A GREEN APPROACH: MALACHITE GREEN ADSORPTION ONTO WASTE GREEN TEA BIOMASS. ISOTHERM AND KINETIC STUDIES

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1 ACADEMIA ROMÂNĂ Rvu Roumain d Chimi Rv. Roum. Chim., 2016, 61(6-7), Ddicatd to Profssor Dumitru Oanca on th occasion on his 75th annivrsary A GREEN APPROACH: MALACHITE GREEN ADSORPTION ONTO WASTE GREEN TEA BIOMASS. ISOTHERM AND KINETIC STUDIES Silvia BURCĂ, Andrada MĂICĂNEANU and Craslla INDOLEAN * Dpartmnt of Chmical Enginring, Faculty of Chmistry and Chmical Enginring, Babş-Bolyai Univrsity, 11 Arany Janos St., RO Cluj-Napoca, Roumania Rcivd Novmbr 11, 2015 Dy (malachit grn, MG) rmoval from aquous solution using a grn approach, adsorption onto wast grn ta biomass, was considrd in this work. Influnc of th initial concntration ovr th MG uptak was considrd in ordr to collct th xprimntal data ncssary for quilibrium and kintic modlling. Langmuir, Frundlich, Dubinin-Radushkvich and Tmkin isothrm quations wr usd to modl th obtaind xprimntal data. Th bst fit was obtaind for Dubinin-Radushkvich modl (R 2 =0.994) indicating a chmisorption procss (16.01 kj/mol). Th maximum monolayr covrag from Langmuir isothrm modl was dtrmind to b mg/g. Th considrd kintic modls (psudo-first psudo-scond-ordr, Elovich, intra-particl film diffusion) showd that xprimntal data bst fittd on th psudo-scond-ordr modl. Th obtaind rsults showd that th considrd grn and low cost biomass is an fficint matrial for dy rmoval from wastwatrs. INTRODUCTION Th impact of organic pollutants rlas into th nvironmnt is incrasing as a rsult of population xplosion and rapid urbanization, industrial and tchnological dvlopmnt, wast gnration from domstic and industrial sourcs. Ths hav rlasd many toxic and hazardous watrs to humans and othr living organisms. 1 A numbr of clan-up tchnologis hav bn dvlopd ovr th yars to rmov organic dys from th industrial wastwatrs, among thm ar adsorption, coagulation, filtration, ion-xchang, lctrolysis, advancd oxidation procsss, tc. 2-9 Adsorption is a wll-known sparation procss and an ffctiv mthod for watr dcontamination applications. Rcntly low cost agricultural byproducts hav bn usd as adsorbnt matrials. Btwn ths, ric husk, what bran, coconut bunch wast, orang pl, banana pl, garlic pl, papaya sd, pinappl stm wast, sunflowr stalks, silk cotton hull, maiz cob, hav bn xtnsivly rsarchd and valuatd for dys rmoval Dpnding on th ionic charg of th chromophor group, dys ar gnrally classifid as anionic, cationic and non-ionic. Cationic dys ar mor toxic than anionic dys. 2 Th dy fflunts can caus svral halth problms, Corrsponding author: clla@chm.ubbcluj.ro

2 542 Silvia Burca t al. damag th asthtic quality of watr and rduc light pntration and photosynthsis, and som of thm ar toxic or mutagnic, carcinognic and allrgnic. 3 Malachit grn (MG) is a basic triphnylmthan dy, usd in acrylic, txtil, papr, rubbr, food industris and distillris. It is toxic to humans and can caus livr tumour formation. 2,3 Wast grn ta could b an fficint altrnativ for dys rmoval from wastwatr. Grn ta Camllia sinnsis is nativ to South-East Asia, th main producr bing China. 15 Cannd or bottld ta drinks as wll as instant ta drinks ar producd on industrial scal and th producrs ncountr a problm in disposal of th wast ta lavs. Thrfor, th valorisation of such wast as adsorbnt could b a solution. 18,19 In this papr, adsorption of malachit grn dy (MG) onto grn ta wast (WGT) was considrd. Langmuir, Frundlich, Dubinin-Radushkvich and Tmkin isothrm modls wr usd to analys th xprimntal data. Also th adsorption kintics modls (psudo-first psudo-scond-ordr, Elovich, intra-particl film diffusion) wr usd to valuat th xprimntal data. RESULTS AND DISCUSSION Th ffct of initial MG concntration ovr th adsorption procss Exprimnts wr conductd using 100 ml MG aquous solutions with concntrations in th mg MG/L rang in batch conditions, undr magntic stirring at 300 rpm, at room tmpratur (T = 22±2 C) and 4 g of WGT. Exprimntal rsults showd that th quantity of adsorbd MG incrasd with th incras of th MG concntration, from 1.81 to mg/g for 75 and 445 mg MG/L, rspctivly (Fig. 1). As th initial concntration incrasd, adsorption quilibrium was rachd slowr, aftr about 240 minuts, by comparison with only 80 minuts for small concntrations ( mg MG/L). Adsorption isothrms Adsorption isothrms ar mathmatical modls that dscrib th distribution of th adsorbat spcis among liquid and solid phass, basd on a st of assumptions that ar rlatd to th htrognity/homognity of th solid surfac, th typ of covrag and th possibility of intraction btwn th adsorbat spcis. 20 In this study, quilibrium data wr analysd using th Langmuir, Frundlich, Dubinin Radushkvich and Tmkin isothrms modls, which ar th most usd isothrms in adsorption studis, which allow data analysis using linar rgrssion analysis. Langmuir adsorption isothrm Th Langmuir isothrm modl assums a monolayr covrag and also that th adsorbnt surfac contains a finit numbr of idntical sits of uniform nrgy (homognous surfac), on molcul adsorbs on ach adsorption sit and thr ar no intractions btwn adsorbat molculs on adjacnt sits. Th Langmuir isothrm quation has a hyprbolic form: 21,22 q qmax KL C = 1+ K C L (1) whr q is th solid-phas adsorbat concntration at quilibrium (mg/g), q max is th maximum adsorption capacity corrsponding to th monolayr adsorption capacity (mg/g), C is th concntration of MG solution at quilibrium (mg/l), Tabl 1, K L (L/mg) is rlatd to th strngth of adsorbnt-adsorbat affinity. Th linar form of th Langmuir isothrm can b xprssd as: = + q q K C q max L max (2) Th important faturs of th Langmuir isothrm may b xprssd in trms of quilibrium paramtr R L, dimnsionlss constant rfrrd to as sparation factor or quilibrium paramtr. 23 R 1 L = 1 + KL C0 (3) whr, C 0 is th highst intial concntration (mg/l), and R L valu indicats th adsorption natur to b ithr unfavourabl if R L >1, linar if R L = 1, favourabl if 0 < R L < 1 and irrvrsibl if R L = Th maximum monolayr covrag capacity (q max ) from Langmuir isothrm modl was dtrmind to b mg/g, K L is L/mg, whil R L is indicating that th adsorption quilibrium was favourabl. Th R 2 valu is 0.947, Tabl 2.

3 Dy rmoval 543 Fig. 1 Influnc of initial dy concntration ovr th amount of adsorbd MG (100 ml solution, 4 g WGT, 300 rpm, 22±2 C). Tabl 1 Exprimntal data usd to dtrmin isothrm modls paramtrs C 0 (mg/l) q (mg/g) C (mg/l) Tabl 2 Langmuir, Frundlich, Dubinin Radushkvich and Tmkin paramtrs modls calculatd using linar rgrssion analysis for MG dy adsorption on WGT; C 0 = mg/l, 300 rpm, room tmpratur Langmuir Frundlich Dubinin Radushkvich Tmkin K L q max R 2 K n F (L/mg) (mg/g) (mg (1-1/n) L 1/n R 2 q s E R 2 A T B R 2 /g) (mg/g) (kj/mol) (L/g) Frundlich isothrm Frundlich isothrm is an mpirical quation, which assums that th adsorption procss taks plac on a htrognous surfac. 24 Ths data oftn fit th mpirical quation proposd by Frundlich, which has th following linar form: log q = log K + logc n F (4) whr, K F is Frundlich isothrm constant (mg (1 1/n) L 1/n /g), n is rlatd to intnsity of adsorption, C is th quilibrium concntration of adsorbat (mg/l), and q is th amount of MG pr gram of th WGT at quilibrium (mg/g), Tabl 1. K F and n ar paramtrs charactristic of th adsorbnt-adsorbat systm, which must b dtrmind by data fitting using linar rgrssion, which is gnrally usd to dtrmin th paramtrs of isothrm modls. 27 Spcifically, th linar last-squars mthod and th linarly transformd quations hav bn widly applid to corrlat adsorption data whr 1/n is a htrognity paramtr, th smallr 1/n, th gratr th xpctd htrognity. This xprssion rducs to a linar adsorption isothrm whn 1/n = 1. If n lis btwn 1 and 10, this indicats a favourabl adsorption procss. 28,29 From th data calculatd for MG adsorption onto WGT,

4 544 Silvia Burca t al. n = indicating that th adsorption procss is favourabl. Th R 2 valu is 0.893, Tabl 2. Dubinin Radushkvich isothrm modl Dubinin Radushkvich isothrm is mostly applid to xprss th adsorption mchanism with a Gaussian nrgy distribution onto a htrognous surfac. 30,31 2 q = qsxp( KDε ) (5) ln q = ln q K ε s D 2 (6) whr q is th amount of adsorbat in th adsorbnt at quilibrium (mg/g), q s is thortical isothrm saturation capacity (mg/g), K D is Dubinin Radushkvich isothrm constant (mol 2 /kj 2 ), R is th gas constant (8.314 J/mol K), T is absolut tmpratur (K), C is adsorbat quilibrium concntration (mg/l). 1 ε = RT ln(1 + ) C (7) Dubinin Radushkvich isothrm is usually applid to distinguish btwn th physical and chmical adsorption. using th man fr nrgy valu, E pr molcul of adsorbat (<8 kj/mol physical adsorption, 8-16 kj/mol adsorption du to ion xchang, >16 kj/mol chmical adsorption), which can b computd using th following rlationship: 20,32 1 E = 2K D (8) From th linar plot of Dubinin Radushkvich modl, Eq. (6), q s was dtrmind to b mg/g and th man fr nrgy, E = kj/mol, indicating a chmical procss (R 2 = 0.994), du to xchang of ions, Tabl 2. Tmkin isothrm This isothrm contains a factor that xplicitly taks into account th adsorbnt adsorbat intractions. Ignoring th xtrmly low and larg valu of concntrations, th modl assums that th hat of adsorption (function of tmpratur) of all molculs in th layr would dcras linarly rathr than logarithmic with covrag. Th modl is givn by th following quation: q = Bln A + Bln C T (9) RT B = b T (10) whr A T is Tmkin isothrm quilibrium binding constant (L/g), b T is Tmkin isothrm constant (J/mol), R is univrsal gas constant (8.314 J/mol K), T is absolut tmpratur (K), B is a constant rlatd to hat of adsorption. By plotting q against lnc, th constants wr dtrmind from th slop and intrcpt, to b A T = L/g and B = 6.03, whil R 2 valu is 0.981, slightly lowr than in cas of Dubinin Radushkvich, Tabl 2. Basd on th linar rgrssion corrlation cofficint, R 2, th obtaind quilibrium data for MG-WGT systm wr bttr fittd on th Dubinin Radushkvich modl, Tabl 2. Similar systms, malachit grn on lmon pl 26, dgrasd coff ban 32, solar rd and brittl blu on Eucalyptus angophoroids bark 36, brilliant grn on NaOH tratd sawdust 37 wr invstigatd and prsntd in th litratur. Our rsults ar in good agrmnt with prviously rportd studis. Adsorption kintics Svral adsorption kintic modls, such as psudo-first and psudo-scond-ordr, Elovich, intra-particl and film diffusion, wr usd to tst th xprimntal data. Th psudo-first and psudo-scond-ordr kintic modls Psudo-first and psudo-scond-ordr modls can corrlat th adsorbat up-tak rat with th bulk concntration of th adsorbat. Usually linar rgrssion is usd to dtrmin th bst fitting kintic rat quation (corrlation cofficints, R 2 ). 38,39 Lagrgrn suggstd a first-ordr quation for th adsorption of liquid/solid systm basd on solid capacity, which can b xprssd in linar form as follows: 38 ln( q q ) = ln q k t t 1 (11) whr q and q t ar th amounts of adsorbat in th adsorbnt (mg/g) at quilibrium and tim t, rspctivly, t is tim (min), k 1 is th rat constant of th first ordr adsorption (L/min).

5 Dy rmoval 545 Th psudo-scond-ordr kintic modl is drivd on th basis of th adsorption capacity of th solid phas. 22 Th linar form of th modl is xprsss as follows: 39,40 t q t 1 t = + kq q 2 2 (12) whr q and q t ar th amounts adsorbd at quilibrium and tim t, rspctivly (mg/g), t is tim (min), k 2 is th rat constant of th scond ordr adsorption (g/mg min). In ordr to dtrmin th rat constant and quilibrium MG uptak, th straight lin plots of ln(q -q t ) and t/q t against t, wr mad using diffrnt initial MG concntrations. Corrlation cofficints from to for psudo-firstordr and from to for psudo-scondordr modl wr obtaind, Tabl 3 showing that MG adsorption on WGT can b classifid as psudo-scond-ordr, fact confirmd by th litratur rsults. Calculatd valus of q, Tabl 3, ar vry clos to th xprimntal valus, Tabl 1, confirming that MG adsorption on WGT follows th psudo-scond-ordr kintic modl. 19,40 Elovich kintic modl Th simplifid Elovich quation 41,42 is gnrally xprssd as: qt 1 1 = ln( αβ ) + ln t β β (13) whr α is th initial adsorption rat (mg/g min), and β is th dsorption constant (g/mg). Elovich plots of q t vrsus ln(t) givs a linar rlationship, with a slop of (1/β) and intrcpt (1/β)ln(αβ). Calculatd valus of α, β and R 2 ar prsntd in Tabl 3. Th low valus of th corrlation cofficints, btwn and 0.917, suggst that this modl is not suitabl to dscrib th MG on WGT adsorption procss. Intra-particl and film diffusion modl In ordr to valuat th contribution of diffusional procsss during th MG adsorption onto WGT which is a porous matrial, intraparticl and film diffusion modls wr also considrd. Th intra-particl diffusion modl (Wbbr and Morris) can b writtn as follows: 43 q = k t t ip 0.5 (14) whr k ip is th intra-particl diffusion rat constant (mg/g min 0.5 ). Th film diffusion modl (Boyd) is xprssd as: 44 ln(1 F) = kfd t (15) whr F is th fraction attainmnt at quilibrium (F = q t /q ), and k fd is th liquid film diffusion rat constant (L/min). If th obtaind plots giv straight lins passing through origin, intrnal or film diffusion is considrd to b rat dtrmining stp. 45 Also from th slop of ths plots, intra-particl and film diffusion rat constants can b dtrmind, Tabl 4. Vry small valus of th intrcpt in th cas of intra-particl diffusion modl suggst that intraparticl diffusion could b a rat dtrmining stp towards th nd of th adsorption procss (molculs ar diffusing through th pors towards th still availabl adsorption sits). Similar rsults wr obtaind in th cas of MG adsorption on calcium alginat nanoparticls 46 or Avna sativa (oat) hull. 47 Tabl 3 Psudo-first, psudo-scond-ordr and Elovich cofficints for MG adsorption on WGT; C 0 = mg/l, 300 rpm, room tmpratur Psudo-first ordr Psudo-scond ordr Elovich C 0 (mg/l) k 1 q m R 2 k q calc R 2 α β R 2 (1/min) (mg/g) (g/mg min) (mg/g) (mg/g min) (g/mg)

6 546 Silvia Burca t al. C 0 (mg/l) Tabl 4 Intra-particl and film diffusion rat cofficints for MG adsorption on WGT; C 0 = mg MG/L, 300 rpm, room tmpratur Intra-particl diffusion Film diffusion k ip (mg/g min 0.5 ) Intrcpt R 2 k fd (1/min) Intrcpt R 2 EXPERIMENTAL Matrials Th adsorption procss was ralisd using wast grn ta (WGT), collctd from a local coff and ta hous. Th grn ta rsidual lavs wr rpatdly washd svral tims with distillat watr until th filtrd watr was clar. Th sampl was thn ovn drid at 80ºC for 48 h. Finally, th adsorbnt sampl was ground and sivd to obtain th particl siz in th µm rang. Th dy stock solution (1000 mg/l) was obtaind by dissolving th ncssary quantity of solid substanc, malachit grn (MG), analytical purity ragnt, in distilld watr. Solutions with known concntration in mg MG/L rang wr prpard from th stock solution. Adsorption xprimnts Adsorption procss was conductd in batch conditions, in dynamic rgim (300 rpm), through th contact of a crtain amount of adsorbnt (4 g) with a volum of 100 ml MG dy aquous solution of various concntrations ( mg mg/l). Th adsorption procss was conductd until quilibrium was rachd (240 min stablishd from prliminary xprimnts). Dy concntration in solution was dtrmind using a Jnway 6305 UV-VIS spctrophotomtr, at a wavlngth of 618 nm, aftr a prliminary cntrifugation (for 5 min at rpm) and appropriat dilution. Sampls wr collctd at stablishd tim intrvals. All th xprimnts wr rpatd thr tims, th valus prsntd wr calculatd using avragd concntration valus. Th MG amount adsorbd by WGT was calculatd using th following quation: ( C0 Ct ) V q = (16) m 1000 whr C 0 is th initial MG concntration (mg/l), C t is tim t MG concntration (mg/l), V is th aquous solution volum (ml), and m is th adsorbnt quantity (g). Exprimntal data wr usd to stablish adsorption quilibrium and kintic modls which bttr dscrib th adsorption procss. CONCLUSIONS Th adsorption procss of MG from aquous solution using WGT has bn invstigatd in batch mod. Th maximum xprimntal amount of MG adsorbd was calculatd to b mg/g for an initial concntration of 445 mg MG/L, whil th maximum monolayr covrag capacity dtrmind from Langmuir isothrm modl was mg/g. Btwn th four isothrm modls considrd, xprimntal data bst fittd on th Dubinin Radushkvich modl. Also basd on th rsults obtaind from th isothrm modls, th considrd adsorption procss was idntifid to tak plac as a chmical procss. Th adsorption xprimntal data follows psudo-scond-ordr raction kintics (R 2 > 0.994). Basd on th obtaind data it can b concludd that wast grn ta biomass could b usd as an ffctiv adsorbnt for malachit grn rmoval from wastwatrs. REFERENCES 1. S. D. Pardshi, J. P. Sonar, A. M. Zin and S. N.Thor, J. Iran Chm. Soc., 2013, 10, S. J. Culp, L. R. Blanchnship, D. F. Kuswitt, D. R. Dorg, L.T. Mulligan and F. A. Bland, Chm. Biol. Intract., 1999, 122, S. Srivastava, R. Sinha and D. Roys, Aquat. Toxicol., 2004, 66, Z. Aksu, Procss Biochm., 2005, 40, B. H. Tan, T.T. Tng and A. K. M. Omar, Watr Rs., 2000, 34, A. I. Zouboulis, N. K. Lazaridis and A. Grohman, Sp. Sci. Tchnol., 2002, 37, B. Bolto, D. Dixon, R. Eldridg, S. King and K. Ling, Watr Rs., 2002, 36, L. Szpyrkowicz, J. Naumczyk and F. Zilio-Grandi, Watr Rs., 1995, 29, S. Esplugus, J. Giméns, S. Contrras, E. Pascual and M. Rodriguz, Watr Rs., 2002, 36, P. Mavros, A. C. Daniilidou, N. K. Lazaridis and L. Strgiou, Environ. Tchnol., 1994, 15, S. Dawood and T. K. Sn, Watr Rs., 2012, 46, H. Dakhil, J. Krbala Univ., 2013, 1, M. Rafatullah, O. Sulaiman, R. Hashim and A. Ahmad, J. Hazard. Matr., 2009, 170, H. Ali, Watr Air Soil Pollut., 2010, 213,

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8 548 Silvia Burca t al.