Isotherm and Thermodynamic Analysis on the Adsorption of Rhoda mine B Dye onto Borassus flabellifer bark Nano Carbon

Transcription

1 IOSR Journal of Applid Chmistry (IOSR-JAC) -ISSN: Volum 11, Issu 4 Vr. I (April. 2018), PP Isothrm and Thrmodynamic Analysis on th Adsorption of Rhoda min B Dy onto Borassus flabllifr bark Nano Carbon M.Thiruchlvi 1, M.M.Snthamilslvi 2, B.R.Vnkatraman 3, S. Arivoli 4, And N.Muruganantham 5 1 Dpartmnt of Scinc, Nagammai Tachr Training Institut, Priyar Cntnary Educational Complx, Tiruchirappalli, Tamil Nadu, India. 2 Offic of th Rgional Joint Dirctorat of Collgiat Education, Tiruchirappalli, Tamil Nadu, India. 3 Post Graduat and Rsarch Dpartmnt of Chmistry, Priyar E.V.R.Collg (Autonomous), Tiruchirappalli, Tamil Nadu, India. 4 Associat Profssor, Dpartmnt of Chmistry, Thiru.Vi. Ka. Govrnmnt Arts Collg, Thiruvarur, Tamil Nadu, India. 5 Post Graduat and Rsarch Dpartmnt of Chmistry, Thanthai Hans Rovr Collg (Autonomous), Prambalur, Tamil Nadu, India. Abstract: Application of activatd Borassus flabllifr bark nano carbon (ABNC) for th rmoval of a Cationic dy, Rhodamin B, from aquous solutions has bn invstigatd. Th xprimnts wr carrid out in batch mod. Effct of th paramtrs such as ph, initial dy concntration and tmpratur on th rmoval of th dy was studid. Equilibrium was achivd in 60 min. Maximum adsorption of dy was achivd at ph 6.6. Rmoval prcntag was found to b dpndnt on th initial concntration of dy solution, and maximum rmoval was found to b 96% at 25 mg/l of Rhodamin B. Th rmoval incrass from 80% to 96%whn th initial concntration of dy solution dcrass from 125 mg/l to 25 mg/l. Th quilibrium adsorption data wr analyzd by Langmuir, Frundlich, Tmkin and Dubinin Radushkvich isothrm modls. Th (Langmuir) adsorption capacity of th adsorbnt is found to b mg/g at303 K. Kintic modling of th procss of rmoval was carrid out and th procss of rmoval was found to follow a psudo scond ordr modl. Th thrmodynamic paramtrs such as chang in fr nrgy (ΔG 0 ), nthalpy (ΔH 0 ) and ntropy (ΔS 0 ) wr dtrmind and th ngativ valus of ΔG 0 indicatd that th procss of rmoval was spontanous at all valus of tmpraturs. Furthr, th valus of ΔH 0 indicatd th ndothrmic natur of th procss of rmoval. Ky words: Activatd Borassus flabllifr bark nano carbon (ABNC); Rhodamin-B dy; Adsorption isothrm; Kintics; Equilibrium modls Dat of Submission: Dat of accptanc: I. Introduction With th rvolution in txtil industris, thy discharg colord fflunts such as organic dys lik mthyln blu and rhodamin-b to watr bodis. Ths colord fflunts hav larg amounts of suspndd organic solids which ar harmful to human bings and toxic for organisms. Th rmoval of ths dys from wastwatr has a considrabl attntion ovr th past dcads to dcras thir impact on th nvironmnt [1]. Svral physical and chmical mthods hav bn dvlopd for th rmoval of organic dys from industrial fflunts [2]. Physical mthods, mainly adsorption on various supports wr rcognizd to b a promising and ffctiv procss to rmov dys from industrial wast watr compltly [3, 4]. Th main advantags of adsorption ar th rusability of matrial, low-cost, as of opration and short tim of opration. So it is ncssary to dvlop ffctiv adsorbnts for th rmoval of dys from txtil fflunts. Activatd carbon is th most widly usd adsorbnt and can b prpard by physical activation in which carbonation or pyrolysis of th carbonacous matrial at highr tmpratur ( ºC) in an inrt atmosphr followd by thrmal activation at th sam tmpratur in th prsnc of oxidizing agnt such as air, stam and carbon dioxid or chmical activation in which pyrolysis and activation carrid out only in on stp simultanously in prsnc of dhydrating agnt such as H 3 PO 4, HNO 3, KOH, NaOH, H 2 O 2, H 2 SO 4.Chmically activatd carbon has highr yild, mor surfac ara and bttr dvlopmnt of porous structur than that obtaind by physical activation [5]. Svral attmpts hav bn mad for th prparation of activatd carbon from agricultur wasts. In this articl, w hav rportd th us of natural bio matrials as an altrnativ du to thir rlativ abundanc and thir low commrcial valus. Borassus flabllifr bark is th most ancint plant of India. It is found throughout India, spcially in Tamil Nadu, Krala and Bngal. Th arial parts of th tr hav DOI: / Pag

2 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto mdicinal valus and this work aimd at th possibility of using wasts of a Borassus flabllifr bark as an adsorbnt for th adsorption of cationic dy Rhodamin-B from aquous solution. II. Matrials and Mthods All ragnts usd in th xprimnts wr of analytical (AR) grad and wr obtaind from scintific quipmnt company Trichy. Stock solutions of th tst ragnts wr prpard by dissolving th dy in distilld watr. 2.1 Prparation of adsorbnt Th natural plant matrial Borassus flabllifr bark usd in th prsnt invstigations was collctd from Muthupt narby Thiruvarur district. Th bark wasts wr washd with distilld watr svral tims to rmov th dirt and dust and wr subsquntly drid in a hot air ovn at C. Aftr that, carbonization of th Borassus flabllifr bark was carrid out by w/v ratio of concntratd sulphuric acid for 24 hour; th primary carbon was activatd at 1100 o C for 6 hours undr optimizd conditions to obtain activatd nano carbon. Th activatd nano carbon was thraftr transfrrd to room tmpratur in an inrt atmosphr of nitrogn and washd with hot distilld watr and 0.5 N hydrochloric and until th ph of th matrial rachd 7.0. Th activatd nano carbon was also drid in a hot air ovn at C, ground and sivd to obtain th dsird particular siz (45nm) and stord in dsiccators for furthr us. 2.2Exprimntal Procdur Batch xprimnts wr conductd to study th influnc of important paramtrs lik th ph, contact tim, initial dy concntration and tmpratur on th rmoval of Rh-B onto activatd Borassus flabllifr bark nano carbon (ABNC). For Adsorption isothrms, dy solution of diffrnt concntrations ( mg/l) and at diffrnt tmpraturs (30-60 ºC) with known ph and known amount of adsorbnt (25mg/L) wr agitatd at 120rpm until th quilibrium was rachd. Thn th solution was kpt to sttl down and th rsidual concntration of Rh-B was analyzd by UV-Visibl spctrophotomtr at 554 nm. All xprimnts wr carrid out at normal ph for Rh-B. Effct of ph on dy rmoval was studid ovr a ph rang of Th initial ph of th solution was adjustd by addition of actat or phosphat buffrs. Th ffct of sorbnt dosag on adsorption rat was invstigatd using th procdurs dscribd abov. Th prcntag of dy rmoval was calculatd using th following quation. C (i) C( t) x v q () t (1) m Whr, q (t) is th mass of adsorbd dy pr unit mass of adsorbnt (mg -1 ) C (i) and C (t) ar th initial and actual concntration (g dm -3 ) of dy at tim t, rspctivly. V is th volum of th tratd solution (ml) and m is th mass of adsorbnt (g) Th adsorption dgr, AD as a function of tim was also dtrmind from th xprimntal data using th following rlationship AD % = () t 1- C X 100 Ci (2) Basd on th adsorption kintics xprimnts, th procss tim for th quilibrium adsorption xprimnts was chosn, long nough assuming that th considrd sorbnt / sorbat systm is quilibratd. III. Rsult and Discussion 3.1Effct of Contact tim: In ordr to stablish th quilibration tim for maximum uptak and to know th kintics of th adsorption procss, Rh-B adsorption on ABNC adsorbnt was invstigatd as a function of contact tim and th rsults wr shown in fig 1. Th figur shows that th uptak rat was initially rapid with 50% of th adsorption compltd within 30min, Equilibrium was achivd within 45 min thrfor, an quilibration priod of 1hr was slctd for all furthr xprimnts. Th tim profil of Rh-B uptak is a singl smooth and continuous curv lading to saturation suggsting th possibl monolayr covrag of Rh-B on th surfac of th adsorbnt. DOI: / Pag

3 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto Fig, 1-Effct of contact tim on th adsorption of Rh-B dy on ABNC 3.2 Effct of adsorbnt dosag Th adsorption of th Rh-B dy on ABNC was studid by varying th adsorbnt dos ( mg/50ml) for 50 mg/l of dy concntration. Th prcntag of adsorption incrasd with incras in th ABNC dos, which is attributd to incrasd carbon surfac ara and th availability of mor adsorption sits [6, 7]. Hnc, all studis wr carrid out with 0.025g of adsorbnt/50 ml of th varying adsorbat solutions.25, 50, 75, 100 and 125 mg/l. Th rsults obtaind from this study ar shown in figur 2. Th amount of Rh-B adsorbd pr gram is rducd with incras in th dosag of ABNC. This rvals that th dirct and quilibrium capacitis of Rh-B ar functions of th activatd ABNC dosag. Fig.2-Effct of Adsorbnt dos on th rmoval of Rh-B [RhB]=50mg/L;contact tim =60 min;tmpratur 30 o C 3.3 Effct of Initial ph. Prvious rsarch [8] has shown that th adsorption of dy molculs onto an adsorbnt is highly ph dpndnt sinc, th functional groups, which ar rsponsibl for intraction btwn dy molculs and adsorbnt, can b protonatd or dprotonatd to produc diffrnt surfac chargs in solution at diffrnt ph valus. Thrfor th ffcts of initial solution ph wr studid in th ph rang of 2-9 for Rh-B. Th prcntag rmoval incrasd from76 % to 92 % upto ph7 whras it dcrasd aftr ph 7 for Rh-B (Fig 3). Th ph zpc of any adsorbnt is a vry important charactristic that dtrmins th ph at which th surfac has nt lctrical nutrality. It is wll-known that for basic dy adsorption, ngativly chargd groups on th adsorbnt ar DOI: / Pag

4 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto ncssary. At lowr ph valus (ph <ph zpc ) th surfac charg of th surfac of ABNC may gt positivly chargd as a rsult of bing surroundd by H 3 O + ions and thus th comptitiv ffcts of H 3 O + ions as wll as th lctrostatic rpulsion btwn th dy molculs and th positivly chargd activ adsorption sits on th surfac of th ABNC lad to a dcras in th uptak of dy molculs. In contrast at highr ph valus (ph >ph zpc ) th surfac of ABNC may acquir a ngativ charg lading to an incras in dy uptak du to th lctrostatic forc of attraction. On th othr hand no valid rason can b givn for th dcras in th adsorption amount of Rh-B aftr ph 7. Similar rsults wr obtaind for th adsorption of Rhodamin-B onto ABNC. As a rsult, th initial ph valu was optimizd as 6.6 for dy. Fig,3-Effct of ph on th adsorption of Rh-B dy on ABNC 3.4 Effct of othr ions: Th ffct of othr ion lik Cl - on th adsorption procss studid at diffrnt concntrations. Th ions addd to 50mg/L of Rh-B solutions and th contnts wr agitatd for 60 min at 30 o C. Th rsults shown in th Fig. 4 rvals that low concntration of Cl - dos not affct th prcntag of adsorption of Rh-B on ABNC, bcaus th intraction of Cl - at availabl sits of adsorbnt through comptitiv adsorption is so ffctiv. Whil th concntration of othr ion incrass, th intrfrnc of ths ions at availabl surfac sits of th sorbnt through comptitiv adsorption is not so ffctiv and du to th formation of lctrical doubl layr, hnc th prcntag adsorption incrass [9]. Fig,4 -Effct of othr ion on th adsorption of Rh-B dy on ABNC DOI: / Pag

5 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto 3.5Adsorption Modls Adsorption isothrm [6-10] dscribs th rlation btwn th amount or concntration of adsorbat that accumulats on th adsorbnt and th quilibrium concntration of th dissolvd adsorbat. Equilibrium studis wr carrid out by agitating a sris of bakrs containing 100 ml of rhodamin B dy solutions of initial concntration mg/l with g of ABNC at 30 0 C with a constant agitation. Agitation was providd for 1.0 h, which is mor than sufficint tim to rach quilibrium. Formula usd for calculation of q is as follows: C0 C q V m Frundlich adsorption isothrm Th Frundlich adsorption isothrm is basd on th quilibrium sorption on htrognous surfacs. This isothrm is drivd from th assumption that th adsorption sits ar distributd xponntially with rspct to hat of adsorption. Th adsorption isothrm is xprssd by th following quation q =K C 1/nF F. (3) Which, can b linarizd as 1 ln q =lnk + lnc...(4) F n F Whr, q is th amount of MG dy adsorbd at quilibrium (mg/g) and C is th concntration of MG dy in th aquous phas at quilibrium (ppm). K F (L/g) and 1/n F ar th Frundlich constants rlatd to adsorption capacity and sorption intnsity, rspctivly. Th Frundlich constants K F and 1/n F wr calculatd from th slop and intrcpt of th lnq Vs lnc plot. Th modl paramtrs ar shown in Tabl 2. Th magnitud of K F showd that ABNC had a high capacity for Rh-B dy adsorption from th aquous solutions studid. Th Frundlich xponnt, n F, should hav valus in th rang of 1 and 10 (i.., 1/n F < 1) to b considrd as favourabl adsorption [23].1/n F valu of lss than 1 indicatd that RH-B dy is favorably adsorbd by ABNC. Th Frundlich isothrm did not show a good fit to th xprimntal data as indicatd by SSE and Chi-squar statistics. Tabl: 1. Equilibrium paramtrs for th adsorption of Rh-B dy Langmuir adsorption isothrm Th Langmuir adsorption isothrm is basd on th assumption that all sorption sits possss qual affinity to th adsorbat. Th Langmuir isothrm in a linar form can b rprsntd as: [23] (5) C 1 C = + q q K q m L m Whr q is th amount of Rh-B dy adsorbd at quilibrium (mg/g), C is th concntration of Rh-B in th aquous phas at quilibrium (ppm), q m is th maximum Rh-B dy uptak (mg/g), and K L is th Langmuir constant rlatd to adsorption capacity and th nrgy of adsorption (g/mg).a linar plot of C /q Vs C was mployd to dtrmin th valu of q m and K L, th data so obtaind ar also prsntd in Tabl 2. Th modl prdictd a maximum valu that could not b rachd in th xprimnts. Th valu of K L dcrasd with an incras in th tmpratur. A high K L valu indicats a high adsorption affinity. Wbr and Chakraborti [24] xprssd th Langmuir isothrm in trm of dimnsionlss constant sparation factor or quilibrium paramtr (R L ) which is dfind in th following quation: DOI: / Pag

6 1 R =.. (6) 1+K C L L 0 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto Whr, C 0 is th initial Rh-B dy concntration (ppm). Four scnarios can b distinguishd: Th sorption isothrm is unfavorabl whn R L > 1, th isothrm is linar whn R L = 1, Th isothrm is favorabl whn 0 < R L < 1 and th isothrm is irrvrsibl whn R L = 0. Th valus of dimnsionlss sparation factor (R L ) for Rh-B dy rmoval wr calculatd at diffrnt concntrations and tmpraturs. As shown in Tabl 3, at all concntrations and tmpraturs tstd th valus of R L for Rh-B dy adsorptions on th ABNC wr lss than 1 and gratr than zro, indicating favorabl adsorption. Th Langmuir isothrm showd a bttr fit to th adsorption data than th Frundlich isothrm. Th fact that th Langmuir isothrm fits th xprimntal data wll may b du to homognous distribution of activ sits on th ABNC surfac, sinc th Langmuir quation assums that th adsorbnt surfac is nrgtically homognous. Modl Constant Tmpratur ( o C) Frundlich K f(mg/g) (L/mg) 1/n n Langmuir Q m(mg/g) b (L/mg) Tmkin b T (J/mol) K T (L/mg) Hurkins-Jura B H (mg 2 /L) A H (g 2 /L) Halsay n Ha K Ha(mg/L) Radlich-Ptrson K R (L/g) g Dubinin-Radushkvich K D 10-4 mol 2 kj q s (mg/g) Jovanovic q max (mg/g) K J (L/g) BET C BET (L/mg) qs (mg/g) Tabl: 2. Isothrm paramtrs for th adsorption of Rh-B dy Tmkin adsorption isothrm: Th Tmkin adsorption isothrm assums that th hat of adsorption dcrass linarly with th sorption covrag du to adsorbnt-adsorbat intractions [25]. Th Tmkin isothrm quation is givn as: RT q = ln(k C )...(7) bt T Which, can b rprsntd in th following linar form RT RT q = lnk + lnc...(8) b T b Whr, K T (L/g) is th Tmkin isothrm constant, b T (J/mol) is a constant rlatd to hat of sorption, R is th idal gas constant (8.314 J/mol K), and T is absolut tmpratur (K). A plot of q vrsus lnc nabls th dtrmination of isothrm constants K T and b T from th slop and intrcpt, Th modl paramtrs ar listd in Tabl 2. Th Tmkin isothrm appars to provid a good fit to th Rh-B dy adsorption data. Th adsorption nrgy in th Tmkin modl, b T, is positiv for Rh-B dy adsorption from th aquous solution, which indicats that th adsorption is ndothrmic. Th xprimntal quilibrium curv is clos to that prdictd by Tmkin modl. Consquntly, th adsorption isothrm of Rh-B dy on ABNC can b dscribd rasonably wll by th Tmkin isothrm Hurkins-Jura adsorption isothrm Th Hurkins-Jura adsorption isothrm can b xprssd as [26]: A q = H...(9) B H+logC This can b rarrangd as follows: 1 BH 1 = - logc...(10) q 2 AH AH DOI: / Pag

7 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto Whr, A H (g 2 /L) and B H (mg 2 /L) ar two paramtrs charactrizing th sorption quilibrium. Th isothrm quation accounts for multilayr adsorption and can b xplaind by th xistnc of a htrognous por distribution. Th Harkins Jura isothrm paramtrs ar obtaind from th plots of of 1/q 2 vrsus log C nabls th dtrmination of modl paramtrs A H and B H from th slop and intrcpt in tabl Halsay adsorption isothrm Th Halsay adsorption isothrm can b givn as [27]: lnkha -lnc q =xp...(11) nha And, a linar form of th isothrm can b xprssd as follows: lnkha lnc lnq = -...(12) nha nha Whr, K Ha (mg/l) and n Ha ar th Halsay isothrm constants. A plot of lnq Vs lnc, nabls th dtrmination of n Ha and K Ha from th slop and intrcpt. This quation is suitabl for multilayr adsorption and th fitting of th xprimntal data to this quation attst to th htroporous natur of adsorbnt. Th rsult shows that th xprimntal data and th modl prdictions ar basd on th non-linar form of th Halsay modls. Th modl paramtrs ar listd in Tabl 2. This rsult also shows that th adsorption of Rh-B dy on ABNC was not basd on significant multilayr adsorption. Th Halsay modl is also not suitabl to dscrib th adsorption of Rh-B dy on ABNC, bcaus this modl also assums a multilayr bhavior of th adsorption of adsorbat onto adsorbnt Radish-Ptrson adsorption isothrm Th Radlich-Ptrson adsorption isothrm contains thr paramtrs and incorporats th faturs of Langmuir and Frundlich isothrms into a singl quation. Th gnral isothrm quation can b dscribd as follows [28]: KRC q =...(13) g 1+aRC Th linar form of th isothrm can b xprssd as follows: C ln =glnc -lnk...(14) q R Whr, K R (L/g) and a R (L/mg) ar th Radlich-Ptrson isothrm constants and g is th xponnt btwn 0 and 1. Thr ar two limiting cass: Langmuir form for g = 1 and Hnry s law for g = 0.A plot of lnc /q vrsus lnc nabls th dtrmination of isothrm constants g and K R from th slop and intrcpt. Th valus of K R, prsntd in Tabl 2, indicat that th adsorption capacity of th ABNC dcrasd with an incras tmpratur. Furthrmor, th valu of g lis btwn 0 and 1, indicating favorabl adsorption. (C i) Tmpratur C 30 o C 40 o C 50 o C 60 o C Tabl: 3. Dimnsionlss spration factor (r l ) for th adsorption of Rh-B dy Dubinin-Radushkvich adsorption isothrm Th Dubinin-Radushkvich adsorption isothrm is anothr isothrm quation [32]. It is assumd that th charactristic of th sorption curv is rlatd to th porosity of th adsorbnt. Th linar form of th isothrm can b xprssd as follows [29] : 2 1 lnq =lnq -B RTln 1+...(15) D D C Whr, Q D is th maximum sorption capacity (mol/g), and B D is th Dubinin-Radushkvich constant (mol 2 /kj 2 ). A plot of lnq Vs R T ln (1+1/C ) nabls th dtrmination of isothrm constants B D and Q D from th slop and intrcpt. DOI: / Pag

8 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto Jovanovich adsorption isothrm Th modl of an adsorption surfac considrd by Jovanovic [30] is ssntially th sam as that considrd by Langmuir. Th Jovanovic modl lads to th following rlationship [29]: max q =q 1- KC J Th linar form of th isothrm can b xprssd as follows: lnq = lnq -K C max J Whr, K J (L/g) is a paramtr. q max (mg/g) is th maximum Rh-B dy uptak. Th q max is obtaind from a plot of ln q and C, Thir rlatd paramtrs ar listd in Tabl 2. By comparing th valus of th rror functions, it was found th Langmuir and Tmkin modls ar bst to fit th Rh-B adsorption on th ABNC. Both modls show a high dgr of corrlation. This is clarly confirming th good fit of Langmuir and Tmkin modls with th xprimntal data for rmoval of RH-B dy from th solution Th Brunaur Emmtt Tllr (BET) isothrm modl Brunaur Emmtt Tllr (BET) [31] isothrm is a thortical quation, most widly applid in th gas solid quilibrium systms. It was dvlopd to driv multilayr adsorption systms with rlativ prssur rangs from 0.05Pa to 0.30Pa corrsponding to a monolayr covrag lying btwn 0.50Pa and 1.50Pa. Its xtinction modl rlatd to liquid solid intrfac is xhibitd as: qscbetc q =...(16) (Cs -C )[1+(CBET -1)(C /C s )] Whr, CBET, Cs, qs and q ar th BET adsorption isothrm (L/mg), adsorbat monolayr saturation concntration (mg/l), thortical isothrm saturation capacity (mg/g) and quilibrium adsorption capacity (mg/g), rspctivly. As C BET and C BET (C /C s ) is much gratr than 1,th linar form is rprsntd as C 1 CBET -1 C = +...(17) qc -C qsc s BET qsc BET C s Whr, C is quilibrium Concntration (mg/l), C s is adsorbat monolayr saturation concntration (mg/l) and C BET is BET adsorption rlating to th nrgy of surfac intraction (l/mg).th rsults of BET modl ar also shown in tabl 2. Th rsults prdict th physisorption mchanism and monolayr covrag of adsorbat on ABNC 3.6Kintic paramtrs Th rat and mchanism of th adsorption procss can b lucidatd basd on kintic studis. Dy adsorption on solid surfac may b xplaind by two distinct mchanisms: (1) An initial rapid binding of dy molculs on th adsorbnt surfac; (2) rlativly slow intra-particl diffusion. To analyz th adsorption kintics of th dy, th psudo-first-ordr, th psudo-scond-ordr, and intra-particl diffusion modls wr applid [38, 39]. Each of ths modls and thir linar mods of th quations ar prsntd in blow. Kintic Modls and Thir Linar Forms Modl Nonlinar Form Linar Form Psudo-first-ordr dq t/d t= k 1(q -q t) ln (q -q t) = ln q -k 1t. (18) Psudo-scond-ordr dq t/d t= k 2(q -q t) 2 t/q t= 1/k 2 q 2 + (1/q )t.(19) Whr, q and q t rfr to th amount of (Rh-B) dy adsorbd (mg/g) at quilibrium and at any tim, t (min), rspctivly and k 1 (1/min), k 2 (g/mg. min) ar th quilibrium rat constants of psudo-first ordr and psudo-scond ordr modls, rspctivly. Psudo-first ordr modl is a simpl kintic modl, which was proposd by Lagrgrn [40] during 1898 and is usd for th stimation of th surfac adsorption raction rat. Th valus of ln (q - q t ) wr linarly corrlatd with t. Th plot of ln (q - q t ) vs. t should giv a linar rlationship from which th valus of k 1 will b dtrmind from th slop of th plot. In many cass, th first-ordr quation of Lagrgrn dos not fit wll with th ntir rang of contact tim and is gnrally applicabl ovr th initial stag of th adsorption procsss (41). In th psudo-scond ordr modl (42), th slop and intrcpt of th t/qtvs t plot wr usd to calculat th scond-ordr rat constant, k 2. Th valus of quilibrium rat constant (k 2 ) ar prsntd in Tabl 4. According to Tabl 4, th valu of r 2 (0.999) rlatd to th psudo-scond ordr modl rvald that Rh-Bdy adsorption followd this modl, which is in agrmnt with th rsults obtaind by Karagozt al.[23], Hamd DOI: / Pag

9 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto t al.[24], and Altnort al. [37]. Nvrthlss, psudo-first ordr and psudo-scond ordr kintic modls cannot idntify th mchanism of diffusion of dy into th adsorbnt pors. C Tmp Psudo scond ordr Elovich modl Intraparticl diffusion C q k 2 h K id C Tabl: 4 th kintic paramtrs for th adsorption of Rh-B dy onto ABNC Th Elovich quation Th Elovich modl quation is gnrally xprssd as dq t / d t = α xp (-βq t )..(20) Whr; α is th initial adsorption rat (mg g -1 min -1 ) and β is th dsorption constant (g/mg) during any on xprimnt. To simplify th Elovich quation, Chin and Clayton [18] assumd t>>t and by applying boundary conditions q t = 0 at t= 0 and q t = q t at t = t Eq. (13) bcoms: q t = 1/ln () + 1/ln t (21) Th Rh-B adsorption fits with th Elovich modl, a plot of q t vs ln(t) yilds a linar rlationship with a slop of (1/β)and an intrcpt of (1/β)ln (αβ). Th Elovich modl paramtrs α, β, and corrlation cofficint () ar summarizd in tabl 4. Th xprimntal data such as th initial adsorption rat () adsorption constant (β) and th corrlation co-fficint (γ) calculatd from this modl indicats that th initial adsorption (α) incrass with tmpratur similar to that of initial adsorption rat (h) in psudo-scond ordr kintics modls. This may b du to incras th por or activ sit on th ABNC adsorbnt Wbr and Morris intra-particl diffusion modl:- Kintic data was furthr analyzd using th Intra particl diffusion modl basd on th thory proposd by Wbr and Morris [19]. Th amount of Rh-B adsorbd (q t ) at tim t was plottd against th squar root of tim (t ½ ), according to q. Qt=k id t ½ +C.. (22) Whr, k id is th Intraparticl diffusion rat constant and c is th intrcpt rlatd to th thicknss of th boundary layr. According to abov quation a plot of qt vrsus t ½ givsa straight lin from th origin which says that th adsorption mchanism follows th intra-particl diffusion procss only. Howvr, th data xhibit multi linar plots, says th procss ar govrnd by two or mor stps, It is clar from that, thr ar two sparat zons: first linar portion (phas I) and scond linar part (phas II). Th first linar portion (Phas I) can b attributd to th immdiat utilization of th most radily availabl adsorbing sits on th adsorbnt surfac, phas II may b attributd to vry slow diffusion of th adsorbat from th surfac sit in to th innr pors. Thus initial portion of Rh-B adsorption by adsorbnt may b govrnd by th initial intra particl transport of Rh-B controlld by surfac diffusion procss and th latr part controlld by por diffusion. Howvr, th intrcpt of th lin fails to pass through th origin which may b du to th diffrnc in th rat of mass transfr in th initial and final stags of adsorption. Furthr, such dviation of th straight lins from th origin rvals that th por diffusion is not th sol rat - controlling. 3.7 Thrmodynamic paramtrs Thrmodynamic paramtrs [15] wr valuatd to confirm th adsorption natur of th prsnt study. Th thrmodynamic constants, fr nrgy chang, nthalpy chang and ntropy chang wr calculatd to valuat th thrmodynamic fasibility and th spontanous natur of th procss. Enthalpy chang (ΔH), and ntropy chang (ΔS) may b dtrmind from Van t Hoff quation: DOI: / Pag

10 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto S H ln K (23) R RT By plotting ln K as ordinat and 1/T as abscissa, ΔS and ΔH wr obtaind by using th following quation th valu of ΔG wr obtaind. G H T S (24) Whr, ΔG is th fr nrgy chang (kj mol 1 ), R is th univrsal gas constant (8.314 J mol 1 K 1 ), K th thrmodynamic quilibrium constant and T is th absolut tmpratur (K). G H TS RT ln K. (25) c S H ln K c..(26) R RT q S H 2.30log (27) C R RT q S H log (28) C R2.303 RT Th valus of ΔS, ΔH, ΔG was obtaind from a plot of log (q /C ) vs. 1/T. Hat of raction (ΔH) for physical adsorption is rportd to b 4.2 to 63 kj/ mol in litratur. Th valu of ΔH rang from to kj/mol from Tabl-5, which indicats that th natur of adsorption of Rhodamin B dy onto ABNC is a physical adsorption on. Th positiv valu of ΔH &ngativ ΔG indicat ndothrmic and spontanous procss of adsorption of Rhodamin B (Rh-B) dy on ABNC rspctivly. G o (C 0) 30 o C 40 o C 50 o C 60 o C H S E a S * E E E E E-02 Tabl: 5. Thrmodynamic paramtr for th adsorption of Rh-B dy onto ABNC In ordr to support that physical adsorption is th prdominant mchanism, th valus of activation nrgy (E a ) and sticking probability (S*) wr calculatd from th xprimntal data. Thy wr calculatd by using th modifid Arrhnius typ quation rlatd to surfac covrag (θ) as follows 49 : C = 1-. (29) C i Ea S* (1 ) (30) RT Th sticking probability, S*, is a function of th adsorbat/adsorbnt systm undr considration but must satisfy th condition 0 < S*< 1 and is dpndnt on th tmpratur of th systm. Th valus of E a and S* wr calculatd from slop and intrcpt of th plot of ln(1-θ) vrsus 1/T rspctivly and ar listd in Tabl 5. From Tabl 5 it is clar that th raction is spontanous in natur as ΔG 0 valus ar ngativ at all xprimntal tmpraturs. Again positiv ΔH 0 valu confirms that th sorption is ndothrmic in natur. Th positiv valu of ΔS 0 rflcts th affinitis of th adsorbnts for th Rh-B dy. Th rsults shown in Tabl 5 indicat that th probability of th Rh-B dy to stick on surfac of biomass is vry high as S*<< 1, ths valus confirm that, th sorption procss is physisorption. IV. Dsorption studis In ordr to assss th rusability of Rh-B-loadd ABNC biomass dsorption xprimnts wr carrid out. Th ffct of strngth of dsorbing solution (HCl) on th rcovry of Rh-B was analyzd. It is vidnt from th abov rsult that whn th strngth of th dsorbing solution incrasd from 0.5 to 2.0 M, Rh-B dsorption prcntag incrasd from 45 to 90%. Thus a significant amount of Rhodamin B is bing dsorbd, which shows that th ABNC biomass can b ffctivly rusd aftr dsorption [20]. DOI: / Pag

11 Isothrm and thrmodynamic analysis on th adsorption of Rhodamin B dy onto V. Conclusions On th basis of th abov studis, th following can b concludd: I. Charactrization of activatd Borassus flabllifr bark nano carbon (ABNC) was carrid out which rvald that th surfac of th adsorbnt was rough and suitabl for adsorption. II. ABNC has shown a potntial to rmov Rhodamin B from aquous solution. III. Initial concntration of th dy plays an important rol in th rmoval procss. IV. Kintics of th procss rmoval was studid and th valus of rat constants wr dtrmind. Th dy rmoval was found to b govrnd by film diffusion mchanism whr xtrnal transport of th adsorbat ovr th surfac of th adsorbnt is gratr than intrnal transport which was confirmd by th Ho plot and th procss of rmoval was found to follow scond ordr kintics. V. Thrmodynamic paramtrs wr calculatd for th rmoval of dy and thir valus indicatd that th procss of rmoval was spontanous and ndothrmic. VI. Th data wr found to bst fit in all isothrm modls. It can thrfor b concludd that activatd Borassus flabllifr bark nano carbon (ABNC) offrs promis as an conomically viabl altrnativ for squstring th dy from th aquous solution. Th work can b xtndd for th rmoval of dys from fflunts as wll. Rfrnc [1] Al Duri, B.; Mckay, G.; El Gundi, M. S.; Wahab Abdul, M. Z. Thr Rsistanc Transport Modl for dy Adsorption onto Bagass Pitch. J. Environ. Eng. Div. ASCE, 1990,116, 487. [2] S Arivoli, M Hma, S Parthasarathy and N Manju,.Adsorption dynamics of mthyln blu by acid activatd carbon.j. Chm. Pharm. Rs, 2010, 2(5), [3] M Hma and S Arivoli, Rhodamin B adsorption by activatd carbon: Kintic and quilibrium studis, Indian Journal of Chmical Tchnology, 2009, 16(1), [4] V Vijayakumaran, S Arivoli, and S Ramuthai, Adsorption of nickl ion by low cost carbon-kintic, thrmodynamic and quilibrium studis, 2009, 6 (S1), S347-S357. [5] Alln, S. J.; Mckay, G.; Khadr, K. Y. H. Intraparticl Diffusions of Basic Dy During Adsorption onto Sphagnum Pat. Environ. Pollut. 1989, 56, 39. [6] Alprt, N. L.; Ksi, W. E.; Szymanaki, H. A. Thory and Practic of Infrard Spctroscopy, 2nd d.; Plnum: Nw York, [7] Crank, J. Th Mathmatics of Diffusion Clarndn Prss: Oxford, [8] El-Gundi, M. S. Colour Rmoval from Txtil Efflunts by Adsorption Tchniqu Wat. Rs., 1991, 25, 271. [9] Fornwalt, H. J.; Hutchins, R. A. Purifying Liquids with Activatd Carbon. Chm. Eng. J, 1966, 73, 179. [10] Frndlich H, Th dy adsorption is losungn (Adsorption in Solution), Z Phys, Chm. 1906, 57: [11] Langmuir I, Th adsorption of gass plan surfacs of glass, mica and platinum. J. Am.Soc., 1918, 579, [12] Fridal, R. A.; Quisr, J. A. Infrard Analysis of Bitumnous Coal and Othr Carbonacous Matrials. Anal. Chm, 1956, 28, 22. [13] Gadsn, J. A. Infrard Spctra of Minrals and Rlatd Inorganic Compounds Buttr worths: London, [14] Gupta, G. S.; Prasad, G.; Singh, V. N. Rmoval of Chrom Dy from Carpt Efflunts using Coal II (Rat procss). Environ. Tchnol. Ltt., 1988, 9, [15] Namasivayam C, Munisamy N, Gayathri K, Rani M and Rnganathan K, BiorsTchnol, 1995, 57, 37. [16] Wbr T W, Chakravorti R K, Por and Solid diffusion modls for fixd bd adsorbrs. J. Am. Inst, Chm. Eng, 1974, 20, 228. [17] McKay G, Blair H S, Gardnr J R, Adsorption of dys on chitin. I. Equilibrium Studis J. Appl, Polym, Sci. 1982, 27, [18] Chin S H, Clayton W R, Application of Elovich Equation to th kintics of Phosphat rlas and sorption on soil, Soil Sci. Sco, Am. J. 1980, 44, [19] Wbr W J, Morris J C, Kintics of adsorption on Carbon from solution. J, Sanitary Eng, Div. 1964, 90, 79. [20] Arivoli S Vnkataraman B R, Rajachandraskar T and Hma M, Rs. J. Chm Environ., 2008, 17, IOSR Journal of Applid Chmistry (IOSR-JAC) is UGC approvd Journal with Sl. No. 4031, Journal no M.Thiruchlvi "Isothrm and Thrmodynamic Analysis on th Adsorption of Rhoda min B Dy onto Borassus flabllifr bark Nano Carbon." IOSR Journal of Applid Chmistry (IOSR- JAC) 11.4 (2018): DOI: / Pag