Available on line at Association of the Chemical Engineers of Serbia AChE. Chem. Ind. Chem. Eng. Q. 20 (1) (2014)

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1 Availabl on lin at Association of th Chmical Enginrs of Srbia AChE Chmical Industry & Chmical Enginring Quartrly Chm. Ind. Chm. Eng. Q. 2 (1) (214) CI&CEQ MOHAMMAD A. BEHNAJADY SHAHRZAD YAVARI NASSER MODIRSHAHLA Dpartmnt of Chmistry, Collg of Scinc, Tabriz Branch, Islamic Azad Univrsity, Tabriz, Iran SCIENTIFIC PAPER UDC :677:54 DOI /CICEQ126115B INVESTIGATION ON ADSORPTION CAPACITY OF TIO 2 -P25 NANOPARTICLES IN THE REMOVAL OF A MONO-AZO DYE FROM AQUEOUS SOLUTION: A COMPREHENSIVE ISOTHERM ANALYSIS Articl Highlights TiO 2 -P25 nanoparticls show considrabl adsorption capacity Th dsird ph for adsorption of AR27 onto TiO 2 -P25 nanoparticls was 3 W rport a comprhnsiv isothrm analysis for adsorption of AR27 onto TiO 2 -P25 nanoparticls Th kintics of th adsorption procss is found to follow th psudo-scond-ordr kintic modl Abstract In this work TiO 2 -P25 nanoparticls with high surfac ara hav bn usd as adsorbnt for th rmoval of C.I. Acid Rd 27 (AR27), as an organic contaminant from auous solution. Charactristics of phass and crystallit siz of TiO 2 -P25 nanoparticls wr achivd from XRD and th surfac ara and por siz distribution wr obtaind from BET and BJH tchnius. TiO 2 -P25 nanoparticls with almost 8% anatas and 2% rutil phass, th avrag crystallit siz of 18 nm, hav spcific surfac ara of m 2 g 1. Th ffct of various paramtrs lik initial AR27 concntration, ph, contact tim and adsorbnt dosag was carrid out in ordr to find dsird adsorption conditions. Th dsird ph for adsorption of AR27 onto TiO 2 -P25 nanoparticls was 3. Th uilibrium data wr analyzd with various 2-, 3- and 4-paramtr isothrm modls. Euilibrium data fittd vry wll by th 4-paramtr Fritz- Schlundr modl. Th rsults of th adsorption kintics study indicatd that th psudo-scond ordr kintics providd th bst fit with corrlation cofficints clos to unity. Kywords: adsorption; TiO 2 -P25 nanoparticls; isothrm analysis; nonlinar rgrssion analysis; kintics. Wastwatrs producd from industris contain diffrnt typs of organic and inorganic pollutants. Th txtil industry uss larg volums of watr and gnrats considrabl uantitis of wastwatr containing larg amount of dissolvd dy compounds [1-6]. Amongst synthtic dys, azo dys constitut th largst and th most important class of commrcial dys with wid rang applications [7]. Som dys ar carcinognic, and th biodgradation of many dys Corrspondnc: M.A. Bhnajady, Dpartmnt of Chmistry, Faculty of Scinc, Tabriz Branch, Islamic Azad Univrsity, Tabriz, I.R. Iran. bhnajady@iaut.ac.ir; bhnajady@gmail.com Papr rcivd: 1 Jun, 212 Papr rvisd: 3 Novmbr, 212 Papr accptd: 4 Novmbr, 212 yilds toxic aromatic amins [8,9]. C.I Acid Rd 27 (AR27) was usd as a food dy, txtil dy for wool and silk as wll as in photography [1]. Howvr, in 197, Russian studis [11] showd that AR27 was carcinognic. Th disposal of wastwatrs containing dy compounds is a thrat to th nvironmnt. Th rmoval of dys from fflunts is a major problm for txtil industris. Th various chmical and physical tratmnt mthods may b fficint for th rmoval of dys from auous solutions including prcipitation, coagulation-flocculation, rvrs osmosis and oxidation with ozon or hydrogn proxid [12 14]. Adsorption has provn to b on of th most ffctiv mthods for rmoval of organic and inorganic pollutants from auous solutions. This procss has low 97

2 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) capital invstmnt cost, simplicity of dsign and opration. Adsorption onto oxids such as NiO, MgO and TiO 2 has bn found to b important for rmoval of organic and inorganic pollutants. TiO 2 is widly usd as a pigmnt in paints and as a smiconductor in photocatalytic rmoval of pollutants [15]. Adsorption is a vital stag in photocatalytic dgradation of organic pollutants on TiO 2 surfac [16]. Th aim of this work was to study th charactristics of TiO 2 -P25 nanoparticls using som tchnius and invstigation of thir adsorption capacity for AR27, as an organic pollutant from txtil industry. Non-linar trial and rror mthod was usd for analysis of uilibrium data with various 2-, 3- and 4-paramtr isothrm modls. EXPERIMENTAL Matrials Th commrcial azo dy AR27 as a modl pollutant from txtil industry was purchasd from Mrck. Th AR27 is a monoazo anionic dy with C.I. numbr and λ max 522 nm. Th chmical structur of AR27 is givn in Figur 1. Th TiO 2 sampl was supplid by Dgussa, Grmany (TiO 2 -P25). Also, HCl and NaOH wr usd for adjusting ph of solutions. Figur 1. Chmical structur of C.I. Acid Rd 27. Charactrization of TiO 2 nanoparticls XRD analysis (Simns D5 diffractomtr) using CuKα radiation at 2θ angl from 5 to 7 was usd in ordr to dtrmin th crystallit siz and phas composition of th TiO 2 -P25 nanoparticls. Th avrag crystallit siz of th particls was calculatd according to Schrrr s uation [17]: k D = λ β cosθ (1) whr D is th avrag crystallit siz (nm), k is a constant ual to.89, λ is th X ray wavlngth ual to nm, β is th full width at half maximum intnsity (FWHM) and θ is th diffraction angl. If a sampl contains only anatas and rutil, th mass fraction of rutil can b calculatd from th following uation [18]: 1 Rutil phas% = A 1.8 I + IR (2) whr I A and I R ar intgratd intnsitis of th anatas and rutil paks, rspctivly. Surfac ara and porosity wr dfind by Brunaur Emmtt Tllr (BET) and Barrtt-Joynr-Halnda (BJH) masurmnts using Blsorp mini II instrumnt basd on N 2 adsorption-dsorption. Adsorption studis Th adsorption xprimnts wr prformd via th batch tchniu at th tmpratur of 25 C. Adsorption of AR27 onto TiO 2 -P25 nanoparticls was don undr various conditions such as initial ph (3, 5 and 9), adsorbnt dosag (.2,.5 and 1 g L 1 ) and initial AR27 concntration (1, 2, 4, 6 and 8 mg L 1 ). A stock solution of AR27 was prpard in 2 mg L 1 concntration and th dilutd to th appropriat concntration. Th initial ph was adjustd to th ruird valus with small amount of NaOH or HCl solutions bfor mixing with th TiO 2 -P25 nanoparticls. Sampls wr cntrifugd at 4 rpm for 5 min and masurmnt of AR27 rmaining concntration in th solution was don using a UV-Visibl spctrophotomtr (Pharmacia Biotch Ultrospc 2). Th adsorption yild (%) was calculatd from th following uation: C C = t (3) Adsorption% 1 C whr C : initial AR27 concntration (mg L 1 ); C t : AR27 concntration at any tim (mg L 1 ). Th amount of AR27 adsorbd onto TiO 2 -P25 nanoparticls at uilibrium, (mg g 1 ), was calculatd by th following rlationship: ( C C ) V W = (4) whr C is th uilibrium concntration of AR27 (mg L 1 ), V is th volum of th solution (L) and W is th wight of th TiO 2 -P25 nanoparticls as an adsorbnt (g). In th all xprimnts th volum of th solution was 1 ml. 98

3 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) RESULTS AND DISCUSSION Charactrization of TiO 2 nanoparticls Th XRD pattrn of TiO 2 -P25 nanoparticls (Figur 2) for 2θ diffraction angls btwn 5 and 7 shows fiv primary paks at 25.2, 38, 48.2, 55 and 62.5, which can b attributd to diffrnt diffraction plans of anatas TiO 2 and four diffrnt paks at 27.5, 36, 54 and 69, which can b attributd to diffrnt diffraction plans of rutil phas of TiO 2. According to th XRD rsults TiO 2 -P25 nanoparticls hav almost 8% anatas and 2% rutil phass. Th avrag particl siz of TiO 2 -P25 nanoparticls was dtrmind from th XRD pattrn according to Schrrr s uation as 18 nm.figur 3a shows nitrogn adsorption-dsorption isothrms onto TiO 2 - P25 nanoparticls, which is in accordanc with classical typ III isothrm of IUPAC classifications suggsting th prsnc of msoporous structur [19]. BET surfac ara and total por volum of th TiO 2 -P25 nanoparticls which dtrmind by N 2 physisorption xprimnts wr m 2 g 1 and.3879 cm 3 g 1, rspctivly. Figur 3b shows th por siz distribution of th TiO 2 -P25 nanoparticls as stimatd according to th BJH mthod from th adsorption branch. As it is vidnt, th sampl Figur 2. XRD Pattrn of TiO 2 -P25 nanoparticls. (a) (b) Figur 3. Nitrogn adsorption and dsorption isothrms and por siz distribution curv calculatd from th adsorption branch for TiO 2 -P25 nanoparticls. 99

4 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) prsnts a uit xtndd por siz distribution rang from 2 to ovr 1 nm. TiO 2 -P25 nanoparticls producd through hydrolysis of TiCl 4 in a hydrogn flam do not contain pors in ach TiO 2 crystallits. Thrfor, th formation of th por structurs in th sampls could b attributd to th aggrgations of TiO 2 crystallits [2]. TiO 2 -P25 nanoparticls with high surfac ara can b usd for fficint adsorption of nvironmntal pollutants with optimization of oprational paramtrs. Adsorption bhavior Th ffct of initial ph Th adsorption of AR27 was studid at diffrnt initial phs and adsorbnt dosags. Figur 4 indicats th ffct of initial ph on th adsorption prcnt of AR27 onto TiO 2 at 25 C aftr 3 min uilibration for 6 mg L 1 initial AR27 concntration. Th rsults show that th ph of th systm plays an important rol in this procss and highr adsorption can b obtaind at lowr ph valus; thus, highst adsorption occurrd at ph 3. Adsorption% Adsorbnt = 1 g/l Adsorbnt =.2 g/l ph Figur 4. Effct of initial ph on th adsorption of AR27 onto TiO 2 -P25 nanoparticls. [AR27] = 6 mg L 1. Th intraction of solut with mtal oxid surfac is dtrmind by surfac charg of mtal oxid and ionization stat of solut. Nanoparticls of TiO 2 in watr ar of amphotric natur and ar known to hav th following acid-bas uilibrium [21]: + 1 TiOH pk a + 2 TiOH H > + (5) pk a 1 TiOH + TiO H > + (6) Th ph of zro point of charg (ph zpc ) rprsnts surfac charg of mtal oxid at diffrnt initial phs. At low ph undr conditions in which ph < < ph zpc th positivly chargd surfac sits on th adsorbnt incras, whil at high ph undr conditions in which ph > ph zpc th ngativly chargd surfac sits incras. Th ph zpc for TiO 2 -P25 nanoparticls is 6.25 [22]. Intractions btwn AR27 molculs with anionic charactr and adsorbnt sits will b favord at low ph (ph < ph zpc ). In th othr words, formation of > TiOH + 2 at low ph valus and lctrostatic attraction is mainly rsponsibl for AR27 adsorption onto TiO 2 surfac [8,24,25]. Th ffct of initial dy concntration, contact tim and adsorbnt dosag Figur 5 shows th ffct of contact tim and initial AR27 concntration in th adsorption prcnt onto TiO 2 -P25 nanoparticls. Rsults in this figur indicat that adsorption prcnt dcrass significantly from 97 to 39% with incrasing of initial concntration of AR27 from 1 to 8 mg L 1. Lowr adsorption prcnt at highr initial concntrations of AR27 can b rlatd to th saturation of adsorption sits onto TiO 2 -P25 nanoparticls. According to th rsults in this figur majority of adsorption occurrd in th first 5 min and thn th adsorption % incrass 1 Adsorption% [AR27] = 1 mg/l [AR27] = 2 mg/l [AR27] = 4 mg/l [AR27] = 6 mg/l [AR27] = 8 mg/l Tim (min) Figur 5. Th ffct of contact tim and initial AR27 concntration on th adsorption of AR27 onto TiO 2 -P25 nanoparticls. TiO 2 -P25 = 1 g L 1, ph 3. 1

5 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) with a vry low slop. Th rapid adsorption at th initial 5 min indicats surfac bound adsorption to availabl positivly chargd surfac of TiO 2 -P25 nanoparticls as a rsult of lctrostatic attraction and th slow scond phas is du to th slow diffusion of solut onto th pors of TiO 2 -P25 nanoparticls [23]. Th rsults in this figur show that th ruird contact tim to rach th uilibrium of AR27 onto TiO 2 - -P25 nanoparticls is 2 min. Th rsults in Tabl 1 show th ffct of initial AR27 concntration in th adsorbd amount at uilibrium tim ( ). As can b sn from ths rsults, incrass with incrasing of initial AR27 concntration. This is probably du to a high driving forc for mass transfr. In th othr words, highr initial concntrations provid an important driving forc for adsorption of AR27 onto TiO 2 - -P25 nanoparticls. Th rsults in Tabl 1 indicat that adsorption prcnt incrass and dcrass with incrasing of adsorbnt dosag. Incrasing of adsorption % is du to th nhancing of adsorbnt surfac ara which rsults from incrasing of adsorbnt dosag. Th dcras in th rsult of adsorbnt dosag incras can b rlatd to th unsaturation of som adsorption sits in th high adsorbnt dosags. Adsorption isothrm analysis Th adsorption isothrms can b usd to uantify th amount of adsorbd substrat on an adsorbnt as a function of concntration at a givn tmpratur. Various 2, 3 and 4-paramtr isothrm modls wr proposd in litratur for dscribing th amount of adsorbat at uilibrium conditions. Th diffrnt paramtrs in adsorption modls provid som information about sorption mchanism, surfac proprtis and affinity of sorbnt [26]. Two-paramtr (2-p) isothrm modls A list of 2-p isothrm modls is givn in Tabl 2. All th modl paramtrs wr valuatd by non- -linar trial and rror mthod using Polymath 6. softwar, bcaus non-linar mthod avoids th variation in rror distribution du to linarization and is mor appropriat mthod to dtrmin optimum sorption isothrm [26]. Th calculatd adsorption modls paramtrs at 95% confidnc intrval; rgrssion cofficint (R 2 ) and adjustd rgrssion cofficint (R 2 adj) ar rportd in Tabl 3. In this work R 2 and R 2 adj wr usd to gaug th goodnss-of-fit. For th rgrssion modl to b stabl and statistically valid, th confidnc intrvals must b much smallr than th rspctiv paramtr valus. Figur 6 show non-linar rgrssion of 2-p isothrm modls to xprimntal data. Tabl 2. 2-Paramtr isothrm modls Modl Euation Paramtrs 2-p Langmuir mklc m, K L = 1 + KC L 2-p Frundlich 1 K F, n = KFC n 2-p Tmkin RT K T, ΔQ = ln( KC T ) Δ Q Langmuir isothrm modl Th Langmuir adsorption modl is th most common isothrm modl, which dscribs th monolayr covrag of adsorbat molculs on adsorbnt sits without any intractions btwn adsorbat molculs on adjacnt sits. In this isothrm all sits ar uivalnt and th surfac is homognous [27]. Th rsults of non-linar rgrssion analysis of Langmuir modl for adsorption of AR27 onto TiO 2 -P25 indicat a rlativly high R 2 btwn 2-p isothrm modls and also good accordant btwn R 2 and R 2 adj. Th maximum mono-layr capacity ( m ) obtaind from Langmuir modl was mg g 1. Tabl 4 lists maximum capacity of th mono-layr adsorption of TiO 2 -P25 and othr mtal oxid nanoparticls rportd in th litratur. In gnral tstd TiO 2 -P25 in this work xhibitd comparabl adsorption capacity in comparison with othr mtal oxid nanoparticls. K L in th Langmuir modl is a constant attributd to th affinity btwn th adsorbat and adsorbnt [29]. A dimnsionlss constant calld th sparation factor (K R ) can b usd for indicating th typ of adsorption using th Langmuir constant (K L ) as follows: Tabl 1. Th AR27 adsorption and in diffrnt adsorbnt dosags and initial adsorbat concntrations TiO 2 dosag g L 1 Adsorption % AR27 concntration, mg L Adsorption % Adsorption % Adsorption % Adsorption %

6 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) Tabl 3. 2-Paramtr isothrm modl paramtr valus (±95% confidnc lvl) Modl R 2 R 2 adj Paramtrs Paramtrs valus 2-p Langmuir m K L (±.145).242 (±.4) 2-p Frundlich K F n (± ) (± ) 2-p Tmkin RT/ΔQ (± ) (± ) 4 K T 3 ( ) C (mg L -1 ) Exprimntal Langmuir Frundlich Tmkin Figur 6. 2-paramtr isothrm modls for adsorption of AR27 onto TiO 2 -P25 nanoparticls. TiO 2 -P25 = 1 g L 1, ph 3. 1 K R = (7) 1 + KC L K R valu indicat th typ of adsorption as: K R = irrvrsibl adsorption, <K R <1 favorabl adsorption, K R = 1 linar adsorption, K R >1 unfavorabl adsorption. K R valus obtaind for adsorption of AR27 onto TiO 2 -P25 at diffrnt initial concntrations of adsorbat ar btwn zro and on, indicating th adsorption is favorabl. Frundlich isothrm modl Th Frundlich isothrm is th most important adsorption isothrm for rough and htrognous surfacs with intraction btwn adsorbd molculs. In this isothrm 1/n is th htrognity factor and indicats dviation from linar adsorption. If th valu of n = 1, th adsorption is linar; if n < 1, th adsorption is chmical; and if n > 1, th adsorption is a favorabl physical procss [3]. Th R 2 valu obtaind for Frundlich isothrm is slightly lowr than othr 2-p isothrm modls. According to th xprimntal data in high concntrations of adsorbat a platau is rachd (Figur 6). Th Frundlich isothrm cannot prdict this platau [29]. Th valu of for n indicats that adsorption of AR27 onto TiO 2 -P25 is a favorabl physical procss. Tmkin isothrm modl Tmkin studid [31] th hat of adsorption and th adsorbat-adsorbat intractions. This isothrm gav a satisfactory fit to xprimntal data. In this isothrm ΔQ is rlatd to th hat of adsorption, T is Tabl 4. Comparison of th maximum adsorption capacity of TiO 2 -P25 with othr mtal oxid nanoparticls Dy Adsorbnt m / Rfrnc Ractiv Brilliant Rd X-3B NiO nanoshts 3.4 [28] Congo Rd [28] Fuchsin Acid 22 [28] Ractiv Yllow 145 TiO 2 /SiO [25] Ractiv Black [25] Acid Rd 27 TiO 2 -P This work 12

7 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) th absolut tmpratur (K), R is th univrsal gas constant (8.314 J mol 1 K 1 ) and K T is th Tmkin modl constant (L mg 1 ) [31]. Th adsorption nrgy obtaind for adsorption of AR27 onto TiO 2 -P25 was J mol 1, which indicats an ndothrmic adsorption procss. Thr-paramtr (3-p) and four-paramtr (4-p) isothrm modls A list of 3-p and 4-p isothrm modls is givn in Tabl 5. All th modl paramtrs for ths isothrms valuatd by non-linar mthod and R 2 and R 2 adj valus ar rportd in Tabl 6. Figur 7 also shows non-linar rgrssion of 3-p and 4-p isothrm modls to th xprimntal data. Tabl and 4-Paramtr isothrm modls Modl Euation Paramtrs 3-p Rdlich- AC A, B, g = g Ptrson 1 + BC α 3-p Sips m( K ac) m, K a, α = α 1 + ( KC a ) 3-p Toth mk THC m, K Th, β = 1 [1 + ( K THC ) β ] β K 4-p Fritz- JC J, K, L, M = Schlundr M 1 + LC Rdlich-Ptrson isothrm modl Th Rdlich-Ptrson isothrm is an mpirical uation with thr paramtrs, which has faturs of th both Langmuir and Frundlich isothrm uations. In this uation A, B and g ar modl constants, which th valu of g lis btwn and 1 [32]. Whn g = 1, this isothrm transforms to Langmuir isothrm and whn g = transforms to linar form of Frundlich isothrm (Hnry s law) [26]. Th valu of.9 for g in Rdlich-Ptrson isothrm indicats that th isothrm is approaching th Langmuir but not Frundlich isothrm, which provs prvious rsults of bttr fitting of xprimntal data by th Langmuir isothrm modl. Sips isothrm modl An isothrm was proposd by Sips in 1948 [33] that has a similar form to th Frundlich isothrm and at low adsorbat concntrations rducs to this isothrm. Th Sips isothrm at high adsorbd concntrations prdicts a mono-layr adsorption capacity similar to th Langmuir isothrm. Th paramtr of α in this isothrm is rlatd to th systm s htrognity [34]. Th Sips isothrm shows a good prdiction of AR27 adsorption onto TiO 2 -P25 nanoparticls, with rlativly high valu of R 2. Th valu of α is closr to 1 and indicats that th adsorption of AR27 onto TiO 2 -P25 nanoparticls is approaching Langmuir form mor than Frundlich form. Toth isothrm modl Toth isothrm was drivd from potntial thory for adsorption in htrognous systms. This isothrm assums most adsorption sits hav sorption nrgy lss than th man valu [35]. Unlik to Frundlich and Sips isothrm modls, this isothrm rducs into th corrct Hnry law in th low concntrations and for β = 1 this isothrm transforms to th Langmuir isothrm. Th valu of β in this study is closr to 1, maning that AR27 adsorption onto TiO 2 - -P25 nanoparticls is mor of a Langmuir form. Fritz-Schlundr isothrm modl This isothrm contains mor paramtrs than any othr isothrms and is an mpirical isothrm [36]. In th absnc of a thortical modl that could account for th chmical htrognity of th surfac Tabl and 4-Paramtr isothrm modl paramtr valus (±95% confidnc lvl) Modl R 2 R 2 adj Paramtrs Paramtrs valus 3-p Rdlich-Ptrson A B g (±.145).7 (±.9).9 (±.2) 3-p Sips m K a α (± ).156 (± ).691 (± ) 3-p Toth m K Th β (±4.1813).654 (±2.6475).873 (±.445) 4-p Fritz-Schlundr J K L M 1.69 (± ).426 (± ).2 (± ) 2.71 (± ) 13

8 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) 4 3 ( ) C (mg L -1 ) Exprimntal Rdlich-Ptrson Sips Toth Fritz-Schlundr Figur and 4-paramtr isothrm modls for adsorption of AR27 onto TiO 2 -P25 nanoparticls. TiO 2 -P25 = 1 g L 1, ph 3. and simultanous prvalnc of diffrnt adsorption mchanisms; prhaps a modl with mor paramtrs could b abl to prdict uilibrium data bttr [29]. A comparison btwn R 2 valus for fitting xprimntal data by various isothrm modls indicating that th 4-p Fritz-Schlundr modl fits xprimntal data bttr than othr isothrms. In comparison with othr curvs obtaind for various isothrms in Figurs 6 and 7, bttr coincidnc was obtaind btwn xprimntal and rsults obtaind from th 4-p Fritz- Schlundr modl. Adsorption kintic studis Kintic modling Adsorption kintics is xprssd as th adsorbnt rmoval rat which is important in stimating th ruird rsidnc tim of adsorbnt in th systm. Various kintic modls hav bn usd in adsorption procss. Th psudo-first-ordr and psudo-scondordr ar th widly usd kintic modls in this procss [34]. Th Lagrgrn psudo-first-ordr kintic modl is xprssd as follows [37]: log( ) log kt t = (8) whr is th adsorption capacity at uilibrium (mg g 1 ), t is th adsorption capacity at tim t (mg g 1 ) and k 1 is th psudo-first-ordr rat constant (min 1 ). Th plot of log( t ) against t givs a slop of k 1 and intrcpt of log. Th valus of R 2 for th psudofirst-ordr kintic modl in th adsorption of diffrnt concntrations of AR27 onto TiO 2 -P25 ar lowr than.92 (Tabl 7), which indicats that th psudo-firstordr kintic modl can not fit prfctly th xprimntal data. Th Ho psudo-scond-ordr kintic modl is xprssd as follows [38]: t 1 t = k + (9) t 2 2 Th constants of this uation wr dtrmind xprimntally by plotting t/ t vrsus t (Figur 8). Th valus of k 2, and R 2 for psudo-scond-ordr kintic modl ar givn in Tabl 7. Rsults in Tabl 7 show that AR27 adsorption onto TiO 2 -P25 nanoparticls has vry good complianc with psudo-scond- Tabl 7. Th psudo-first-ordr, psudo-scond-ordr and intraparticl diffusion kintic modl constants for th adsorption of th AR27 onto TiO 2 -P25 for diffrnt AR27 initial concntrations. TiO 2 -P25 = 1 g L -1, ph 3 [AR27] mg L -1 (xp.) Psudo-first-ordr kintic modl Psudo-scond-ordr kintic modl Intraparticl diffusion kintic modl k 1 (cal.) R 2 k 2 (cal.) R 2 k p,2 C i R 2 min -1 g mg -1 min -1 min

9 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) ordr kintic modl. Th valus of R 2 ar gratr than.99 for all xprimnts. Also, th calculatd valus ar in good agrmnt with th xprimntal data. According to this modl two ractions occur, th first on is fast and rachs uilibrium uickly and th scond is slow that can continu for a long tim [39]. t/t [AR27] = 1 mg/l [AR27] = 2 mg/l [AR27] = 4 mg/l [AR27] = 6 mg/l [AR27] = 8 mg/l Tim (min) Figur 8. Th psudo-scond-ordr kintic plot for adsorption of AR27 onto TiO 2 -P25 nanoparticls. TiO 2 -P25 = 1 g L 1, ph 3. Adsorption mchanism In ordr to idntify adsorption mchanism Wbr and Morris [4] intraparticl diffusion modl was tstd. This modl is xprssd as follows:.5 t pi i = k t + C (1) whr k pi is th rat paramtr of stag i (mg g 1 min.5 ) and C i is th intrcpt of stag i that givs an ida about th thicknss of boundary layr. Th plot of t against.5 t (Figur 9) indicats that th adsorption procss is comprisd of two phass, involving adsorption on th xtrnal surfac and intraparticl or por diffusion. In th othr words, th initial linar portion of th plot indicats boundary layr ffct, whil th scond linar portion is du to intraparticl diffusion. Thrfor th slop of scond linar portion of th plot has bn considrd as th k p (Tabl 7) [39,41]. CONCLUSION In this work TiO 2 -P25 nanoparticls with 18 nm crystallit siz and 58.6 m 2 g 1 surfac ara containing 8% anatas and 2% rutil wr usd as an fficint adsorbnt for rmoval of AR27 as a monoazo anionic dy from auous solutions. Exprimntal data indicat that ph is a vry important factor in this procss and optimal ph for highst adsorption of AR27 onto TiO 2 -P25 nanoparticls is 3. Adsorption prcnt is snsitiv to AR27 initial concntration and dcrass from 97 to 39% with incrasing initial concntration of AR27 from 1 to 8 mg L 1. Th maximum mono-layr capacity of TiO 2 -P25 in th adsorption of AR27 rachd mg g 1, which is comparabl with othr mtal oxid nanoparticls. A comprhnsiv isothrm analysis for adsorption of AR27 onto TiO 2 -P25 nanoparticls indicats that th bst fit to th uilibrium data was providd by th 4-p Fritz-Schlundr modl. Th kintics of th adsorption procss was found to follow th psudo-scond-ordr kintic modl. Gnrally, th TiO 2 -P25 nanoparticls wr ffctivly capabl to rmov th wid rang concntrations of AR27 from auous solutions in acidic phs. t ( ) [AR27] = 1 mg/l [AR27] = 2 mg/l [AR27] = 4 mg/l [AR27] = 6 mg/l [AR27] = 8 mg/l Tim.5 (min.5 ) Figur 9. Th intraparticl diffusion plot for adsorption of AR27 onto TiO 2 -P25 nanoparticls. TiO 2 -P25 = 1 g L -1, ph 3. 15

10 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) Acknowldgmnts Th authors would lik to thank th financial support of Tabriz branch, Islamic Azad Univrsity, and th Iranian Nanotchnology Initiativ Council, Iran. REFERENCES [1] S.A. Figuirdo, J.M. Louriro, A.R. Boavntura, Watr Rs. 39 (25) [2] C. Sourja, D. Sirshndu, D. Sunando, K.B. Jayanta, Chmosphr 58 (25) [3] C. Namasivayam, S. Sumithra, J. Environ. Manag. 74 (25) [4] O. Abdlwahab, A. El Nmr, A. El-Sikaily, A. Khald, Chm. Ecol. 22 (26) [5] A. El-Sikaily, A. Khald, A. El Nmr, O. Abdlwahab, Chm. Ecol. 22 (26) [6] B. Noroozi, G. A. Sorial, H. Bahrami, M. Arami, J. Hazard. Matr., B 139 (27) [7] M. Namtu, I. Siminicanu, A. Ydilr, A. Kttrup, Dys Pigmnts 53 (22) [8] M.F. Bonigr, in Carcinognity of azo dys drivd from bnzidin, Pub. No , Cincinnati, OH, 198 [9] T. Zhng, T.R. Holford, S.T. Mayn, P.H. Owns, P. Boyl, B. Zhang, Eur. J. Cancr 38 (22) [1] M. Karkmaz, E. Puznat, C. Guillard, J.M. Hrrmann, Appl. Catal., B 51 (24) [11] M. Prz-Uruiza, J. L. Bltran, J. Chromatogr., A 898 (2) [12] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Biorsour. Tchnol. 77 (21) [13] P. Coopr, J. Soc. Dyrs Colour. 19 (1993) 97-1 [14] Y.M. Slokar, A. Majcn L Marchal, Dys Pigmnts 37 (1998) [15] I.K. Konstantinou, T.A. Albanis, Appl. Catal., B 49 (24) 1-14 [16] V. Blssi, D. Lambropoulou, I. Konstantinou, R. Zboril, J. Tuck, D. Jancik, T. Albanis, D. Ptridis, Appl. Catal., B 87 (29) [17] A.L. Pattrson, Phys. Rv. 56 (1939) [18] R.A. Spurr, H. Myrs, Anal. Chm. 29 (1957) [19] K.S.W. Sing, D.H. Evrtt, R.A.W. Haul, L. Moscou, R.A. Pirotti, J. Rouurol, T. Siminiwska, Pur Appl. Chm. 57 (1985) [2] J. Yu, H. Yu, B. Chng, M. Zhou, X. Zhao, J. Mol. Catal., A 253 (26) [21] K. Bourikas, M. Stylidi, D.I. Kondarids, X. Vrykios, Langmuir 21 (25) [22] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnmann, Chm. Rv. 95 (1995) [23] M. Ahmaruzzaman, S.L. Gayatri, J. Chm. Eng. Data 55 (21) [24] P.K. Dutta, A.K. Ray, V.K. Sharma, F.J. Millro, J. Colloid Intrf. Sci. 278 (24) [25] A. Agudach, S. Brosillon, J. Morvan, E.K. Lhadi, Appl. Catal., B 57 (25) [26] K. Vasanth Kumar, S. Sivansan, Dys Pigmnts 72 (27) [27] I. Langmuir, J. Am. Chm. Soc. 38 (2) [28] Z. Song, L. Chn, J. Hu, R. Richards, Nanotchnol. 2 (29) [29] J.U.K. Oubagaranadin, Z.V.P. Murthy, AICHE J. 56 (21) [3] H.M.F. Frundlich, Z. Phys. Chm. 57A (196) [31] M.J. Tmkin, V. Pyzhv, Acta Physiochim. URSS 12 (194) [32] O. Rdlich, D.L. Ptrson, J. Phys. Chm. 63 (1959) [33] R. Sips, J. Chm. Phys. 16 (1948) [34] J. Fbrianto, A. Natasia Kosasih, J. Sunarso, Y. H. Ju, N. Indraswati, S. Ismadji, J. Hazard. Matr. 162 (29) [35] J. Toth, J. Colloid Intrf. Sci. 225 (2) [36] W. Fritz, E. U. Schlundr, Cram. Eng. Sci. Proc. 29 (1974) [37] S. Lagrgrn, Handlingar 24 (1898) [38] Y.S. Ho, G. McKay, Procss Biochm. 34 (1999) [39] Y. Khambhaty, K. Mody, S. Basha, B. Jha, Chm. Eng. J. 145 (29) [4] W.J. Wbr, J.C. Morris, J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89 (1963) 31-6 [41] M. Dogan, H. Abak, M. Alkan, J. Hazard. Matr. 164 (29)

11 M.A. BEHNAJADY t al: INVESTIGATION ON ADSORPTION CAPACITY Chm. Ind. Chm. Eng. Q. 2 (1) (214) MOHAMMAD A. BEHNAJADY SHAHRZAD YAVARI NASSER MODIRSHAHLA Dpartmnt of Chmistry, Faculty of Scinc, Tabriz Branch, Islamic Azad Univrsity, Tabriz, Iran NAUČNI RAD ISPITIVANJE ADSORPCIONOG KAPACITETA TIO 2 -P25 NANOČESTICA ZA UKLANJANJE MONO-AZO BOJE IZ VODENOG RASTVORA: SVEOBUHVATNA ANALIZA IZOTERMI U ovom radu, TiO 2 -P25 nanočstic vlik spcifičn površin su korišćn kao adsorbnt za uklanjanj azo boj Acid Rd 27 (AR27) iz vodnog rastvora. Karaktristik faza i vličina kristala TiO 2 -P25 nanočstica su odrđn XRD analizom, dok su spcifična površina i raspodla vličin pora dobijn BET i BJH thnikom. TiO 2 -P25 nanočstic sa gotovo 8% anataz faz i 2% rutil faz, srdnj vličin kristala 18 nm, imaju spcifičnu površinu 56,82 m 2 g -1. Da bi s odrdili žljni uslovi adsorpcij, ispitivan j uticaj različitih paramtara (počtna koncntracija AR27, ph, kontaktno vrm i doza adsorbnta). Požljna ph vrdnost za adsorpciju AR27 na TiO 2 -P25 nanočsticama j bio 3. Ravnotžni podaci su analizirani dvo-, tro- i čtvoro-paramtarskim modlima adsorpcion izotrm. Ravnotžni podaci dobro fituju čtvoro-paramtarski modl Fritz-Schlundra. Rzultati proučavanja kintik adsorpcij su pokazali da modl sa kintikom psudo drugog rda daj najbolj slaganj, sa koficijntom korlacij blizu jdan. Ključn rči: TiO 2 -P25 nanočstic, analiza izotrmi, nlinarna rgrsiona analiza, kintika. 17