Adsorption Studies on the Removal of Fe(II) Ion onto Posidonia Oceanica Nano Carbon

Transcription

1 DOI: /cst Chmical Scinc Transactions ISSN: , 6(1), RESEARCH ARTICLE Adsorption Studis on th Rmoval of F(II) Ion onto Posidonia Ocanica Nano Carbon S. SUMITHRA and S. ARIVOLI * PG and Rsarch Dpartmnt of Chmistry, Thiru Vi Ka Govrnmnt Arts Collg, Thiruvarur, Tamilnadu, India arivu6363@gmail.com Rcivd 4 Dcmbr 2016 / Accptd 21 Dcmbr 2016 Abstract: Adsorption of F(II) ions by activatd Posidonia ocanica nano carbon was studid by using batch adsorption tchniqus. Th influnc of contact tim, initial concntration, dosag of adsorbnt and ffct of solution ph wr invstigatd. Th quilibrium adsorption data wr corrlatd with Langmuir, Frundlich, Tmkin, Dubinin-Radushkvich, Hurkins-Jura, Halsay, Radlich-Ptrson, Jovanovic and BET isothrm modls. Th isothrm studis of R L valus showd that th adsorption procss was favorabl. Thrmodynamic paramtrs such as H 0, S 0 and G 0 wr valuatd. Th data indicat that, th adsorption was spontanous and is an ndothrmic natur. Adsorption kintics was tstd with psudo- scond-ordr, Elovich modl and intra particl diffusion modls. Kintic studis indicat an adsorption psudo-scond-ordr raction. This study shows that intra-particls playd a major rol in th adsorption of F(II) ions mchanism. Th activatd Posidonia ocanica nano carbon has high adsorption capacity and adsorption rat for th rmoval of F(II) ions from aquous solution. Kywords: Adsorption, F(II) ions, Kintics, Activatd Posidonia ocanica nano carbon, Thrmodynamics Introduction On of today's nvironmntal challngs is th xcssiv us of havy mtals for industrial and domstic practics contaminats ground and surfac watr 1, bfor ths pollutants discharg to th nvironmnt, it is important to rmov from watr and wastwatr 2. Th high F(II) concntrations also causd gastrointstinal accumulation, low hmoglobin lvls and nurotoxicity. Industris such as thos involvd in th production of frtilizr, ptrochmicals, lctroplating, tannris, mtal procssing, and mining industris ar rlasd F(II) into th nvironmnt 3-5. Activatd carbon has bn usd as an adsorbnt in wastwatr tratmnt application throughout th world, but bcaus of its cost in fficincy it is no longr attractiv to b widly usd in small-scal industris. In rcnt yars rsarch intrst into th production of adsorbnts to rplac th costly activatd carbon has intnsifid 6. Svral studis rlatd to wastwatr tratmnt wr carrid out using low-cost matrials, Posidonia ocanica is usd as adsorbnt bcaus of its asily availabl, conomically viabl and biodgradabl 7 and also Jordanian Pottry matrials was chosn as adsorbnt du to its low cost, its granular structur, insolubility in watr, chmical stability and local availability 8.

2 142 Chm Sci Trans., 2017, 6(1), In th prsnt invstigation th adsorption of frrous ion on activatd nano carbon prpard from Posidonia Ocanica Ash by carbonization with sulphuric acid has bn achivd. Th kintic and quilibrium adsorption data obtaind wr utilizd to charactriz th sampl prpard 9. Th amounts and rats of adsorption of Iron using abov activatd nano carbon from watr wr thn masurd. Thr simplifid kintic modls including psudo first ordr, psudo scond ordr quations and Elovich quations wr usd to dscrib th adsorption procss. Exprimntal Th Posidonia ocanica collctd (Figur 1) from narby Thiruvarur district was carbonizd with con. H 2 SO 4 and activatd around C in a muffl furnac for 5 hours thn it was takn out, ground wll to fin powdr and stord in a vacuum dsiccators. Figur 1. Photograph of Posidonia ocanica Adsorbnt charactrization Tabl 1. Physicochmical charactristics of adsorbnt Analysis Valu ph slurry ph zpc Spcific gravity Moistur contnt, % Bulk dnsity, g cm Particl dnsity, g cm Conductivity, µs/cm Surfac ara, m 2 /g Na +, mg L K +, mg L Adsorbnt charactrization was prformd by mans of spctroscopic and quantitativ analysis (Tabl 1). Th surfac ara of th adsorbnt was dtrmind by quanta chrom surfac ara analyzr. Th ph of aquous slurry was dtrmind by soaking 1 g of biomass in 50 ml distilld watr, stirrd for 24 h and filtrd and th final ph was masurd 8. Th physicochmical charactristics of th adsorbnt wr dtrmind using standard procdurs 9. Th concntrations of sodium and potassium wr dtrmind by Flam Photomtr (Modl No. Systronics126). Th quilibrium Cr(VI) concntration was dtrmind by using 1,5- diphnylcarbazid as th complxing agnt and a UV-Vis Spctrophotomtr (Systronics, Vis doubl bam Spctro 1203) at a λ max of 540 nm. For stirring purpos magntic stirrr was usd. Th ph of zro-point charg or ph ZPC was dtrmind basd on th prvious mthod 10. Th Fourir transform infrard (FTIR) spctra of th adsorbnt was rcordd with Fourir transform infrard spctrophotomtr in th rang of cm -1. Batch adsorption studis Th ffct of various paramtrs on th rmoval of F(II) onto activatd Posidonia ocanica nano carbon was studid. All chmicals usd wr in high lvl purity of th commrcially availabl AR grad. A stock solution of th adsorbat containing mg/l of F(II) was prpard by dissolving th calculatd quantity of ammonium frrous sulphat dcahydrat in dionizd watr. Th stock solution was dilutd to th rquird initial concntration (rang 10 to 50 mg/l). In ach adsorption xprimnt, 50 ml of F(II) ion solution with a known concntration was addd 25 mg of activatd Posidonia ocanica nano carbon in a 250 ml stoppr glass flask at 30, 40, 50 and 60 C and th mixtur was stirrd on a mchanical shakr of 60 minuts.

3 Chm Sci Trans., 2017, 6(1), Th sampls wr withdrawn at th appropriat tim intrvals and th adsorbnt was sparatd by cntrifugation at 1000 rpm for 10 minuts. Th suprnatant was analyzd for th rsidual F(II) concntration and was masurd bfor and aftr tratmnt with an atomic absorption spctrophotomtr (Prkin Elmr 2380). Th ffct of ph on th rat of adsorption was invstigatd using F(II) concntration of 50 mg/l for constant activatd Posidonia ocanica nano carbon. Th ph valus wr adjustd with 1N HCl and in 1N NaOH solution. Th adsorption of procss was carrid out at diffrnt tmpratur (30, 40, 50 and 60 o C). This was hlpd to stimat th impact of changs of thrmodynamic paramtrs causd by th tmpratur ffct. Th amount of adsorption at tim t, q t (mg/g), can b dtrmind using th following formula; q t = (C 0 -C t )V/ W (1) Whr, C t is th F(II) ions liquid phas concntration(mg/l), at any tim, C 0 is th initial concntration of F(II) ions in solution (mg/l), V is th volum of solution (L), W is th mass of adsorbnt (g). Th amount of adsorption at quilibrium q (mg/g) was computd using th following quation q = ( C 0 C ) V/(W) (2) Whr, C 0 and C ar th liquid phas concntration of F(II) ions (mg/l) initially and at quilibrium. Th rmoval prcntag of F(II) ions can b calculatd as: Rmoval % of F(II)= (C 0 -C )/ C (3) Whr, C 0 is th initial concntration of th F(II) ions in solution (mg/l) and C is th quilibrium concntration of F(II) ions in solution (mg/l). Rsults and Discussion Effct of contact tim on F(II) ions adsorption In batch adsorption procss contact tim is on of th potnt factors. In th rsultant procss all of th paramtrs xcpt contact tim, tmpratur (30, 40, 50 and 60 C), adsorbnt dos and agitation spd (120 rpm), wr kpt constant. Th maximum rmoval of F(II) by activatd Posidonia ocanica nano carbon rquird contact tim of 60 minuts, it is shown in Figur 2, It was rvald that th rmoval of F(II) incras with incras in contact tim and th optimal rmoval fficincy was rachd within 45 min. Thr is th maximum adsorption occurs at 45 minuts aftr which th adsorption phas rachs an quilibrium. At this point maximum amount of F(II) adsorbd undr th particular conditions. Figur 2 indicats that, th tim variation curv is singl, smooth and continuous and it shows th formation of monolayr covrag on th outr intrfac of th adsorbnt % Rmoval of F(II) Contact in tim in min Figur 2. Effct of contact tim on th rmoval of F(II) ion [F(II)]=20 mg/l; Absorbnt dos=25 mg/50 ml; Tmp=30 o C

4 144 Chm Sci Trans., 2017, 6(1), Effct of initial F(II) concntration To study th ffct of initial F(II) ions on th adsorption lvl by varying concntration (10, 20, 30, 40 and 50 mg/l) undr th constant tmpratur (30, 40, 50 and 60 C), ph 6.5 agitation spd (120 rpm) and g of adsorbnt dos. Th rmoval fficincy by th ffct of initial F(II) ions concntration was obtaind from th xprimntal rsults wr prsntd in Tabl 2. It shows that th incrasing initial F(II) concntration rsults dcras of th rmoval fficincy of F(II). In cas of low F(II) ion concntrations th ratio of th initial numbr of mols of F(II) ions to availabl surfac ara of adsorbnt is larg and subsquntly th fractional adsorption bcoms indpndnt of initial concntration 10. Howvr at highr concntrations of F(II) ions th availabl sits of adsorption bcoms fwr and hnc th prcntag of F(II) ions which dpnds upon initial concntration. Tabl 2. Equilibrium paramtrs for th adsorption of F(II) ion onto PONC C M, Mg/L Q, Mg/L Rmoval % 0 30 o C 40 o C 50 o C 60 o C 30 o C 40 o C 50 o C 60 o C 30 o C 40 o C 50 o C 60 o C Effct of adsorbnt dosag Th ffct of varying adsorbnt doss was invstigatd by mploying 25, 50, 75, 100 and 125 mg. Thy wr agitatd with 50 ml of F(II) ions solution. Th data ar tabulatd in Tabl 2. Th adsorbnt dosags hav impact on th adsorption of F(II) ions by PONC ar rprsntd in Figur 3, It is rvald that th incrasd adsorbnt doss with incras th F(II) ions rmoval. This is bcaus th contact surfac aras of adsorbnt hav incrasd. It would b mor probabl for F(II) ions on to b adsorbd on adsorption sits and th adsorption fficincy incrasd. Hnc th ntir studis wr carrid out with th adsorbnt dosag of 25 mg 50 ml of adsorbat solution % Rmoval of F(II) % Rmoval of F(II) Absorbnt dos in mg Figur 3. Effct of absorbnt dos on th rmoval of F(II) ion [F(II)]=20 mg/l; Contact tim=50 min; Absorbnt dos=25 mg/50 ml; Tmp=30 o C Initial ph Figur 4. Effct of initial ph on th rmoval of F(II) ion [F(II)]=20 mg/l; Contact tim=50 min; Absorbnt dos=25 mg/50 ml; Tmp=30 o C

5 Chm Sci Trans., 2017, 6(1), Effct of solution ph Th solution ph is on of th most important factors that control th adsorption of F(II) ions on th sorbnt matrial. Th adsorption capacity may b attributd to th chmical form of havy F(II) ion in th solution at spcific ph (i..pur ionic mtal form or mtal hydroxyl form). In addition, du to diffrnt functional groups on th adsorbnt surfac, which bcom activ sits for th F(II) binding at a spcific ph th ffct of adsorption can vary substantially. Thrfor, an incras in ph may caus an incras or dcras in th adsorption, rsulting diffrnt optimum ph valus dpndnt on th typ of adsorbnt. To xamin th ffct of ph on th % rmoval of F(II) ions, th solution ph wr varid from 2.0 to 10.0 by adding acid and bas to th stock solution This incrass may b du to th prsnc of ngativ charg on th surfac of th adsorbnt that may b rsponds for th F(II) binding. Howvr, as th ph is lowrd, th hydrogn ions compt with F(II) ions for th adsorption sits in th adsorbnt, th ovrall surfac charg on th particls bcom positiv and hinds th binding of positivly chargd F(II) ions. On othr hand, dcras in th adsorption undr ph >6.5 may b du to occupation of th adsorption sits by OH - ions which rtard th approach of such ions furthr toward th adsorbnt surfac. From th xprimntal rsults, th optimum ph rang for th adsorption of th F( III) ions is 2.0 to 6.5 shown in Figur 4. Adsorption isothrms Adsorption isothrm 4-8 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 50 ml of F(II) ion solutions of initial concntration 20 mg/l with g of activatd nano carbon at 30 0 C with a constant agitation. Agitation was providd for 1.0 h, which is mor than sufficint tim to rach quilibrium. 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 12,18. Th adsorption isothrm is xprssd by th following quation Which, can b linarizd as 1/nF q =K FC 1 ln q =lnk + lnc. F n F (5) Whr, q is th amount of F(II) adsorbd at quilibrium (mg/g) and C is th concntration of F(II) 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 and th modl Frundlich paramtrs ar shown in Tabl 3. Th magnitud of K F showd that PONC had a high capacity for F(II) 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 9. A 1/n F valu of lss than 1 indicatd that F(II) is favorably adsorbd by PONC. Th Frundlich isothrm did not show a good fit to th xprimntal data as indicatd by SSE and Chi-squar statistics. (4)

6 146 Chm Sci Trans., 2017, 6(1), 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 10 in a linar form can b rprsntd as: C 1 C = + (6) q q K q m Whr q is th amount of F(II) adsorbd at quilibrium (mg/g), C is th concntration of F(II) in th aquous phas at quilibrium (ppm), q m is th maximum F(II) 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 and th data so obtaind wr also prsntd in Tabl 3. Th modl prdictd a maximum valu that could not b rachd in th xprimnts. Th valu of K L dcrass with an incras in th tmpratur 13,19. A high K L valu indicats a high adsorption affinity. Wbr 22 xprssd th Langmuir isothrm in trm of dimnsionlss constant sparation factor or quilibrium paramtr (R L ) dfind in th following quation: 1 R = (7) 1+K C L Whr, C 0 is th initial F(II) concntration (ppm). Tabl 3. Isothrms paramtr for th adsorption of F(II) ion onto PONC Modl Frundlich Langmuir Tmkin Hurkins-Jura Halsay Radlich- Ptrson Dubinin- Radushkvich Jovanovic BET L L 0 m Constant Tmpratur ( o C) K f (mg/g) (L/mg) 1/n n Q m (mg/g) K L (L/mg) b T (J/mol) K T (L/mg) A H (g 2 /L) B H (mg 2 /L) K Ha (mg/l) n Ha g K R (L/g) q s (mg/g) K D 10-4 mol 2 kj K J (L/g) q max (mg/g) C BET (L/mg) qs (mg/g) 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 F(II) rmoval wr calculatd at diffrnt concntrations and tmpraturs. As shown in Tabl 4, at all concntrations and tmpraturs tstd th valus of R L for F(II) adsorptions on th PONC wr lss than 1 and gratr than zro, indicating favorabl adsorption.

7 Chm Sci Trans., 2017, 6(1), 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 PONC surfac, sinc th Langmuir quation assums that th adsorbnt surfac is nrgtically homognous. Tabl 4. Dimnsionlss spration factor (R L ) for th adsorption of F(II) ion onto PONC (C i ) Dimnsionlss spration factor, R L 30 o C 40 o C 50 o C 60 o C Tmkin adsorption isothrm Th Tmkin adsorption isothrm assums that th hat of adsorption dcrass linarly with th sorption covrag du to adsorbnt-adsorbat intractions 14. Th Tmkin isothrm quation is givn as: RT q = ln(k C ) bt T (8) Which, can b rprsntd in th following linar form RT RT q = lnk + lnc. b T b (9) 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 3. Th Tmkin isothrm appars to provid a good fit to th F(II) adsorption data. Th adsorption nrgy in th Tmkin modl, b T, is positiv for F(II) 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 F(II) on PONC can b dscribd rasonably wll by th Tmkin isothrm. Hurkins-Jura adsorption isothrm Th Hurkins-Jura 12 adsorption isothrm can b xprssd as: A q = H. B H +logc (10) This can rarrangd as follows: 1 BH 1 = - logc. q 2 AH AH (11) 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 15.

8 148 Chm Sci Trans., 2017, 6(1), Halsay adsorption isothrm Th Halsay 13 adsorption isothrm can b givn as lnkha -lnc q =xp n Ha (12) and a linar form of th isothrm can b xprssd as follows: lnkha lnc lnq = - nha nha (13) 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 xprimntal data and th modl prdictions basd on th non-linar form of th Halsay modls. Th modl paramtrs ar listd in Tabl 3. This rsult also shows that th adsorption of F(II) on PONC was not basd on significant multilayr adsorption. Th Halsay modl is also not suitabl to dscrib th adsorption of F(II) on PONC, bcaus this modl also assums a multilayr bhavior for th adsorption of adsorbat onto adsorbnt. Rdlich-Ptrson adsorption isothrm Th Rdlich-Ptrson 16 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: K R C q =. g 1+a R C (14) Th linar form of th isothrm can b xprssd as follows: ln C =glnc -lnk. q R (15) 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 ln C /q vrsus ln C nabls th dtrmination of isothrm constants g and K R from th slop and intrcpt. Th valus of K R, prsntd in Tabl 3, indicat that th adsorption capacity of th PONC dcrasd with an incras tmpratur. Furthrmor, th valu of g lis btwn 0 and 1, indicating favorabl adsorption. Dubinin-Radushkvich adsorption isothrm Th Dubinin-Radushkvich 15 adsorption isothrm is anothr isothrm quation 17. 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: 2 1 lnq =lnq -B RTln 1+ D D C (16) 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.

9 Chm Sci Trans., 2017, 6(1), Jovanovich adsorption isothrm Th modl of an adsorption surfac considrd by Jovanovic 16 is ssntially th sam as that considrd by Langmuir. Th Jovanovic modl lads to th following rlationship 18 : q =q 1- max KJC ( ) Th linar form of th isothrm can b xprssd as follows: lnq = lnq max -K JC. Whr, K J (L/g) is a paramtr. q max (mg/g) is th maximum F(II) uptak. Th q max is obtaind from a plot of ln q and C, Thir rlatd paramtrs ar listd in Tabl 3. By comparing th valus of th rror functions, it was found th Langmuir and Tmkin modls ar bst to fit th F(II) adsorption on th PONC. 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 F(II) from th solution. Th Brunaur-Emmtt-Tllr (BET) isothrm modl Brunaur Emmtt Tllr (BET) 19 isothrm is a thortical quation, most widly applid in th gas solid quilibrium systms. It was dvlopd to driv multilayr adsorption systms with rlativ concntration rangs from 10 to 50 mg/l corrsponding to a monolayr covrag lying btwn 20 and 30 mg/l. Its xtinction modl rlatd to liquid solid intrfac is xhibitd as: qscbetc q = (Cs -C )[1+(CBET -1)(C /C s )] (19) Whr, C BET, 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, In th linar form as usd is rprsntd as C 1 CBET -1 C = +. q( C -C ) qsc s BET qsc BET C s (20) 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 BET modl. Kintic paramtrs Th rat and mchanism of th adsorption procss can b lucidatd basd on kintic studis. F(II)adsorption on solid surfac may b xplaind by two distinct mchanisms: (1) An initial rapid binding of F(II) molculs on th adsorbnt surfac; (2) rlativly slow intra-particl diffusion. To analyz th adsorption kintics of th F(II), th psudo-firstordr, th psudo-scond-ordr, and intra-particl diffusion modls wr applid 18. Each of ths modls and thir linar mods of thm quations prsntd in blow. Modl Nonlinar Form Linar Form Psudo-first-ordr dq t /d t = k 1 (q -q t ) ln (q -q t ) = ln q -k 1 t (21) Psudo-scond-ordr dq t /d t = k 2 (q -q t ) 2 t/q t = 1/k 2 q 2 + (1/q )t (22) (17) (18)

10 150 Chm Sci Trans., 2017, 6(1), Whr, q and q t rfr to th amount of F(II)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 during 1898 and is usd for 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 wr 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. In th psudo-scond ordr modl, th slop and intrcpt of th t/qt vs. 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 5. According to Tabl 5, th valu of γ(0.999) rlatd to th psudoscond ordr modl rvald that F(II) adsorption followd this modl, nvrthlss, psudo-first ordr and psudo-scond ordr kintic modls cannot idntify th mchanism of diffusion of F(II) into th adsorbnt pors 20. C 0 Tabl 5. Th kintic paramtrs for th adsorption of F(II) ion onto PONC Tmp C Psudo scond ordr Elovich modl Intraparticl diffusion q k 2 γ h α β γ K id γ C Simpl Elovich modl Th simpl Elovich modl 21 is xprssd in th form, q t = α + β ln t (23) Whr, q t is th amount adsorbd at tim t, α and β ar th constants obtaind from th xprimnt. A plot of q t vs. lnt should giv a linar rlationship for th applicability of th simpl Elovich kintic. Th Elovich kintics of F(II) on to PONC for various initial concntrations (10, 20, 30, 40 and 50 mg/l) of volum 50 ml (ach), adsorbnt dos 0.025g, tmpratur 30 o C and ph 6.5.

11 Chm Sci Trans., 2017, 6(1), Th intra-particl diffusion modl Th Wbr and Morris 22 suggst th following kintic modl to idntifying th mchanism involvd in th adsorption procss is of an intra-particl diffusion modl or not. It is gnrally xprssd as q t = K id t 1/2 + C (24) Whr, K id is th intra-particl rat constant (mg/g/min 1/2 ), c is th intrcpt, q t is th amount of F(II) ions adsorbd (mg/g), at tim t. From th plot of q t vs. t 1/2, th intra-particl rat constant can b dtrmind from th slop of th plot. Th valu of C givs an ida about th boundary layr thicknss. Th calculatd intra-particl diffusion paramtrs prsnt in Tabl 5. Th γ valus indicat that, intra-particl diffusion procss is th controls th sorption rat. Thrmodynamic paramtrs Thrmodynamic paramtrs such as standard fr nrgy ( G 0 ) standard nthalpy chang ( H 0 ) and standard ntropy changs ( S 0 ) wr calculatd by using quilibrium constant (K 0 ) chang with tmpratur (T).Th fr nrgy chang can b dtrmind by th following quation 21. G 0 = -RT lnko (25) Whr, G 0 is th fr nrgy chang of sorption procss (kj/mol), K o is th quilibrium constant, T is th tmpratur in (K), R is th univrsal gas constant. Th fr nrgy chang may b xprssd in trms of nthalpy chang of sorption as a function of tmpratur as follows G 0 = H - T S (26) Th adsorption cofficint K 0 can b obtaind by combind and rarranging Eqs. 25 and 26. ln K 0 = H 0 / RT + S 0 /R (27) Whr, H 0 is th standard hat changs of th sorption, S 0 is th ntropy chang of sorption (kj/mol). Th standard nthalpy and ntropy changs valus ar valuatd from th slop and intrcpt of linar plot lnk 0 against 1/T. Thrmodynamic paramtr valus ar obtaind from th quation (8) for th sorption of F(II) ions on activatd Posidonia ocanica nano carbon and th valus ar tabulatd in Tabl 6. Th ngativ valus of fr nrgy changs confirm th spontanous natur of sorption of F(II) on activatd Posidonia ocanica nano carbon and th ngativ valus of H 0 confirm th sorption procss of an xothrmic natur. Th positiv S 0 valus show incrasd randomnss at solid-solution intrfac during th sorption of F(II) ions on th activatd Posidonia ocanica nano carbon. In ordr to support that physical adsorption is th prdominant mchanism, th valus of activation nrgy (Ea) and sticking probability (S * ) wr calculatd from th xprimntal data. Thy wr calculatd using modifid Arrhnius typ quation rlatd to surfac covrag (θ) as follows: C θ = 1- C i Ea S* = (1 θ ) (29) 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 23. Th valus of Ea and S * can b calculatd from slop and intrcpt of th plot of ln(1-θ) vrsus 1/T rspctivly and ar listd in Tabl 6. (28)

12 152 Chm Sci Trans., 2017, 6(1), Tabl 6. Thrmodynamic paramtr for th adsorption of F(II) ion onto PONC (C 0 ) G o, kj/mol H, S, Ea, 30 o C 40 o C 50 o C 60 o C kj/mol J/Kmol kj/mol S * From Tabl 6 it is clar that th raction is spontanous in natur as G 0 valus ar ngativ at all th tmpratur studid. Again positiv H 0 valu confirms that th sorption is ndothrmic in natur. Th positiv valu of S 0 rflcts th affinitis of th adsorbnts for th F(II). Th rsult as shown in Tabl 6 indicat that th probability of th F(II) to stick on surfac of biomass is vry high as S * << 1, ths valus confirm that, th sorption procss is physisorption 24. Conclusion Th adsorption of F(II) on to activatd Posidonia ocanica nano carbon was invstigatd in this rsarch work. Th adsorption quilibrium wll corrlatd with both Langmuir and BET isothrm modls. Th adsorption kintic procss was found psudo-scond-ordr modl. Isothrm and kintic study indicats that th PONC can b ffctivly mployd for th adsorption of F(II) ions. Thrmodynamic rsults show that adsorption of F(II) ions on to PONC was spontanous and physical adsorption. Rfrncs 1. Amin N K, Dsalination, 2008, 223(1), ; DOI: /j.dsal Amin N K, J Hazardous Matr., 2009, 165, 52-62; DOI: /j.jhazmat Gad H M and El-Sayd A A, J Hazardous Matr., 2009, 168(2), ; DOI: /j.jhazmat Gansh P S, Ramasamy E V, Gajalakshmi S and Abbasi S A, Biochm Engg J., 2005, 27(1), 17-23; DOI: /j.bj Garg V M, Amita M, Kumar R and Gupta R, Dys Pigmnts, 2004, 63(3), ; DOI: /j.dypig Giri A K, Patl R and Mandal S, Chm Engg J., 2012, 185, 71-81; DOI: /j.cj Hamd B, Ahmad A and Latiff K, Dys Pigmnts, 2007, 75(1), ; DOI: /j.dypig Hamd B A, Din M and Ahmad A, J Hazardous Matr., 2007, 141(3), ; DOI: /j.jhazmat Pavan F A, Mazzocato A C and Gushikm Y, Biorsourc Tchnology, 2008, 99(8), ; DOI: /j.biortch Rahman M A, Amin S R and Alam A S, Dhaka Univrsity J Sci., 2012, 60(2), Arivoli S, Marimuthu V and Jahangir A R M, Intr J Bioassays, 2015, 4(01), (2015) Arivoli S, Ros Judith T and Marimuthu V, Eur J Appl Sci Tchnol [EUJAST], 2014, 1(1), Arivoli S, Ros Judith Tand Marimuthu V, Rs Rv J Chm., 2014, 3(1),

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