COMPETITIVE ADSORPTION OF DYE SPECIES ONTO BIOMASS NANOPOROUS CARBON IN SINGLE AND BICOMPONENT SYSTEMS

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1 razilian Journal of Chmical Enginring ISSN Printd in razil Vol. 35, No. 0, pp , January March, 208 dx.doi.org/0.590/ ss dx.doi.org/0.590/ s COMPETITIVE DSORPTION OF DYE SPECIES ONTO IOMSS NNOPOROUS CRON IN SINGLE ND ICOMPONENT SYSTEMS Huijing Yu, Tingting Wang, Wi Dai,*, L Yu and Na Ma 2,* Ky Laboratory of th Ministry of Education for dvancd Catalysis Matrials, Collg of Chmistry and Lif Scinc, Zhjiang Normal Univrsity, Zhjiang Provinc Jinhua 32004, Popl s Rpublic of China 2 Collg of Gography and Environmntal Scinc, Zhjiang Normal Univrsity, Zhjiang Provinc Jinhua 32004, Popl s Rpublic of China (Submittd: January 26, 206; Rvisd: Octobr 7, 206; ccptd: Novmbr 23, 206.) bstract W first prsnt a cost-ffctiv approach to simultanously dispos of rutaca plant wast (th discardd pls of orang, fingr citron, pomlo and lmon) to yild biomass nanoporous carbons (NCs). Th adsorption of orang II (OII) and acid chrom blu K (CK) from auous solutions in singl and binary dy systms by four typs of NCs wr studid in a batch adsorption systm. Th adsorption studis includ both uilibrium adsorption isothrms and intics. Four adsorption modls for prdicting th multicomponnt uilibrium sorption isothrms hav bn compard in ordr to dtrmin which on is th bst fit modl to prdict or corrlat binary adsorption data. Th intic data wr wll dscribd by th psudo-scond-ordr intic modl. It was found that th adsorption capacity of orang pl-basd nanoporous carbon (OPC) is much highr than thos of th othr typs of NCs. In addition, OPC also shows highr OII upta capacitis from binary dy solutions. Th four typs of NCs could b mployd as a low-cost altrnativ for th rmoval of txtil dys from fflunts. Kywords: Comptitiv dsorption; atch procssing; Wast-watr tratmnt; zo dys INTRODUCTION Nanostructurd carbon matrials hav attractd trmndous attntion in that thy possss rmarabl proprtis and xhibit promising potntial in a varity of important application aras rlatd to snsing (Kharat t al., 205), adsorption (Gong t al., 203), catalysis (Sun t al., 203), and nrgy convrsion/storag (Hu t al., 203). Manwhil, in paralll with th aggravating nrgy and nvironmntal problms such as pollution, fossil ful dpltion and global warming ris, intrsts in clan and rnwabl nrgy matrials, as wll as thir dvics hav spid in rcnt yars. s a rnwabl accss and nvironmntal frindlinss. Thrfor, nanoporous carbon matrials obtaind from biomass hav bn xplord with sourcs as divrs as watrmlon (Wu t al., 203), hmp fibr (Wang t al., 203), banana pl (Lv t al., 202), bactrial fibr (Wu t al., 204), and so on. s th mmbrs of rutaca plants, orang, pomlo, lmon and fingr citron ar favorit halth food, but a lot of wast pls ar producd during daily lif and by th food industry. Th four typs of wast pls ar natural, abundantly availabl, and yarly rnwabl biomass sourcs. s solid wast matrials, most of th pls (approximatly 2 hundrd millions tons annually in China alon) (Dai t al., 200) ar still * Corrsponding authors: Wi Dai. daiwi@zjnu.du.cn. Fax: Tl: ; Na Ma. mana@zjnu.cn. Fax: Tl:

2 254 H. Yu, T. Wang, W. Dai, L. Yu and N. Ma sourc, biomass rsourcs hav attractd a grat dal of attntion in th prparation of carbon matrials, bcaus of its low valu, hug amount, rapid rgnration, asy bcom an important issu that nds to b solvd impriously. iomass usually posssss natural plant fibr structur and this structur could provid an opportunity to prpar nanoporous carbon matrials (Wu t al., 203). Low-cost carbon matrials prpard from th othr biomass byproducts and wast matrials hav bn invstigatd for a long tim (Wu t al., 203; Wang t al., 203; Lv t al., 202; Wu t al., 204). Th aim bhind using wast matrials as an altrnativ low-cost prcursor to prpar nanoporous carbon matrials is that it will provid a twofold advantag with rspct to nvironmntal pollution. On on hand, th hug volum of wast matrials could b partly rducd and hlp rduc th cost of wast disposal. On th othr hand, th low-cost adsorbnt, if dvlopd, can provid a potntially inxpnsiv raw matrial for commrcial nanoporous carbon and rduc th pollution of wastwatrs at a rasonabl cost. In th last dcad, rmoval of azo dys from wast watr has attractd considrabl attntion bcaus of thir long-trm nvironmntal toxicity and short-trm public halth damag (Ofomaja and Ho, 2008). mong ths azo dys, orang II (OII) and acid chrom blu K (CK) hav wid applications in papr coloring, tmporary hair colorant, dying cottons and wools (Hu t al., 204). Thy can caus som harmful ffcts in humans such as y burns, dysfunction of idny, cyanosis, convulsions, tachycardia, dyspna and, irritation to th sin (Gong t al., 203; Hu t al., 204). Thrfor, rmoval of OII and CK from wastwatr and/or procss fflunt has bcom on of th major nviron- burnd dirctly in th fild or disposd as garbag, causing srious nvironmntal pollution. Thrfor, th consumption and application of ths wast pls hav mntal concrns. In addition, although considrabl information has bn accumulatd for th adsorption of singl-componnt dys by various adsorbnts, many industrial situations still rsult in companis discharging fflunts which contain binary dy componnts. Exprimntal data on bi-componnt sorption systms ar still vry limitd in th litratur. OII and CK for th rasons statd abov wr slctd in this study as th modl dys. Ovrall, th systmatic rsarch on similar structur dy adsorption onto similar raw matrials is still rlativly scarc. Orang, pomlo, lmon and fingr citron com from th rutaca family. Thrfor, thy hav similar shap, componnt and structur. In this wor, th wast pls of orang, pomlo, lmon and fingr citron (Schm ) wr invstigatd for th first tim as an altrnativ low-cost prcursor to prpar nanoporous carbon matrials (orang pl-basd nanoporous carbon, OPC; fingr citron pl-basd nanoporous carbon, FPC; pomlo pl-basd nanoporous carbon, PPC; lmon pl-basd nanoporous carbon, LPC) undr th sam prparation procss conditions for th rmoval of OII and CK from auous solutions. Two inds of anionic azo dys (orang II (OII) and acid chrom blu K (CK)) with similar structur and diffrnt numbr of functional groups ar slctd as typical dyd for adsorption onto four typs of biomass nanoporous carbons for th first tim. Th adsorption studis includ both uilibrium adsorption isothrms and intics, which could provid usful information and insight in this rsarch fild. (a) (a`) (b) (b`) (c) (c`) (d) (d`) Schm. Photos of four typs of biomass plants (a)-lmon; (a`)-lmon pls; (b)- pomlo; (b`)- pomlo pls; (c)-fingr citron; (c`)-fingr citron pls; (d)-orang; (d`)-orang pls. Matrials EXPERIMENTL SECTION Potassium hydroxid (KOH) and hydrochloric acid (HCl) usd in this study wr purchasd from th Sinopharm Chmical Ragnt Co., Ltd, China. Thy wr both of analytical grad and wr usd as rcivd without furthr purification. n auous stoc solution of OII and CK was prpard by dissolving OII (C 6H N 2NaO 4S, MW: , Sigma-ldrich) and CK (C 6H 9N 2Na 3O 2S 3, MW: , Sigma-ldrich) in distilld watr. Distilld watr was usd to prpar th dsird concntrations of dy solutions. Th chmical structurs of OII and CK ar shown in Schm 2. razilian Journal of Chmical Enginring

3 Comptitiv dsorption of Dy Spcis onto iomass Nanoporous Carbon in Singl and icomponnt Systms 255 (a) (b) Schm 2. Chmical structurs of OII (a) and CK (b). Prparation of OPC, PPC, LPC and FPC nanoporous carbons Four typs of nanoporous carbons wr prpard by a KOH activation procdur that was prviously proposd by our group (Gong t al., 203; Dai t al., 204). In a typical prparation, 2 g of prcursor in th particl siz 50 μm was mixd with 8 g of KOH powdr. Hnc, th mass ratio of KOH and biomass pl prcursor was 4: and th rsulting mixtur was placd into a horizontal pip ractor (50 mm o.d.) for activating as follows. (i) Nitrogn gas was allowd to flow through th ractor at a rat of 40 ml/min and maintaind at this flow rat throughout th whol activation procss. (ii) Th tmpratur of th ractor was raisd to th activation tmpratur (073 K) at a hating rat of K/min. (iii) Th ractor was hld at th activation tmpratur for 40 min. (iv) Finally, it was coold down to room tmpratur. Th sampls thus obtaind wr washd with distilld watr until th filtrat appard nutral. Th final products (OPC, FPC, PPC and LPC) wr obtaind by hating ths sampls at 423 K undr vacuum for 24 h. Nitrogn adsorption Spcific surfac aras and por volums wr dtrmind by N 2 adsorption. n automatd adsorption apparatus (Micromtrics, SP2020) was usd for ths masurmnts. N 2 adsorption was carrid out at liuid N 2 tmpratur (77 K). Th spcific surfac aras wr calculatd using th ET uation by assuming a crosssction ara of th nitrogn molcul of 0.62 nm (Gong t al., 203). Th t-plot mthod was applid to calculat th micropor volums and surfac aras. Th total por volum was stimatd to b th liuid N 2 volum at a rlativ prssur of Th por siz distribution was calculatd by dnsity functional thory (DFT). atch uilibrium studis Th uilibrium isothrms of OII and CK adsorption on th four typs of NCs wr dtrmind by prforming adsorption tsts in 00 ml rlnmyr flass whr 50 ml of OII and CK solutions with diffrnt initial concntrations ( mg/l) wr placd in ach flas. Th ph valu of th solutions was gradually adjustd to 7 by adding small amount of 0. M HCl solution g of ach of th prpard nanoporous carbons, with particl siz of 50 μm, wr addd to ach flas and pt in a shar with 50 rpm at room tmpratur (298 K) for 4 h to rach uilibrium. Th ph of dy solutions was 7 aftr th adsorption procss, which had no chang. Thn th sampls wr filtrd and th rsidual concntrations of OII and CK in th filtrat wr analyzd by a UV-Visibl spctrophotomtr (Shimadzu UV-60) at maximum wavlngths of 485 and 524 nm, rspctivly. It was found that th calibration curv was vry rproducibl and linar ovr th concntration rang usd in this wor. Th adsorbd amount of OII and CK at uilibrium, was calculatd by th following xprssion: ( C o C) V W () whr C o and C (mg/l) ar th initial and uilibrium concntrations of OII and CK solution, rspctivly; V (L) is th volum of solution, and W (g) is th wight of nanoporous carbons usd. Duplicat xprimnts wr carrid out for all th oprating variabls studid and only th avrag valus wr tan into considration. Th avrag dviation of duplicat rsults in th units of concntration was found to vary btwn ±%. Th batch xprimnts of binary dy solution wr prformd with a similar procdur. In a binary systm razilian Journal of Chmical Enginring Vol. 35, No. 0, pp , January March, 208 3

4 256 H. Yu, T. Wang, W. Dai, L. Yu and N. Ma with componnts (OII) and (CK), th masurmnt is carrid out at thir maximum absorbanc wavlngths λ max and λ max2, rspctivly, giving absorbancs of and 2. Concntrations of dy solution wr thn stimatd uantitativly using th linar rgrssion uations obtaind by plotting a calibration curv for ach dy ovr a wid rang of concntrations. In a binary dy solution, th concntrations of OII and CK wr calculatd according to th litratur (tar t al., 20). In a binary systm with componnts and, dy concntrations wr calculatd by th following uations (tar t al., 20): 2 2 (2) C C (3) whr,, 2, and 2 ar th calibration constants for componnts and at wavlngths λ max and λ max2, rspctivly, giving absorbancs of and 2.,, 2, and 2 for componnts and wr obtaind using th linar rgrssion uations according to th calibra tion curv. For binary dy solutions, initial dy concntrations wr maintaind at : (w/w). RESULTS ND DISCUSSION Matrial charactrization s illustratd in Fig., th adsorption and dsorption isothrms of N 2 at 77 K for th OPC, FPC, PPC and LPC sampls ar clarly of typ I, according to th IUPC classification (Dai t al., 203) of adsorption isothrms. Typ I isothrms charactristically show that all of th NCs invstigatd in this wor ar mainly composd of micro nanoporous structur. Th spcific runaur Emmtt Tllr (ET) surfac aras of OPC, FPC, PPC and LPC sampls ar 2289, 866, 359 and 05 m 2 /g, rspctivly. Th por siz distributions (PSD) of all th sampls wr calculatd using th dnsity function thory (DFT) modl and ar shown in Fig. 2. Th nanoporous carbon matrials of OPC, FPC, PPC and LPC ar mainly composd of micropors btwn. 2.0 nm and small msopors pad at 2.5 nm. Th proprtis of th adsorbnts ar collctd in Tabl. Th adsorption prformanc can b gratly improvd by incrasing th spcific surfac ara of th adsorbat matrial. Tabl. Structural proprtis of NCs. Sampls SET (m 2 /g) Vtotal (ml/g) Vmso (ml/g, %) Vmic (ml/g, %) vrag por diamtr (nm) LPC (30) 0.52 (70).68 PPC (22) 0.64 (78).48 FPC (26).9 (74) 2.8 OPC (32).00 (68) 2.07 Fig.. dsorption isothrms of N2 at 77 K on LPC, PPC, FPC and OPC sampls, rspctivly. Fig. 2. Por siz distribution of LPC, PPC, FPC and OPC sampls, rspctivly. razilian Journal of Chmical Enginring 4

5 Comptitiv dsorption of Dy Spcis onto iomass s Nanoporous Carbon in Singl and icomponnt Systms 257 dsorption isothrms Euilibrium data, commonly nown as adsorption isothrms, dscrib how th adsorbat intracts with adsorbnts, and giv a comprhnsiv undrstanding of th natur of intraction. It is important to optimiz th dsign of an adsorption systm (Royr t al., 2009). Th paramtrs obtaind from th diffrnt modls provid important information on th surfac proprtis of th adsorbnt and its affinity for th adsorbat. Svral isothrm uations hav bn dvlopd and mployd for such analysis and th thr important isothrms, th Langmuir, Frundlich and Tmin isothrms ar applid in this study. Th adsorption isothrms of OII and CK at 298 K on th OPC, FPC, PPC and LPC at a solid/liuid d ratio of 0.4 g/l in singl and binary solutions ar pr- Fig. 5. dsorption isothrms of OII and CK onto OPC in th sntd in Fig. 3, Fig. 4 and Fig. 5, rspctivly. binary systm. (t: 4 h, ph: 7, dos: 0.4 g/l, T: 298 K, Particl siz: 50 μm, Initial concntrations: mg/l). Fig. 3. dsorption isothrms of OII onto LPC, PPC, FPC and OPC in th singl systm. (t: 4 h, ph: 7, dos: 0.4 g/l, T: 298 K, Particl siz: 50 μm, Initial concntrations: mg/l). Th Langmuir adsorption isothrm dscribs uantitativly th formation of a monolayr of adsorbat on th outr surfac of th adsorbnt and, aftr that, no furthr adsorption tas plac. Thrby, th Langmuir rprsnts th uilibrium distribution of dy molculs btwn th solid and liuid phass (Langmuir, 98; Hamd, 2009; El-Gundi, 99; fhami t al., 2009). Th Langmuir isothrm is valid for monolayr adsorption onto a surfac containing a finit numbr of idntical sits. Th modl assums uniform nrgis of adsorption onto th surfac and no transmigration of adsorbat in th plan of th surfac. asd upon ths assumptions, th linar form of Langmuir s isothrm modl is rprsntd as follows: C ( ) C (4) K L L L whr L is th Langmuir maximum upta of OII and CK pr unit mass of adsorbnt, K L (L/mg) is th Langmuir constant rlatd to th rat of adsorption. Th Frundlich isothrm is an mpirical uation assuming that th adsorption procss tas plac on a htrognous surfac through a multilayr adsorption mchanism and adsorption capacity is rlatd to th concntration of dy at uilibrium (Mafra t al, 203). Th Frundlich uation is givn as: ln ln K f ( ) lnc n (5) Fig. 4. dsorption isothrms of CK onto LPC, PPC, FPC and OPC in th singl systm. (t: 4 h, ph: 7, dos: 0.4 g/l, T: 298 K, Particl siz: 50 μm, Initial concntrations: mg/l). whr K f and n ar Frundlich constants, with n indicating th favorablnss of th adsorption procss and K f th adsorption capacity of th adsorbnt. K f can b dfind as th adsorption or distribution cofficint and it rprsnts th uantity of dy adsorbd onto activatd carbon adsorbnt for a unit uilibrium concntration. razilian Journal of Chmical Enginring Vol. 35, No. 0, pp , January March, 208 5

6 258 H. Yu, T. Wang, W. Dai, L. Yu and N. Ma Th slop /n, ranging btwn 0 and, is a masur of adsorption intnsity or surfac htrognity, bcoming mor htrognous as its valu gts closr to zro. Th Tmin isothrm contains a factor that xplicitly tas into account th adsorbnt adsorbat intractions. y ignoring th xtrmly low and larg valu of concntrations, th modl assums that th hat of adsorption (a function of tmpratur) of all molculs in th layr should dcras linarly rathr than logarithmically with covrag (Dotto t al, 203). Th linar form of Tmin isothrm is xprssd as: ln ln C (6) whr is th Tmin constant rlatd to th hat of adsorption and is th uilibrium binding constant (L/mg). Th constants and can b dtrmind by a plot of vrsus ln C. Th adsorption isothrms wr L-curv in both dy systms (Fig. 3-5). Hnc w could say that th adsorption mchanisms wr not affctd undr th conditions of comptition. Th L-typ curv shows th highr affinity of th adsorbat for th adsorbnt. Th calculatd constants according to th two isothrm uations along with valus (standard dviation) ar prsntd in Tabl 2. This tabl shows that th Langmuir isothrm givs th bst fits with > Th good fit to th Langmuir modl for th dys also suggsts that th adsorption is limitd to a monolayr covrag and th surfac is rlativly homognous. On th othr hand, for OII and CK dys, th maximum monolayr adsorption capacity ( L) is significantly highr on OPC. Th upta capacity of OII is also significantly highr than that of th CK (approximatly.5-fold highr). This may b du to th diffrnt molcular sizs and functional groups of th two dys. OII and CK ar idally planar molculs and thrfor can asily adsorb on porous carbon by π-π stacing intractions btwn th aromatic bacbon of th dy and th hxagonal slton of porous carbon. s shown in Schm 2, CK has mor functional groups (3 hydroxyl and 3 sulfonic acid groups) than OII ( hydroxyl and sulfonic acid group), th rlativly complicatd structur of CK has high stric hindranc in th por channls of th carbon matrials. Thus, OII shows highr upta capacitis than CK. Th rsult suggstd that th adsorption mchanism was monolayr covrag on th surfac of th adsorbnt. In addition, th valus of 0 valuatd from th Langmuir modl wr clos to th xprimntal valus of. On th othr hand, for OII and CK th maximum monolayr adsorption capacitis ( L) ar significantly highr on OPC and vary in th ordr of OPC>FPC>PPC>LPC. Thus, it is prdictd that th dy upta capacity of nanoporous carbons is significantly highr with incrasd surfac ara. To tst th dpndnc of dy capacity on carbon structur, th maximum adsorption capacitis wr in turn corrlatd with th spcific surfac ara, por volum, and nominal por siz. Linar corrlation cofficints of OII and CK on OPC, FPC, PPC and LPC obtaind ar , 0.956, 0.82 and 0.952, 0.99, 0.734, rspctivly. It sms that spcific surfac ara xrts th largst ffct and th corrlation is shown in Fig. 6. Th adsorption capacitis of OII and CK on th four typs of NCs in this wor ar summarizd in Tabl 3, togthr with thos of th othr nanoporous carbons. It is clar that th adsorption capacity of OPC is suprior to th othr prviously rportd nanoporous carbon matrials (Ma t al., 205; Guzl t al., 204; Rodríguz t al., 2009; Yan t al., 202; Wang, 204). Tabl 2. Constants and corrlation cofficints of OII and CK adsorption from singl solutions NCs LPC PPC FPC OPC Dy L Langmuir Frundlich Tmin KL (L/mg) R2 Kf (L/g) n R2 (L/mg) OII CK OII CK OII CK OII CK R2 razilian Journal of Chmical Enginring 6

7 Comptitiv dsorption of Dy Spcis onto iomass Nanoporous Carbon in Singl and icomponnt Systms 259 Tabl 3. Comparison of th maximum upta capacitis of OII and CK dys on various nanoporous carbons. Dy OII CK dsorbnt Maximum monolayr upta capacitis Rfrnc OPC 930 this wor FPC 835 this wor PPC 645 this wor LPC 547 this wor PC TWNC C OPC 592 this wor FPC 555 this wor PPC 446 this wor LPC 35 this wor C JC xprimntal data in th binary systms wr applid to th comptitiv Langmuir uations (Tabl 4). Th corrlation cofficints in th binary systm wr lowr than in singl dy systm. W can say that th adsorbnt surfac is homognous and thr is no intraction btwn th adsorbd molculs. Ths ar applid to ral systms du to th ffct of surfac htrognity and intraction btwn azo dy molculs. dsorption intics Th intics of adsorption ar important bcaus this is what controls th fficincy of th procss and th tim to rach uilibrium. It also dscribs th rat of adsorbat upta on nanoporous carbons. In ordr to idntify th potntial rat-controlling stps involvd in th procss of adsorption, thr intic modls wr studid and usd to fit th xprimntal data from th adsorption of dys onto nanoporous carbons. Ths modls ar th psudo-first-ordr (Dotto t al., 203), psudo-scond-ordr (Ho and McKay, 998) and intra-particl diffusion modls (nnadurai t al., 2002). Ths modls can b xprssd as: Psudo-first ordr modl: ln( ) ln( ) K t t (9) Psudo-scond ordr modl: Fig. 6. Corrlation of OII and CK capacitis with spcific surfac ara of nanoporous carbons. t Intra-particl diffusion modl: t K 2 t (0) Th uations of a comptitiv Langmuir modl (Choy t al., 2000) ar as follows: 2 max L K LC K L2C2 (7) (8) whr K L and K L2 ar th Langmuir constants of th adsorbats and 2, max and max2 ar th maximum adsorption capacity of th adsorbats and 2. For binary dy adsorption systms (Fig. 5), th adsorption capacitis of OII and CK onto OPC wr rducd from 930 mg/g (singl systm) to 690 mg/g (binary systm) and from 555 mg/g (singl systm) to 30 mg/g (binary systm), rspctivly, at ph 7 bcaus of th highly comptition for activ sits btwn two typs of dy molculs in th binary systm. OII has a lowr molcular wight than CK and th adsorption capacity of OII is highr than that of CK at ph 7. Th K K C C max 2 L2 2 K LC K L2C2 / 2 t K 3 t () whr and t ar th upta of OII and CK at uilibrium and at tim t (min), rspctivly, K (/min) is th adsorption rat constant, K 2 (g/mg min) is th rat constant of th scond-ordr uation, K 3 (mg/g min /2 ) is th intra-particl diffusion rat constant. In ordr to uantitativly compar th applicability of diffrnt intic modls in fitting to data, a normalizd standard dviation, (%), was calculatd as blow: ( (%),xp,xp, cal ) 00% (2) Th ffcts of contact tim on adsorption capacitis of th four typs of NCs for OII and CK from singl and binary dy solutions ar shown in Fig. 7, Fig. 8 and Fig. 9, rspctivly. Ths figurs show that th adsorption capacitis for OII and CK incras with th incras of contact tim, and th adsorption rachs uilibrium within about h. Th saturation capacitis of razilian Journal of Chmical Enginring Vol. 35, No. 0, pp , January March, 208 7

8 260 H. Yu, T. Wang, W. Dai, L. Yu and N. Ma Tabl 4. Isothrm paramtrs of OII and CK adsorption from binary solutions. Comptitiv-Langmuir isothrm Langmuir Frundlich Tmin NCs Dy (L/mg) n Kf (L/g) KL (L/mg) L KL2 (L/mg) max2 (mg/l) KL (L/mg) max (mg/l) OII OPC CK OII and CK onto OPC, FPC, PPC and LPC in th singl dy solution ar 930, 835, 645, 547 mg/g and 592, 555, 446, 35 mg/g at room tmpratur (298 K), 4 h contact tim, 450 mg/l initial concntration, ph 7 and 0.4 g/l adsorbnt dos. For singl and binary dy adsorption systms, th adsorption capacitis of OII and CK wr rducd from 930 mg/g (singl systm) to 689 mg/g (binary systm) and from 592 mg/g (singl systm) to 20 mg/g (binary systm), rspctivly, at ph 7 bcaus of th comptition for activ sits btwn th two typs of dy molculs in th binary systm. Th capacity is constant whn all th paramtrs ar fixd, and with th volution of tim, th upta or adsorbd amount may chang. Th fast adsorption at th initial stag may b du to th availability of th uncovrd surfac ara and th rmaining activ sits on th adsorbnt. Fig. 7. Effct of contact tim on th adsorption capacitis of CK on LPC, PPC, FPC and OPC in th singl systm. Fig. 8. Effct of contact tim on th adsorption capacitis of OII on LPC, PPC, FPC and OPC in th singl systm. razilian Journal of Chmical Enginring 0

9 Comptitiv dsorption of Dy Spcis onto iomass Nanoporous Carbon in Singl and icomponnt Systms 26 Fig. 9. Effct of contact tim on th adsorption capacitis of OII Fig. 0. Wbr Morris intra-particl diffusion plots for th ad- and CK on OPC in th binary systm. sorption of OII on LPC, PPC, FPC and OPC, rspctivly. Th xprimntal intic data of OII and CK, calculatd from Es. 9, 0 and, wr corrlatd by thr intic modls: psudo-first ordr, psudo-scond d ordr and intra-particl diffusion modls. Th calculatd constants of th thr intic uations, along with valus at diffrnt tmpraturs, ar prsntd in Tabl 5 and 6. s sn in th Tabls, thr is a larg diffrnc btwn th xprimntal and calculatd adsorption capacity valus whn th psudo-first ordr modl was applid. Howvr, high valus (>0.999) ar obtaind with th linar plot of t/ t vrsus t, suggsting scond ordr adsorption intics. dditionally, th psudo-scond ordr intic modl is in a good agrmnt with th xprimntal and calculatd adsorption capacity valus Δ (%). If th intra-particl diffusion is th mchanism of th adsorption procss, thn th plot of t vrsus t /2 will b linar and if th plot passs through th origin, thn th rat limiting procss is only du to th intra-particl diffusion. Othrwis, som othr mchanism along with intraparticl diffusion is also involvd (hattacharyya and Sharma, 2005). Howvr, as shown in Figs. 0 and, th plots ar not linar ovr th whol tim rang and, instad, can b sparatd into multi-linar curvs, illustrating that multipl stags wr involvd in th adsorption procss. Th first straight portion was attributd to th macropor diffusion (phas I) and th scond linar portion was attributd to micro-por diffusion (phas II). Th rsults indicatd that th adsorption of OII and CK dys onto NCs involvd mor than on procss, and th intra-particl transport is not th rat-limiting stp. This finding is similar to that mad in prvious wors (hattacharyya and Sharma, 2004; Mahmoudi t al., 202; Emad t al., 2006). Fig.. Wbr Morris intra-particl diffusion plots for th adsorption of CK on LPC, PPC, FPC and OPC, rspctivly. CONCLUSION In summary, LPC, PPC, FPC and OPC with a high surfac ara wr synthsizd from solid wast, which is a natural, abundantly availabl, and constantly rnwabl sourc. dsorption paramtrs for th Langmuir, Frundlich and Tmin isothrms wr dtrmind and th uilibrium data wr bst dscribd by th Langmuir isothrm modl, with maximum uilibrium adsorption capacity of 930 mg/g (OII) and 592 mg/g (CK), rspctivly. Th adsorption intics can b succssfully fittd to a psudo-scond-ordr intic modl. It suggsts that th NCs could b mployd as a promising low-cost adsorbnt for rmoval of OII and razilian Journal of Chmical Enginring Vol. 35, No. 0, pp , January March, 208

10 262 H. Yu, T. Wang, W. Dai, L. Yu and N. Ma Tabl 5. Kintic paramtrs for OII and CK adsorption from singl solutions. Psudo-first-ordr rat uation Psudo-scond-ordr rat uation Intra-particl diffusion modl Sampls Dy,xp,cal K (/min) (%),cal K2 (g/mg min) (%) C K3 (mg/g min /2 ) LPC PPC FPC OPC OII CK OII CK OII CK OII CK Tabl 6. Kintic paramtrs or OII and CK adsorption from binary solutions. Psudo-first-ordr rat uation Psudo-scond-ordr rat uation Intra-particl diffusion modl Sampls Dy,xp,cal K (/min) (%),cal K2 (g/mg min) (%) C K3 (mg/g min /2 ) OPC OII CK razilian Journal of Chmical Enginring

11 Comptitiv dsorption of Dy Spcis onto iomass Nanoporous Carbon in Singl and icomponnt Systms 263 CK from singl and binary dy solutions. Th intic and uilibrium data will b usful for fabrication and dsigning dy wastwatr tratmnts. caus of thir hug adsorption capacity, such matrials can act as a promising catalyst for nxt-gnration ful clls and still hav vast unxplord potntial in th filds of supr capacitors, watr purification, CO 2 adsorption, and hydrogn storag. W bliv that our as-synthsizd carbon will crtainly b a trnd sttr and hav gratr conomic ramifications by crating valu-addd matrials from wast, which othrwis would bcom an nvironmntal burdn. 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