活性炭微波催化降解PCP

TemperaturemeasurementofGACanddecompositionofPCPloadedonGACandGAC-supportedcoppercatalystinmicrowaveirradiation

XitaoLiu1,XieQuan∗,LongliBo,ShuoChen,YazhiZhao,MingChang

SchoolofEnvironmentalandBiologicalScience&Technology,DalianUniversityofTechnology,2LinggongRoad,116024Dalian,China

Receivedinrevisedform22November2003;accepted17December2003

Abstract

Ashelteredtype-Kthermocouplewasappliedtorecordthetemperaturerisingcoursesofgranularactivatedcarbon(GAC)inamicrowaveirradiationfieldundervariousconditions.TheresultsshowedthatGACcouldabsorbmicrowaveenergyeffectivelyanditstemperatureroseupto1100◦Cinafewminutes.ThisinteractionofGACandmicrowavewasutilizedtothepreparationofGAC-supportedcoppercatalyst.ThecatalystwascharacterizedbyX-raydiffraction(XRD),scanningelectronmicroscopy(SEM),iodinenumberandadsorptionisotherm.ItwasfoundthatelementalcopperdistributeduniformlyonthesurfaceofGAC,andafterloadingcopper,theadsorptioncapacityofGACdecreasedduetooccupationofadsorptionsitesbycopper.Decompositionofatypicalchlorinatedorganicchemical,pentachlorophenol(PCP),onvirginGACandcopper-loadedGACwasassistedbymicrowaveirradiation.Firstly,PCPinwaterwasadsorbedontoGAC,thenPCP-loadedGACirradiatedbymicrowaveinaquartzreactor.TheresultsindicatedthatmostofPCPadsorbedonvirginGACwasdecomposedorboundirreversiblytoGACunder850wmicrowaveirradiationfor10min,andlessthan2%wastransformedintointermediates.AmorerapiddecompositionrateofPCPwasobservedoncopper-loadedGACwithlargeramountofintermediatesformed.Identificationofintermediateswasaccomplishedbygaschromatography/massspectrometry(GC/MS)analysis.©2004ElsevierB.V.Allrightsreserved.

Keywords:Microwave;Activatedcarbon;Catalyst;Preparation;Pentachlorophenol;Decomposition

1.Introduction

Microwavesareelectromagneticwavesofwhichspec-trumliesbetweeninfraredradiationandradiofrequenciescorrespondingtowavelengthsof1mmto1m(frequenciesof300GHzto300MHz).Microwaveradiationwhenap-pliedtomaterialsmakesthedipolarmoleculesrotateandtheionsmigrate.Theenergyabsorbedisdissipatedasheat[1].Microwaveheatingisthereforeinternalascomparedtoconventionalheatingwhichisexternal.Sourcesofmi-crowaveirradiationallowhightemperaturesandhighratesofheatingtobeobtained[2].

Atypicalexampleofmicrowaveheatingmaterialisitseffectoncarbon.Whencarbonisexposedtoamicrowavefield,itstemperaturecanriseto1000◦Cinafewminutes[2].Thereasoncanbeexplainedbyspacechargepolarization

Correspondingauthor.Tel.:+86-411-4706140;fax:+86-411-4706263.

E-mailaddress:quanxie@dlut.edu.cn(X.Quan).

1Presentaddress:NortheastNormalUniversity,Changchun,China.0926-860X/$–seefrontmatter©2004ElsevierB.V.Allrightsreserved.doi:10.1016/j.apcata.2003.12.026

∗

[3].Somecarbonshavefreeelectronswhosedisplacementisrestrictedbygrainboundaries.Whenthesecarbonsaresubjectedtoanelectromagneticfield,spacechargepolariza-tiontakesplace.Entiremacroscopicregionsofthematerialbecomeeitherpositivelyornegativelysynchronizingtheirorientationwiththefield.Atlowfrequency,thepolarizationsynchronizesitsorientationwiththefield,butasthefre-quencyofwavesincreasesthereisaphaselagbetweenthepolarizationandtheappliedfield.ThisleadstoabsorptionofenergyandJouleheatingofthecarbonparticles.

Thetemperaturemeasurementinmicrowavefieldisre-gardedcrucialforreactions.Someresearchers[4]believethattraditionaltechniqueofthermocouplesfortemperaturemeasurementscannotbeappliedinsidemicrowaveovensduetotheelectromagneticfieldandthemetalprobesinterac-tions,whiletherearereportsthatathermocoupleintroducednormaltothedirectionoftheelectromagneticfielddoesnotinfluencetheelectromagneticfielddistribution[5,6].Menéndezetal.[7]comparedanInconelshelteredtype-Kthermocoupleandaninfraredpyrometerinmeasuringthetemperatureofcarbonbedduringmicrowavetreatmentand

54X.Liuetal./AppliedCatalysisA:General264(2004)53–58

foundthattheobtainedresultsforthesetwotechniqueswerecomparable.

Theselective-heatingcharacterofmicrowavegivesusanadvantageofenergysavingintheheatingprocesses.Mi-crowavedielectricheatinghasbeenwidelyappliedtocata-lystpreparation[8],catalysisreaction[9],andenvironmen-talremediation[10–13].

Amongvariousnovelmethodsusedinthepreparationofcatalysts,microwaveirradiationisdevelopedaseffec-tivetechniquewhichcanofferrapiddrying,uniformdis-tributionofactivecomponents,physicallystrongerpelletduringpreparationofcatalystsandenhanceconversionrateandselectivitywithsignificantenergysavingduringtheperformance[14].Lingaiahetal.[15]preparedaseriesofsilica-supportedPd-Febimetalliccatalystsbyconventionalaswellasmicrowaveheatingmethods.Theyfoundthatthecatalystspreparedwithmicrowaveirradiationhadadifferentmorphologyandpossessedahigherhydrodechlorinationac-tivitycomparedtotheirconventionallypreparedanalogues.Microwave-assistedtreatmenthasbeenappliedtotheinsitusoilremediationofsitescontaminatedwithPCBs[11],PAHs[12],aswellasthedisposalofsludgecontainingheavymetals[13].Anothertypicalapplicationofmicrowaveisintheprocessingofpackagingwastes[2].Processesapplyinggranularactivatedcarbon(GAC)adsorptionandmicrowavedecompositiontothetreatmentofVOCshaveshowncon-siderablesavingsinenergyconsumptionandprocesseffi-ciency[16].

ThepurposesofthisstudyaretomonitorthetemperaturerisingcoursesofGACexposedto2450MHzmicrowavefieldundervariousconditionswithashelteredtype-Kther-mocoupleprobe,andtoexploretheeffectsofmicrowaveirradiationonthepreparationofGAC-supportedcoppercatalystaswellasonthedecompositionofPCPloadedonvirginGACandcopper-loadedGAC.

2.Experimental

Commercialcoal-basedGAC(TangshanCorp.,China)wasfirstimmersedin10%dilutedhydrochloricacidfor24h,heatedinboilingwaterfor30min,washedwithdeionedwatertoremovefinesandimpuritiesanddriedat105◦Covernightbeforeimpregnatingitwiththeactivecomponent.Catalystwith10wt.%Cuwaspreparedbyimpregnat-ingtheGACwithanaqueoussolutionofcoppernitrate(ShenyangAgentCompany,China).Thesuspensionwasmixedinashakingbedat250rpmfor2handevaporatedtonear-drynessinamicrowaveovenat640wintermittentpowerfor2min.Thecatalystwassubsequentlycalcinedinaquartzreactor(Fig.1)withnoairinputbymicrowaveirradiationat100%power(850w,2.45GHz)for10min.PowderX-raydiffraction(XRD)patternofthecatalystwasrecordedwithaShimadzuLabXXRD-6000X-raydiffractometerusingCuK␣radiation.Thesurfacemorphol-ogyofthecatalystwasdeterminedbyscanningelectron

Fig.1.Bench-scalemicrowaveapparatus.(1)Microwavesource;(2)Booster;(3)Amperemeter;(4)Quartzreactor;(5)Thermocouple;(6)Condensor;(7)Distillatereceiver;(8)Offgasesabsorptionbottles.

microscopy(SEM)usingOxfordJSM-5600LVmicroscopeassistedwithenergydispersiveX-ray(EDX)toanalyzetheapproximateatomiccompositionontheexaminedsurface.Thesampleswerecharacterizedattensionvoltagesof15and20eV,andtheresultswereexpressedassecondaryelectronimages(SEI).

DecompositionofPCPloadedonGACandGAC-supportedcoppercatalystwascarriedoutinaquartzreactor.LoadedGACwas−1obtainedbymixing100mlofPCPsolu-tion(2000mgl,pH10.0)with10gGACin250mlflasks.Theflasksweresealedandplacedinthermostaticshaker(250rpm,20◦C)for6htoobtainequilibrium.SeparationofGACfromthesolutionwascompletedbyfiltration.TheschematicdiagramoftheexperimentalapparatusisshowninFig.1.

An850wmodifieddomesticmicrowaveovenatthefre-quencyof2450MHzwithcontinuousadjustablepowerset-tingswasused.Thequartzcolumnreactor(34mmi.d.)wasinstalledintothemicrowaveoven.Atthebottomofthecol-umn,aperforatedquartzplatewasfixedtosustainGAC.GACloadedwithPCPwasputintothecolumnandtreatedbymicrowaveheatingundervariousconditions.Thetem-peraturerisingcoursesofGACwererecordedwithashel-teredtype-Kthermocoupleprobe,whichwasinsertedtoapointnearthecenterofthecarbonbed.Thetopofthecol-umnwasconnectedtoacondensingsystem.Avesselwasusedtocollectdistillateandthecontaminantvaporgener-atedpassedthroughtwobottlesbothcontaining20mlof0.1moll−1NaOHsolution.

ThedeterminationofPCPconcentrationsinthefiltrate,distillateandalkalineabsorptionsolutionwasperformedbyHPLC(PU-1580,UV-1575,JascoChromatography,Japan)usingaKromasilODS(5␮m,4.6mm×250mm)reversephasecolumn,amethanol:water=0.8:0.2mlmin−1ofthemobilephaseandUV-absorbancedetection(220nm).Totalorganiccarbonanalyzer(TOC-VCPH,Shimadzu,Japan)wasemployedfordistillateanalysis.

PCPamountsinGACbeforeandaftermicrowaveirradi-ationwerealsodetectedbyHPLC.Thepretreatmentproce-durewas◦asfollows:approximately1gofGACwasheatedat103Cfor6htoconstantweight.Aftercoolingtotheroomtemperature,0.100gofGACwasaccuratelyweighed.

X.Liuetal./AppliedCatalysisA:General264(2004)53–5855

PCPinGACwasextractedby20mlmixtureofacetoneanddichloromethane(3:2(v/v)),with0.2mlof37%hy-drochloricacidadded(shakingat250rpmfor2h,thenultra-sonicextractingfor30min).Theextractionprocedurewasrepeatedfor◦sixtimes.Afterwards,theextractwasevapo-ratedin60Cwaterbathtoincipientdryness.Theresultantsamplewasdissolvedin10mlacetonitrileandanalyzedbyHPLC.

Agaschromatograph(GC)(HP6890)withacapillarycolumn(HP-5MS,30m×0.25mm×0.25␮m)andamassspectrometer(MS)(HP5973)wereemployedtotheidentifi-cationofintermediatesanddecompositionproducts.Asol-ventdelayat5min,andfullscanmodewereused.Theoventemperaturewasprogrammed◦from60to260◦C(20min)ataramp◦rateof15Cmin−1.Theinjectortemperaturewas260Candthetransferlinewasmaintainedat280◦C.TheMSDwasoperatedintheelectronimpact(EI)mode.Theionsourcetemperaturewas200◦Candtheelectronenergywas70eV.

3.Resultsanddiscussion

3.1.TemperaturerisingcoursesofGACinmicrowavefieldAccordingtothemethodpresentedbyMenéndezetal.[7],thetemperaturerisingcoursesofGACinmicrowavefieldunderdifferentmicrowavepower,GACdoseandmoisturecontent,wererecordedbyashelteredtype-Kthermocouple.3.1.1.Microwavepower

Thetemperatureattainedinthecarbonbeddependsonthenatureofthecarbon(dielectricproperties)aswellasonthemicrowavepowerappliedtothesample.Foragivencarbon,thetemperaturecaninprinciple,bemodifiedbyadjustingtheinputpower[7].Onespecialpointtobenotedisthatthepowerlevelsusedherearecontinuous,notjusttimedmark/spaceratiocontrol.Theinvestigatedpowerserieswas160,320,480,640and850w.GACdoseandwatercontentinvolvedwere10gand52.5%,respectively.TheresultswereillustratedinFig.2.

Itcanbeclearlyseenthatatlargermicrowaveoutputpower,thetemperatureofGACbedrisesmorerapidly.Whenthemicrowavepowerwasashighas640w,thetemperatureroseupto1100◦Cin4min.Sincethehighest◦temperaturethatthethermocouplecanendureis1200C,assoonasthedisplayedvalueiscloseto1150◦C,themicrowaveovenmustbeturnedoff.

3.1.2.GACdose

AsdifferentGACdosemeansdifferentvolumeandheightofGACinthereactor,thusdifferentGACloadtomicrowaveirradiation,GACdosegreatlyinfluencesthereceivingofmicrowaveenergy.TheGACdosesinvestigatedwere5,10,15,20and25g,with850wpowerand52.5%moisturecontent.

1200 160w1000 320w 480w)g800 640we 850wd(eru600tarepme400t 20000100200300400500600time(s)

Fig.2.TemperaturerisingcoursesofGACinmicrowavefieldatvariouspowers.

Duringtheexperiment,itwasfoundthatwhentheGACdosewasassmallas5g,thethermocouplecouldnotbeuti-lizedtoindicateitstemperature.BecausewhentheamountofGACistoosmall,theprobeofthermocouplecouldnotbeimmersedintoGACbedanditisexposedtomicrowaveirradiationdirectly,whichcausessparksonthetipoftheprobe.Inthatcase,thedisplayedtemperaturevaluewasnotthatofGACbed,butthatofthesparks.Althoughthetem-peratureof5gGACbedcouldnotbedeterminedbythethermocouple,itwasobservedthattheGACbeddidnotturnredin10minirradiation.Inasubsequentexperiment,thepositionofGACbedwasraiseduptothecenterofreactorandthesamephenomenonwasobserved.ThetemperaturerisingcoursesofGACbedinotherdoseswereexhibitedinFig.3.

ItseemsthatalargerGACdoseabsorbsmicrowaveenergymoreeffectivelyanditstemperaturerisesmorerapidlyatthebeginning.However,thetemperaturerisingrateoflargerGACdosedecreasedlater.Thereasonwasconsideredtobethatmoreenergywasneededtomaintainhightemperatureforlargerdose.Andthe15gdosewastakenasthebest

1200

10g1000

15g 20g 25g)g800

ed(eru600

tarepm400

et200

0020406080100120140160180time(s)

Fig.3.TemperaturerisingcoursesofGACinmicrowavefieldwithdifferentdoses.

56

1200X.Liuetal./AppliedCatalysisA:General264(2004)53–58

3.2.DecompositionofPCPonvirginGACandcopper-loadedGAC

XRDmeasurementwascarriedouttoanalyzethestatusandcrystalstructureofcopperonthesupport.Fig.5showstheXRDspectroscopyofvirginGACandcopper-loadedGAC.Sharpintensivepeakswereobservedinthecharac-teristicpositionsofelementalcopperstructureat2θ=43.3and2θ=50.4◦forthepreparedcatalyst(dottedline).Un-likethepreparedcatalyst,thevirginGAC(solidline)showsverysmallcrystallinestructurerelatedtocopperat2θ=43.3◦.Thisindicatesthatthecrystallinestructureofcopperpresentedinthepreparedcatalystisduetothedecomposi-tionofcoppernitrate.

ThetwoSEMpictures(Fig.6)obtainedonvirginGACandcopper-loadedGACcorroboratetheresultsobtainedonXRD.InthecaseofGAC-supportedcoppercatalyst,agglomerationofelementalcopperintolargeparticlesisclearlyvisible.FromEDXanalysis,itwasfoundthatthecopperloadingonthiscatalystisabout12.6wt.%.

IodinenumberprovidesanindicationoftheadsorptionabilityofGACtosmallmolecularcompounds.Thisin-dexwastestedforthetwoGACsamplesaccordingtotheNationalStandardTestingMethodsofP.R.China(GB/T12496.8-1999).ThecorrespondingvaluesforvirginGACandcopper-loadedGACwere944.1and824.0mgg−1,re-spectively.Itwasbecausethatforthelattersample,someadsorptionsiteswereoccupiedbyelementalcopperafterloading,ascanbeseenfromtheSEMimages.Theadsorp-tionisotherms(Fig.7)ofthetwoGACsamplestoPCPwerealsomeasuredaccordingtothemethodprovidedbyMollahandRobinson[19],theresultswereinconsistencywiththatofiodinenumber.

ForthedecompositionofPCP,theinitialamountsofPCPloadedon10gvirginGACandonGAC-supportedcoppercatalystwere199.52and198.78mg,respectively.TheoperatingparametersforPCPdecompositionexperi-mentwere:microwaveoutputpower850w,irradiationtime10minandmoisturecontent52.5%.Thetemperatureris-ingcourses(Fig.8)ofthetwoGACbedsduringPCP

1000temperature(deg)800600400200 0% 16.8% 36.4% 52.5%0020406080100120140160180time(s)

Fig.4.TemperaturerisingcoursesofGACinmicrowavefieldwithdifferentmoisturecontents.

inviewofabsorbingmicrowaveenergyandkeepinghightemperature.

3.1.3.MoisturecontentofGAC

Themoisturecontentofasamplehasaneffectonthefinaltemperatureitattainsduringmicrowaveheating[17].Changesinmoisturecontentwillaltertheconductivityandpermittivityofthesample,andhencethestrengthoftheelectricfieldsinthematerialandthepowerdissipatedinit.Waterhasahighdielectriclossfactor,sorelativelysmalldifferencesinmoisturecontentsbetweensampleswillresultintemperaturedifferencesbetweenthem.

Generally,itisbelievedthatmicrowaveactivationoccursmuchfasterwithdrycarbonthanwithwetcarbon.AseriesoffourmoisturecontentsofGACwerestudied,i.e.0,16.8,36.4and52.5%,withmicrowavepower850wandGACdose10g.TheresultswereshowninFig.4,whichwereconsistentwiththatofHaqueetal.[18].Theyfoundthattoheat100gofdrycarbonfromroomtemperatureto650◦C,about0.2–0.25kWhofmicrowavepowerinputwasrequired,whereasthesamemassofwetcarbonofapproximately50%moisturerequiredabout0.4–0.6kWh.

Fig.5.XRDspectroscopyofvirginGACandcopper-loadedGAC.

X.Liuetal./AppliedCatalysisA:General264(2004)53–58

57

Fig.6.SEMpictures:(a)virginGAC;(b)copper-loadedGAC.

decompositionwerealsorecordedbytheshelteredtype-Kthermocouple.Itseemedthatwaterevaporatedfasterfromthesurfaceofcopper-loadedGACduetoitslessadsorptioncapacitytowatermolecules,soitstemperaturebegantoin-creaserapidlyafter60smicrowaveirradiation(about40searlierthanthatofvirginGAC).Buttheoveralltemperaturerisingrateofcopper-loadedGACwassmalleranditsfi-naltemperatureafter10minmicrowaveirradiationmightbelowerasobservedfromappearancestatus.Thereasonwas

140120virgin GAC100)g/g80mcopper-loaded GAC(q604020020040060080010001200140016001800Ce(mg/L)

Fig.7.AdsorptionisothermsoftwoGACsamplestoPCPat20◦CandpH10.0.

12001000 virgin GAC copper-loaded GAC)g800ed(eru600tarepm400et2000020406080100120140160180200time(s)

Fig.8.TemperaturerisingcoursesofthetwoGACbedsduringPCPdecomposition.

thatelementalcopperloadingontheGACsurfacedecreaseditsabilityinabsorbingmicrowaveenergy(somemicrowaveirradiationwasreflectedbycopper).

FromtheHPLCanalysisfortheoff-gasbasicabsorptionsolutions,itwasfoundthatanythingcouldhardlybedetectedinthesetwocases.OrganicsolventandacidextractionofthePCP-loadedGACbeforeirradiationledtoa55.4±1.5%recoveryrate.ThetotalamountofchemicalsindistillatewasindicatedbytheindexofTOC.PCPresiduesleftinvirginGACandcopper-loadedGACandTOCindistillateafterdifferentmicrowaveirradiationtimeswereplottedinFigs.9and10.

AscanbeseenfromFig.9,PCPwasdecomposedpromptlyonvirginGACoroncopper-loadedGAC.Morethan95%wasdecomposedorboundirreversibly(carboniza-tion)toGACafter6minmicrowaveirradiationforPCPonvirginGACandnearly100%forPCPoncopper-loadedGAC.OnespecialissuetobementionedisthatPCPwasdecomposedmorerapidlyonthelatteralthoughitstem-peraturemightbelower.Thefasterdecompositionratewasdeemedduetothecontributionfromthecatalysiseffectofcopper.DatainFig.10indicatedthattheamountofTOCindistillatewasminorcomparedtotheinitialamountofPCPloadedonGAC.AndforthedecompositionofPCPloaded

200 virgin GAC copper-loaded GAC)CA150G g01/PC100P gm(C5000246810irradiation time(min)

Fig.9.PCPresiduesleftinvirginGACandcopper-loadedGAC.

58

X.Liuetal./AppliedCatalysisA:General264(2004)53–58

4 virgin GAC copper-loaded GAC3)gm(etallit2sid ni COT10024681012irradiation time(min)

Fig.10.TOCformedindistillateduringthecoursesofPCPdecomposition.

onGAC-supportedcoppercatalyst,muchmoreTOCwasformedindistillate.Thereasonwasthesameasthatoftemperaturerising,i.e.fasterwaterevaporatingratebroughtoutmorePCPanditsderivativesintodistillate.

IdentificationofintermediateswasperformedbyGC/MSanalysis.ForthedistillatefromvirginGAC,threemaindechlorinationintermediateproducts,tetrachlorophenol,trichlorophenolanddichlorophenol,weredistinguishedandsomeminoramountofdehydroxylationproducts,pen-tachlorobenzeneandtrichlorobenzenewerealsoidentified.ForthedistillatefromGAC-supportedcoppercatalyst,fur-therdechlorinationintermediates,chlorophenolandphenolwerefoundbesidesthosementionedabove.ThedetaileddegradationmechanismofPCPloadedonGACexposedtomicrowaveirradiationwillbediscussedelsewhere[20].

4.Conclusions

Thepotentialofmicrowaveheatingasanalternativetoconventionalconductiveheatingfortheintroductionofen-ergyintoreactionsencouragesresearcherstousemicrowavepowerinvariousfields.Inthisstudy,thetemperaturerisingcoursesofGACexposedtomicrowaveirradiationwererecordedwithashelteredtype-Kthermocouple,anditwasfoundthatmicrowavepowerandmoisturecontentofGACsamplewerethetwokeyparameters.Microwaveovenwithadjustablepowersettingsandwithfull-powerlevelof850wwasemployedtothepreparationofGAC-supportedcop-percatalyst.Comparedtoconventionalcatalystpreparationmethod,thisnovelmethodisenergyandtimesaving,does

notneedinertgasprotectionandhydrogenreductionwithhighlydispersedGAC-supportedelementalcoppercatalystobtained.PCPadsorbedonvirginGACorcopper-loadedGACwasalmostcompletelydecomposedortightlyboundtoGACundermicrowaveirradiationinafewminutes.Allthishasdemonstratedthepotentialeffectivenessofmicrowaveirradiationincatalystpreparationandenvironmentalremediation.

Acknowledgements

TheauthorsaregratefultoNationalNaturalScienceFoundationandMinistryofScienceandTechnology,P.R.Chinaforfinancialsupport(ProjectNo.20337020and2002AA649090,respectively).

References

[1]F.J.Berry,L.E.Smart,P.S.SaiPrasad,N.Lingaiah,P.KantaRao,

Appl.Catal.A204(2000)191.

[2]C.Ludlow-Palafox,H.A.Chase,Ind.Eng.Chem.Res.40(2001)

4749.

[3]A.Zlotorzynski,Crit.Rev.Anal.Chem.25(1995)43.

[4]G.Cuccurullo,P.G.Berardi,R.Carfagna,InfraredPhys.Technol.

43(2002)145.

[5]F.Liu,I.Turner,M.Bialkowski,J.MicrowavePowerE.E.29(1994)

138.

[6]G.Roussy,S.Jassm,J.M.Thiebaut,J.MicrowavePowerE.E.30

(1995)178.

[7]J.A.Menéndez,E.M.Menéndez,A.Garc´ıa,J.B.Parra,J.J.Pis,J.

MicrowavePowerE.E.34(1999)137.

[8]R.Gopinath,K.NarasimhaRao,P.S.SaiPrasad,S.S.Madhavendra,

S.Narayanan,G.Vivekanandan,J.Mol.Catal.A181(2002)215.

[9]I.Plazl,S.Leskovsek,T.Koloini,Chem.Eng.J.59(1995)253.[10]S.Horikoshi,H.Hidaka,Environ.Sci.Technol.36(2002)1357.[11]R.A.Abramovitch,B.Z.Huang,D.A.Abramovitch,J.Song,Chemo-sphere38(1999)2227.

[12]R.A.Abramovitch,B.Z.Huang,D.A.Abramovitch,J.Song,Chemo-sphere39(1999)81.

[13]Q.Gan,WasteManage.20(2000)695.

[14]G.Bond,R.B.Moyes,D.A.Whan,Catal.Today17(1993)427.[15]N.Lingaiah,P.S.SaiPrasad,P.KantaRao,F.J.Berry,L.E.Smart,

Catal.Commun.3(2002)391.

[16]G.Chih-JuJou,H.S.Tai,Chemosphere37(1998)685.[17]M.F.Diprose,PlantSoil229(2001)271.

[18]K.E.Haque,P.D.Kondos,R.J.C.MacDonal,USPatent2,008,242

(2000).

[19]A.H.Mollah,C.W.Robinson,WaterRes.30(1996)2901.

[20]X.T.Liu,X.Quan,L.L.Bo,S.Chen,Y.Z.Zhao,Carbon42(2004)

415.