ARAŞTIRMA MAKALESİ / RESEARCH ARTICLE

Transcription

1 ANADOU ÜNİVERSİTESİ BİİM VE TEKNOOJİ DERGİSİ A Uygulamalı Bilimlr v Mühndislik ANADOU UNIVERSITY JOURNA OF SCIENCE AND TECHNOOGY A Applid Scincs and Enginring Cilt/Vol.: 13-Sayı/No: 1 : (2012) ARAŞTIRMA MAKAESİ / RESEARCH ARTICE ADSORPTION OF Ni(II) IONS FROM AQUEOUS SOUTIONS ONTO MAGNETIC- POY(DIVINYBENZENE-CO-VINYIMIDAZOE) MICROBEADS: PHYSICOCHEMICA STUDIES Ali KARA 1, Eml DEMİRBE 1 ABSTRACT A modifid suspnsion polymrization was usd for th prparation of th msoporous magntic-poly(divinylbnzn-co-vinylimidazol) (m-poly(dvb-vim)) microbads in siz μm of avrag diamtr. Th spcific surfac ara and th DVB/VIM mol ratio of th microsphrs wr dtrmind as m 2 /g and 1:4 mol/mol with F 3 O 4, rspctivly. Th physicochmical studis of adsorption of Ni(II) ions from aquous solutions such as ph, initial concntration, amount of msoporous m-poly(dvb-vim) microbads, contact tim, and tmpratur onto th m-poly(dvb- VIM) microsphrs wr carrid out. Th maximum adsorption capacitis of th m-poly(dvb-vim) microsphrs towards Ni(II) ions wr dtrmind as 13.51, 20.14, and mg/g at 277 K, 298 K, 318 K, and 338 K, rspctivly. Th dynamic and quilibrium adsorption bhaviours of th systm wr adquatly dscribd by th psudo-scond-ordr kintic and th angmuir isothrm modls, rspctivly. Various thrmodynamic paramtrs, such as th Gibbs fr nrgy chang (ΔG o ), th standard nthalpy chang (ΔH o ) and th standard ntropy chang (ΔS o ) wr also dtrmind. Morvr, aftr us in th adsorption, th m-poly(dvb-vim) microbads with paramagntic proprty was sparatd from th via th applid magntic forc. Ths rsults indicat that th matrial studid could b usd as a purifir for th rmoval of Ni(II) ions from watr and wastwatr undr magntic fild. Kywords: Magntic polymrs; Adsorption isothrm; Adsorption kintic; Adsorption thrmodynamic; Ni(II) ions. 1, Dpartmnt of Chmistry, Uludag Univrsity, Görükl Campus, Nilüfr 16059, Bursa, Turky. Tl and Fax: (90) mail: akara@uludag.du.tr -mail: Eml Dmirbl: mldmirbl@uludag.du.tr Rcivd: 12 March 2012; Rvisd: 15 May 2012; Rvisd: 11 Jun 2012; Accptd: 27 Jun 2012

2 32 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik MANYETİK-POİ (DİVİNİBENZEN-KO-VİNİİMİDAZO) MİKROKÜREER İE SUU ÇÖZETİERDEN Ni(II) İYONARININ ADSORPSİYONU: FİZİKOKİMYASA ÇAIŞMAARI ÖZ Ortalama çapı μm olan mzogöznkli manytik-poli(divinilbnzn-ko-vinilimidazol) (mpoli(dvb-vim)) mikrokürlrinin hazırlanması için modifiy süspansiyon polimrizasyonu kullanıldı. Mikrokürlrin spsifik yüzy alanı m 2 g -1 v F 3 O 4 ilavsiyl birlikt, DVB/VIM mol oranı 4:1 mol/mol olarak blirlndi. Fizikokimyasal çalışmalar m-poli (DVB-VIM) mikrokürlri üzrin ph, başlangıç konsantrasyonu, mikrokür miktarı, tmas sürsi v sıcaklık gibi paramtrlrl inclndi. m-poli(dvb-vim) mikrokürlrinin Ni(II) iyonlarına karşı maksimum adsorpsiyon kapasitsi 277 K, 298 K, 318 K v 338 K d sırasıyla 13.51, 20.14, v mg.g -1 olarak blirlndi. Sistmin dinamik v dng adsorpsiyon davranışları sırasıyla yalancı ikinci drc modl v angmuir izotrm modliyl açıklandı. Gibbs srbst nrji dğişimi (ΔG 0 ), standart ntalpi dğişimi (ΔH 0 ) v standart ntropi dğişimi (ΔS 0 ) gibi trmodinamik paramtrlr blirlndi. Ayrıca adsorpsiyonda kullanımdan sonra, paramanytik özllikli m-poli (DVB-VIM) mikrokürlri uygulanan manytik kuvvt yardımıyla ayrıldı. Bu sonuçlar, çalışılan malzmnin manytik alan altında su v atık sulardan Ni(II) iyonlarının uzaklaştırılması için kullanılabilir olduğunu göstrdi. Anahtar Klimlr: Manytik polimrlr; Adsorpsiyon izotrmi, Adsorpsiyon kintiği; Adsorpsiyon trmodinamiği; Ni (II) iyonları. Notation C concntration of Ni(II) ions at quilibrium (mg -1 ) C 0 initial concntration of Ni(II) ions in solution (mg -1 ) E a activation nrgy of adsorption (kj mol -1 ) E f fr nrgy of adsorption (kj mol -1 ) G Gibbs fr nrgy of adsorption (J mol -1 ) H isostric nthalpy of adsorption (J mol -1 ) S ntropy chang of th adsorption procss (J mol -1 K -1 ) q th amount of Ni(II) ions adsorbd on th adsorbnt at quilibrium (mg g -1 ) q t th amount of Ni(II) ions adsorbd on th adsorbnt at any tim (mg g -1 ) q m th maximum amount of Ni(II) ions adsorbd pr unit mass adsorbnt (mg g -1 ) Q th maximum amount of Ni(II) ions adsorbd pr unit mass adsorbnt (mg g -1 ) K th angmuir constant rlatd to th affinity of binding sits (m mg -1 ) n th htrognity factor K F th Frundlich constant Q D-R th maximum amount of Ni(II) ions adsorbd pr unit mass adsorbnt (mg g -1 ) K D-R th Dubinin-Radushkvich constant (mol 2 J -2 ) ε th Polanyi potntial (J mol -1 ) R th dimnsionlss sparation factor k 1 th rat constant of psudo first-ordr adsorption (min -1 ) k 2 th rat constant of psudo scond-ordr adsorption ((g/mg) min -1 ) k R th rat constant for th modifid Ritchi s-scond-ordr modl (min -1 ) k i th intraparticl diffusion rat constant (mg/g min 0.5 ) R 2 linar rgrssion cofficint t tim (min) T tmpratur (K)

3 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring INTRODUCTION Nickl, comparativly a rar mtal in natur, is a toxic havy mtal ion prsnt in watr and wastwatr. Th main sourc of nickl pollution in th watr and wastwatr drivs from industrial production procsss such as stainlss stl, galvanization, lctroplating, battris manufacturing, th manufacturing of magntic tap, jwlry and coinag, in wlding rods, as a catalyst in oil hydrognation and coal gasification, dntal procdurs, lctric storag battris, pigmnts and so on. Th prsnc and accumulation of nickl in industrial fflunts has a toxic or carcinognic ffct such as hadach, dizzinss, nausa and vomiting, chst pain, tightnss of th chst, shortnss of brath, rapid rspiration, cyanosis, xtrm waknss on human halth. Thrby, it is of grat importanc to liminat nickl ions from wast and wastwatrs (Patil and Shrivastava, 2010, Strkalj t al, 2010, Akgol t al, 2006). Th high consumption of nickl-containing products invitably lads to nvironmntal pollution by nickl and its drivativs at all stags of production, utilization, and disposal. Th physicochmical mthods such as prcipitation/nutralization, ultrafiltration, rvrs osmosis, lctrodposition, solvnt xtraction, foamflotation, cmntation, complxation, filtration, vaporation, ion xchang, and adsorption hav bn usd to rmov Ni(II) ions from wastwatr. Adsorption is on of th most vrsatil mthods for th rmoval of Ni(II) ion contamination from aquous systms. Som of th adsorption procsss hav managd to complt in a short tim. In rcnt yars, th adsorption of Ni(II) ions by magntic polymrs has attractd significant attntion. Magntic polymrs hav svral potntial advantags ovr convntional approachs. In this tchniqu, Ni(II) ions to b sparatd can b dirctly transportd by convction to th binding sits on th surfac of th adsorbnt, highr throughput and fastr procssing tims onto th magntic particls can b achivd. (Monir t al, 2010, Ozay t al, 2009, Hua t al, 2011, Mahdavian and Mirrahim, 2010, Wang t al, 2010) Th physicochmical studis of adsorption for Ni(II) ions prsntd hrin is a part of th invstigations conductd to valuat th ffctivnss of magntic polymrs. This study provids insight into Ni(II) ions adsorption from aquous solutions in trms of quilibrium and kintics. It also provids important information that could b usd in th dsign and optimization of Ni(II) ions adsorption oprations. Furthrmor, th rsults of this study could b hlpful in th prdiction of th Ni(II) ions rat of transport. Th ffcts of various systm paramtrs such as ph, initial concntration, contact tim, tmpratur, amount and rpatd us of m-poly(dvb-vim) microbads wr systmatically studid and th rsults obtaind ar discussd. 2. EXPERIMENTA 2.1 Matrials Divinilbnzn (DVB, 98%) obtaind from Mrck (Darmstadt, Grmany) was vacuumdistilld aftr bing washd with an aquous 10% NaOH solution. 1-vinylimidazol (VIM, Aldrich, Stinhim, Grmany) was distilld undr vacuum (74-76 C, 10 mmhg). 2,2'- Azobisisobutyronitril (AIBN) was obtaind by Mrck (Darmstadt, Grmany). Poly(vinyl alcohol) (PVA; Mw: 72000, 98% hydrolyzd) was supplid from Mrck (Darmstadt, Grmany). Magntit nanopowdr (F 3 O 4 ; diamtr nm) was obtaind from Aldrich (USA). Nickl nitrat hxahydrat was supplid by Fluka (Hannovr, Grmany). All othr ragnts, unlss spcifid, wr of analytical grad and wr usd without furthr purification. aboratory glasswar was kpt ovrnight in a 5% nitric acid solution. Bfor us th glasswar was rinsd with dionizd watr and drid in a dust-fr nvironmnt. All watr usd in th adsorption xprimnts was purifid using a Barnstad (Dubuqu, IA, USA) ROpur P rvrs osmosis unit with a high flow cllulos actat mmbran (Barnstad D2731) followd by a Barnstad D3804 NANOpur organic/colloid rmoval and ion xchang packd-bd systm. 2.2 Synthsis of m-poly(dvb-vim) Microbads DVB and VIM wr copolymrizd in suspnsion by using AIBN and poly(vinyl alcohol)

4 3 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik as th initiator and stabilizr, rspctivly. Tolun was includd in th polymrization rcip as th dilunt (as a por formr). A typical prparation procdur is dscribd hr. A continuous mdium was prpard by dissolving poly(vinyl alcohol) (200 mg) in th purifid watr (50 m). For th prparation of th disprsion phas, DVB (2.9 ml; 20 mmol) magntit F 3 O 4 nanopowdr (0.5 g) and tolun (10 m) wr stirrd for 10 min at room tmpratur. Thn, VIM (7.3 ml; 80 mmol) and AIBN (100 mg) wr dissolvd in th homognous organic phas. Th organic phas was disprsd in th aquous mdium by stirring th mixtur magntically (500 rpm) in a sald-cylindrical pyrx polymrization ractor. Th ractor contnt was hatd to polymrization tmpratur (i.., 65 o C) within 4 h and th polymrization was conductd for 2 h with a 600 rpm stirring rat at 80 o C. Th final microbads wr xtnsivly washd with thanol and watr to rmov any unractd monomr or dilunt and thn drid at 50 o C in a vacuum ovn. Th microbads thn wr sivd to diffrnt sizs. An inspction with a microscop showd that almost all th microbads wr prfctly sphrical form of μm in diamtr. 2.3 Charactrization Exprimnts of m-poly(dvb-vim) Microbads Th porosity of th microbads was masurd by a N 2 gas adsorption/dsorption isothrm tchniqu (Quantachrom Corporation, Pormastr 60, USA). Th spcific surfac ara of bads in a dry stat was dtrmind by a multipoint Brunaur-Emmtt-Tllr (BET) apparatus (Quantachrom Corporation, Autosorb-6, USA) g of bad was placd in th sampl holdr of th BET and dgassd by passing through N 2 gas onto th bads at 60 o C for 315 min. Th adsorption of th N 2 gas onto th microbads was prformd at K whil its dsorption was prformd at room tmpratur. Exprimntal valus obtaind from th dsorption stp wr usd to calculat th spcific surfac ara of th bads. Por volums and avrag por diamtr for th bads wr dtrmind by th BJH (Barrtt, Joynr, Halnda) modl. Th avrag siz and siz distribution of th bads wr dtrmind by scrn analysis prformd using standard sivs (Modl AS200, Rtsch Gmb & Co., KG, Haan, Grmany). Th watr uptak ratios for th bads wr dtrmind using distilld watr. Th watr uptak xprimnts wr conductd as follows: Dry bads wr carfully wighd out ( g) bfor bing soakd into 50 m vials containing distilld watr. Th vials wr thn placd in an isothrmal watr bath at 25 o C for 2 h aftr which th wt bad sampls wr takn out of th vials, wipd out with a filtr papr, and wighd out. Th watr contnt of th bads was calculatd by using th following xprssion: WS W O Watr uptak (%) = x100 WO (1) whr and ar th wights of bads bfor and aftr watr uptak, rspctivly. Aftr th bad sampls wr drid at 25 o C for 7 days, tiny fragmnts of th bad sampls wr mountd on SEM sampl holdrs on which thy wr sputtr coatd for 2 min. Th sampls wr thn conscutivly mountd in a scanning lctron microscop (Carl Ziss EVO 40, UK) to visualiz th surfac structurs of ach bad sampl at dsird magnification lvls. In ordr to valuat th dgr of VIM incorporation, th synthsizd m-poly(dvb-vim) microbads wr subjctd to lmntal analysis using a co Elmntal Analyzr (Modl CHNS-932, USA). Th magntization curv of th bad sampl was masurd by a vibrating sampl magntomtr (VSM, Princton Applid Rsarch, Modl 150A, USA). Th prsnc of magntit nano-powdrs in th bad sampls was invstigatd with an lctron spin rsonanc (ESR) spctrophotomtr (E 9, Varian, USA). 2.4 Adsorption Exprimnts Batch adsorption xprimnts wr prformd using g of th m-poly(dvb-vim) microbads in 100 m-erlnmyr flasks with 50 m of aquous mtal ion solutions. Th sampl was shakn at 300 rpm in a shaking watr bath (Clifton, England). Aftr th dsird contact tim, th suspnsion was filtrd. Th filtrat was analyzd for mtal ions by using ICP-OES (Prkin Elmr, Optima 2100 DV). Th amount of Ni(II) ions adsorbd onto th

5 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring 35 microbads was calculatd from th diffrnc btwn th initial and th final concntrations. 2.5 Dsorption and Rpatd Us Exprimnts Ni(II) ions adsorbd onto th m-poly(dvb- VIM) microbads wr dsorbd in 0.1 M HNO 3 in a shaking watr bath (Clifton, England) at 300 rpm for 2 h at room tmpratur. Th final Ni(II) ions concntration in th dsorption mdium was dtrmind using ICP-OES (Prkin Elmr, Optima 2100 DV). Th dsorption ratio was calculatd from th amount of Ni(II) ions adsorbd on th m-poly(dvb-vim) microbads and th final Ni(II) ions concntration in th dsorption mdium by using th following xprssion. Amountof Ni( II) ionsdsorbd tothdsorptionmdium Dsorption ratio = x 100 Amountof Ni( II) ionsadsorbd onthmicrobads (2) In ordr to dtrmin th rusability of th msoporous magntic microbads, conscutiv adsorption dsorption cycls wr rpatd 10 tims using th sam magntic microbads. 3. RESUTS AND DISCUSSION 3.1 Charactrization of m-poly(dvb- VIM) Microbads Th suspnsion polymrization procdur providd hr cross-linkd th m-poly(dvb- VIM) microbads in th sphrical form of μm in diamtr. Th N 2 adsorption/dsorption isothrms for th m-poly(dvb- VIM) and th calculatd por siz distributions ar plottd (not shown). Th BET surfac ara (S BET = m 2 g -1 ), por volum (V P = cm 3 g -1 ), and BJH por siz (P BJH = nm) wr found (not shown). Th sampl gav a typ IV Standard isothrm with a dp inflction btwn rlativ prssur P/P o = 0.4 and 0.9, charactristic of capillary condnzation, indicating th uniformity of th msopor-siz distribution (Duan t al, 2008, Souza t al, 2009, Fu t al, 2007). This indicatd that th magntic bads containd mainly msopors. Th quilibrium swlling ratio for th m-poly(dvb-vim) microbads is 44%. It should b also notd that du to thir highly cross-linkd structur, ths microbads ar strong nough to b suitabl for column applications. Th surfac morphology and bulk structurs of th m-poly(dvb-vim) microbads wr visualizd by SEM, as prsntd in Figur 1. All th bads hav a sphrical form and rough surfac. In th SEM photograph of th bulk structur, a larg quantity of wlldistributd pors could b obsrvd and thy hav a ntlik structur. In ordr to facilitat diffusion of Ni(II) ions, th m-poly(dvb-vim) microbads prpard in this study had larg pors. Th m-poly(dvb-vim) microbads wr synthsizd by copolymrizing DVB with VIM at a 1:4 molar ratio with F 3 O 4 in th prsnc of th initiator AIBN. To valuat th dgr of VIM incorporation into th m-poly(dvb-vim) microbads, lmntal analysis (C: 80.74%; H: 7.48%; N: 4.23%) of th synthsizd m- poly(dvb-vim) microbads was prformd. Th incorporation of th VIM was found to b mmol/g polymr from th nitrogn stoichiomtry. Magntic charactristics of magntic matrials ar usually rlatd to th contnt of th magntic componnt. It follows that F 3 O 4 contnt is vry important to th magntic rsponsivnss of magntic matrials. In gnral, a highr F 3 O 4 contnt shows a strongr magntic rsponsivnss (Tsng t al, 2007). For this rason, th avrag F 3 O 4 contnt of th m- poly(dvb-vim) microbads was dtrmind by dnsity analysis. Th hydratd dnsity of th m- poly(dvb-vim) microbads masurd at 25 o C was 1.41 g/m. By th sam procdur, th dnsity of F 3 O 4 particls was found to b 4.94 g/m at 25 o C. Th dnsity of non-magntic poly(dvb-vim) microbads masurd at 25 o C was 1.01 g/m. Th magntic particls volum fraction in th m-poly(dvb-vim) microbads can b calculatd from th following quation drivd from th mass balanc: Ø = ( ρ ρ )/( ρ ρ ) (3) C M C A Whr, ar th dnsitis of non-magntic poly(dvb-vim) microbads, F 3 O 4 nanopowdr, and th m-poly(dvb-vim) microbads, rspctivly. Thus, with th dnsity data mntiond abov, th m-poly(dvb-vim)

6 3 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik microbads gl volum fraction in th magntic bads was stimatd to b 89.2%. Thrfor, th avrag F 3 O 4 contnt of th rsulting m- poly(dvb-vim) microbads was 10.2%. Th prsnc of magntit nanopowdr in th polymr structur was also confirmd by th ESR (not shown). A pak of magntit was dtctd in th ESR spctrum. It should b notd that th non-magntic bads cannot b magntizd undr this condition. It rflcts rspons ability of magntic matrials to th chang of xtrnal magntic fild firstly and it charactrizs th ability of magntic matrials to kp magntic fild strngth whn th xtrnal magntic fild is rmovd. In ordr to show th magntic stability, th m-poly(dvb-vim) microbads wr kpt in distilld watr and ambint air for 3 months, and th sam ESR spctrum was obtaind. With th goal of tsting th mchanical stability of th m-poly(dvb-vim) microbads, a bad sampl was tratd in a ball mill for 12 h. SEM photographs showd that a zro prcntag of th sampl was brokn. Th g factor can b considrd as th quantity charactristic of th molculs in which th unpaird lctrons ar locatd, and it is calculatd from Equation (4). Th masurmnt of th g factor for an unknown signal can b a valuabl aid in th idntification of a signal. In th litratur, th g factor for F(III) is dtrmind btwn for low spin and for high spin complxs (Snl t al, 2008). Th g factor was found to b 2.44 for th m-poly(dvb-vim) microbads structur. g = h. ϑ/ β. H (4) r Hr, is th Planck constant (6.626x10-27 rg s -1 ); is th univrsal constant (9.274x10-21 rg G -1 ); ϑ is frquncy (9.707x10 9 Hz), and is th rsonanc of th magntic fild (G). 3.2 Effct of ph on Adsorption of Ni(II) ions Th adsorption of th mtal ions onto an adsorbnt varis gnrally with ph bcaus ph causs changs to th radius of th hydrolyzd cation and th charg of th adsorbnt surfac. Thrfor, in this study, th adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads was studid as a function of ph. Th initial ph valus of Ni(II) solutions wr kpt btwn 2.0 and 6.0. Th rlationship btwn initial ph and th amounts of Ni(II) ions adsorbd on th m- poly(dvb-vim) microbads for initial solution concntrations of 100 mg dm -3 for at 298 K and a contact tim of 60 min is illustratd in Figur 2. Whn initial ph valus of Ni(II) solutions wr incrasd from 2.0 to 6.0, th amounts of Ni(II) ions adsorbd pr unit mass of adsorbnt incrasd. For xampl, th amounts of Ni(II) ions adsorbd pr unit mass of adsorbnt incrasd from 2.08 to mg g -1 for Ni(II) ions whn th ph valu incrasd from 2.0 to 6.0. As sn in Figur 2, ph 6.0 is a valu for th maximum adsorption of Ni(II) ions. Th m- poly(dvb-vim) microbads xhibitd a low affinity for Ni(II) ions in acidic conditions (ph=4.0), with a somwhat highr affinity at ph=6.0. Th diffrnc in binding bhavior of Ni(II) ions can b xplaind by th diffrnt affinity of Ni(II) ions for th donor atoms (i.., nitrogn) in th VIM (Kara t al, 2004). 3.3 Effct of Tmpratur on Adsorption of Ni(II) ions Th uptak of Ni(II) ions (mg g -1 ) was incrasd from to mg g -1 with th ris in tmpratur from 277 K to 338 K (Figur 3). Equilibrium tim was found to b 60 min. indicating that th quilibrium tim was indpndnt of tmpratur. Th abov rsults also showd that th adsorption was ndothrmic in natur. Th imidazol groups of th m-poly(dvb-vim) microbads ar partially protonatd at all tmpraturs but thir dprotonation dgr dcrass at highr tmpraturs, rsulting in a slight incras in th capacitis of Ni(II) ions at high tmpratur. Whr only adsorption of Ni(II) ions is involvd, th tmpratur ffct on rtntion tim is rlativly small. Empirical studis show that tmpratur has a small ffct on adsorption (Tsng t al, 2007, Ozr t al, 2004, Bayramoglu t al, 2006, Bajpai and Johnson, 2007, Hanafiah t al, 2010, Taqvi t al, 2008). 3.4 Effct of Adsorbnt Dosag on Adsorption of Ni(II) ions Th ffct of adsorbnt dosag on th adsorption of Ni(II) ions is shown in Figur 4. Th prcntag rmoval incrass from 16.3% to 100.0% by incrasing th adsorbnt dosag from 50 to 1000 mg.

7 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring 37 Figur 1. SEM photograph of th m-poly(dvb-vim) microbads. Figur 2. Effct of ph on adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads. Figur 3. Effct of tmpratur on adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads.

8 3 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik Figur 4. Effct of adsorbnt dosag on adsorption of Ni(II) ions. Th adsorption capacity droppd from 16.3 to 5.01 mg/g by incrasing th adsorbnt dosag from 50 to 1000 mg. It is apparnt from Figur 4 that by incrasing th rsin amount, th adsorption fficincy incrass but adsorption dnsity, th amount adsorbd pr unit mass, dcrass. It is radily undrstood that th numbr of availabl adsorption sits incrass by incrasing th adsorbnt amount but th drop in adsorption capacity is basically du to th sits rmaining unsaturatd during th adsorption procss (Olgun and Atar, 2011, Ghassabzadh t al, 2010, Ngah and Fatinathan, 2010, Hanafiah t al, 2009). 3.5 Effct of Initial Concntration of Ni(II) ions on Adsorption of Ni(II) ions Tn diffrnt concntrations for Ni(II) ions, i.., concntrations of 25, 50, 75, 100, 150, 200, 250, 300, 350 and 400 mg.dm -3, wr slctd to invstigat th ffct of th initial concntration of Ni(II) ions onto th m-poly(dvb-vim) microbads. Th amounts of Ni(II) ions adsorbd at quilibrium at 277, 298, 318, and 333 K, rspctivly, and ph 6.0 ar graphd in Figur 5. As shown in Figur 5, with incrasing initial concntration of Ni(II) ions from 25 to 400 mg dm -3, th amount of Ni(II) ions adsorbd by adsorbnt incrass from 3.60 to 14.92, from 4.11 to 21.16, from 4.85 to 22.59, and from 5.97 to mg g -1 of polymr at 277, 298, 318, and 333 K, rspctivly. 3.6 Adsorption Kintics Numrious adsorption procsss hav bn invstigatd, particularly during th past 25 yars. It has bn known that adsorption procss could b dpndnt on and controlld by diffrnt kinds of mchanisms such as diffusion control, mass transfr, chmical ractions and particl diffusion. Th psudo-first-ordr kintic modl, psudo-scond-ordr kintic modl, modifid Ritchi s-scond-ordr kintic modl, and intraparticl diffusion modl wr usd for tsting dynamic xprimntal data at th initial concntration, 100 mg/, of Ni(II) ions and four tmpraturs (277, 298, 318 and 338 K) in ph 6.0. Th psudo-first-ordr kintic modl of agrgrn is givn as follows (agrgrn, 1898) log ( q q ) = log q k t t 1 (5) whr q and q t (mg/g) ar th amounts of th Ni(II) ions adsorbd at quilibrium and at tim (min), rspctivly. k 1 (1/min) is th rat constant of psudo-first-ordr adsorption and q is th adsorption capacity at quilibrium. Th psudo-scond-ordr kintic modl can b xprssd as follows (Ho and McKay, 1999)

9 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring 3 Figur 5. Effct of initial concntration of Ni(II) ions onto th m-poly(dvb-vim) microbads at various tmpraturs. t 1 1 = + t (6) q k q q 2 t 2 q t (mg/g) hav th sam dfini- k is th psudo- whr q and tions as in Equation (5), and 2 scond-ordr rat constant at th quilibrium ((g/mg)/min). Th initial adsorbnt rat h ((mg/g)/min) can b dtrmind from k 2 and q valus using th following quation: h = k q (7) 2 2 Th modifid Ritchi s-scond-ordr kintic modl (Ritchi, 1977) = + (8) qt krqt q whr q t and q (mg/g) hav th sam dfinitions as in Equation (5), and k is th rat constant (1/min) of th modifid Ritchi s-scond- R ordr kintic modl. Th intraparticl diffusion modl can b dscribd as follows (Osman t al, 2011) q 12 t = kit (9) whr q t (mg/g) has th sam dfinitions as in Equation (5), and k i is th intraparticl diffusion rat constant ((mg/g)/min 1/2 ). Th validity of th ordr of th adsorption procss is basd on two critria; th first on is th rgrssion cofficints and th scond on is prdictd q valus (Daoud t al, 2010). Th validitis of ths four kintic modls for all tmpraturs ar chckd and dpictd in Figur 6a-d. Among ths figurs, Figur 6b shows a good agrmnt with th psudo-scond-ordr kintic modl. Th valus of th paramtrs and corrlation cofficint obtaind from ths four kintic modls ar listd in Tabl 1. As shown in Tabl 1, th valus of R 2 for th psudoscond-ordr kintic modl ar xtrmly high, all gratr than , followd by thos of th modifid Ritchi s-scond-ordr kintic modl (Figur 6c), th psudo-first-ordr kintic modl (Figur 6a) and th intraparticl diffusion modl (Figur 6d), rspctivly. Manwhil, th calculatd q valus obtaind from th psudoscond-ordr plots ar found to agr with th xprimntal q valus. Th calculatd q valus stimatd from th Ritchi s-scondordr kintic modl agr slightly with th xprimntal q valus. Thn, bcaus of mass transfr ffcts, th intraparticl diffusion modls wr obtaind for all tmpraturs.

10 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik Figur 6. (a) Figur 6. (b) Figur 6. (c)

11 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring Figur 6. (d) Figur 6. Adsorption kintics of adsorption of Ni(II) ions by th m-poly(dvb-vim) microbads at diffrnt tmpraturs: (a) psudo-first-ordr (b) psudo-scond-ordr (c) Ritchi s-scondordr (d) intraparticl diffusion. Th plots for th intraparticl diffusion modl ar dmonstratd in Figur 6d. Th intraparticl diffusion of Ni(II) ions within th particls of th m-poly(dvb-vim) microbads usd as an adsorbnt was found to b rat-controlling in th adsorbnt procss. Consquntly, th adsorption procss could b bst dscribd by th psudoscond-ordr kintic modl (Plazinski t al, 2009, Zhao t al, 2010). Th valus of th psudo-scond-ordr rat constant, k 2, wr found to incras from 5.019x10-3 to 7.695x10-3 g/mg min, for an incras in th solution tmpratur of 277 to 338 K. Thr is a linar rlationship btwn th k 2 and tmpratur (Figur 7). Th adsorption rat constant is usually xprssd as a function of solution tmpratur by th following Arrhnius typ rlationship (Duan t al, 2008): Ea ln k2 = ln ko (10) RT whr k 2 is th rat constant of th psudoscond-ordr modl of adsorption (g/(mg min)), k o is th indpndnt tmpratur factor (g/(mg min)), R is th gas constant (8.314 J mol -1 K -1 ), and T is th solution tmpratur (K). Thrfor, th rlationship btwn k 2 and T can b rprsntd in an Arrhnius form as: lnk 2 = (11) T From this quation, th activation nrgy for adsorption, E a, is kj mol -1. Th magnitud of activation nrgy xplains th typ of adsorption. Two main typs of adsorption can occur, physical or chmical. In physical adsorption, th quilibrium is usually attaind rapidly and is asily rvrsibl, bcaus th nrgy rquirmnts ar small. Th activation nrgy for physical adsorption is usually not mor than kj mol 1 (1.0 kcal mol 1 ), bcaus th forcs involvd in physical adsorption ar wak. Chmical adsorption is spcific and involvs forcs much strongr than physical adsorption. Two kinds of chmical adsorption ar ncountrd: activatd and, lss frquntly, nonactivatd. Activatd chmical adsorption mans that th rat varis with tmpratur according to a finit activation nrgy in th Arrhnius quation (high E a ). Howvr, in som systms chmical adsorption occurs vry rapidly, suggsting th activation nrgy is nar zro. This is trmd nonactivatd chmical adsorption. It is difficult to dcid which mchanism is ffctiv in th adsorption of Ni(II) ions on m-poly(dvb-vim) microbads, only taking activation nrgis into considration. As th obsrvd valu of th acti-

12 42 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik vation nrgy of adsorption of Ni(II) ions on m- poly(dvb-vim) microbads is gratr for lss than 4.184, th adsorption procss may involv both physical and chmical adsorption. (Rstani t al, 2010, Fu t al, 2007). 3.7 Adsorption Isothrms Th rlationship btwn th amount of Ni(II) ions adsorbd onto th adsorbnt surfac and th rmaining Ni(II) ions concntration in th aquous phas at quilibrium can b obsrvd by th adsorption quilibrium isothrm analysis, as shown in invstigating th ffct of th initial concntration of Ni(II) ions. This rlationship showd that th adsorption capacity incrasd with th quilibrium concntration of th Ni(II) ions in solution, progrssivly raching saturation of th adsorbnt. Adsorption isothrm curvs indicat that th adsorption phnomnon may b rprsntd by isothrms of typ I, which rprsnt a monolayr adsorption until th saturation of activ sits. Th adsorption isothrms wr invstigatd using thr quilibrium modls, th angmuir, Frundlich, and Dubinin- Radushkvich (D R) isothrm modls. Th Frundlich adsorption isothrm quation is givn as (Frundlich, 1906), q = K C (12) 1 n f In logarithmic form, 1 ln q= K f + ln C ( linar form) (13) n whr q is th amount of mtal ions adsorbd at quilibrium tim (mg/g), C is th quilibrium concntration of th mtal ions in solution (mg/), and K f (mg/g)(/mg) 1/n and n ar isothrm constants that indicat capacity and intnsity of th adsorption, rspctivly. Th Frundlich and D-R isothrms ar not as adquat as th angmuir modl ( R ). Th valus of K f and n wr calculatd from th slop and intrcpt of th plot ln q vrsus ln C (not shown). Th valus of K f and n obtaind ar shown in Tabl 2. Th valu of n rangs btwn and If th valu of n is in th rang 1< n <10, th adsorption is favorabl (Kara, 2009). Th angmuir isothrm is xprssd as (angmuir, 1916) C q 1 = Q K C + Q (14) whr Q (mg/g) is th maximum amount of Ni(II) pr unit wight of th m-poly(dvb-vim) microbads ndd to form complt monolayr covrag on th surfac bound at high quilibrium Ni(II) concntration C, and K is th angmuir constant rlatd to th affinity of binding sits (/mg). Q rprsnts a particl limiting adsorption capacity whn th surfac is fully covrd with Ni(II) and assists in th comparison of adsorption prformanc. Q and K ar calculatd from th slops and intrcpts of C th straight lins of plot of vrsus C (not q shown). Paramtrs of th angmuir and Frundlich isothrms computd ar givn in Tabl 2. Th angmuir isothrm fits quit with th xprimntal data corrlation cofficint 2 ( R >0.9905), whras th low corrlation cofficints of th Frundlich isothrm ( R > ) show poor agrmnt with th xprimntal data. Calculatd maximum capacitis ar clos to maximum capacitis obtaind at quilibrium Tabl 2. Th fact that th angmuir isothrm fits th xprimntal data vry wll may b du to homognous distribution of activ sits on th m-poly(dvb-vim) microbads surfac, sinc th angmuir quation assums that th surfac is homognous (Dogan t al, 2000). Furthrmor, th ssntial charactristic of th angmuir isothrm can b xprssd by a dimnsionlss sparation factor calld th quilibrium paramtr R (Namasivayam and Kavita, 2002).

13 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring 43 Figur 7. Arrhnius plot. R 1 = (15) 1 + KC whr K is th angmuir constant (dm 3 mg -1 ) and C is th initial mtal ion concntration (mg dm -3 ). Th paramtr R indicats th shap of th isothrm as follows: Valu of R Typ of isothrm isothrm). This isothrm modl prdicts th natur of th adsorbat sorption onto th adsorbnt and is usd to calculat th man fr nrgy of adsorption. Th nonlinar D-R isothrm is xprssd as: Q = Q K ε (16) 2 D R xp ( D R ) and th linarizd form of th quation is givn as: 2 ln Q ln QD R ( KD Rε ) = (17) R > 1 R = 1 0< R <1 R = 0 Unfavorabl inar Favorabl Irrvrsibl whr Q is th amount of solut adsorbd pr mass of adsorbnt (mg/g), Q D-R is th maximum adsorption capacity (mg/g), K D-R is th D-R constant (mol 2 /J 2 ), and ε is th Polanyi potntial (J/mol), which can b calculatd as: Hr, th valus of R btwn 0 and 1 indicat a favorabl adsorption. R obtaind ar listd in Tabl 2. Th fact that all th R valus for th adsorption of Ni(II) ions onto th m- poly(dvb-vim) microbads ar in th rangs shows that th adsorption procss was favorabl. Although th angmuir and Frundlich isothrm modls ar widly usd, thy do not giv information on th adsorption mchanism. To this aim, th quilibrium data wr tstd with th Dubinin-Radushkvich isothrm modl (D-R ε = RT (ln1 + 1 C ) (18) whr R is th gas constant (J/mol K), T th absolut tmpratur (K), and C th quilibrium concntration of th adsorbat in aquous solution (mg/) (aus t al, 2010, Chn t al, 2008, Tripathy and Raichur, 2008). Th valus of Q D-R and K D-R wr calculatd and ar shown in Tabl 2. Th man fr nrgy of adsorption (E f ) was calculatd from th K D-R valus using th quation: E f = 1 2 (19) KD R

14 32 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik Tabl 1. Kintic paramtrs for th adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads. Paramtrs Tmpratur (K) Exprimntal q (mg/g) Psudo-first-ordr kintic modl Psudo-scond-ordr kintic modl Ritchi s-scond ordr kintic Intraparticl diffusion modl k1 x 10 2 (1/min) qq k2 x 10 3 (mg/g) R2 h ((mg/g)/min ((g/mg)/min) q q(mg/g) R2 kr x 10 2 (1/min) q q(mg/g) R2 ki ((mg/g)/min 0.5 ) R Tabl 2. Paramtrs of angmuir, Frundlich and Dubinin-Raduskhvich isothrm modls, for th adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads. angmuir isothrm constants Frundlich isothrm constants Dubinin-Raduskhvich isothrm constants Paramtrs Tmpratur (K) K x 10 2 (/mg) Q (mg/g) R 2 R rang KF (mg/g)(/mg) 1/n n R 2 QD-R (mg/g) KD-R x10 9 (mol 2 /J 2 ) Ef (kj/mol) R 2 R Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) 44 Uygulamalı Bilimlr v Mühndislik

15 Anadolu Univrsity Journal of Scinc and Tchnology - A 13 (1) Applid Scincs and Enginring 45 Th valu is usd to ascrtain th typ of adsorption procss undr considration. If this valu is btwn 8 and 16 kj mol -1, th adsorption procss can b assumd to involv chmical adsorption. On th othr hand, valus lowr than 8 kj mol 1 indicat that th adsorption procss is of a physical ion xchag mchanism (Ozcan t al, 2005, Unlu and Ersoz, 2006, Tassist t al, 2010). In this study, th D-R isothrm modl is in th rangs and th valus obtaind using th D-R constant, in th nonlinar form, wr kj mol 1 for 277 K, kj mol 1 for 298 K, kj mol 1 for 318 K, and kj mol 1 for 338 K, indicating that th adsorption of Ni(II) ions onto th m- poly(dvb-vim) occurs via a chmical ion xchang mchanism procss for all th tmpraturs. 3.8 Adsorption Thrmodynamics Tmpratur dpndnc of th quilibrium constant, K, can b usd to dtrmin th thrmodynamic paramtrs (Zhou t al, 2009). Th van t Hoff quation is usd to valuat th variation of th quilibrium constant with tmpratur. Th intgratd form of this quation is givn as: o o ΔS ΔH 1 ln K = ( ) (20) R R T 0 0 Th nthalpy ( Δ H ) and ntropy ( Δ S ) changs of th procss can b dtrmind from th slop and intrcpt of th lin obtaind by plotting ln K vrsus 1 T. Th quation of fr nrgy for ach tmpratur is thn obtaind as: 0 0 py ( Δ H ) and ntropy ( Δ S ) changs wr dtrmind as kj/mol and J/mol K, rspctivly, from lnk vrsus 1/T plot (Figur 8). Th positiv valu of ΔH confirmd th 0 ndothrmic charactr of th adsorption procss. 0 Th positiv valus of ΔS also rvald th incras of randomnss at th solid-solut intrfac during th adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads. Th low valu 0 of ΔS indicatd that no rmarkabl changs on ntropy occur. 3.9 Dsorption and Rpatd Us Th us of an adsorbnt in th adsorption procss dpnds not only on th adsorption capacity, but also on how wll th adsorbnt can b rgnratd and usd again. For rpatd us of an adsorbnt, adsorbd mtal ions should b asily dsorbd undr suitabl conditions. Dsorption of th adsorbd Ni(II) ions from th m-poly(dvb-vim) microbads was also studid in a batch xprimntal systm. Dsorption xprimnts rsultd in dsorption of Ni(II) ions aftr 1 h of contact with HNO 3 solutions (0.1 mol/, dsorption prcntag 99%). Rpatd us of HNO 3 solutions of th m-poly(dvb-vim) microbads showd that th adsorption dsorption procss is a rvrsibl procss. Tn cycls of adsorption dsorption xprimnts wr conductd to xamin th capability of th m-poly(dvb-vim) microbads to rtain Ni(II) ions rmoval capacity. Th adsorption capacity of th msoporous m-poly(dvb-vim) microbads dcrasd only 3% during th 10 adsorption dsorption cycls. o o o Δ G = ΔH TΔ S (21) From Equation (21), th Gibbs fr nrgy 0 chang of adsorption ( Δ G ) was calculatd as , , and kj/mol for th adsorption of Ni(II) ions onto th m-poly(dvb- VIM) microbads at 277, 298, 318, and 338 K, 0 rspctivly. Th ngativ Δ G valus indicatd that th adsorption of Ni(II) ions onto th m- poly(dvb-vim) microbads was thrmodynamically fasibl and spontanous. Th nthal-

16 46 Anadolu Ünivrsitsi Bilim v Tknoloji Drgisi - A 13 (1) Uygulamalı Bilimlr v Mühndislik Figur 8. Th plot of ln K vrsus 1/T for th dtrmination of thrmodynamic paramtrs for adsorption of Ni(II) ions onto th m-poly(dvb-vim) microbads. 4. CONCUSIONS In this study, th magnticpoly(divinylbnzn-co-vinylimidazol) (mpoly(dvb-vim)) microbads (avrag diamtr = μm) wr synthsizd and charactrizd. Th physicochmical paramtrs affcting adsorption of Ni(II) ions from aquous solutions wr invstigatd. Th psudo-first-ordr kintic modl, psudo-scond-ordr kintic modl, modifid Ritchi s-scond-ordr kintic modl, and intraparticl diffusion modl wr usd for tsting dynamic xprimntal data at th initial concntration. Th adsorption procss could b bst dscribd by th psudo-scond-ordr kintic modl. Th quilibrium data wr analyzd using th angmuir, Frundlich, and Dubinin-Radushkvich isothrm modls. It was found that th adsorption of Ni(II) ions was wll fittd to th angmuir quation. Thrmodynamic paramtrs rvald that th adsorption was thmodynamically fasibl, spontanous, and ndothrmic in natur. Most importantly, th m- poly(dvb-vim) microbads xhibitd a high stability and good rusability. This showd that th m-poly(dvb-vim)] microbads in this study hav a grat potntial in practical application. ACKNOWEDGMENT This work was supportd by th Rsarch Foundation of Uludag Univrsity (Projct No: UAP(F)-2011/35). REFERENCES Akgol, S., Kusvuran, E., Kara, A., Şnl, S. and Dnizli, A. (2006). Porous dy affinity bads for nickl adsorption from aquous solutions: A kintic study. Journal Applid Polymr Scinc 100(6), Bajpai, S.K. and Johnson, S. (2007). Rmoval of Ni 2+ ions from aquous solution by sorption into poly(acrylamid co sodium acrylat) hydrogls. Journal of Macromolcular Scinc A: Pur and Applid Chmistry 44(3), Bayramoglu, G., Snl, A.U. and Arica, M.Y. (2006). Effct of spacr-arm and Cu(II) ions on prformanc of l-histidin immobilizd on poly(gma/mma) bads as an affinity ligand for sparation and purification of IgG. Sparation and Purifcation Tchnology 50(2), Chn, A.H., iu, S.C. and Chn, C.Y. (2008). Comparativ adsorption of Cu(II), Zn(II) and Pb(II) ions in aquous solution on th

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