Photocatalytic Organic Pollutants Degradation in

Photocatalyticorganicpollutantsdegradationinmetal–organicframeworksChong-ChenWang,abJian-RongLi,*bXiu-LiangLv,bYan-QiuZhangcandGuangshengGuo*bEfficientremovaloforganicpollutantsfromwastewaterhasbecomeahotresearchtopicduetoitsecologicalandenvironmentalimportance.Traditionalwatertreatmentmethodssuchasadsorption,coagulation,andmembraneseparationsufferfromhighoperatingcosts,andevengeneratesecondarypollutants.Photocatalysisonsemiconductorcatalysts(TiO2,ZnO,Fe2O3,CdS,GaP,andZnS)hasdemonstratedefficiencyindegradingawiderangeoforganicpollutantsintobiodegradableorlesstoxicorganiccompounds,aswellasinorganicCO2,H2O,NO3
,PO43
,andhalideions.However,thedifficultpost-separation,easyagglomeration,andlowsolarenergyconversionefficiencyoftheseinorganiccatalystslimittheirlargescaleapplications.Exploitationofnewcatalystshasbeenattractinggreatattentionintherelatedresearchcommunities.Inthepasttwodecades,aclassofnewly-developedinorganic–organichybridporousmaterials,namelymetal–organicframeworks(MOFs)hasgeneratedrapiddevelopmentduetotheirversatileapplicationssuchasincatalysisandseparation.Recentresearchhasshowedthatthesematerials,actingascatalysts,arequiteeffectiveinthephotocatalyticdegradationoforganicpollutants.ThisreviewhighlightsresearchprogressintheapplicationofMOFsinthisarea.Thereportedexamplesarecollectedandanalyzed;andthereactionmechanism,theinfluenceofvariousfactorsonthecatalyticperformance,theinvolvedchallenges,andtheprospectarediscussedandestimated.ItisclearthatMOFshaveabrightfutureinphotocatalysisforpollutantdegradation.BroadercontextOnaccountofitsecologicalandenvironmentalimportance,removingorganicpollutantswithhightoxicityandharddegradationpropertiesfromwastewaterhasbeenattractingagreatdealofattentionandbecomingahotresearchtopic.Traditionalmethodssuchasadsorptionandcoagulationusuallysufferfromhighoperatingcostsand,worsestill,generateothersecondarypollutantsintheprocess.Alternately,photocatalyticdegradationhasdemonstratedgreenimplementationandhighefficiency,inwhichphotocatalysisplaysacrucialrole.Metal–organicframeworks(MOFs),aclassofnewly-developedfunctionalmaterials,havegivenrisetorapiddevelopmentintheeldofcatalysis.Anumberofstudieshaveshownthattheyaresuitablematerialsforbeingthepho-tocatalyststhatfunctioninthecatalyticdegradationoforganicpollutants.Inthisreview,wesummarizeresearchadvanceswithregardtothistopic,empha-sizingtherelatedcatalyticreactionmechanisms,factorsthataffectthecatalyticperformances,andchallengesinvolvedinthesestudies.ItisclearthatMOFshaveapromisingfutureinthisregard,andmightbecomeoneofthemostpowerfulphotocatalyststhatcouldhelpgenerateagreenenvironment,therebyhavingasignicantimpactonenvironmentalscience.1.IntroductionIndustrialplantsgenerateincreasingamountsofwastewater,whichoencausessevereenvironmentalproblems.Wastewaterproducedinmanyindustrialprocessesoencontainsorganiccompoundsthataretoxicandnotamenabletodirectbiologicaltreatment.1–4Thereareahugenumberofdifferenttypesoforganicpollutants,includingorganicdyes,phenols,biphenyls,pesticides,fertilizers,hydrocarbons,plasticizers,detergents,oils,greases,pharmaceuticals,proteins,carbohydrates,andsoon.5Eachtypeofpollutanthasalotofvarieties.Takeorganicdyesforexample,therearemorethan100000commerciallyavailabledyes,withover7105tproducedannually.Theseorganicdyesarechemicallystableandnotverybiodegradableinwater,whichmakesthempotentiallyharmfultotheeco-environment.6,7Oneofthegreatestenvironmentalconcernswithorganicdyesistheirabsorptionandreectionofsunlightenteringthewater,whichfurtherinterfereswiththegrowthofbacteriatoalevelsufficienttobiologicallydegradeimpuritiesinthewater.8Organicpollutantsinwastewater,beinghighlytoxicaKeyLaboratoryofUrbanStormwaterSystemandWaterEnvironment(MinistryofEducation),BeijingUniversityofCivilEngineeringandArchitecture,Beijing,100044,ChinabDepartmentofChemistryandChemicalEngineering,CollegeofEnvironmentalandEnergyEngineering,BeijingUniversityofTechnology,Beijing100022,China.E-mail:[e-mail]esponseResearchandEducationCenter,BeijingUniversityofCivilEngineeringandArchitecture,Beijing,100044,ChinaCitethis:EnergyEnviron.Sci.,2014,7,2831Received26thApril2014Accepted6thJune2014DOI:10.1039/c4ee01299b©TheRoyalSocietyofChemistry2014EnergyEnviron.Sci.,2014,7,2831–2867|2831Energy&EnvironmentalScienceREVIEWPublishedon17July2014.Downloadedon13/08/201423:47:13.ViewArticleOnlineViewJournal|ViewIssueanddifficulttodegrade,havebecomeoneofthemostseriousglobalenvironmentalissuestoday.Organicpollutantsoncereleasedintotheaquaticecosystemcancausevariousenvi-ronmentalproblems,suchascloggingsewagetreatmentplants,adverselyaffectingaquaticbiota,andincreasingbiochemicaloxygen.9,10Therefore,aneffectiveandeconomicaltechniqueneedstobedevelopedtoreducetheconcentrationoforganicpollutantsbeforereleasingthewastewaterintotheaquaticenvironment.Currently,industriallyavailablewastewatertreatmenttechnologiessuchasadsorptionandcoagulationmerelyconcentrateorseparatethesepollutantsfromwater,butdoesnotcompletely“eliminate”or“destroy”the