Adsorption of Rhodamine B on activated carbon obtained from pericarp of rubber fruit in comparison with the commercial activated carbon

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1 Songklanakarin J. Sci. Tchnol. 36 (2), , Mar. - Apr Original Articl Adsorption of Rhodamin B on activatd carbon obtaind from pricarp of rubbr fruit in comparison with th commrcial activatd carbon Farda Hayy*, Maimoon Sattar, Surajit Tkasakul, and Orawan Sirichot Dpartmnt of Chmistry, Faculty of Scinc, Princ of Songkla Univrsity, Hat Yai, Songkhla, Thailand. Rcivd 15 May 2013; Accptd 6 Dcmbr 2013 Abstract Adsorption of th dy, Rhodamin B, on activatd carbon obtaind from pricarp of rubbr fruit (PrAC) was invstigatd in comparison with th commrcial activatd carbon (CAC). Both activatd carbons wr charactrizd by scanning lctron microscopy (SEM), spcific surfac ara, and ph at point of zro charg (ph pzc ). Th ffcts of various xprimntal paramtrs such as contact tim, dy concntration, amount of activatd carbon, ph and tmpratur wr analysd. Th adsorption isothrm fittd wll into th Langmuir modl. By kping ph constant at 4.0 and varying tmpraturs at 30, 40, 50, and 60 C, th maximum adsorption wr , , , and mmol g -1 for PrAC and , , , and mmol g -1 for CAC, rspctivly. Study of th ffct of tmpratur dpndnc of ths adsorptions indicatd that thy wr ndothrmic procsss. Th adsorption fficincy of Rhodamin B on PrAC is about 80-90%. Kywords: activatd carbon, pricarp of rubbr fruit, Rhodamin B, Langmuir adsorption isothrm 1. Introduction Wast watr including wast watr from manufacturing procsss, buildings, rsidncs, and shops may contain substancs such as organic substancs, inorganic substancs, acid alkalin, havy mtals, som chmical substancs, radioactivity substancs, toxic substancs, sandy soil, and othr wasts. Whn ths wasts ar xplld into th rivr, th quantity of thos substancs may b toxic is living things in th watr. Most of th contaminants in wast watr from th dy industry ar dys and chmical substancs which ar lft ovr part in th watr using in manufacturing procss and bing thrown into th wast watr. Evn in low concntrations, dys affct aquatic lif and th food wb. Bcaus many organic dys ar harmful to human bings, th rmoval of color from th wast fflunts is nvironmntally important (Arivoli t al., 2009). * Corrsponding author. addrss: hin_999@hotmail.com Thr ar many communitis in various provincs of th lowr part of southrn Thailand that produc Krajood products or products mad from Bulrush plant such as mats, bags, hats and shopping baskts. Th dying of raw matrials in diffrnt colors is ndd to incras th varity and improv th quality of th products. Rhodamin B, which is a dark pink basic dy, was xclusivly usd for many pattrns of Krajood products. In this rsarch th Rhodamin B was slctd for th adsorption xprimnt du to its prsnc in th wastwatr of svral industris (such as txtil, lathr, jut and food industris). Its structur in aquous solution is displayd in Figur 1. Thr ar many mthods to rmov th color but on of th intrsting ways is adsorption by activatd carbon. Activatd carbon is th most widly usd adsorbnt for this purpos bcaus of its xtnsiv surfac ara, microporous structur, high adsorption capacity, and high dgr of surfac ractivity (Bhatnagar t al., 2005). In th prsnt work th activatd carbon obtaind from pricarp of rubbr fruit (PrAC) wr usd to study th adsorption of Rhodamin B in comparison with commrcial activatd carbon (CAC). Th pricarp of rubbr fruit (PrAC)

2 178 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , 2014 Figur 1. Structur of Rhodamin B in aquous solution. was usd obtaind from th rubbr plantation and usd of prpar activatd carbon using chmical activation with ZnCl 2. Th chmical activation is considrd of a suitabl mthod for producing highly microporous activatd carbons. Th most common activating agnt is zinc chlorid (ZnCl 2 ). In comparison with th physical activation, th chmical activation mchanism is not wll undrstood (Lozano- Castllo t al., 2001) but it sms that th chmical agnt dhydrats th sampl, inhibits th tar formation and volatil compound volution, and thrfor nhancs th yild of th carbonization procss (Williams and Rd, 2004). Aftr imprgnating th prcursor by chmical agnt and hat tratmnt of th mixtur, th imprgnating agnt is liminatd by washing with acid/bas and watr. Th washing stp maks th por structur availabl, by rmoving th imprgnating agnt and its salts. Figur 2 shows th gnral flow chart for chmical activation by zinc chlorid (ZnCl 2 ). Th activatd carbon producd by ZnCl 2 activation is dominantly microporous, but with a significant componnt of msopors which incrass with an incras in th imprgnation ratio (ZnCl 2 /prcursor) (McEnanny, 2002; Azargohar, 2009). 2. Matrials and Mthods 2.1 Matrials and ragnts Rhodamin B was procurd from Fluka, UK. Th CAC was obtaind from Sigma Aldrich, UK. Th production procsss of activatd carbon from pricarp of rubbr fruit wr carbonization and chmical activation with ZnCl 2. Pricarp of rubbr fruit was drid in th sun and cut into small pics approximatly 1 inch and placd into a stainlss stl box with covr. Th carbonization was thn conductd in a muffl furnac at 400C for 1 h. Aftr carbonization th rsidual char was ground in a laboratory jar mill to pass throughs msh sivs. Thn, th chmical activation was prformd by mixing th ground char with concntratd solution of ZnCl 2 at a ratio of 1:2. Th sampl was activatd at 600C for 3 h in th muffl furnac. Th obtaind activatd carbon was washd with 1% HCl solution. In th nxt stp, th carbon was soakd in hot watr for fiv minuts and subsquntly th watr was draind off through a Buchnr funnl. This stp was rpatd two mor tims to obtain a nutral ph valu. Finally, it was drid in th ovn at 110C for 24 h. Th obtaind activatd carbon was kpt in a dssicator (Chunchom, 2004; Sirichot t al., 2008). 2.2 Charactrization of th activatd carbons A scanning lctron microscop (JSM-5800 LV) at th Scintific Equipmnt Cntr, PSU, was usd to analyz th porosity of both activatd carbon sampls. Nitrogn adsorption isothrms at 77 K (Coultr SA 3100) wr usd to dtrmin spcific surfac ara and micropor volums of activatd carbons by using Brunaur- Emmtt-Tllr (BET) and t-plot quations, rspctivly. Th por siz distribution was calculatd by using th Barrtt- Joynr-Halnda (BJH) modl. Prior to th adsorption xprimnts, for maintaining th intgrity of th chmical surfac proprtis, all sampls wr dgassd for 1 h at 120 C. Th ph pzc was dtrmind by using th ph drift mthod (Jia t al., 1998; Jia t al., 2002) for all activatd carbon sampls. Th ph of solution of 0.1 M NaCl was adjustd btwn 2-12 by using 0.01 M HCl or NaOH. Activatd carbon sampl ( g) was addd into 100 ml of NaCl solution in a 250 ml flask. Th flask was sald to liminat any contact with air and thn lft at ambint tmpratur. Th final ph was rcordd aftr th ph had stabilizd (typically aftr 24 h). Th graph of final ph (ph f ) vrsus initial ph (ph 0 ) was usd to dtrmin th point at which initial ph and final ph of activatd carbon solution wr qual. At this point, (ph pzc ), th surfac of activatd carbon is nutral. 2.3 Adsorption studis Figur 2. Th gnral flow chart for chmical activation by zinc chlorid (ZnCl 2 ) mg L -1 stock solution of Rhodamin B was prpard by dissolving in distilld watr. Thn th stock solution was dilutd with distilld watr to obtain sris of standard solutions with concntrations ranging from mg L -1. Th ffcts from othr variabl paramtrs such as th amount of activatd carbon, contact tim, ph and tmpratur wr also studid.

3 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , Th various doss of th activatd carbons in th rang g for PrAC and g for CAC wr mixd with 50 ml of th dy solutions and th mixturs wr agitatd in a mchanical thrmostat shakr at 30 C. Th adsorption capacitis of activatd carbons for diffrnt doss wr dtrmind at dfinit tim intrvals by kping ph at 4, initial concntration of dy 300 mg L -1 and tmpratur at 30 C. Th ffct of contact tim on th adsorption of dy by th adsorbnt in a singl cycl was dtrmind by kping ph at 4, initial concntration 300 mg L -1, th amount of activatd carbon g for PrAC and g for CAC and tmpratur at 30 C. Th ph of Rhodamin B solution of 300 mg L -1 was adjustd btwn 2-13 using 0.01 M HCl or 0.01 M NaOH. A crtain amount of activatd carbon was addd into 50 ml of dy solution. Th contnts wr thn shakn at 30 C in th thrmostat shakr watr bath. Aftr th quilibriums wr obtaind (24 h for PrAC and 6 h for CAC) about 2 ml of dy solution was transfrrd to tst tub and cntrifugd. Th suprnatant was dcantd and analyzd for th concntration of Rhodamin B. Th paramtrs lik dosag of th adsorbnts ( g of PrAC and g of CAC), dy concntration (300 mg L -1 ) and tmpratur (30 C) wr kpt constant. Th adsorption xprimnts wr prformd at 30, 40, 50 and 60 C in a thrmostatd watr bath shakr at ph 4.0, which is th natural ph of dy solution, to dtrmin th ffct of tmpratur for adsorption. All othr factors wr kpt constant as mntiond abov Adsorption isothrm studis of Rhodamin B on activatd carbons A crtain amount of activatd carbon ( g of PrAC and g of CAC) was addd into 50 ml of dy solution. Adsorption quilibrium studis of Rhodamin B on ithr PrAC or CAC wr carrid out in a batch procss at 30, 40, 50 and 60 C. Th concntrations of dy solutions at ph 4.0 wr varid in th rang of mg L -1. Th contnts wr cntrifugd aftr gntl shaking for a priod of tim to rach quilibrium. Rhodamin B concntrations bfor and aftr adsorption wr thn dtrmind by UV-Vis spctrophotomtr at a wavlngth 554 nm. Th adsorbd amount of Rhodamin B was calculatd from th quation (1) (Mikap t al., 2006) as follows: V ( C0 C) Q (1) W whr Q is th amount of dy adsorbd onto activatd carbon (mg g -1 ), V is th volum of th solution (L), C 0 is th initial liquid-phas concntration of dy (mg L -1 ), C is th quilibrium liquid-phas concntration of dy (mg L -1 ), and W is th mass of th adsorbnt (g). Th amount of dy adsorbd onto activatd carbon was calculatd basd on th prviously dtrmind calibration curv. 3. Rsults and Discussion 3.1 Charactrization of PrAC and CAC Scanning lctron microscopy (SEM) In Figur 3, th scanning lctron micrographs of th xtrnal structurs of both activatd carbons, PrAC msh and CAC msh ar shown. From micrographs, it can b sn that both sampls ar full of hols with diamtrs ranging from around µm and 4-20 µm, rspctivly. Ths hols ar dfind as macropor of th activatd carbon (>50 nm). Both micropor and msopor ar not rsolvd by scanning lctron microscopy vn at highr magnification bcaus of th limit of dtction of th instrumnt Surfac ara Nitrogn adsorption isothrms masurd for PrAC and CAC ar shown in Figur 4. It is vidnt that th isothrms can b classifid into two typs. In th cas of PrAC, its isothrm is approximatly typ I according to IUPAC classification (Hu and Vansant, 1995) sinc most of th adsorbd volum is containd in th micropors. Th isothrms show a stp ris of th initial part whr micropors ar filld by nitrogn molcul compltly at ~0.2 P s /P 0. Aftr 0.2 P s /P 0, th isothrm bcoms a platau. It is now widly accptd that th initial part of th typ I isothrm rprsntd micropor filling and that th slop of th platau at high rlativ prssur is du to monolayr adsorption on th nonmicroporous structurs, such as in msopors, in macropors, and on th xtrnal surfac. If nitrogn adsorption isothrm of any porous matrial can b fittd with typ I isothrm, it can b assumd that th matrial has significant micropors. Thrby, PrAC has th contnts largly of micropor. On th othr hand, isothrm of CAC blongs to a mixd typ in th IUPAC classification (Juang t al., 2002). In th initial parts it is typ I, with an important uptak at low rlativ prssurs. It is typ II at intrmdiat and high rlativ prssurs. Th stp ris of Figur 3. SEM micrographs of (a) PrAC ( 1000 magnification)and (b) CAC ( 1300 magnification).

4 180 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , 2014 Figur 4. Adsorption isothrms of N 2 at 77 K for th PrAC and CAC (P s /P 0 is rlativ prssur). th initial part of th isothrms vidncs th prsnc of micropors. Howvr, th prsnt sampls do not rach a clar platau unlik othr activatd carbons. This indicatd that PrAC and CAC ar mainly micro- and msoporous in charactr with a minor prsnc of widr pors whr capillary condnsation occurrd. From Tabl 1, furthr undrstanding of th porous charactrs of th two sampls of activatd carbon can b obtaind. Th rsults show that ach sampl posssss a wll-dvlopd porous structur. PrAC and CAC xhibit diffrnt BET surfac aras. Th diffrnc among BET surfac ara of th two sampls is about 30%. Hnc, BET surfac ara may affct th adsorption fficincy in this study. Gnrally, th pors of activatd carbon ar classifid into thr groups, micropor (< 2 nm), msopor (2-50 nm) and macropor (> 50 nm). In this study, howvr, por siz distribution in th micropor rgion cannot b masurd du to th limitation of th instrumnt. Thr ar many mthods for dtrminations of por siz distribution in th micropor rgion such as th potntial thory of Dubinin, t-plot mthod, plot or MP mthods (Strlko and Malik, 2002), which ar widly usd for micropor valution. This rsarch has usd t-plot mthod for dtrmining micropor surfac ara, micropor fraction and micropor volum but this mthod cannot b usd for dtrmination of th distribution of micro porous. Por siz distribution abov 2 nm, howvr, can b assssd accuratly using th mthod of Barrtt, Joynr and Halnda (BJH) modl (Barrtt t al., 1951). It can b sn from Tabl 1 that PrAC posssss gratr micropor surfac ara and prcntag of micropor fraction ((micropor surfac ara/ BET surfac ara) 100) around 75% which is mor dus th CAC. Noticably, CAC has mor BET surfac ara than PrAC but CAC shows lss micropor fraction. From Figur 4, CAC rmarkably has mor incrmntal por volum of msopor and macropor than PrAC. Thrfor, th physical charactristics of raw matrial sm to b important factor for porous natur of activatd carbon. Figur 5 shows th mso- and macropor natur of all activatd carbon. PrAC dos not hav significant msopors and macropors In contrast, CAC posssss a significant amount of msopor with a maximum at 6 nm and 16 nm. PrAC also shows vidnc of th prsnc of msopors and macropors Point of zro charg (ph pzc ) Graphs of final ph vrsus initial ph obtaind by using th ph drift mthod for all activatd carbon sampls ar plottd as shown in Figur 6. Th rsults show that ph pzc of PrAC and CAC ar 6.5 and 3.5, rspctivly. It is suggstd that th surfac of th PrAC in dy solution at ph 4.0 (<ph pzc ) has positiv charg which causs th lctrostatic rpulsion with th positiv charg of th dy. In contrast to th surfac of CAC in dy solution at ph 4.0 (>ph pzc ) has ngativ charg that can attract with th positiv charg of th dy. Figur 5. BJH por siz distribution of PrAC and CAC. Tabl 1. BET and micropor surfac aras of PrAC and CAC Sampl BET surfac ara Micropor Micropor Micropor (m 2 g -1 ) surfac ara fraction volum (m 2 g -1 ) (%) (ml g -1 ) PrAC CAC 1,

5 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , and Kadirvlu, 1999). In this study, th appropriat wights of CAC and PrAC wr and , rspctivly bcaus ths wights of adsorbnt did not hlp too long a tim to rach quilibrium for adsorption of Rhodamin B. Ths find amounts of activatd carbon dos wr picking up to study th adsorption isothrm. 2) Contact tim and initial dy concntration In most adsorption isothrm studis, th rsults showd that quilibrium was achivd within around 24 h and 6 h for PrAC and CAC as shown in Figur 8 by kping th ph at 4, initial concntration 300 mg L -1, with wight of PrAC and CAC of g and g, rspctivly, and tmpratur at 30 C. Howvr, th solutions wr lft longr than quilibrium tim to nsur complt quilibration which wr uss of to study th adsorption isothrms. 3) ph In Figur 9, it shows th ffct of solution ph valus on th adsorption of Rhodamin B on all of th activatd Figur 6. Graphs of final ph vrsus initial ph for dtrmination th point of zro charg (ph pzc ) of PrAC (a) and CAC (b). Th amphotric charactr of surfac oxids S-CO 2 whr S rprsnts th activatd carbon surfac can b xplaind as follows (Kadirvalu t al., 2000). For ph < ph pzc, th dominant raction is: S CO 2 H O S C( OH ) 2OH Th rlas of hydroxyl ions inducs an incras of ph and a protonatd surfac of activatd carbon. For ph> ph pzc, th following raction taks plac: S CO 2 H O S C( O ) 2H O Th activatd carbon surfac is dprotonatd and th rlas of protons inducs a dcras in ph. 3.2 Adsorption studis Effct of various paramtrs 1) Wight of activatd carbon By kping th initial concntration at 300 mg L -1 th prcntag of dy adsorption at quilibrium incrasd with incrasing wight of both activatd carbons as shown in Figur 7. Effct of wight of activatd carbon was attributd to th incras of surfac ara and availability of mor adsorption sits (Namasivayam t al., 1996; Navasivayam Figur 7. Effct of wight of PrAC ( msh), g/50 ml (a) and ffct of wight of CAC ( msh), g/50 ml (b) for adsorption of dy to rach th quilibrium at 30 C, ph = 4.0 and dy concntration 300 mg L -1.

6 182 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , 2014 Figur 8. Equilibrium tim of 300, 400 and 500 mg L -1 Rhodamin B on PrAC ( g) (a) and CAC ( g) (b) at 30 C and ph = 4.0. Figur 9. Adsorption of Rhodamin B on PrAC and CAC with ph rang 2-13 and dy concntration 300 mg L -1. carbons. Rhodamin B displays a gnral trnd of slightly incrasd adsorption on ach th activatd carbons with th incras of solution ph valus. At ph highr than 2, th adsorption amount of Rhodamin B on PrAC and CAC slightly incrasd with th incras of solution ph valus. In addition, at low ph thr was comptition for th surfac sitd of activatd carbon btwn protonation (H + adsorption on th carbon surfac) and adsorption of Rhodamin B. Sinc th surfac of CAC and PrAC ar ngativ at ph > ph pzc (3.5) and ph > ph pzc (6.5), rspctivly. Whn ph of solution incrass with incrasing amount of adsorbd bcaus th incras of solution ph valus, th lctrical rpulsion forc bcom wakr and th Rhodamin B may b transportd to th surfac of th activatd carbons and bcom to attachd on th surfac du to th action of othr factors such as lss comptitiv from protonation. 4) Tmpratur Th adsorption capacity of th adsorbnt incrasd with incras in th tmpratur of th systm from C as shown in Tabl 2 and 3 for PrAC and CAC, rspctivly. Th prcntag of adsorption incrass with incrasing tmpratur. This indicats that th adsorption procs s is ndothrmic. This rsult is rlatd with thrmodynamic study. 3.3 Adsorption isothrm studis of Rhodamin B on activatd carbons Th xprimntal data wr analyzd by th linar form of th Langmuir isothrms (Langmuir, 1918). Th Langmuir isothrm was rprsntd by th following quation (2): C 1 C (2) Q Qmb Qm whr C is th quilibrium concntration (mmol L -1 ), Q is th amount adsorbd at quilibrium (mmol L -1 ) and Q m and b ar Langmuir constants rlatd to th maximum adsorption at monolayr covrag (mmol g -1 ) and th adsorption quilibrium constant (L mmol -1 ), rspctivly. According to th Langmuir quation th quilibrium concntration of dy ovr th adsorbd amounts of dy ( C / Q, g L -1 ) wr plottd against th quilibrium concntrations of dy ( C ) at various tmpraturs for PrAC and CAC as shown in Figur 10. For ach tmpratur th graph was fittd to a straight lin. Thn th maximum amount of dy adsorption, Q m (mmol g -1 ), was calculatd from th slop (= 1/ Q m ) and th quilibrium constant rlatd to th hat of adsorption, b (Lmmol -1 ), was calculatd from th intrcpt (= 1/ ( bq m) ). Th valus of Q m and b including 2 th corrlation cofficints, R, ar tabulatd in Tabl 4.

7 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , Tabl 2. Equilibrium paramtrs for th adsorption of Rhodamin B mmol L -1 on PrAC C 0 (mmol L -1 ) C (mmol L -1 ) % dy adsorbd Tmpratur ( C) Tabl 3. Equilibrium paramtrs for th adsorption of Rhodamin B mmol L -1 on CAC C 0 (mmol L -1 ) (mmol L -1 ) % dy adsorbd Tmpratur ( C) Figur 10 show that adsorption capacitis of CAC for Rhodamin B ar gratr than PrAC at ph = 4 and 30 C, 40 C, 50 C, and 60 C. W can imagin that in th cas of th high ionic radius of Rhodamin B, th rsult may b xplaind in trms of por accssibility (Kadirvalu t al., 2000). Sinc PrAC has mor micropors than CAC, som micropor ntrancs may b blockd by hydrolyzd dy spcis which ar largr than th dy ions. Accordingly, surfac groups locatd in micropors ar no longr accssibl and som surfac sits ar not usd for adsorption. In th cas of CAC which contain mor msopors, accssibility to micro- and msopors is not blockd by hydrolyzd spcis and almost all surfac sits can b usd for adsorption of Rhodamin B. In addition, acidity of th surfac bcoms anothr factor to dfin adsorption capacitis (Frro-Garcy t al., 1998). CAC, which has lowr phpzc valus, should hav mor adsorption capacitis than PrAC. Thrfor, it is unquivocal that th Figur 10. Langmuir adsorption isothrms for linar form of CAC has highr adsorption of Rhodamin B than PrAC Rhodamin B on PrAC and CAC at 30 C, 40 C, 50 C bcaus CAC has th highr msopor and lowr phpzc and 60 C, dy concntrations mg L -1 and ph valu. = 4.0. Th dimnsionlss sparation factor ( R L ) is usd to confirm th favorability of th adsorption procss, which is 1 calculatd by th following quation (3) (Arivoli and Thnkuzhali, 2007): 1 bc (3) R L 0

8 184 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , 2014 Tabl 4. Paramtr valus of th Langmuir quations for linar form fittd to th xprimnt of Rhodamin B adsorption on PrAC and CAC at diffrnt tmpraturs PrAC CAC Tmp Q m b R 2 Q m b R 2 ( C) (mmol g -1 ) (L mmol -1 ) (mmol g -1 ) (L mmol -1 ) Whr R L is its dimnsionlss sparation factor, b is an quilibrium constant rlatd to th hat of adsorption and C0 is th initial dy concntration. Th R L valus wr found btwn 0 and 1 confirming that th ongoing adsorption procss was favorabl. Thir valus ar prsntd in Tabl 5 and Tabl 6 for PrAC and CAC, rspctivly. 3.4 Thrmodynamic considrations From th prvious study, som gnral conclusions can b drawn rgarding th nrgtic changs occurring Tabl 5. Dimnsionlss sparation factor ( R L ) of Rhodamin B adsorption on PrAC at diffrnt tmpratur C o (mg L -1 ) R L Tmpratur( C) during th procss. Th b paramtr from Langmuir quation can b rlatd to th nthalpy or hat of adsorption (H ads ) as follows (Adamson and Gast, 1997) ΔH ads / RT b b' (4) whr R is th univrsal gas constant (8.314 J K -1 mol -1 ), T is th tmpratur in Klvin and b ' is a pr-xponntial factor constant. Th hat of th adsorption (H ads ) can b dtrmind from its slop of th obsrvd linarity from th van t hoff plot of ln b vrsus 1/T that lads to th hat procss involvd in adsorption at monolayr covrag on PrAC and CAC Th valus of hat adsorption (H ads ) wr kj mol -1 and kj mol -1 for PrAC and CAC, rspctivly, and th rsults ar shown in Figur 11. Thr is anothr altrnativ us th Clausius-Clapyron quation to xplain hat of adsorption. Th hat of adsorption was calculatd by applying th Clausius-Clapyron quation to th adsorption isothrm as following quation (Albrty and Silby, 1992; Sirichot, 2002): dp PH vap 2 (5) dt RT whr P is th quilibrium prssur of gas, T is th absolut tmpratur, H vap is th hat of vaporization, and R is th gas constant. On rarrangmnt quation (5) bcoms Tabl 6. Dimnsionlss sparation factor ( RL ) of Rhodamin B adsorption on CAC at diffrnt tmpratur C o (mg L -1 ) R L Tmpratur( C) Figur 11. Th van t hoff plots for adsorption of Rhodamin B on PrAC and CAC at 30 C, 40 C, 50 C and 60 C, dy concntrations mg L -1 and ph = 4.0.

9 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , dp H vap dt 2 (6) P RT H vap 0 2 P d ln dt (7) P RT whr P 0 is th standard prssur usd. Rplacmnt of P by CRT and P 0 by C 0 RT from idal gas law whr C is th molar concntration and C 0 is th standard valu of th molar concntration (1 mol L -1 ) quation (7) bcoms H vap 0 2 C d ln dt (8) C RT For adsorption in solution th H vap is rplacd by H ads which is th hat of adsorption. Intgrating on th assumption that th H ads is indpndnt of tmpratur and concntration and sinc th trm ln C 0 is qual to zro, quation (8) yilds C H ads 2 d ln C T dt C R Hads ln C c (10) RT whr C is th quilibrium concntration (mmol L -1 ), H ads is th isostric hat of adsorption (kj mol -1 ), R is th univrsal gas constant (8.314 J K -1 mol -1 ), and c is th intgration constant. Th plots of applid Clausius-Clapyron quation to adsorption isothrm in quation (10) as ln C vrsus 1/ T should giv a straight lin of slop -(H ads /R) and th rsults ar shown in Figur 12(a) and Figur 12(b). Th valus of th hat of adsorption (H ads ) ar shown in Tabl 7 Th positiv valus of th hat of adsorption (H ads ) from van t hoft quation and Clausius-Clapyron quation (9) Figur 12. Clausius-Clapyron plots for adsorption of Rhodamin B on PrAC and CAC at 30 C, 40 C, 50 C and 60 C, dy concntrations mg L -1 and ph = 4.0. indicatd that thy wr ndothrmic procsss and th H ads of btwn 0 40 kj mol -1 confirms that it govrns th possibility of physical adsorption (Bond, 1987). Tabl 7. Th hat of adsorption (H ads ) of Rhodamin B adsorption on PrAC and CAC from Clausius-Clapyron quation at 30C, 40C, 50C and 60C, mg L -1 and ph = 4.0 PrAC CAC C0 H ads R 2 H ads R 2 (mg L -1 ) (kj mol -1 ) (kj mol -1 ) ± ± ± ± ± ± ± ± ± ± ± ± Avrag valu of H ads

10 186 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , Conclusions Th charactristics of adsorption of Rhodamin B on PrAC and CAC can b corrlatd rasonably wll by th Langmuir adsorption isothrm. By kping ph 4.0 and varying tmpraturs at 30, 40, 50 and 60 C, th maximum adsorption (Q m ) wr , , and mmol g -1 for PrAC and , , and mmol g -1 for CAC, rspctivly. Th valus of maximum adsorption ( Q m ) for CAC ar gratr than for PrAC, showing th importanc of porosity, por siz for adsorption and th charg on th surfac of activatd carbon. CAC has a significantly largr amount of msopors and macropors than PrAC, indicating that th adsorption of dy occurs in msopors and macropors of CAC. Th ph of dy solution at 4.0 causs th surfac of CAC to hav ngativ chargs which will attract th positivly chargd dy. In contrast, th surfac of PrAC with positiv chargs causs lctrostatic rpulsion of th dy. Howvr, th aromatic rings of dy molcul can b attract of wakly to th nutral part of PrAC surfac by van dr Waals intraction. Th R L valus ar found to in th rang btwn 0 and 1, which confirms that th ongoing adsorption procss is much mor favorabl. Th avrag valus of hat adsorption (ΔH ads ) wr kj mol -1 and 5.67 kj mol -1 for PrAC and CAC, rspctivly. Ths ΔH ads ar btwn 0 40 kj mol -1 confirm th adsorption procsss to b ndothrmic and controlling th physical adsorption. Th fficincy of adsorption of Rhodamin B on PrAC is about 80-90%. Thrfor, on of th agricultural products lik PrAC can rplac th commrcial activatd carbon for rmoval of dys from wast watr. Acknowldgmnts This rsarch was supportd by Dpartmnt of Chmistry, Faculty of Scinc, Princ of Songkla Univrsity, Hat Yai, and partially supportd by th Cntr of Excllnc for Innovation in Chmistry: Post Graduat Education and Rsarch Program in Chmistry (PERCH CIC), and th Graduat School, Princ of Songkla Univrsity. Rfrncs Adamson, A. W. and Gast, A. P Physical Chmistry of Surfacs, John Wily and Sons Canada, Ltd., Canada, pp Albrty, R.A. and Silby, R. J Physical Chmistry (1 st d.), John Wily and Sons, Inc., Nw York, U.S.A., p Arivoli, S. and Thnkuzhali, M Kintic, mchanistic, thrmodynamic and quilibrium studis on th adsorption of Rhodamin B by acid activatd low cost carbon. E-Journal of Chmistry. 5, Arivoli, S., Thnkuzhali, M.; and Martin Dva Prasath, P Adsorption of Rhodamin B by acid activatd carbon kintic, thrmodynamic and quilibrium Studis. E-Journal of Chmistry. 1(2), Azargohar, R Production of activatd carbon and its catalytic application for oxidation of hydrogn sulphid. Doctor of Philosophy in th dpartmnt of Chmical Enginring Univrsity of Saskatchwan. Canada. Barrtt, E. P., Joynr, L. G. and Halnda, P. P Por siz distribution for porous matrials. Journal of th Amrican Chmical Socity. 73, Bhatnagar, A. and Jain, A.K A comparativ adsorption study with diffrnt industrial wasts as adsorbnts for th rmoval of cationic dys from watr. Journal of Colloid and Intrfac Scinc. 281, Bond, G. C Htrognous Catalysis: Principls and Applications. Oxford Univrsity Prss, Nw York, U.S.A. Chunchom, L Adsorption of cadmium (II) and lad (II) ions on activatd carbons obtaind from bagass and pricarp of rubbr fruit. Mastr of Scinc Thsis in Physical Chmistry, Princ of Songkla Univrsity, Thailand. Frro-Garcy, M. A.; Rivra-Utrilla, J.; Bautista-Toldo, I. and Morno-Castilla, C Adsorption of Humic Substancs on Activatd Carbon from Aquous Solutions and Thir Effct on Th Rmoval of Cr(III) Ions. Langmuir. 14, Hu, Z. and Vansant, E. F A nw composit adsorbnt producd by chmical activation of lutrilith with zinc chlorid. Journal of Colloid and Intrfac Scinc. 176, 422 Jia, Y. F.; Stl, C. J.; Hayward, I. P. and Thomas. K. M Mchanism of adsorption of gold and silvr spcis on activatd carbons. Carbon. 36, Jia, Y. F.; Xiao, B. and Thomas, K. M Adsorption of mtal ions on nitrogn surfac functional groups in activatd carbons. Langmuir. 18, Juang, R., Wu, F. and Tsng, R Charactrization and us of activatd carbons prpard from bagasss for liquid-phas adsorption. Colloid. Surfac: A. 201, Kadirvalu, K.; Faur-Brasqut, C. and L Cloirc, P Rmoval of Cu(II), Pb(II), and Ni(II) by Adsorption onto Activatd Carbon Cloths. Langmuir. 16, Langmuir, I Adsorption of gass on plan surfacs of glass, mica and platinum. Journal of th Amrican Chmical Socity. 40, Lozano-Castllo,D.; M.A. Lillo-Rodnas, D.; Cazorla-Amoros, and Linars-Solano, A Prparation of activatd carbons from Spanish anthracit I. Activation by KOH, Carbon. 39(5), Mikap, B.C., Thammu Naidu, J., Biswas, M.N. and Kaustubha, M Rmoval of crystal violt from wastwatr by activatd carbons prpard from ric husk. Industrial and Enginring Chmistry Rsarch, Eng. 45,

11 F. Hayy t al. / Songklanakarin J. Sci. Tchnol. 36 (2), , McEnany B Handbook of porous solids; Schuth, F., Sing, K. S. W.; Witkamp, J., Volum 3, Wily-VCH Vrlag GmbH, Winhim, Grmany. Namasivayam, C., Muniasamy, N., Gayathri, K., Rani, M. and Rnganathan, K Rmoval of dys from aquous solution by cllulosic wast orang pl. Bio Rsarch Tchnology. 57, 37. Namasivayam, C. and Kadirvlu, K Uptak of mrcury (II) from wastwatr by activatd carbon from an unwantd agricultural solid by-product: coirpith. Carbon. 37, Sirichot, O., Innajitara, W., Chunchom, L., Chunchit, D. and Nawkan, K Adsorption of iron (III) ions on activatd carbons obtaind from bagass, pricarp of rubbr fruit and coconut shll. Songklanakarin Journal of Scinc and Tchnology. 24, Sirichot, O., Innajitara, W., Chunchom, L., Panumati, S., Chudcha, K., Vankhaw, P. and Choolrt, V Adsorption of phnol from dilutd Aaquous solutions by activatd carbons obtaind from bagass, oil plam shll and pricarp of rubbr fruit. Songklanakarin Journal of Scinc and Tchnology. 30(2), Strlko, V Jr. and Malik, D. J Charactrization and mtal sorption proprtis of oxidizd activ carbon. Journal of Colloid and Intrfac Scinc. 250, Williams P. T. and A. R. Rd High grad activatd carbon matting drivd from th chmical activation and pyrolysis of natural fibr txtil wast. Journal of Analytical and Applid Pyrolysis. 71(2),