金屬有機(jī)骨架材料(MOFs)（課堂PPT）

Metal–OrganicFrameworks

TeamMembers:CaoChangFuChuXian

Reporter:DuMengYuan1PublishedonNatureReviewsMaterials2CONTENTSIntroduction1Stabilityofmetal–organicframeworks2MOFstabilityincatalyticsystems3Futureperspectives43Introduction14Metal–organicframeworks(MOFs)areascientificallycompellingandfunctionallyevolvingclassofmeso-,micro-andultramicroporousmaterials.MOFstructuresencompassdozensoftopologies,includingseveral,suchassodaliteandRho,thatarealsowellknownforzeolites.MOFshavebeenexploredformanyapplicationsincluding,butnotlimitedto,gasstorageandrelease,chemicalseparations,drugdelivery,catalysis,lightharvestingandenergyconversion,and,recently,thedegradationoftoxicsubstancessuchaschemicalwarfareagents5MOFsarecomposedofmetalnodesandorganiclinkersthatcanbesystematicallytunedintermsofchemicalcompositionandprecisearrangement—anattributethatdiffersfrompurelyinorganiczeolites,whichconsistlargelyofsiliconoraluminiumionslinkedbyoxygenatoms.6Inrecentyears,thenumberanddiversityofMOFstructureshavegrownsignificantly,andmanywater-stableandthermallystableMOFsnowexist,Enablinganexcitingexpansionoftheirapplication.Dependingontheapplicationenvisaged,differentfunctionalstabilitiesareimportant.7Stabilityofmetal–organicframeworks28Stabilityisdefinedasresistanceofthestructuretodegradation.However,anotherpossibledefinitionisthermodynamicinorigin:manyfunctionallystableMOFs(aswellaszeolites)arethermodynamicallyunstablewithrespecttoalternative—typically,denser—polymorphs.AnactiveareaofMOFresearchisthedevelopmentofroutestothermodynamicallyunstable,butfunctionallystable,polymorphs.9Chemicalstability12Thermalstability3Hydrothermalstability4MechanicalstabilityStabilityofmetal–organicframeworks101ChemicalstabilityThegreatestconcernsfortheimprovementofMOFchemicalstabilityhavebeenlargelyrelatedtoliquidwaterandwatervapour;accordingly,wefocusonaqueoussolutions.InmostMOFstructures,thechemicalweakpointsareatthenodes—morespecifically,themetal–linkerbonds—withhydrolysisyieldingaprotonatedlinkerandahydroxide(orwater)ligatednode.Acidicsolutionscanacceleratetheformationoftheformer,andbasicsolutionscanacceleratetheformationofthelatter.AlthoughthereisnostandardmethodforassessingthestabilityofMOFsinacidic,basicorneutralsolutions,itisoftenjudgedbycomparingthepowderX-raydiffraction(PXRD)patternofaMOFbeforeandaftersoakingitinagivenaqueoussolution.11Thechemical(acid–base)stabilityofsomerepresentativemetal–organicframeworksbasedonliteraturedata.ThebarlengthindicatesthepHrangethatthemetal–organicframeworks(MOFs)cantolerate.AnarrowindicatesthattheMOFcanwithstandpH<0orpH>14.

12Selectedsectionsofrepresentativemetal–organicframeworkmaterials

a|ZIF-8b|Cu-BTTric|MIL-53(Al)d|MIL-101(Cr)e|PCN-426-Cr(iii)f|[(CH3)2NH2]2[Eu6(μ3-OH)8(1,4-NDC)6(H2O)6].13ConnectivityofZr6nodesinzirconium-basedmetal–organicframeworksandtheassociatedcarboxylatemoleculesrequiredtolinknodestogether.142ThermalstabilityThermaldegradationofMOFsis,inmostcases,aresultofnode–linkerbondbreakage,accompaniedorfollowedbylinkercombustion.Asaconsequence,thermalstabilityisgenerallyrelatedtonode–linkerbondstrengthandthenumberoflinkersconnectedtoeachnode.Frameworkcatenation—morespecifically,interpenetrationorinterweavingofnetworks—canenhancestabilitythroughfavourableframework–frameworkinteractions.Thermogravimetricanalysis(TGA)andinsituPXRDarebothtechniquesthatcanbeusedtogaugethethermalstabilityofMOFs.153HydrothermalstabilityExperimentally,hydrothermalstabilityisassessedbyexposingMOFstosteamatvariouspressuresandtemperatures,followedbyPXRDanalysisandporosityorsurface-areameasurements.MOFhydrothermalstabilitycanbeenhancedbyintermolecularorintramolecularforces,suchasinternalhydrogenbondingorπstacking.ZIFsasaclasscompriseexcellentexamplesofhydrophobicMOFs,andmanyZIFsarehydrothermallystable,makingthemreasonablecandidatesforuseinhumidconditions.164MechanicalstabilityMOFsareknownfortheirextraordinaryporosity—anattributethatinherentlydecreasesmechanicalstability.Therefore,asexpected,MOFsarelessmechanicallystablethanzeolites.Thisinstabilitycanmanifestitselfasphasechanges,partialcollapseofporesorevenamorphization,inresponsetomechanicalloading.SomearrangementsoflinkersandconnectorsrenderMOFsmoreresistanttodeformationanddestructionthanothers.Somecomputationalstudiesshowthatmechanicalstabilitytendstobeenhancedwithshorterlinkers.AnimportantpracticaldevelopmentthatgreatlyreducesthemechanicalperformancerequirementsforMOFsinapplications.17MOFstabilityincatalyticsystems318Thecatalyticactivesitecanbeseveraldifferentlocationswithinthestructure.ItcanbeincorporatedintheMOFlinkersornodes,orencapsulated,isolatedorstabilizedbyaMOF,orattachedtotheframeworkpostsynthetically.Regardlessofthemethodusedtointroducecatalyticallyactivesites,theframeworkmustbestableundercatalysisconditions.19Solution-phasecatalysis12High-temperaturecatalysisofgas-phasereactionsMOFstabilityincatalyticsystems201Solution-phasecatalysisThiscanconstituteacidic,neutralorbasicconditions.Morespecifically,theMOFcatalystsneedtobeabletowithstandtheconditionsappropriateforthechosenreaction.21CatalyticoxidationofwaterusingIr-containingderivativesofUiO-67.TheimageshowsthestructureofUiO-67andIr-containinglinkers1and2thatareutilizedforwateroxidationcatalysisatpH1.22Catalytichydrolysisofthenerveagentsoman(knownasGD)byNU-1000232High-temperaturecatalysisofgas-phasereactionsTheuseofMOFsforgas-phasecatalysisisinanearlyphase,andmostinvestigationshavefocusedonproof-ofconceptreactionssuchastheoxidationofCOtoCO2.WebelievethatthenotionofMOFsasstableanduniformsupportsforsingle-sitecatalystsisanespeciallyexcitingone,meritingfurtherdevelopment.24OxidativedehydrogenationofcyclohexenetobenzeneusingV-UiO-66asacatal