Enhanced Photocatalytic Properties Of Defect-Engineered Metal-Organic Frameworks

Metal-organic frameworks（MOFs）,as a new class of porous coordination polymers composed of organic ligands and metal nodes,have fascinated remarkable research interest due to their unique porous structure with high porosity,large surface area as well as superior catalytic activity.However,as a photocatalyst,MOF often faces the problems of limited types of MOF with visible light absorption,low photocatalytic efficiency and micropores blocking the transfer of substances.As a type of crystal material,MOF inevitably contains crystal defects in its structure.A large number of studies have shown that it is an effective method to modify the intrinsic properties of the material by controlling defects.Through"defect engineering",defects are introduced into the MOF structure in a targeted way,so as to adjust the absorption range of the MOF spectrum,create carrier migration paths,customize appropriate pore sizes,and improve the photocatalytic efficiency.In this paper,the influence of MOF structure on its photocatalytic efficiency is explored based on the defective MOF photocatalyst.The main results are as follows:1.A series of Ui O-66-NH₂ with hierarchical porosity was prepared from Ui O-66-NH₂ via a straightforward defect-engineering strategy of controlled partial linker thermolysis.The prepared defective Ui O-66-NH₂ was sponge-like with significant mesopores across the nanocrystals,had a wide spectral band of visible light absorption and high efficiency of photogenerated charge separation,and is an ideal candidate for photocatalyst.We used Ui O-66-NH₂ compound as the photocatalyst for the thiol-ene reaction,phenylacetylene and benzyl mercaptan as the model substrate and benzyl styryl sulfide as the target product to explore the photocatalytic properties of the Ui O-66-NH₂ in the reaction under the irradiation of visible light.The photocatalytic experiment showed that defective Ui O-66-NH₂ had better catalytic effect than the Ui O-66-NH₂.It had good universality for thiols and alkynes with different functional groups.The proton-coupled electron transfer mechanism has been confirmed by mechanism research experiments.2.Considering the unique pore structure and undamaged amine groups of photoactive Ui O-66-NH₂,single-site catalyst of Cu@Ui O-66-NH₂ was prepared by anchoring single-site Cu in the pore of MOF through photoreduction method.The photoelectrochemical characterization showed that Cu@Ui O-66-NH₂ exhibited better charge separation efficiency of electron-hole pairs than defective Ui O-66-NH₂.The local structure of the Cu site in defective Ui O-66-NH₂ his studied by X-ray absorption fine structure（XAFS）.The isolated Cu sites in Ui O-66-NH₂ were coordinated to two O atoms and two N atoms,and was positively charged+1 valance.The application of the single-site Cu@Ui O-66-NH₂ was studied for visible-light-induced functionalization of terminal alkynes via either alkylation or oxidation coupling reactions.Both photocatalytic reactions involving single-site Cu catalysis exhibit good efficiency,considerable yield and general compatibility.Mechanistic studies show that the Cu single-site can effectively activate alkynes to initiating these reactions.