Electrochemical oxidation of__ organic pollutants

Electrochemicaloxidationoforganicpollutantsforthewastewatertreatment:directandindirectprocesses{{CarlosA.Martı´nez-Huitle*andSergioFerroReceived21stApril2006FirstpublishedasanAdvanceArticleontheweb10thJuly2006DOI:10.1039/b517632hInrecentyears,therehasbeenincreasinginterestinfindinginnovativesolutionsfortheefficientremovalofcontaminantsfromwater,soilandair.Thepresenttutorialreviewsummarizestheresultsofanextensiveselectionofpapersdealingwithelectrochemicaloxidation,whichisproposedasanalternativefortreatingpollutedwastes.Boththedirectandindirectapproachesareconsidered,andtheroleofelectrodematerialsisdiscussedtogetherwiththatofotherexperimentalparameters.Apartfromdiscussingthepossibilityofremovingselectedcontaminantsfromwaterusingdifferentanodes,efficiencyratesforpollutantremovalhavebeencollected,thedependenceoftheseratesonoperationalconditionsadvantagesanddisadvantagesdeterminingthefurtherfull-scalecommercialapplication.IntroductionTheintensificationofindustrialactivities,sincethelatterhalfoftheXIXcenturyandthroughouttheXXcentury,hasinevitablycausedsevereenvironmentalpollutionwithdra-maticconsequencesinatmosphere,waters,andsoils.Theconsequentrestrictionsimposedbynewlegislationrequireeffectiveinitiativesforpollutionreduction,notonlyingaseousemissionsandindustrialaqueouseffluentsbutalsoadequatedecontaminationinsoils.Typically,inthecaseofthelatter,differentclassesofpollutantsmayhaveaccumulatedduringlongperiodsofuncontrolledwastedisposalandreclamationmayrepresentaserioustechnologicalproblem.Duetotheextremelydiversefeaturesofpollutionphenomena,universalstrategiesofreclamationhavenotbeenfound.1Generally,wastewatertreatmentiscarriedoutusingprimary,secondaryortertiarymethods,dependingonthenatureofthepollutants.Asfarasorganicpollutantsinwastewatersareconcerned,biologicalabatementmaysometimesbeimpossible,duetothebio-refractorycharacterofthesubstrates.Forthisreason,physical-chemicalmethodsarepreferablyapplied,butanoxidationwithozoneorchlorinedioxideisnotalwayseffectiveandalsotransportationandstorageofreactantsmaybeasignificantinconvenienceforsafeprocessing.2Analternativecanbetheapplicationofelectrochemicaltechnologiesforwastewatertreatment,benefitingfromadvan-tagessuchasversatility,environmentalcompatibilityandDepartmentofChemistry,UniversityofFerrara,viaL.Borsari46,I-44100Ferrara,Italy.E-mail:[e-mail];Fax:[phone]{Electronicsupplementaryinformation(ESI)available:TablesS1andS2:directandindirectanodicoxidationoforganiccompounds(anodematerialslistedinalphabeticalorder).SeeDOI:10.1039/b517632h{GraphicalabstractphotobyDavideSemeraro(Italy),reproducedwithpermission.CarlosA.Martinez-HuitlewasborninMexicoCity,in1977.HegraduatedinchemistryattheUniversidaddelasAme´ricas—Puebla(2000).AfteraworkexperienceinCiba—SpecialtyChemicals,hemovedtotheUniversityofFerrara,Italy(2002),toworkunderthesupervisionofProf.AchilleDeBattisti.Here,heearnedaPhDinchemicalsciences(2005).Duringthesameperiod,heworkedasvisitingscientistinthegroupofProf.ChristosComninellisattheEPFLInstitute,Switzerland.HeisafacultymemberattheUniversityofMilan.Hisresearchinterestsincludeelectro-chemicaloxidation,electrocatalysisandelectroanalysis.SergioFerrowasbornin1972.Hewasawardedhis‘‘Laurea’’inChemistryin1997,andearnedaPhDinChemicalSciencesattheUniversityofFerrarain2001,whereheisnowworkingasaresearchassistant.Authorofabout30papersininternationaljour-nals,co-authorof2bookchap-tersand3patents,hehasreceivedawardsfromnationalandinternationalscientificcommittees.Hisworkdealsmostlywithelectrocatalysis,regardedasanextensionofheterogeneouscatalysis(itsprinciplesandmethods)toelectrochemicalreactions.CarlosA.Martinez-HuitleSergioFerroCRITICALREVIE|ChemicalSocietyReviews1324|Chem.Soc.Rev.,2006,35,1324–1340Thisjournalis
TheRoyalSocietyofChemistry2006Downloadedon26August2010Publishedon10July2006on|doi:10.1039/B517632HViewOnlinepotentialcosteffectivenessamongothersdescribedbelow.2Bothdirectandmediatedelectrochemicaloxidationscanbeconsidered,andhaveprovedtobeinterestingsubjectsfordifferentresearchgroupsandindustriesseekingnewtechnol-ogiesforwastewatertreatment.3Inrecentyears,theapplicationsofelectrochemistryforenvironmentalpollutionabatementhavebeenthoroughlyinvestigated.3,4Thefeasibilityofelectrochemicalconversion/destructionoforganicsubstratesinwastewater,inparticular,hasattractedmuchattentionsincepioneeringstudiesbyDabrowskiinthe70’s,Kirk,Stucki,Kotz,ChettiarandWatkinsoninthe80’s,andComninellisintheearly90’stothepresentday.Inthesestudies,theinfluenceofthenatureoftheelectrodematerialduringtheanodicmineralizationoforganicshasbeenconsideredindetail,showingthatoptimalconditionsfortheprocessinquestionareobtainedathigh-oxygen-overpotentialanodes.Briefly,electrochemicaloxidationisperformedbytheactionofstrongoxidants,similartochemicaldestruction,butthein-situelectro-generationallowsbetterefficiencyoftheabatementoftheorganicsubstrates.Directelectrochemicaldestructionhasbeeninvestigatedwithparticularfocussincetheendoftheeighties,throughthe