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Catalytic

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Catalytic

    Catalytic

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    JournalofEnvironmentalSciences19(2007)362-366

    JOURNALoF

    ENVIRoNMENTAL

    SCIENCES

    ISSN1001.0742

    CNl.2629

    www.jese.ae.en

    Catalyticreductivedechlorinationofp-chlorophenolinwater usingNi/Fenanoscaleparticles

    ZHANGWeihua',QUANXie,ZHANGZhuo.yong

    

    -CollegeofUrbanandEnvironmentalSciences,NortheastNormalUniversity,Changchun130024,China.E?mail:zhangwh282@163.corn

    2.SchoolofEnvironmentalandBiologicalScienceandTechnology,DalianUniversityofTechnology,Dalian116023,China

    3.CollegeofChemistry,InnerMongoliaUniversityfortheNationalities,Tongliao028043,China

    Received12January2006;revised10October2006;accepted10September2006 Abstract

    NanoscalebimetallicNi/Feparticlesweresynthesizedfrom

    ereactionofsodiumborohydride(NaBI-I4)witl1reductionofNi2and Feinaqueoussolution.TheobtainedNi/FeparticleswerecharacterizedbyTEM(transmissio

nelectronmicroscope),XRD(X.ray

    diffractometer),andN2

    BET.ThedechlorinationactivityoftheNi/FewasinvestigatedusingPchiorophenol(P

    CP)asaprobeagent.

    ResultsdemonstratedthatthenanoscaleNi/FecouldeffectivelydechlorinateP

    CPatrelativelyowmetaltosolutionratioof0.4(Ni

    5wt%).ThetargetwithinitialconcentrationofP

    CP0.625mnlo1/Lwasdechlorintedcompletelyin60minunderambienttemperature

    andpressure.Factorsaffectingdechlorinationefficiency,includingreactiontemperature,p

    H,NiloadingpercentageoverFe,andmetal

    tosolutionratio,wereinvestigated.ThepossiblemechanismofdechlorinationofP

    CPwasproposedanddiscussed.Thepseudofirst-

    orderreactiontookplaceonthesurfaceoftheNi/Febimetallicparticles,andtheactivationener

    gyofthedechlorinationreactionwas

    determinedtobe21.2kJ/molatthetemperaturerangof287313K.

    Keywords:Ni/Febimetal;nanoscaleparticles;catalyticreduction;PCP;dechlorination Introduction

    Chlorophenolsareextensivelyusedastheintermediates fororganicsynthesis,pesticides,andwoodpreservatives. Mostchlorophenolsare1istedasprioritypollutantsby theUnitedStatesEnvironmenta1ProtectionAgency(Larry andWilliam,19791duetotheirhightoxicityandresistance todegradation.Thereisanurgentneedtounderstand theirtransportandfateintheenvironmentandtodevelop effectivecontro1methods.

    Theuseofzerovalentironforthetreatmentofcon

    taminantsofhalogenatedorganiccompoundsfHOCs) inwastewaterandgroundwaterrepresentsoneofthe latestinnovativetechnologiesforenvironmentalremedi

    ation(GillhamandO'Hannesin.1994;Johnsoneta1.,

    1996;AmoldandRoberts.2000;Lookmanetal,.2004). ResearchershavefoundthatnanoscaleFeandPd/Fe bimetallicparticlesexhibitedmuchhigheractivityforthe transformationofHOCsthancommerciallyavailableiron powderduetotheirhighactivityinreductionandcatalysis (WangandZhang1997;LowryandJohnson.2004;WleiPf a1.,2004;Liueta1.,2005).Pd,apreciousmetal,exhibited excellentcatalysiscapabilityinreductivedechlorinationof HOCs(WangandZhang,1997;Liuetal.,2001).However, highexpenseofPdcatalysis1imiteditswideapplication. ProjectsupportedbytheNationalBasicResearchProgram(973)ofChina (No.2003CB415006)andtheNationalNaturalScienceFoundationof China(No.2033702o1.Correspondingauthor.

    Email:quanxie@dlut.edu.cn.

    Thus.itisofsignificancetoexplore1owerpriceandmore effectivecatalysts.

    C'larkIIeta1.(20031foundthatNiplatedFewasmore effectivethantheacidtreatedanduntreatedFeinper-

    ch1oroethv1enedegradation.WangPfal.(2004)illustrated thatNjappearedtobeagoodcatalystjnproductionof methaneoverchloroforl/1(CF)duringthereductionof carbontetrachloridefCT1.NanoscaleNi/Feparticleswere alsopreparedfortreatmentoftrichloroethylene(TCE) (Schricketal.,2002),CTandCF(FengandLim,2005). Schricketal.(20021reporteda280timefasterdehalo

    genationofTCEwithalabsynthesizednanoscaleNi/Fe

    comparedwithacommercialFe.

    However,dechlorinationofchlorophenolswithnano

    scaleNi/Febimetallicparticleshasnotbeenreported

intheliteraturesofar.Inthepresentwork,zerovelant

    bimetallicNi/Fenanoscaleparticlesweresynthesizedand usedtodechlorinatePchlorophenol(pCP)inaqueous

    solution.Theobjectiveofthisworkwastoinvestigatethe reactivityofnanoscaleNi/Febimetallicparticlesonthe dechlorinationofchlorophenolandtoidentifythepotential parametersaffectingthedechlorinationratesofPCPby

    theNi/Feparticles.

    1Materialsandmethods

    1.1Mate15als

    Thefollowingchemicalswereused:PCP(i>99%,Fei

No.3CatalyticreAuctivede.chlorinationofp-chlorophenolinwaterusingNi/Fenanoscalep

    articles363

    xiangChemicalPlant,Shanghai,China),ferroussulfate (FeSO4?7H2O)andnickelsulfate(NiSO4.7H2O)(99%, ShenyangAgentManufactory,China),sodiumborohy. dride(NaB,96%,ShanghaiAgentCompany,China1. andmethanol(HPLCgrade,TediaAgentCompany,USA). 1.2PreparationandcharacterizationofNi/Fenanopar- ticies

    ThebimetallicNi/Fenanoscaleparticleswereprepared usingthemethodsimilarlytothatproposedbySchricket a1.(2002).AfterthepHwasadjustedto12witll6mol/L NaOH,theaqueoussolutionofNaBH4(0.5mol/L)was addeddropwiseintoanaqueousmixtureofFeSO4(0.2 mo1/L)andNiSO4(0.01mo1/L)atroomtemperature.The processisshownasbelow:

    2Fe2+(Ni)+2H20+BH42Fe(Ni)J,+BO2

    fl1

4H+2H2T'.

    NaBH4wasaddedexcessivelytoensurethecomplete reductionofthemetallicionsinthesolution.Duringthe additionofNaBH4,thesolutionwasstirredvigorously. Nospecialprecautionsweretakentoeliminateoxygen fromthereactionvesse1.AtiertheadditionofNaBH4,the mixturewasstirredfor5min,andthenfilteredthrough 0-45Ixmmembranewitllavacuumpump.Togetrid oftheexcessborohydride,theparticleswerewashedby deionizedwaterforfivetimes.rinsedwithabsoluteethanol toeliminatewater,andfollowedbyfiltrationasdryas possible.Atlast.blackpowderwasspreadinathinlayeron afilterpaperandthendriedatroomtemperatureinargon. ThedriedNi/Feparticleswerethencollectedandstoredat 4.Cinrefrigeratorforsubsequentuse.

    Brunauer-EmmettTeller(BET)surfaceareaofthe obtainedNi/Fenanoparticlesweremeasuredusingthe nitrogenadsorptionmethodwithaNOVA4200eSurface AreaandPoreSizeAnalyzer(USA).Morphologyofthe Ni/FenanoparticleswasobservedwithaPhillipsEM 400Ttransmissionelectronmicroscope(TEM)toobt~n thesizeandsizedistributionofthemetalparticles.X

    raydifiractionpatternsoftheNi/Fenanoparticleswere obtainedusingtheX.raydiffractometer(XRD,LabxXRD

    6000)withCuXraysource.

    1.3Experimentalprocedure

    TheexperimentsfordechlorinationofpCPwerecarried

    outinabatchreactor.Agivenamountofthenanoscale Ni/Feparticleswasplacedina130mlglassreactor.

    andagivenamountofdeionizedwaterwasadded.The

initialpHvalueofthemixturewasadjustedwi0.1

    moIH2S04,thenagivenamountofstocksolution of.CPwasadded.Thefinalvolumeofthemixture was125m1.Thedechlorinationreactionswereperformed undermagneticstirring(200r/min)todispersetheNi/Fe particlesthroughoutthereactorevenly.Inmostcases, thereactionswereconductedattheconstanttemperature of25~1.C.Afterthereactionslastedfordesiredtime, aliquotsofthesamples(5m1)weretransferredtoaglass via1.InordertominimizetheadsorptionofPCPand

    phenolontheparticles,Imol/LNaOHwasaddedtothe vialtoadjustthepHvalueto12.Thepreliminaryresults indicatedthatthedechlorinationreactionsdidnotoccurat pHvalueapproximately10,whichwasconsistentwiththe workofCheneta1.(2001).AdditionofNaOHcanstop thedechlorinationreactionimmediatelyanddesorbp.CP anditsdechlorinatedproductsfromthesurfaceofNi/Fe particlestothesolution.Themixturewasthenfiltered witll0.45mnmembranetoremovetheprecipitatesfor subsequentanalysis.

    1.4Analyticalmethod

    ConcentrationsofPCPandphenolweredetermined

    withahighperformanceliquidchromatographyfPU

    l580,equippedwithaUV-1575detectorandaKromasil ODScolumn(5Ixm,4.6rainx250mill,Jasco,Japan). Amobilephaseof67%methanoland33%waterwas employedataflowrateof0.9ml/min,andthewavelength wassetat280nm.

    Concentrationofchlorideionwasanalyzedwithanion

chromatography(HICVPSuper,Shimadzu,Japan)COU

    piedwithaShim.PackICA3non.suppressorcolumnf4.6

    mmxl501TlIn,andaCDD.10AVPconductivitydetector. Aneluentsolutioncontaining8mlno1/LPhydroxybenzoic

    acid.3.2mmol/Lbistris,and50mmol/Lboricacidwas

    pumpedataflowrateof1.2ml/min.

    Thetotalcontentofironandnickelinthebimetallic particlesweremeasuredbyaflameatomicabsorption spectrometer(AAS.PerkinE1metAanalyst7oo). 2Resultsanddiscussion

    2.1CharacterizationofNi/Fenanoscaleparticles ThemorphologyandsizeoftheNi/Febimetallic nanoscaleparticles,determinedbytransmissionelectron microscopefTEM).areshowninFig.1.Mostofthe particlesareintherangeof1050nmindiameter.It

    isbelievedthatnanoscalezerovalentmetalparticlescan

    offerseveraladvantages.includinghighspecificsurface area,highsurfacereactivity,andflexibilityindeployment fZhangeta1.,1998;Liueta1.,2005),sotheFeobased

    bimetallicparticleswithnanosizemaybeimportantin environmentalapplications.

    Fig.1TEMimageofNi/Fenanoscaleparticles

ZHANGWeihuaeta1.,,0l_l9

    Fig.2showstheXRDpatternsofNi/Fenanoparticles beforeandafterdechlorinationreaction,respectively.Only onebroadpeakataround20=45.wasobserved.which indicatedthatNiandFeformedamorphousalloy.Similar resultswerereportedbySchricketa1.(20021andLiu

    ,.r20051.Itisbelievedthatsuchamorphousalloy structurewasbeneficialforboththeactivityandselectivity owingtothestrongersynergisticeffectbetweenactive sites(Liueta1.,2005;Yamashitaeta1.,1985).TheBET surfaceareaofthenanoscaleparticleswas22.8m/g.In comparison,acommerciallyavailablefineironpowder fJinshanMetallurgicalFctory,>98.0%,<100mesh)has aspecificsurfaceareaofapproximately0.49m/g(Wei fa1.,2004).Ni/Feratioof1:20w/w(Ni5wt%)was obtainedbyAmericanAcademyofSciences(AAS1. 0

    :--.__-----_..--__-

    a_?_-..

    20406080

    Degree(2e)

    Fig.2XRDpauemsofNi/Vesamples(a)andfleshsample(b)reaction for30min.

    2.2Transformationofp-CP

    Fig.3showsexperimentalresultsforthereactionofthe nanoscaleNi/FeparticleswithP.-CRInitialP.-CPconcen- trationwas0.625mmol/L,metaltosolutionratiowas50 mg/125m1(0.4g/L),themassfractionofNiinthebimeta1 was5wt%.andtheinitialpHwas5.2.AsshowninFig.3, theconcentrationofP.CPdeclinedrapidlywithreaction time.TheP.CPwasalmostcompletelydechlorinatedand transformedtophenolandchlorideionbynanoscaleNHe within60min.ItseemedthatP.CPwasadsorbedonthe surfaceofNi/Feparticlesandthendechlorinationreaction tookplacefGrahamandJovanovic,1999).Itcanalsobe O8

0.6

    0.4

    O.2

    0

    Reactiontimefmin)

    Fig.3TransformationofP.CPoverNi/Fenanoscaleparticles.Condi

    ons:Cn=0.625mmol/L;Niloading5%;Ni/Fepowder0.4;T= 25.C:pH0=5.2.

    100

    80

    60

    40

    20

    0

    Reactiontime(rain)

    Fig.4EffectofinitialpHonthedechlorinationrateofpCEConditions

    Co=0.625mmol/L;Ni/repowder0.4;T=25.C. seenfromFig.3thatnootherchlorinatedintermediatesor finalproductsweregenerated.

    2.3Factorsaffectingreactionrateconstants 2.3.1EffectofinitialpH

    Fig.4showsthedechlorinationefficiencyincreasedas initialpHdecreased.?leninitia1pHwasselectedat3.0, 4.0.5.2.and6.5,theobtaineddech1OrinatiOnefficiencies within20minwere98%,90%,84%and72%,respectively. Thep.CPwascompletelydechlorinatedwimin30min underinitialpHof3.0.whereasthereactiontookmore than180minunderinitialpHof6.5forcompletion(not showninFig41.

    Thechlorinatedcompoundsadsorbedonthebimetallic

    surfacewerereductivelydechlorinatedthroughaseries ofreactions.Thecurrentmodelforthedehalogenation reactionusingNi/Fenanoparticlesinvolvedtheoxidation ofirontogalvanicallyprotectNi(Schricketa1.,2002). Asironcorrodes,protonsfromsolutionwerereducedto atomicandmolecularhydrogenatthecatalyticNisurface. Chlorinatedcompoundswerealsoadsorbedonthesurface ofNi/FeparticleswheretheCC1bondwasbroken.and

    thechlorineatomwasreplacedbyhydrogen.Similarto GrahamandJovanovic(1999),thechemicalprocesscan berepresentedasfollows:

    Surfacereactions:

    He-N_-?iH

    Dechlorinationreaction

    H+RC1RH+C1

    (2)

    (3)

    (4)

    Theoveralldechlorinationreactionprocessonbimetal

    liccatalystsurfacecanberepresentedas:

    Fe0+R-C1+H+RH+Fe2++C1

    AtlowerpH,moreatomichydrogenonthecatalyst surfaceattackedchlorophenoltoreplacethechlorineand toformphenolandchlorineion(Eqs.(4)(6)).Meanwhile,

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