Simultaneous Removal of Hg(II)

15 Pages·2017·4.23 MB·English

metals
Article
Simultaneous Removal of Hg(II) and Phenol Using
Functionalized Activated Carbon Derived from Areca
Nut Waste
Lalhmunsiama1,SeungMokLee1,SukSoonChoi2andDiwakarTiwari3,*
1 DepartmentofEnvironmentalEngineering,CatholicKwandongUniversity,522Naegok-dong,
Gangneung210-701,Korea;[email protected](L.);[email protected](S.M.L.)
2 DepartmentofBiologicalandEnvironmentalEngineering,SemyungUniversity,Jecheon27136,Korea;
[email protected]
3 DepartmentofChemistry,SchoolofPhysicalSciences,MizoramUniversity,Aizawl796004,India
* Correspondence:[email protected];Tel.:[phone];Fax:[phone]
Received:30April2017;Accepted:28June2017;Published:3July2017
Abstract: Arecanutwastewasutilizedtoobtainhighsurfaceareaactivatedcarbon(AC),anditwas
furtherfunctionalizedwithsuccinicanhydrideundermicrowaveirradiation.Thesurfacemorphology
andsurfacefunctionalgroupsofthematerialswerediscussedwiththehelpofscanningelectron
microscope(SEM)imagesandfouriertransforminfra-red(FT-IR)analysis. Thespecificsurfacearea
oftheACandfunctionalized-ACwasobtainedbytheBrunauer-Emmett-Teller(BET)method,and
found to be 367.303 and 308.032 m2/g, respectively. Batch experiments showed that higher pH
favouredtheremovalofHg(II),whereasthephenolremovalwasslightlyaffectedbythechanges
inthesolutionpH.Thekineticdatafollowedpseudo-firstorderkineticmodel,andintra-particle
diffusionplayedasignificantroleintheremovalofbothpollutants. Themaximumsorptioncapacity
ofHg(II)andphenolwereevaluatedusingLangmuiradsorptionisotherms,andfoundtobe11.23
and5.37mg/g, respectively. TheremovalofHg(II)wassignificantlysuppressedinthepresence
of chloride ions due to the formation of a HgCl species. The phenol was specifically adsorbed,
2
formingthedonor–acceptorcomplexesorπ–πelectroninteractionsatthesurfaceofthesolid. Further,
afixed-bedcolumnstudywasconductedforbothHg(II)andphenol. Theloadingcapacityofthe
columnwasestimatedusingthenonlinearThomasequation,andfoundtobe2.49and2.70mg/g,
respectively. Therefore,thestudyshowedthatfunctionalizedACobtainedfromarecanutwastecould
beemployedasasustainableadsorbentforthesimultaneousremovalofHg(II)andphenolfrom
pollutedwater.
Keywords: arecanutwaste;activatedcarbon;Hg(II);phenol;adsorption
1. Introduction
Waterpollutionisaseriousenvironmentalconcern,andisgrowingrapidlyduetotheextreme
use of harmful substances/chemicals by various industries. The wastewaters produced from
manufacturing processes and petroleum refineries usually contain heavy metals and other toxic
organic pollutants [1,2]. The partly treated or untreated effluents from these industries greatly
contaminate the receiving water bodies. Heavy metals and phenolic compounds, which are the
most common water pollutants, are found to be highly toxic towards living organisms and are
difficulttoeliminatefromwaterbodiesorevenfromthebiosystemonceentered[3–5]. Mercuryhas
receivedgreaterenvironmentalconcernduetoitshightoxicity,persistenceintheenvironment,and
highbioaccumulation[6,7]. DissolvedHg(II)inanaquaticenvironmentisreadilytransformedinto
methylmercury,whichisahighlytoxic,persistent,andbioaccumulativeformofmercurypresentin
Metals2017,7,248;doi:10.3390/met7070248 www.mdpi.com/journal/metals
Metals2017,7,248 2of15
nature. Mercuryspeciesarevolatile,andtheinhalationofitsvapourproducesdetrimentaleffects
tothenervous,digestive,andimmunesystems[8]. Moreover,theintakeofmercurywasreported
toaffectthenormalgrowthofthecentralnervoussystem, andalsocausesDNAdamagethrough
multiplemechanisms[9]. Ontheotherhand,phenolanditsderivativesarepotentialwaterpollutants,
andhaveshownadverseeffectstowardslivingorganisms[10]. Exposuretophenolisreportedtobe
relatedtoproteindegeneration,malfunctioninthecentralnervoussystem,andisabletodisturbthe
functionofthekidney,liver,andpancreasinthehumanbody[11]. Furthermore,thephenolpresent
inaquaticenvironmentiseasilytransformedthroughasimpleoxidationprocessintochlorophenol,
acarcinogeniccompound[12]. Therefore,mercuryandphenolareclassifiedasprioritycontaminants,
andtheiracceptableconcentrationindrinkingwateraccordingtotheUnitedStatesEnvironmental
ProtectionAgency(USEPA)is2µg/Land0.5mg/L,respectively[12,13].
Anadsorptiontechniqueislargelyemployedfortheremovalofawiderangeofwaterpollutants,
as it offers several advantages over the conventional methods. The advantages of an adsorption
processincludehighremovalefficiencyevenatalowconcentrationofpollutants,easyoperationand
maintenance,flexibility,andthepossibilityofrecoveringthematerial[14]. Activatedcarbons(ACs)
havebeenextensivelyusedintheremovalofmercuricionsfromaqueoussolutions[15,16]. Moreover,
differenttypesofmaterials,suchaselectrospunsulfurcopolymers[17],lignocellulosicmaterialderived
fromtheSpanishbroomplant[18],andlignin[19]werereportedaseffectiveadsorbentsforreducing
Hg(II) concentrations in aquatic media. Recently, Li and co-workers [20] synthesized a mercury
“nano-trap”byfunctionalizingahighsurfaceareaporousorganicpolymerwithahighdensityof
strongmercurychelatinggroups.Thismercury“nano-trap”exhibitsanextremelyhighuptakecapacity
ofmercury,i.e.,over1000mg/gandcaneffectivelyreduceHg(II)concentrationtoacceptablelimits
ofdrinkingwaterstandards. ACsandtheirmodifiedmaterialswerealsoefficientlyutilizedforthe
treatment of aqueous effluents polluted with phenol [21–23]. AC is undoubtedly one of the most
effectivematerialsinwastewatertreatmentduetoitslargespecificsurfacearea,porousstructure,and
highperformance. Inspiteofpossessinghighsorptioncapacity,theuseofcommercialACisnotviable
becauseofitshighcost. Therefore,manyresearchershaveutilizedwastematerials,suchasricehusk,
sugarcanebagasse[24],grapebagasse[25],peanutshell[26],andcoconuthusk[27],forobtaininglow
costACstoemployintheremovalofvariouspollutantsfromanaquaticenvironment.
Areca nut, popularly known as betel nut, is widely cultivated in many Asian countries and
parts of Africa. Areca nut waste, a lignocellulose material, is available in large quantities in many
countriesandthereisnoreportaboutitspossibleapplicationforusefulpurposes[28]. Theconversion
of areca nut waste into AC could probably be an alternative method to exploit this agriculture
by-productinbioremediation[29]. Previously,theACpreparedfromarecanutwastewasutilizedin
theremovalofhexavalentchromium[30,31],congored[32],directblue[33],andacidblue[34]from
aqueoussolutions. Therefore,thepresentworkaimstoutilizethisabundantlyavailableagriculture
by-productforthepreparationofACanditsfurtherfunctionalizationwithsuccinicanhydrideunder
microwaveirradiation.Theincorporationofsuccinicanhydridepossiblyincreasesthenumberofactive
functionalgroupsontotheAC’ssurface,andsubsequentlyenhancestheinteractionofthematerials
with pollutants. Previously, agriculture waste materials such as maize straw [35], olive stone [36],
corncob[37],andsugarcanebagasse[38]weremodifiedwithsuccinicanhydride,andthematerials
werefoundtobeefficientintheremovalofseveraltoxicmetalionsfromaqueoussolutions. Inthis
study,ACwaspreparedfromarecanutwasteanditwasfurtherfunctionalizedusingsuccinicanhydride
undermicrowaveirradiation. Themicrowave-assistedmethodemployedforthefunctionalizationof
ACoffersseveraladvantagesovertheconventionalmethodsintermsofselectivityinoperation,fast
anduniformirradiation,andreducingreactiontimeandenergy. Furthermore,thereisnoreportonthe
simultaneousremovaloforganicandinorganicpollutantsusingsuccinicanhydridefunctionalized
activatedcarbons,soitisinterestingtoassessthesematerialsforthesimultaneousremovaloftoxic
heavymetalsandorganiccontaminantsfromaqueousmedia. Therefore,thefunctionalized-ACwas
Metals2017,7,248 3of15
assessedforitscapabilitytoremoveHg(II)andphenolsimultaneouslyfromaqueoussolutionsunder
batchandfixed-bedadsorptionsystems.
2. MaterialsandMethods
2.1. Materials
ThearecanutwastewascollectedfromAizawlcity,Mizoram,India. Itwasrepeatedlywashed
with pure water to remove any impurity, and then dried in an oven (Chang Shin Scientific Co.,
Busan, South Korea) (at 80 ◦C. Dry areca nut waste was soaked in concentrated H SO for 2 h at
2 4
thetemperatureof120◦C.Thesolidbiomasswasthencompletelytransformedintoitscarbonform.
Theobtainedcarbonwascarefullywashedwithpurewatertoeliminateexcessacids,anddriedat
70◦C.Anyexcessacidremainingwithinthecarbonsolidwasthentitratedwithammoniasolutionfor
neutralization. ThecarbonwasagainwashedwithdistilledwaterseveraltimesuntilthepHreached
~7.0, and then finally dried at 70 ◦C. The solid sample was cooled and then ground to obtain fine
powder. Furthermore,thecarbonpowderwasactivatedinamufflefurnace(ChangShinScientificCo.,
Busan,SouthKorea)at500◦Cfor4hunderanN atmosphere. Theactivatedcarbonobtainedwas
2
thenkeptinsideacloseplasticcontainerforfurtheruse.
2.2. ModificationofActivatedCarbon
The functionalization of the activated carbon was carried out as follows: 5.0 g of succinic
anhydridewasdissolvedin100mLofacetone. Tengrams(10g)ofactivatedcarbonobtainedfrom
arecanutwastewasaddedtothissuccinicanhydridesolution. Themixturewaskeptundermicrowave
irradiationat60◦Cfor60minwithconstantstirring(Model: MASII,SineoMicrowaveChemistry
TechnologyCo.,Ltd.,Shanghai,China).Thefunctionalizedactivatedcarbonwasseparatedandwashed
withdistilledwaterthreetimesandthendriedcompletelyat80◦C.Thefunctionalized-ACwasused
forthesimultaneousremovalofHg(II)andphenolunderbatchandfixed-bedcolumnsystems.
2.3. CharacterizationofMaterials
The surface morphology of the AC before and after functionalization was observed by the
SEM(scanningelectronmicroscope)analysis(FE-SEM-Model: SU-70, Hitachi, Tokyo, Japan). The
specificsurfaceareaoftheactivatedcarbonbeforeandafterfunctionalizationwasmeasuredbythe
Brunauer-Emmett-Teller(BET)surfaceareaanalyzer(Model:ASAP2020,ProtechKoreaCo. Ltd,Seoul,
SouthKorea). Moreover,FourierTransformInfra-Red(FT-IR)spectroscopy(Tensor27,BrukerCo.,
Billerica,MA,USA)wasusedfortheidentificationofvariousfunctionalgroupspresentintheACand
functionalized-ACsolids.
2.4. BatchAdsorptionExperiment
BatchexperimentswereperformedtostudytheeffectofpH,initialHg(II)/phenolconcentrations,
contacttime,andbackgroundelectrolyteconcentrationsontheremovalofHg(II)andphenolusing
functionalized-AC.Theexperimentswereperformedusing0.10goffunctionalized-ACtakeninto
50mLofHg(II)/phenolsolutionandkeptinanautomaticshaker(KukjeMachineryCo.,Ltd.,Okcheon,
SouthKorea)for12hat25◦C.Thesolutionwasfilteredusinga0.45µmsyringefilter,andthefinal
concentrationofHg(II)wasanalyzedbyafastsequentialatomicabsorptionspectrometer(AAS)(Model:
AA240FS, Varian, Australia), whereas the phenol concentration was measured using a UV-visible
spectrophotometer(Model: HumasHS3300,HumasCo.,Ltd.,Daejeon,SouthKorea). ThepHofthe
solutionswasadjustedbyaddingdropsof1MHClor1MNaOH.
2.5. Fixed-BedColumnAdsorption
A glass column with a 1 cm inner diameter was used for performing a fixed-bed column
experiments. Accurately1.0goffunctionalized-ACwasfirmlypackedinthemiddleofthecolumn
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usingglassbeads. TheaqueoussolutioncontainingbothHg(II)andphenolwaspumpedupwardby
ahigh-pressureliquidchromatographicpump(AcuflowSeriesII,DongwooScienceCo.,Ltd.,Hanam,
SouthKorea),andtheflowratewasmaintainedat0.5mL/min. Theeffluentsampleswerecollected
usingaSpectra/ChromCF-2fractioncollector(Model: Retriever500,TeledyneISCO,Lincoln,NE,
USA),andthenfilteredwitha0.45µmsyringefilter. TheconcentrationofHg(II)andphenolinthe
Metals 2017, 7, 248 4 of 14
effluentwasmeasuredusinganAASandaUV-visspectrophotometer,respectively.
collected using a Spectra/Chrom CF-2 fraction collector (Model: Retriever 500, Teledyne ISCO,
3. ResuLlintscoalnn,d NDEi, sUcSuAss),i oannd then filtered with a 0.45 µm syringe filter. The concentration of Hg(II) and
phenol in the effluent was measured using an AAS and a UV-vis spectrophotometer, respectively.
3.1. CharacterizationofMaterials
3. Results and Discussion
TheSEMmicrographsofthearecanutwasteACandfunctionalized-ACareshowninFigure1.
Thema3c.1r.o Cphoarreacsteprirzeasteionnt oifn MtahteerAialCs solidsareclearlyvisible,andtheporediametersarefoundtobein
therangeof5–15µmasobtainedfromtheSEMimages. Further,thesmallerporeswerealsovisiblein
The SEM micrographs of the areca nut waste AC and functionalized-AC are shown in Figure 1.
theSEMThiem maagceroopfotrhese pAreCs.enFti ginu rthee1 AbCsh soowlidss aanreS cEleMarliym vaisgiebloe,f atnhde tfhuen pcotiroen dailaimzeedte-rAs Car.eI tfoiusnodb stoe rbvee dthat
theincionr tphoer raatnigoen oof f5–s1u5c µcimni acsa onbhtayinderdid freosmig tnheifi ScEaMn tilmyacgheas.n Fguerdthtehr,e thseu srmfaaclelemr poorrpesh woleorge yalsoof vthiseibAle C,and
theporine sthaer eSEleMs simvaisgieb olef tahfet eArCth. Feigfuurnec 1tibo snhaolwizsa atino SnEoMf timheagAe Cof. tAhep fruenvcitoiounsalriezepdo-rAtCa.l sIto ish oabdsesrhvoedw nthat
that the incorporation of succinic anhydride significantly changed the surface morphology of the AC,
thesurfacemorphologyofmaizestrawwassignificantlychangedaftertheincorporationofsuccinic
and the pores are less visible after the functionalization of the AC. A previous report also had shown
anhydride[35]. ThenitrogenadsorptionisothermsoftheACandfunctionalized-ACareshownin
that the surface morphology of maize straw was significantly changed after the incorporation of
Figure2. AccordingtoInternationalUnionofPureandAppliedChemistry(IUPAC)classification,
succinic anhydride [35]. The nitrogen adsorption isotherms of the AC and functionalized-AC are
thetwosolidsamplesdisplayaH4typehysteresisloop[39]. ThespecificsurfaceareaoftheACwas
shown in Figure 2. According to International Union of Pure and Applied Chemistry (IUPAC)
foundctloasbseifi3ca6t7io.3n0, tmhe2 t/wgo. sTohlied ssuamrfpalcees adrisepalasyli ga hHt4ly tydpeec hreyastseeredsitso lo3o0p8 .[0339]m. T2h/eg spaefctiefrict shuerfiancceo arrpeao ration
ofsuccoifn tihcea AnCh ywdarsi dfoeu.nTdh tios bdee 3c6r7e.a30s emi2n/gs. pTehcei fisucrfsaucref aarceea asrliegahtilsy adseccrriebaesedd dtou e30t8o.0t3h me2a/gc cauftmer uthlaet ionof
succiniinccaonrphoyrdatrioidne owf siuthccininitch aenphoydrerisdoe.f Tthhies AdeCcr.eMasoe rieno svpeerc,iftihc esuinrfcaocer paoreraa tiiso nascorfibseudc cdiunei ctoa nthhey dride
accumulation of succinic anhydride within the pores of the AC. Moreover, the incorporation of
withintheporesofACcausedaslightdecreaseintheporesizeandporevolumeoftheAC,from
succinic anhydride within the pores of AC caused a slight decrease in the pore size and pore volume
3.13to2.78nmandfrom0.028to0.016cm3/g,respectively.
of the AC, from 3.13 to 2.78 nm and from 0.028 to 0.016 cm3/g, respectively.

(a) (b)
Figure 1. Scanning electron microscope (SEM) micrograph of (a) activated carbon (AC) and (b)
Figure 1. Scanning electron microscope (SEM) micrograph of (a) activated carbon (AC) and
functionalized-AC.
(b)functionalized-AC.
The FT-IR analytical results are graphically shown in Figure 3. The predominant peak that
ThapepFeTar-eIdR aat naraolyuntidc a3l43r4e scuml−t1s isa artetrigbruatpedh itcoa tlhley sstrheotcwhinngi nvibFriagtuiorne o3f .–OTHh egrporuepds.o Smevineraanl twpeaeka k that
appearpeedakast oabrtoauinnedd 3a4t 32485c6m, 2−9215i,s aantdtr 2ib97u2t ecdm−t1o arteh eatstrtirbeutctehdi ntog tvhieb praretisoenncoe fo–f OalHdehgyrdoeu pgrso.uSpesv aenrdal weak
peaksoasbstiagnineedd toa tth2e8 s5tr6e,t2ch9i2n5g, aanndd s2ci9s7so2ricnmg −of1 Ca–rHe abtotnridbsu. tMedoretoovtehre, tpher ebsaenndcse thoafta olcdceuhrryedde atg 1r6o2u0p sand
and 1700 cm−1 are assigned to the C=C and C=O groups [40]. Further, the vibration peaks in the region
assignedtothestretchingandscissoringofC–Hbonds. Moreover,thebandsthatoccurredat1620and
of 1042 cm−1 are due to the C–O–C stretching [36]. The weak peaks that occurred at around 1458 cm−1
1700cmsh−o1waerde tahses Cig–nHe dvibtoratthioen Cin= –CCaHn2–d dCef=oOrmgartoiounp. sM[o4r0e]o.vFeur, roththeerr, vthiberavtiibonra btaionndsp tehaakt socicnutrhreedr aetg ionof
1042cm87−4 1anarde 7d40u cemto−1 athree dCu–eO to– aCn setxrteetrcnhailn bgen[d3i6n]g. Tofh –eCw–Hea fkorp veaarikosusth sautbsotcitcuuterdre bdenazteanreo ruinngds 1[4415]8. cm−1
showeIdt itsh weoCrt–hH mvenibtiroantiinogn thinat –thCeH int–endseitfyo orfm thaet ipoena.k Mococurerroevde art, 1o7t0h0e crmv−i1 b(irta atpiopneabreadn adss at shhaotuoldcecru),r redat
2
874andwh7i4c0h cinmd−ic1ataerse thdaut ethteo satnretecxhtienrgn vailbbraetniodni nogf tohfe– CC=–OH gfroorupv aisr isoiugnsifsiucabnsttliyt uintecrdeabseendz aefnteer rtihneg s[41].
functionalization of AC. These changes eventually indicate the successful incorporation of succinic
anhydride into the AC solids [42]. Previous studies have shown that a new distinguished peak was
Metals2017,7,248 5of15
Itisworthmentioningthattheintensityofthepeakoccurredat1700cm−1(itappearedasashoulder),
which indicates that the stretching vibration of the C=O group is significantly increased after the
functionalizationofAC.Thesechangeseventuallyindicatethesuccessfulincorporationofsuccinic
anhydMriedtaels 2in01t7o, 7t, h24e8 A Csolids[42]. Previousstudieshaveshownthatanewdistinguished5 opf 1e4a kwas
observMedetaalst 20a1r7o, 7u, n24d8 1730cm−1aftertheincorporationofsuccinicanhydrideintoposidonia5a onf 1d4 maize
observed at around 1730 cm−1 after the incorporation of succinic anhydride into posidonia and maize
straw[o3b5s,e4r3v]e.dH aot waroeuvnedr, 1in73t0h cisms−1t uafdteyr, tahen einwcoprpeoarkatoiovne rolfa spupcceidniwc ainthhytdhreidper ein-teox pisotsiindognipae aankds manaidzec aused
straw [35,43]. However, in this study, a new peak overlapped with the pre-existing peaks and caused
anincrsetaraswe i[n35t,h43e].p Heaokweinvteer,n isni ttyh.isF suturtdhye, ram neowre p,ethake odveecrrlaepapseedin wtihthe tihnet penres-ietxieisstionfg tpheeakasb asnodrp ctaiuosnedb andat
an increase in the peak intensity. Furthermore, the decrease in the intensities of the absorption band
1042cmaatn −1 i10n4ca2rs ecsamisge−n1 iaensd sthigfeon rpedetah fkeo riCn tth–eeOn Cs–i–tCyO. b–FCou nrbtdohnesrdtmr seottrrceeht,c ithnhiegn gds euscugrgeggaeesssett ssin tt hthheee s suinuctcceicnnisyniltyaietliaso tonifo otnfh teoh faeb tAhsoCer pA[3tiC5o,n3[6 3b]5.a ,n3d6 ].
at 1042 cm−1 assigned for the C–O–C bond stretching suggests the succinylation of the AC [35,36].

Figure 2. Nitrogen adsorption–desorption isotherm of AC and functionalized-AC.
Figure2.Nitrogenadsorption–desorptionisothermofACandfunctionalized-AC.
Figure 2. Nitrogen adsorption–desorption isotherm of AC and functionalized-AC.
Functionalized-AC
Functionalized-AC
nce (a.u.)e (a.u.) AACC
ac
nsmittmittan
as
Tran
Tr
0 500 1000 1500 2000 2500 3000 3500 4000
0 500 1000 Wa15v0e0leng2th0 0(0cm-1)2500 3000 3500 4000
Wavelength (cm-1)
Figure 3. Fourier transform infra-red (FT-IR) spectra obtained for AC and functionalized-AC.
FigureFi3g.uFreo u3.r Fieorurtirearn tsrafonrsfmormin firnafr-ar-erded( F(FTT--IIRR)) ssppeeccttrraa oobbtatianiende fdorf oArCA aCnda fnudncftuionncatliiozenda-lAizCe.d -AC.
3.2. Batch Adsorption Experiments
3.2. Batch Adsorption Experiments
3.2. BatchAdsorptionExperiments
3.2.1. Effect of pH on Hg(II)/Phenol Adsorption
3.2.1. Effect of pH on Hg(II)/Phenol Adsorption
3.2.1. EffecptHof ips Ha ocrnuHciagl (IpIa)/raPmheetenro linAflduesnocripntgi otnhe adsorption of Hg(II) and phenol from aqueous
pH is a crucial parameter influencing the adsorption of Hg(II) and phenol from aqueous
solutions, since it determines the speciation of Hg(II) and/or the ionization of phenol as well as the
pHsoliustaiocnrsu, csiinaclep iat rdaemteertmeriniensfl tuhee nspciencgiattihoen aodf sHogr(pIIt)i oanndo/forH tgh(eI Iio)nainzdatipohn eonf oplhfernooml aasq wueelol uass tshoel utions,
surface charge of the adsorbents [44,45]. Therefore, the effect of pH was studied between pH 2.0 and
since i8ts.u0dr fueatsceienr gmch aia nsrogelesu ottifho tneh ecs opandetscaoiianrbtineiongnt 5s .o[44 fm4,H4g5/gL].( IToIfh) Heargne(fdIoIr/)e ao, nrthdte h9 e.e3ff6ei ocmtn goi/zfL ap toHifo wpnhaeosn fsotpul.dh Tiehendeo pbleeatrwcseenwetnae gplleH ar es2m.0toh avenadsl urface
8.0 using a solution containing 5.4 mg/L of Hg(II) and 9.36 mg/L of phenol. The percentage removal
chargeofo fHtgh(IeI) aadnsdo prbheennotsl a[s4 4a, 4fu5n].ctTiohne orfe fionirteia,l tphHe eisf fsehcotwonf pinH Fiwguarse s4t. uTdhiee dpHb edtewpeenednenpcHe s2tu.0dya nd 8.0
of Hg(II) and phenol as a function of initial pH is shown in Figure 4. The pH dependence study
usingashsoowluedti tohnatc Hogn(tIaI)i nreimngov5a.l4 wmasg s/igLniofifcaHngtl(yI Iin)carneadse9d.3 w6hmileg i/ncLreoafsipngh ethneo slo.lTuthioenp peHrc feronmta g2.e0 troe moval
showed that Hg(II) removal was significantly increased while increasing the solution pH from 2.0 to
of Hg(4I.I0), aanndd rpemheainnoeld aaslmaofsut nuncctihoanngoefd ibneiytioanldp pHH i4s.0s. hAotw lonwi pnHF, itghue rpeer4c.enTtahgee psoHrpdtieopn eonf dHegn(IcIe) study
4.0, and remained almost unchanged beyond pH 4.0. At low pH, the percentage sorption of Hg(II)
was relatively low, due to the competition between Hg2+ and H+ ions towards the same active sites on
showewdatsh raetlaHtigve(IlyI) lorewm, douvea tlow thaes csoimgnpeifitictiaonnt blyetwinecerne aHsge2d+ awndh Hile+ iionncsr teoawsainrdgs tthhee ssaomluet aioctnivpe Hsitefrs oomn 2.0to
the functionalized-AC [38]. At higher pH values, the H+ ions concentration is decreased, and
4.0,andthree mfuanicntieodnaallizmedo-sAtCu n[c3h8a].n Aget dhibgehyeor npdHp Hval4u.e0s., Athtelo Hw+ pioHn,st hcoenpceenrctreanttioang eiss odrepctrieoanseodf, Hangd(I I)was
Metals2017,7,248 6of15
relativelylow,duetothecompetitionbetweenHg2+andH+ionstowardsthesameactivesitesonthe
Metals 2017, 7, 248 6 of 14
functionalized-AC[38]. AthigherpHvalues,theH+ionsconcentrationisdecreased,andconsequently
enhancMcoeentsasltseh q20eu1e7u,n p7t,l t2ya4 k8e en hoafnHcegs( ItIh)ei ounpstafkreo mof aHqgu(IeIo) uiosnsso flruotmio nasq.uAeoupsr esvoilouutiosnrse.p Ao rptraelvsiooushs orewpeodrt6 t aholfas 1ot4 Hg(II)
showed that Hg(II) removal using activated biocarbon was relatively low at lower pH values and
removalusingactivatedbiocarbonwasrelativelylowatlowerpHvaluesandincreasedunderhigher
icnocnrseeaqseude nutlnyd eenr hhaingcheesr tphHe ucpontadkieti oonf sH [g46(I]I.) Cioonnsv efrrosemly ,a qpuheeonuosl rseomluotivoanls .w Aas psrleigvhiotluys arfefpecotretd a lbsyo
pHconditions[46]. Conversely,phenolremovalwasslightlyaffectedbychangingthesolutionpH
cshhaonwgeindg t hthate Hsogl(uItIi)o rne mpHov farlo ums i2n.g0 atoc t8iv.0a.t eItd w baiosc raerpboornt ewd atsh aret lpathievneloyl plorwed aotm loinwaenrt lpy Hex visatleude sin a nitds
from2.0to8.0. Itwasreportedthatphenolpredominantlyexistedinitsundissociatedformwithinthe
uinncdriesassoecdia utendd feorr mhi gwheitrh ipnH t hceo npdHit iroengsio [n4 6b]e. tCwoenenve 2r.s0e layn, dp h8.e0n; otlh ereremfoorvea, lt hwea as dssloigrhpttliyo na foffe cptehden boyl
pHregwchiaoasnn ignbisneiggtwn tihefieec ansno2tllu.y0t iioannnfl dupeH8n. c0fer;dotm hbey 2r t.eh0f eot osr oe8l,.u0tt.hi oIetn aw pdaHsso [r3rep]p. toAiro tsneidmo itflhaparth t rpeenhneodnl wowla pas rspeirdneovsmiiogiunnsailfinytc loaybn setexlryivsteiendd fli niun te hintesc edby
thesorluuenmtdiooisvnsaoplc Hioaft [ep3dh] .efonAromls i amws iitalha ifrnut nrthceteni odpnHw o arf espgpHior neu vbsiieontugw sealeycntio v2ba.0ste eadrnv dcea d8rb.i0on; ntt hhfeiebreerfreosmr eao,n vtdha els uoardffsapochrep eftnuioonnlc taoisof napahfliueznneodclt ionof
pHusawincatgisv aianctsetidigv nsaeitfreiiccdaitnceta l[yr4b 7in,o4fn8lu].fie nbceerds bayn dthes usorfluatcieonfu pnHc t[i3o].n Aa lsiizmeidlaar ctrteivnadt wedass perreicviitoeu[s4ly7 ,o4b8s]e.rved in the
removal of phenol as a function of pH using activated carbon fibers and surface functionalized
activated sericite [47,48].

FigureFi4g.uEreff e4c. tEofffepcHt oifn ptHhe irne mthoe vraelmoofvHalg o(IfI )Hagn(dII)P ahnedn oPlhbeynoful nbyct ifounnactliiozneadl-iAzeCd-fA roCm fraoqmu eaoquuesosuosl utions
solutions (Initial (Hg(II)/phenol) concentration: ~10 mg/L, solid dose: 2.0 g/L, contact time: 12 h).
(Initial(Hg(II)/phenol)concentration:~10mg/L,soliddose:2.0g/L,contacttime:12h).
Figure 4. Effect of pH in the removal of Hg(II) and Phenol by functionalized-AC from aqueous
3.2.2.s Aoldustioornps t(iIonnit iKali n(Hetgi(cIsI) o/pfh Hengo(lI)I )c oanncde nPthraetnioonl: ~10 mg/L, solid dose: 2.0 g/L, contact time: 12 h).
3.2.2. AdsorptionKineticsofHg(II)andPhenol
In order to obtain the adsorption equilibrium time of Hg(II) and phenol by functionalized-AC,
3.2.2. Adsorption Kinetics of Hg(II) and Phenol
Inthoe redxteerntt oofo tbhtea rienmtohveala adts voarrpiotuios nineteqruvaillisb orfi utimmet wimase aonfalHyzge(dI,I )wahnilde kpehepeninogl ab cyonfustnanctti soonluatliiozne d-AC,
the exptHen, taInno dof rttdhheeer itnroei tomibalto avcionan ltcheaent atrvdasatoirorinpo tuioosfn Hi enqgtu(eIirIl)vi baarlnisudm op fthiteminmeo loe fa wHt ~ga1(sI0I )am anngad/lLy p.z hTeehdne,o lpw behyrc ifeluenntackgteieoe npraeilmnizgoevdaa-Al coCof,n stant
solutioHthnge(p eIIHx)t/ep,nahtne ondfo ttlh haeet r ievnmairtoiiovaualslc aointn vtecarervnioatulrsas otinifo ttenirmvoeaf lsHis o ggf (itIviIme)nea nwinda Fsp iaghnuearnley oz5le. adTt,h w~e1h t0iwlemo k gepe/oplLliun.tgTa anh tecso penexshtracinbetint s tosailgmuetiiloraenrm oval
spoHrp, taionnd kthine eitnicisti,a lw choinchce natrrearteiolant ivoef lyH gs(lIoIw) a. nTdh ep hpeenrocle natta ~g1e0 amdsgo/Lrp. tTiohne opfe rHcegn(tIaIg) ea rnedm opvhaeln oolf
of Hg(II)/phenol at various intervals of time is given in Figure 5. The two pollutants exhibit
cHogn(tIiIn)u/pohuesnlyo li nact rveaasreiosu, sa nindt eardvsaolrsp otifo tni meqeu iisl igbirviuemn iins Facighuiervee 5d. wThiteh itnw 3o0 p0 omlluint aonft sc oenxthaicbti tt ismime ifloarr
similarsorptionkinetics,whicharerelativelyslow. ThepercentageadsorptionofHg(II)andphenol
bsoorthp tHiogn( IIk)i annetdic psh, ewnohli.c h arerelatively slow. The percentage adsorption of Hg(II) and phenol
continuouslyincreases,andadsorptionequilibriumisachievedwithin300minofcontacttimefor
continuously increases, and adsorption equilibrium is achieved within 300 min of contact time for
bothHbgot(hII H)agn(IdI) panhde npohle.nol.

Figure 5. Percentage removal of Hg(II) and phenol using functionalized-AC at various intervals of

time (Initial (Hg(II)/phenol) concentrations: ~10 mg/L, pH: 5.0, solid dose: 2.0 g/L, contact time: 12 h).
F igureFi5g.uPree r5c. ePnetracegnetargeem roemvaolvoalf oHf gH(gII(I)I)a nanddp phheennooll uussiinngg fufuncntciotinoanliazelidz-eAdC- AatC vaartiovuasr iionutesrvianltse orfv alsof
time (Initial (Hg(II)/phenol) concentrations: ~10 mg/L, pH: 5.0, solid dose: 2.0 g/L, contact time: 12 h).
time(Initial(Hg(II)/phenol)concentrations:~10mg/L,pH:5.0,soliddose:2.0g/L,contacttime:12h).
Metals2017,7,248 7of15
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The pseudo-first order kinetic (Equation (1)) and pseudo-second order kinetic (Equation (2))
modelswereemployedtoperformthekineticmodellingusingthetimedependentadsorptiondataof
The pseudo-first order kinetic (Equation (1)) and pseudo-second order kinetic (Equation (2))
Hg(ImI)oadnedls pwheerne oelmbpylothyeedf uton cpteirofnoramliz tehde -kAinCe.tiTch meoedqeullaintigo nussiwnge trheet atikmeen dineptehnedirenlitn aedasrofroprtimon: data
of Hg(II) and phenol by the functionalized-AC. The equations were taken in their linear form:
ln(q −q ) =lnq −k t (1)
ln(qe −qt)=lnqe−kt1
e t e 1 (1)
t 1 t
= + (2)
qtt = k21q2e + qte (2)
q k q2 q
whereqeisthemaximumamountofHg(II)/ptheno2laedsorebedatequilibrium(mg/g),andqt(mg/g)is
theawmhoeurne tqoe ifst htheeH mga(xIIim)ourmp haemnooulnatd osfo Hrbge(dII)a/tpthimeneolt .akd1so(mrbiend− a1t) eaqnudilkib2r(igu/mm (gm/gm/gi)n, )aanrde qtth (emagd/gs)o irsp tion
ratetchoen asmtaonutnst ooff ththee Hpg(sIeI)u odro p-hfiernstolo arddseorrbaendd at tthimeep ts. ek1u (dmoi-ns−e1)c aonndd k2o (rgd/merg/mmoind) ealrse, threes apdescotripvteiolyn [49].
Theurantek ncoonwstnanvtasl uofe sthseu pcsheuadsoq-f,irkst, oarndderk anwd ethree cpaslecuudloa-tseedcofrnodm oradeprl omtoodfellns,( qres−peqct)ivveelyrs [u4s9]t., Tahned the
e 1 2 e t
plotsuonfkntowagna vinalsutets, srueschp eacst qive,e kl1y, ,afnodr kth2 weeprsee cuadlcou-lfiatresdt ofrrodme rak pilnoet toicf lann(qde −p qste) uvderos-usse ct,o anndd othrde eprloktisn etic
tqt
modoefl s,anadgarientsut rtn, erdesipnecTtaivbelley1, .foTrh tehRe 2pvseauludeos-fiirnsdt iocradteerd kthinaettitch eanadd sposreputdioo-nsekcionnedt icorddaetra kfiintteetdic well
q
tothepsetudo-secondorderkineticmodelratherthanthepseudo-firstorderkineticmodelforboth
thepmoollduetlasn, tasn.d returned in Table 1. The R2 values indicated that the adsorption kinetic data fitted well
to the pseudo-second order kinetic model rather than the pseudo-first order kinetic model for both
In porous materials, intra-particle diffusion usually plays a crucial role in controlling the
the pollutants.
adsorptionofvariouspollutantsfromaqueoussolutions. Therefore,thetime-dependentintra-particle
In porous materials, intra-particle diffusion usually plays a crucial role in controlling the
diffusion rate of Hg(II)/phenol from the outer surface active sites to the inside pores of the
adsorption of various pollutants from aqueous solutions. Therefore, the time-dependent intra-
functionalized-ACwasevaluatedusinganintra-particlediffusionmodel(Equation(3))developedby
particle diffusion rate of Hg(II)/phenol from the outer surface active sites to the inside pores of the
WeberandMorris[50]. Theequationistakenas:
functionalized-AC was evaluated using an intra-particle diffusion model (Equation (3)) developed
by Weber and Morris [50]. The equation is taken as:
1
qt = kidt2(cid:3117) +Z (3)
(cid:1869)(cid:2930)=(cid:1863)(cid:2919)(cid:2914)(cid:1872)(cid:3118)+(cid:1852) (3)
wherwehkeidrei skitdh ise tihnet rian-tpraa-rptaicrlteicdlei fdfuifsfuiosnionra rtaetec ocnonstsatanntt( g(g//mmgg//mminin1/21)/, 2a)n,da nZd isZ thise tihneteirncteeprtc. eTphte. Tgrhaepgh raph
waspwlaost tpeldotftoedr tfhore tahme aomunoutnotf oHf gH(gII()I/I)p/phheennooll aaddssoorrbbeedd aat tvvaariroiuous scocnotnactat ctitmtiems (eqst)( aqgt)aaingsat itnhset stqhueasrqe uare
rootroofotti mof eti(mt1e/ 2(t)1/a2)n adndil liullsutsrtartaeteddi ninF Fiigguurree 66.. TThhee iinnttrraa-p-paratritcilcel edidffiuffsuiosnio pnloptslo ftosr fHorg(HII)g a(InId) apnhdenpohl enol
showsehdowaegdo oad glionoeda rliitnyewariitthy awhiitghh aR 2hvigahl uRes2 ,vwalhuiecsh, inwdhiiccaht eidndthicaatteindt rtah-apta rintitcrlae-pdaifrftuicsleio ndicfofunstiroinb uted
avitacolnrotrliebuintetdh ea svoirtaplt iroonleo ifnH thge( IsI)orapntdiopn hoefn Holgo(InI)t oanfud npchtieonnoal loiznetdo -fAuCnc.tHioonwaliezveedr-,AaCm. Hinoowredvivere,r ag ence
minor divergence from the origin was observed in the case of phenol, which was perhaps due to the
fromtheoriginwasobservedinthecaseofphenol,whichwasperhapsduetothevariationinthe
variation in the solutes movement during the initial and final steps of the adsorption process [51].
solutesmovementduringtheinitialandfinalstepsoftheadsorptionprocess[51]. Theintra-particle
The intra-particle diffusion constants along with the R2 values are summarized in Table 1.
diffusionconstantsalongwiththeR2valuesaresummarizedinTable1.
3.5
3
Phenol
2.5 y = 0.13x + 0.803
) R² = 0.995
g 2
/
g
m
(1.5 Hg(II)
e
q
1 Phenol
Hg(II)
y = 0.172x + 0.234
0.5
R² = 0.992
0
0 4 8 12 16 20
t1/2

FiguFreigu6r.e 6P. loPtlostso foft htehe inintrtara-p-paarrttiiccllee ddiiffffuussiioonn mmooddele lfofro rHHg(IgI() IIa)ndan dphepnhoel nroelmroevmalo vuaslingu sing
funcftuionnctailoinzaeldiz-eAdC-A(CIn (iItniaitlia(lH (gH(gII()I/I)p/phheennooll)) ccoonncceennttrraatitoionns:s :~1~01 0mmg/Lg,/ pLH,p: H5.0:,5 s.0o,lisdo ldidosed:o 2s.e0: g2/.L0, g/L,
contact time: 12 h).
contacttime:12h).
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Table1.Rateconstants(k1andk2),sorptioncapacity(qe),andR2valuesobtainedfromthepseudo-first
Table 1. Rate constants (k1 and k2), sorption capacity (qe), and R2 values obtained from the pseudo-first
order and pseudo-second order kinetic models, along with the intra-particle diffusion constants
order and pseudo-second order kinetic models, along with the intra-particle diffusion constants
obtainedfortheadsorptionofHg(II)andphenolbyfunctionalized-AC.
obtained for the adsorption of Hg(II) and phenol by functionalized-AC.
PsPesueduodo-F-Fiirrsstt OOrrddeerrK Kinienteictic PsPesuedudoo-S-Seeccoonndd OOrrddererK Kinientiectic InItnrtara-P-Paarrttiiccllee DDififfufsuisoinon
Sample
Sample k1(k1/1m in) qe(qme g/g) RR22 k2(g/mkg2 /min) qqee ((mmgg/g/g)) RR22 Kid(mKg/igd/ min1/2) ZZ RR22
Hg(II) 5(.10/m×i1n0−) 3 (m1g.7/2g) 0.95 (g1/.0m×g/1m0−i2n) 3.19 0.97 (mg/g0/.m12in1/2) 0.23 0.99
HPgh(eInI)o l 55..00 ×× 1100−−33 11.7.428 00..9950 61..00× × 1100−−32 33..2179 00..9957 00.1.123 00.2.830 00..9999
Phenol 5.0 × 10−3 1.48 0.90 6.0 × 10−3 3.27 0.95 0.13 0.80 0.99
3.2.3. AdsorptionIsothermStudies
3.2.3. Adsorption Isotherm Studies
TheeffectofinitialHg(II)concentrationwasstudied,increasingtheinitialconcentrationfrom
2.0to2T5h.0e mefgfe/cLt oinf itnhiteiapl rHesge(nIIc)e coofn1ce0n.0trmatgio/nL wpahse sntouldaietdp, Hin5cr.0e.asSiinmg itlahrel yin,itthiael ecfofenccteonftriantiiotina lfprohmen ol
co2n.0ce tnot 2ra5t.0io mngw/La sins tthued pierdes,einnccer eoafs 1in0.g0 tmhge/Lin pithiaelncool natc epnHtr 5a.t0i.o Snimfriolamrly1,. 0thteo e2ff0e.c0t mofg in/iLtiainl pphreensoeln ce
ofc1o0n.c0emntgra/tiLonH wg(aIsI )satutdpiHed5, .i0n.crTehaesineqg uthileib irniiutimal sctoangceensotrraptitoionn frdoamta 1o.0b ttoa i2n0e.d0 mwge/rLe pinl optrteesdenbceet wofe en
th1e0p.0e mrcge/nLt aHgge(IrIe)m ato pvHal s5.a0g. Taihnes teqtuhielibinriiutimal sbtauglke ssoorrppttioivne dcaotan coebntatrinateido nwser(me pgl/oLtt)eda nbdetwgreaepnh tihcea lly
shpoewrcnenintaFgieg urerme7oav,abl.s Aagnaeinnsht atnhcee idniptiearlc beunltka gseoropftiavdes ocorpnctieonntrwataiosnosb (smergv/Led) aantdlo gwraeprhciocnaclleyn sthraotwionn of
soilnu Fteigs,uersep 7eac,bia. lAlyn iennhthaencceads epeorfcepnhteangoe lo,fa anddsogrrpatdiouna wllyasr oebdsuecrevdedw aitt lhowinecrr ceoansicnengttrhateioinn iotifa slosluotrepst,i ve
especially in the case of phenol, and gradually reduced with increasing the initial sorptive
concentration. The uptake amount of Hg(II) and phenol was found to be increased from 0.65 to
concentration. The uptake amount of Hg(II) and phenol was found to be increased from 0.65 to 5.65
5.65mg/gand0.58and5.44mg/g,respectively,whileincreasingtheinitialsorptiveconcentrations
mg/g and 0.58 and 5.44 mg/g, respectively, while increasing the initial sorptive concentrations as
as mentioned above. It is interesting to observe that the percentage removal of phenol remained
mentioned above. It is interesting to observe that the percentage removal of phenol remained almost
almostunchangedwhileincreasingtheinitialconcentrationofHg(II)from2.0to25.0mg/L(Figure7a).
unchanged while increasing the initial concentration of Hg(II) from 2.0 to 25.0 mg/L (Figure 7a).
Similarly,therewasnosignificanteffectonHg(II)removalbyincreasingthephenolconcentration
Similarly, there was no significant effect on Hg(II) removal by increasing the phenol concentration
from1.0to20mg/L(Figure7a). Therefore,thesestudiesinferthatthefunctionalized-ACisableto
from 1.0 to 20 mg/L (Figure 7a). Therefore, these studies infer that the functionalized-AC is able to
removeHg(II)andphenolsimultaneouslyfromwater,andsuggestthepresenceofdifferentbinding
remove Hg(II) and phenol simultaneously from water, and suggest the presence of different binding
sitesavailableforthesetwodifferenttypesofpollutants[48].
sites available for these two different types of pollutants [48].
Figure 7. The concentration dependence removal of (a) Hg(II) in presence of ~10 mg/L phenol (Initial
Figure7.Theconcentrationdependenceremovalof(a)Hg(II)inpresenceof~10mg/Lphenol(Initial
(Hg(II)) concentration: 1–25 mg/L, pH: 5.0, solid dose: 2.0 g/L, contact time: 12 h) and (b) phenol in
(Hg(II))concentration:1–25mg/L,pH:5.0,soliddose:2.0g/L,contacttime:12h)and(b)phenolin
presence of ~10 mg/L Hg(II) (Initial (phenol) concentration: 1–20 mg/L, pH: 5.0, solid dose: 2.0 g/L,
presenceof~10mg/LHg(II)(Initial(phenol)concentration:1–20mg/L,pH:5.0,soliddose:2.0g/L,
contact time: 12 h).
contacttime:12h).
The equilibrium state adsorption data obtained at various sorptive concentrations were further
moTdheleedeq uusiilnibgr iLuamngsmtauteir a(dEsqouraptitoionn (4d)a) taanodb tFarienuenddalitcvh a(rEioquusatsioonrp (t5iv))e acdosnocrepntitorna tiisoontshewrmerse. fTuhreth er
maoddseolrepdtiuosni nmgodLealns gwmeruei rta(kEeqnu taot iiotsn n(o4n))linaenadr fForremusn d[5l2ic]:h (Equation (5)) adsorption isotherms. The
adsorptionmodelsweretakentoitsnonlinearfor(cid:1869)ms(cid:1837)[5(cid:1829)2]:
(cid:2923) (cid:2896) (cid:2915)
(cid:1869) = (4)
(cid:2915) 1+(cid:1837) (cid:1829)
q K(cid:2896)C(cid:2915)
q = m L e (4)
e 1+KL(cid:3117)Ce
(cid:1869) =(cid:1837) (cid:1829)(cid:3289) (5)
(cid:2915) (cid:2890) (cid:2915)
1
q = K Cn (5)
e F e
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whereq istheamountofHg(II)/phenoladsorbed(mg/g)byfunctionalized-AC,andC isthebulk
e e
Hgw(hIIe)r/ep qhee ins otlhceo anmceonutnrat toiof nH(gm(IgI)//pLh)eantoelq audilsiobrrbiuemd .(mKgL/igs) tbhye Lfuanncgtmionuairlirzaetde-AcoCn,s atanndt C(Le /isg t)h,ae nbdulqkm is
thHeLg(aInI)g/pmhueinroml coonnocleanyterratsioonrp (tmiogn/Lc)a pata ceiqtyui(limbrgi/ugm).. KKLF iiss tthhee LFarnegumnduliirc hracteo ncostnasntat,nwt (hLi/cgh),c aonrrde sqpm oisn ds
totthhee Laadnsgomrputiior nmcoanpoalcaiytyer( smogrp/tgio),na cnadp1a/cintyi s(mthge/gso).r KptFi iosn thine tFernesuitnyd.lTichhe cnoonnsltianneta, rwphlioctho cfotrhreesLpaonngdms uir
to the adsorption capacity (mg/g), and 1/n is the sorption intensity. The nonlinear plot of the
andFreundlichadsorptionisothermsfortheremovalofHg(II)andphenolareshowninFigure8a,b,
Langmuir and Freundlich adsorption isotherms for the removal of Hg(II) and phenol are shown in
respectively. Moreover,theadsorptioncapacityoffunctionalized-ACforHg(II)andphenolalongwith
Figure 8a,b, respectively. Moreover, the adsorption capacity of functionalized-AC for Hg(II) and
theisothermconstantsvaluesaregiveninTable2. TheadsorptionofHg(II)ontofunctionalized-ACat
phenol along with the isotherm constants values are given in Table 2. The adsorption of Hg(II) onto
variousconcentrationsfollowedtheFreundlichisothermratherthantheLangmuirmodel,whereas
functionalized-AC at various concentrations followed the Freundlich isotherm rather than the
theexperimentaldataobtainedforphenoladsorptiononfunctionalized-ACwerereasonablyfitted
Langmuir model, whereas the experimental data obtained for phenol adsorption on functionalized-
welltoboththeLangmuirandFreundlichmodels. Furthermore,theadsorptionisothermstudieswere
AC were reasonably fitted well to both the Langmuir and Freundlich models. Furthermore, the
conductedforthebareactivatedcarbonundertheidenticalexperimentalconditions. Langmuirand
adsorption isotherm studies were conducted for the bare activated carbon under the identical
FreundlichadsorptionisothermstudieswereconductedfortheadsorptionofHg(II)andphenolbythe
experimental conditions. Langmuir and Freundlich adsorption isotherm studies were conducted for
activatedcarbonobtainedfromarecanutwaste,andtheresultsareshowninFigure8a,b. Theisotherm
the adsorption of Hg(II) and phenol by the activated carbon obtained from areca nut waste, and the
constantsvaluesaresummarizedinTable2. ItisobservedthattheLangmuirmonolayeradsorption
results are shown in Figure 8a,b. The isotherm constants values are summarized in Table 2. It is
caopbasceirtvyefdo rtHhagt (ItIh)ew Laasndgomuubilre dmaofnteorlatyheer fuadnscotiropntiaolniz actaipoanciwtyi thfosru Hccgin(IiIc) awnahsy ddroiudbel.eMd oarfeteorv ethr,et he
fufnucntciotinoanlaizliaztaitoionno wf tihthe sAuCccicnaiuc saendhayndriindcer. eMasoereinovtehre, athdes ofurpntcitoionncaalipzaatciiotny ooff pthhee nAoCl fcraoumse3d. 8a4n6 to
5.5in5c5rmeagse/ ign. the adsorption capacity of phenol from 3.846 to 5.555 mg/g.
Figure 8. Plots of Langmuir and Freundlich adsorption isotherms for the removal of (a) Hg(II) and (b)
Figure8. PlotsofLangmuirandFreundlichadsorptionisothermsfortheremovalof(a)Hg(II)and
phenol using functionalized-AC and bare AC.
(b)phenolusingfunctionalized-ACandbareAC.
Table 2. Langmuir and Freundlich constants along with R2 values obtained for the removal of Hg(II)
Table2.LangmuirandFreundlichconstantsalongwithR2valuesobtainedfortheremovalofHg(II)
and phenol using modified-AC.
andphenolusingmodified-AC.
Langmuir Freundlich
Material Pollutant
Material Pollutant qo (mg/gL)a ngmKuLi r(L/g) R2 1/n FKreF(umndgl/igc)h R2
Functionalized-AC Hg(II) qo(m1g1/g.2)35 KL(L/0g.)079 R02.848 01./7n92 KF0(.m84g3/g ) 0.9R523
AcFtiuvnactteiodn aclairzbedo-nA (CAC) HHg(gII()II) 11.2355.555 0.0790.199 0.804.8977 00..759826 00..894432 00.9.92553
AFcutinvactteiodncaalribzoend(-AACC) HPgh(IeIn)ol 5.5555.376 0.1991.706 0.907.7970 00..518968 30..914024 00.9.96285
FunctionAalCiz ed-AC PhPehneonlol 5.3736.846 1.7060.116 0.907.0997 00..149483 13..130240 00.9.95648
AC Phenol 3.846 0.116 0.997 0.443 1.320 0.954
3.2.4. Effect of Background Electrolyte Concentrations
3.2.4. EffectofBackgroundElectrolyteConcentrations
The effect of background electrolyte concentrations is a significant parameter to study the
Theeffectofbackgroundelectrolyteconcentrationsisasignificantparametertostudythebinding
binding nature of pollutants onto the solid materials, and it is usually exploited to make a distinction
natureofpollutantsontothesolidmaterials,anditisusuallyexploitedtomakeadistinctionbetween
between non-specific and specific adsorption. Specific sorption is unaffected by varying the
non-specific and specific adsorption. Specific sorption is unaffected by varying the background
background electrolyte concentration, whereas non-specific adsorption is significantly affected by
eleincctrroealystinegc othnec ebnactrkagtrioounn,dw ehleercetraoslyntoen c-osnpceecnifitrcataiodnsos r[p53ti,5o4n].i sIns iogrndiefir ctaon sttluydayf ftehcet eaddsboyrpitniocrne naasitnugret he
baocfk Hgrgo(IuIn) adnedl epchteronloyl toenctoon fucenncttiroantiaolnizsed[5-3A,5C4, ]a.nI nefofercdt eorf tboacsktugdroyutnhde ealdecstorroplytitoe nconnacteunrteraotfioHn gst(uIId)ya nd
phwenaso lcoonntdoufcutendc,t iuosnianlgiz Neda-CAl Cas, aan beafcfkegctrooufnbdac eklgecrotruonlydtee.l eScimtroillayrtley,c othnec erenmtroatviaoln bsethuadvyiowuar socfo Hngd(uIIc)t ed,
uswinags NstuaCdileads ina bthaec kpgreroseunncde eolfe NctarNolOyt3e. .TShiem ciolanrcleyn,ttrhaetiorenm oof vHagl(bIIe) haanvdi opuhrenooflH wga(sII )mwaianstasitnueddi eadt in
Metals2017,7,248 10of15
Metals 2017, 7, 248 10 of 14
thepresenceofNaNO . TheconcentrationofHg(II)andphenolwasmaintainedatapproximately
3
ap5prmoxgi/mLaatetlpyH 5 m5.0g,/Lan adt pthHe 5c.o0n, caenndt rtahtei ocnonocfeNntarCatliaonnd oNf NaNaCOl 3anwda sNianNcrOea3 swedasf rinomcre0a.s0e0d1 ftroo0m.1 0m.0o0l1/ L.
to T0.h1e mpoelr/cLe.n Tthaeg eperercmenotvaagleo rfemmeorvcaulr oyf amnedrcpuhreyn aonlda sphaefnuonlc atsio an fuonfcbtaiockng orfo buancdkgerloecutnrodl yelteecstrisolsyhtoesw n
is sinhoFwignu irne F9i.gIutrwe a9s. oItb wsearsv oebdstehravteadn thinact raena sinecirneNasaeC inl cNonaCcel nctornactieonntsraftrioomns0 f.r0o0m1 t0o.000.11 mto o0l./1L mcoalu/Lse d
cauasceodn as icdoenrsaibdleerdabecler edaescerienasteh einu tphtea kueptoafkHe go,f wHhgi,l ewahnilein acnre ianscereinasteh ienc tohnec ceonntrcaetniotrnatoiofnN oafN NOa3NtoOt3 he
to stahme esaemxtee netxdteidntn doitda fnfeoctt athffeecHt gth(IeI) Hregm(IoI)v arle.mAolvaarlg. eAd elacrregaes edeincrmeaesrec uinry mreemrcouvrayl rinemthoevpalr eisne nthcee of
preNseanCclew oafs NexapClla iwneads ewxipthlatihneedh ewlpitho ftmhee rhceulrpy osfp meceiartciuorny. Isnpeacqiuateioouns. Isno lauqtiuoeno,uHs gs(oIIl)uftoiornm, sHvga(rIiIo) us
forcmoms vpalerxioeussw ciothmtphleecxhelso wriditehs ,thi.ee .,chHlgoCrild+e,sH, ig.eC.l, 2H,HgCgCl+,l 3H−g,aCnl2d, HHggCCll43−2,− a,nadlo HnggCwli4t2h−, tahleonmgi xweidths pthecei es
miHxegd( OspHe)cCiels. HIng(tOheHp)CHl. rIeng tihone pbHet wreegeinon3 .b5etawndee5n. 53,.5t haendH 5g.C5,l 2thies HagpCrel2d ios ma ipnraendtosmpiencaienst (sip.ee.c,ioesv er
(i.e8.0, %ov)e[r1 88,109%].) M[18e,a1n9w]. hMileea,nthwehaildes, otrhpet iaodnseoxrppteiroinm eenxptewriamsecnatr rwieads ocuatrraitedp Hou5t. 0aitn ptHhe 5p.0r eisne ntchee of
precshelonrcied oe,f icnhwlohriidche,t hine wprheidcohm thine apnrtesdpoemciiensainstH sgpCecl2ie.sT ihse HregfoCrle2,. tThheeHregfCorle2,s tpheec iHesgwCle2r sepneoctieesf fiwcieernet ly
nort eemffoicvieendtlbyy rtehmeofuvendct iboyn athliez efudn-ActCio,naanldizecdau-AseCd, aanddr acsatuicsedde car edarsaestiinc tdheecrreeamseo vinal tohfe mreemrcouvrayl forof m
metrhceuaryq uferoomus tshoelu atqiouneso.uAs lsteorlnuatitoivnesl.y A,tlhteerunpattiavkeelyo,f tHheg (uIIp)traekme aoifn eHdga(IlIm) oresmtcaoinnsetda natlmwohsilte cionncsretaansitn g
whthilee NinacNreOas3incgo nthceen NtraaNtioOn3s cfornomcen0t.r0a0t1iotnos0 f.1rommo 0l/.0L0.1T thoe 0s.e1r mesoull/tLs.s Tuhgegsees treedsuthltas tstuhgegHesgt(eIdI) tihoants twhee re
Hgs(pIIe)c iifiocnasl lywaedres osrpbeecdifaicnadllyfo ramdseodrb‘iendn earnsdp hfeorremceodm p‘ilnenxeers ’sopnhtehree scuormfapceleoxfesfu’ nocnt iothnea liszuerdfa-AceC o[5f 3].
funOcntiothnealoiztehde-rAhCa n[5d3,]t.h Oenp tehrec eonthtaegre hraenmd,o tvhael poefrpcehnetnaoglew reamsorevmala oinf epdhecnoonls wtaanst rwemhialeiniendc rceoanssintagntth e
whNilaeC inlccroenacseinntgr athtieo nNfarComl c0o.n0c0e1nttora0t.i1onm forlo/mL. 0T.0h0is1 rteos u0.l1t smugogl/eLs.t Tedhitsh raetspuhlte nsuoglsgwesetered atlhsaot sppheecinfioclasl ly
wearde saolrsboe sdptehcriofiucaglhlyt haedsfoorrbmeadt itohnrooufgdho nthoer –faocrcmepattioornc oomf dpolenxoers–,aicncewphtoicr hcothmepclaerxbeos,n iynl gwrhoiucph othfeth e
carfbuonncytilo gnraoliuzpe do-fA tChei sfuanncetiloenctarloizneddo-AnCor iasn adn tehleecatrroomn adtoicnroirn agnsdo fthpeh eanroomlaarteice rleinctgrso nofa pccheepntoolr asr[e5 5].
eleMctororeno avcecre,ppthoernso [l5s5w]. eMreotrreaopvpeerd, pwhiethnionlst hweepreo rtersapopftehde wsoitlhidinm tahtee rpiaolrse,sa onfd thpeo sssoiblildy mfoarmteriniaglsa, astnrdon g
pobssoinbdlyt hforromuginhgt hae sπtr–oπngel ebcotnrodn tihnrtoeuragcht itohne oπf–thπe ebleecntzreonne inritnegraicntipohne onfo tlhaen dbeπn-zeelencet rroinngs pinre psehnetnwoli th
antdh πe-seolleicdtrmonaste priraelsse[n5t6 w,57it]h. the solid materials [56,57].

FigFuirgeu r9e. 9E.ffeEcftf eocft boafcbkagcrkogurnodu nedlecetlreocltyrotely ctoenccoenncteranttiroantiso nins tihnet hreemreomvaolv oafl HofgH(IIg)( IaIn)da npdhepnhoeln boyl by
momdiofdieidfi-eAd-CA fCrofmro maqauqeuoeuosu ssosluotliuotniosn (sIn(Iitniiatli a(lH(gH(gII()I/Ip)/hpehneonl)o cl)oncocnencetrnattriaotniosn: s~:1~0 1m0gm/Lg,/ pLH,p: H5.:05, .s0o,lsido lid
dosdeo: s2e.:0 2g.0/Lg, /cLon,ctaocntt aticmttei:m 12e: h1,2 bha,ckbgacrokugrnodu enldecetlreocltyrtoel:y Ntea:CNl/aNCal/NNOa3N). O ).
3
3.3. Fixed-Bed Column Adsorption
3.3. Fixed-BedColumnAdsorption
In addition to batch reactor experiments, a fixed-bed column adsorption study was conducted.
Inadditiontobatchreactorexperiments,afixed-bedcolumnadsorptionstudywasconducted.
In this study, the pH of the influent solution was maintained at pH 5.0, and the initial concentrations
Inthisstudy,thepHoftheinfluentsolutionwasmaintainedatpH5.0,andtheinitialconcentrations
of Hg(II) and phenol was taken 4.5 and 7.89 mg/L, respectively. It was observed that the
of Hg(II) and phenol was taken 4.5 and 7.89 mg/L, respectively. It was observed that the
functionalized-AC could efficiently remove the Hg(II) and phenol even in a continuous flow system.
functionalized-ACcouldefficientlyremovetheHg(II)andphenoleveninacontinuousflowsystem.
The nonlinear Thomas equation (Equation (6)) was utilized to fit breakthrough data obtained for
ThenonlinearThomasequation(Equation(6))wasutilizedtofitbreakthroughdataobtainedforHg(II)
Hg(II) and phenol to optimize the loading capacity of functionalized-AC under dynamic conditions
[58]. The equation is taken as:
(cid:1829) 1
(cid:2915)
= (6)
(cid:1829)(cid:2925) 1+(cid:1857)(cid:4666)(cid:3012)(cid:3152)(cid:4666)(cid:3044)(cid:3173)(cid:3040)(cid:2879)(cid:3004)(cid:3173)(cid:3023)(cid:4667)(cid:4667)/(cid:3018)