金属有机骨架材料(MOFs).ppt

Metal OrganicFrameworks TeamMembers CaoChangFuChuXianReporter DuMengYuan PublishedonNatureReviewsMaterials CONTENTS Introduction 1 Metal organicframeworks MOFs areascientificallycompellingandfunctionallyevolvingclassofmeso micro andultramicroporousmaterials MOFstructuresencompassdozensoftopologies includingseveral suchassodaliteandRho thatarealsowellknownforzeolites MOFshavebeenexploredformanyapplicationsincluding butnotlimitedto gasstorageandrelease chemicalseparations drugdelivery catalysis lightharvestingandenergyconversion and recently thedegradationoftoxicsubstancessuchaschemicalwarfareagents MOFsarecomposedofmetalnodesandorganiclinkersthatcanbesystematicallytunedintermsofchemicalcompositionandprecisearrangement anattributethatdiffersfrompurelyinorganiczeolites whichconsistlargelyofsiliconoraluminiumionslinkedbyoxygenatoms Inrecentyears thenumberanddiversityofMOFstructureshavegrownsignificantly andmanywater stableandthermallystableMOFsnowexist Enablinganexcitingexpansionoftheirapplication Dependingontheapplicationenvisaged differentfunctionalstabilitiesareimportant Stabilityofmetal organicframeworks 2 Stabilityisdefinedasresistanceofthestructuretodegradation However anotherpossibledefinitionisthermodynamicinorigin manyfunctionallystableMOFs aswellaszeolites arethermodynamicallyunstablewithrespecttoalternative typically denser polymorphs AnactiveareaofMOFresearchisthedevelopmentofroutestothermodynamicallyunstable butfunctionallystable polymorphs Stabilityofmetal organicframeworks 1 Chemicalstability ThegreatestconcernsfortheimprovementofMOFchemicalstabilityhavebeenlargelyrelatedtoliquidwaterandwatervapour accordingly wefocusonaqueoussolutions InmostMOFstructures thechemicalweakpointsareatthenodes morespecifically themetal linkerbonds withhydrolysisyieldingaprotonatedlinkerandahydroxide orwater ligatednode Acidicsolutionscanacceleratetheformationoftheformer andbasicsolutionscanacceleratetheformationofthelatter AlthoughthereisnostandardmethodforassessingthestabilityofMOFsinacidic basicorneutralsolutions itisoftenjudgedbycomparingthepowderX raydiffraction PXRD patternofaMOFbeforeandaftersoakingitinagivenaqueoussolution Thechemical acid base stabilityofsomerepresentativemetal organicframeworksbasedonliteraturedata ThebarlengthindicatesthepHrangethatthemetal organicframeworks MOFs cantolerate AnarrowindicatesthattheMOFcanwithstandpH14 Selectedsectionsofrepresentativemetal organicframeworkmaterialsa ZIF 8b Cu BTTric MIL 53 Al d MIL 101 Cr e PCN 426 Cr iii f CH3 2NH2 2 Eu6 3 OH 8 1 4 NDC 6 H2O 6 ConnectivityofZr6nodesinzirconium basedmetal organicframeworksandtheassociatedcarboxylatemoleculesrequiredtolinknodestogether 2 Thermalstability ThermaldegradationofMOFsis inmostcases aresultofnode linkerbondbreakage accompaniedorfollowedbylinkercombustion Asaconsequence thermalstabilityisgenerallyrelatedtonode linkerbondstrengthandthenumberoflinkersconnectedtoeachnode Frameworkcatenation morespecifically interpenetrationorinterweavingofnetworks canenhancestabilitythroughfavourableframework frameworkinteractions Thermogravimetricanalysis TGA andinsituPXRDarebothtechniquesthatcanbeusedtogaugethethermalstabilityofMOFs 3 Hydrothermalstability Experimentally hydrothermalstabilityisassessedbyexposingMOFstosteamatvariouspressuresandtemperatures followedbyPXRDanalysisandporosityorsurface areameasurements MOFhydrothermalstabilitycanbeenhancedbyintermolecularorintramolecularforces suchasinternalhydrogenbondingor stacking ZIFsasaclasscompriseexcellentexamplesofhydrophobicMOFs andmanyZIFsarehydrothermallystable makingthemreasonablecandidatesforuseinhumidconditions 4 Mechanicalstability MOFsareknownfortheirextraordinaryporosity anattributethatinherentlydecreasesmechanicalstability Therefore asexpected MOFsarelessmechanicallystablethanzeolites Thisinstabilitycanmanifestitselfasphasechanges partialcollapseofporesorevenamorphization inresponsetomechanicalloading SomearrangementsoflinkersandconnectorsrenderMOFsmoreresistanttodeformationanddestructionthanothers Somecomputationalstudiesshowthatmechanicalstabilitytendstobeenhancedwithshorterlinkers AnimportantpracticaldevelopmentthatgreatlyreducesthemechanicalperformancerequirementsforMOFsinapplications MOFstabilityincatalyticsystems 3 Thecatalyticactivesitecanbeseveraldifferentlocationswithinthestructure ItcanbeincorporatedintheMOFlinkersornodes orencapsulated isolatedorstabilizedbyaMOF orattachedtotheframeworkpostsynthetically Regardlessofthemethodusedtointroducecatalyticallyactivesites theframeworkmustbestableundercatalysisconditions MOFstabilityincatalyticsystems 1 Solution phasecatalysis Thiscanconstituteacidic neutralorbasicconditions Morespecifically theMOFcatalystsneedtobeabletowithstandtheconditionsappropriateforthechosenreaction CatalyticoxidationofwaterusingIr containingderivativesofUiO 67 TheimageshowsthestructureofUiO 67andIr containinglinkers1and2thatareutilizedforwateroxidationcatalysisatpH1 Catalytichydrolysisofthenerveagentsoman knownasGD byNU 1000 2 High temperaturecatalysisofgas phasereactions TheuseofMOFsforgas phasecatalysisisinanearlyphase andmostinvestigationshavefocusedonproof ofconceptreactionssuchastheoxidationofCOtoCO2 WebelievethatthenotionofMOFsasstableanduniformsupportsforsingle sitecatalystsisanespeciallyexcitingone meritingfurtherdevelopment OxidativedehydrogenationofcyclohexenetobenzeneusingV UiO 66asacatalyst Futureperspectives 4 TheextendedmechanicalandchemicalstabilitiesofMOFsinthin filmformarealsoattractivegoals ThesystematicpassivationofstructuraldefectswithinMOFsthatmayotherwisebetargetedasweakpointsforattachment andhencethedegradationofthematerial isanotherapproachthatcouldoffermorestablestructures Insummary MOFs asaclassofp