) Determination of Cr(III) and total chro-

mium in water samples by cloud point extraction and flame atomic

absorption spectrometry. Microchim. Acta, 162 (1–2): 121.

17. Hassanien, M.M.; Kenawy, I.M.; Menshawy, A.M.E.; Asmy, A.A.E.

(2008) A novel method for speciation of Cr(III) and Cr(VI) and indi-

vidual determination using Duolite C20 modified with active hydra-

zone. J. Hazard. Mater., 158 (1): 170.

1460 O. OZAY, N. AKTAS, AND N. SAHINER

Dow

nloa

ded

by [

DU

T L

ibra

ry]

at 1

1:58

07

Oct

ober

201

4

18. Lam, K.F.; Yeung, K.L.; Mckay, G. (2007) Selective mesoporous

adsorbents for Cr2O2�7 and Cu2þ separation.Microporous Mesoporous

Mater., 100 (1–3): 191.

19. Ozay, O.; Ekici, S.; Baran, Y.; Aktas, N.; Sahiner, N. (2009) Removal

of toxic metal ions with magnetic hydrogels.Water Res., 43 (17): 4403.

20. Ozay, O.; Ekici, S.; Baran, Y.; Kubilay, S.; Aktas, N.; Sahiner, N.

(2010) Utilization of magnetic hydrogels in the separation of

toxic metal ions from aqueous environments. Desalination, 260 (1–

3): 57.

21. Sahiner, N.; Singh, M. (2007) In situ micro=nano-hydrogel synthesis

from acrylamide derivates with lecithin organogel system. Polymer,

48 (10): 2827.

22. Barakat,M.A.; Sahiner, N. (2008) Cationic hydrogels for toxic arsenate

removal from aqueous environment. J. Environ. Manage., 88 (4): 955.

23. Sahiner, N. (2006) In situ metal particle preparation in cross-linked

poly (2-acrylamido-2-methyl-1-propansulfonic acid) hydrogel net-

works. Colloid Polym. Sci., 285 (3): 283.

24. Pekel, N.; Sahiner, N.; Guven, O. (2001) Use of amidoximated

acrylonitrile=N-vinyl-2- pyrrolidone interpenetrating polymer net-

work for uranyl ion adsorption from aqueous systems. J. Appl. Polym.

Sci., 81 (10): 2324.

25. Saraydın, D.; Isıkver, Y.; Sahiner, N. (2001) Uranyl ion binding

properties of poly(hydroxamic acid) hydrogels. Polym. Bull., 47 (1): 81.

26. Kundakci, S.; Uzum, O.B.; Karadag, E. (2009) Behaviors of chemi-

cally crosslinked CAAMPS hydrogels in uptake of uranyl ions from

aqueous solutions. Polym.-Plast. Technol. Eng., 48 (1): 69.

27. Dadhaniya, P.V.; Patel, A.M.; Patel, M.P.; Patel, R.G. (2009) A new

cationic poly[1-vinyl-3-ethyl imidazolium iodide], p(VEII) hydrogel

for the effective removal of chromium (VI) from aqueous solution.

J. Macromol. Sci., Part A: Pure Appl. Chem., 46 (4): 447.

28. Langmuir, I. (1918) The adsorption of gases on plane surfaces of

glass, mica and platinum. J. Am. Chem. Soc., 40 (9): 1361.

29. Freundlich, H.M.F. (1906) Over the adsorption in solution. Z. Phys.

Chem., 57: 385.

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