金属有机骨架材料.pptx

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1、Published on Nature Reviews Materials第1页/共28页CONTENTSIntroduction1Stability of metalorganic frameworks2MOF stability in catalytic systems3Future perspectives4第2页/共28页Introduction1第3页/共28页Metalorganic frameworks(MOFs)are a scientifically compelling and functionally evolving class of meso-,micro-and u

2、ltramicroporous materials.MOF structures encompass dozens of topologies,including several,such as sodalite and Rho,that are also well known for zeolites.MOFs have been explored for many applications including,but not limited to,gas storage and release,chemical separations,drug delivery,catalysis,lig

3、ht harvesting and energy conversion,and,recently,the degradation of toxic substances such as chemical warfare agents第4页/共28页MOFs are composed of metal nodes and organic linkers that can be systematically tuned in terms of chemical composition and precise arrangement an attribute that differs from pu

4、rely inorganic zeolites,which consist largely of silicon or aluminium ions linked by oxygen atoms.第5页/共28页In recent years,the number and diversity of MOF structures have grown significantly,and many water-stable and thermally stable MOFs now exist,Enabling an exciting expansion of their application.

5、Depending on the application envisaged,different functional stabilities are important.第6页/共28页Stability of metalorganic frameworks2第7页/共28页Stability is defined as resistance of the structure to degradation.However,another possible definition is thermodynamic in origin:many functionally stable MOFs(a

6、s well as zeolites)are thermodynamically unstable with respect to alternative typically,denser polymorphs.An active area of MOF research is the development of routes to thermodynamically unstable,but functionally stable,polymorphs.第8页/共28页Chemical stability12Thermal stability3Hydrothermal stability4

7、Mechanical stabilityStability of metalorganic frameworks第9页/共28页1Chemical stabilityThe greatest concerns for the improvement of MOF chemical stability have been largely related to liquid water and water vapour;accordingly,we focus on aqueous solutions.In most MOF structures,the chemical weak points

8、are at the nodes more specifically,the metallinker bonds with hydrolysis yielding a protonated linker and a hydroxide(or water)ligated node.Acidic solutions can accelerate the formation of the former,and basic solutions can accelerate the formation of the latter.Although there is no standard method

9、for assessing the stability of MOFs in acidic,basic or neutral solutions,it is often judged by comparing the powder X-ray diffraction(PXRD)pattern of a MOF before and after soaking it in a given aqueous solution.第10页/共28页The chemical(acidbase)stability of some representative metalorganic frameworks

10、based on literature data.The bar length indicates the pH range that the metalorganic frameworks(MOFs)can tolerate.An arrow indicates that the MOF can withstand pH14.第11页/共28页Selected sections of representative metalorganic framework materials a|ZIF-8b|Cu-BTTric|MIL-53(Al)d|MIL-101(Cr)e|PCN-426-Cr(ii

11、i)f|(CH3)2NH22 Eu6(3-OH)8(1,4-NDC)6(H2O)6.第12页/共28页Connectivity of Zr6 nodes in zirconium-based metalorganic frameworks and the associated carboxylate molecules required to link nodes together.第13页/共28页2Thermal stabilityThermal degradation of MOFs is,in most cases,a result of nodelinker bond breakag

12、e,accompanied or followed by linker combustion.As a consequence,thermal stability is generally related to nodelinker bond strength and the number of linkers connected to each node.Framework catenation more specifically,interpenetration or interweaving of networks can enhance stability through favour

13、able frameworkframework interactions.Thermogravimetric analysis(TGA)and in situ PXRD are both techniques that can be used to gauge the thermal stability of MOFs.第14页/共28页3Hydrothermal stabilityExperimentally,hydrothermal stability is assessed by exposing MOFs to steam at various pressures and temper

14、atures,followed by PXRD analysis and porosity or surface-area measurements.MOF hydrothermal stability can be enhanced by intermolecular or intramolecular forces,such as internal hydrogen bonding or stacking.ZIFs as a class comprise excellent examples of hydrophobic MOFs,and many ZIFs are hydrotherma

15、lly stable,making them reasonable candidates for use in humid conditions.第15页/共28页4Mechanical stabilityMOFs are known for their extraordinary porosity an attribute that inherently decreases mechanical stability.Therefore,as expected,MOFs are less mechanically stable than zeolites.This instability ca

16、n manifest itself as phase changes,partial collapse of pores or even amorphization,in response to mechanical loading.Some arrangements of linkers and connectors render MOFs more resistant to deformation and destruction than others.Some computational studies show that mechanical stability tends to be

17、 enhanced with shorter linkers.An important practical development that greatly reduces the mechanical performance requirements for MOFs in applications.第16页/共28页MOF stability in catalytic systems3第17页/共28页The catalytic active site can be several different locations within the structure.It can be inc

18、orporated in the MOF linkers or nodes,or encapsulated,isolated or stabilized by a MOF,or attached to the framework postsynthetically.Regardless of the method used to introduce catalytically active sites,the framework must be stable under catalysis conditions.第18页/共28页Solution-phase catalysis12High-t

19、emperature catalysis of gas-phase reactionsMOF stability in catalytic systems第19页/共28页1Solution-phase catalysisThis can constitute acidic,neutral or basic conditions.More specifically,the MOF catalysts need to be able to withstand the conditions appropriate for the chosen reaction.第20页/共28页Catalytic

20、 oxidation of water using Ir-containing derivatives of UiO-67.The image shows the structure of UiO-67 and Ir-containing linkers 1 and 2 that are utilized for water oxidation catalysis at pH 1.第21页/共28页Catalytic hydrolysis of the nerve agent soman(known as GD)by NU-1000第22页/共28页2High-temperature cata

21、lysis of gas-phase reactionsThe use of MOFs for gas-phase catalysis is in an early phase,and most investigations have focused on proof-ofconcept reactions such as the oxidation of CO to CO2.We believe that the notion of MOFs as stable and uniform supports for single-site catalysts is an especially e

22、xciting one,meriting further development.第23页/共28页Oxidative dehydrogenation of cyclohexene to benzene using V-UiO-66 as a catalyst第24页/共28页Future perspectives4第25页/共28页The extended mechanical and chemical stabilities of MOFs in thin-film form are also attractive goals.The systematic passivation of s

23、tructural defects withinMOFs that may otherwise be targeted as weak points forattachment,and hence the degradation of the material,is another approach that could offer more stable structuresIn summary,MOFs,as a class of porous materials,have moved from the realm of usually delicate and usually moist

24、ure sensitive to nearly routinely designable to withstand harsh physical and chemical conditions.This change will no doubt accelerate the exploration and the application of MOFs,in unique ways,to scientifically and technologically significant problems.第26页/共28页Thanks!Thanks!第27页/共28页感谢您的观看。第28页/共28页