Synthesis,Characterization And Photocatalytic Properties Of Visible-Light-Responsive Metal-Organic Frameworks

Metal-organic framework(MOF)has been widely studied and reported due to its diverse composition and structures.In recent years,MOF as photocatalyst has been gradually studied in photochemical conversion.Numerous successful studies have demonstrated that MOF and its composite can achieve highly efficient photocatalytic reaction.However,this research still faces many problems,such as low photogenerated charge separation efficiency and narrow redox potential.Studies have shown that the synthesis of efficient MOF photocatalyst,as well as the development of novel catalytic strategy,are effective solutions to realize efficient photocatalytic reaction.In this paper,a series of novel MOF photocatalysts with excellent photocatalytic properties are synthesized based on photoactive organic ligands.And new catalytic strategy is explored to improve the photocatalytic performance,realize new photocatalytic reactions,and deeply study the reaction mechanism.The main results are as follows:1.A series of isostructural Ln-MOF(Ln = Gd/Eu/Sm)compounds were synthesized using anthracene-based ligand,and the synthesized MOF as photocatalyst is applied for thiol-ene coupling reaction for the first time.Experiments show that MOF can efficiently oxidize thiol to generate thiyl radical to initiate the coupling reaction,in which a small amount of disulfide by-products produced.Further studies show that the introduction of organophosphine catalyst effectively avoids the dimerization of thiyl radical.This strategy exhibits good generality to selectively synthesize thioether.Mechanistic studies show that the synergistic effect of MOF photocatalyst and organophosphine catalyst leads to the selective generation of thioether in this reaction system.This study enriches the types of MOF photocatalyst and photocatalytic reaction.2.A highly stable Zr-MOF photocatalyst was synthesized using amine functionalized anthracene-based ligand,and its photocatalytic property for C-H arylation was investigated.Experiments show that the Zr-MOF can rapidly carry out the cross-coupling reaction of aryldiazonium salt with heterocyclic hydrocarbon.The Zr-MOF photocatalyst exhibits excellent selectivity for all kinds of diazo substrates and heterocyclic hydrocarbons,especially for aryl diazo substrates containing halogen groups,and the carbon-halogen bond in the products remain intact.Mechanistic study shows that the photogenerated electron of MOF reduces the aryldiazonium substrate to generate active radical,which reacts with heterocyclic hydrocarbon to generate C-H arylation product.This study demonstrates the great potential of photoactive MOF for realizing radical-mediated photochemical reaction.3.Considering the interpenetrating structure and uncoordinated amine groups of photoactive Zr-MOF.A single-atom catalyst of Pd-SAC/MOF was prepared by anchoring single-atom Pd on the amine group in MOF through coordination interaction.The prepared Pd-SAC exists as positively charged species in the MOF.Measurenment shows that there is multiple charge transfer between the photoactive MOF and Pd-SAC,hence Pd-SAC undergoes a continuous change of Pd(II)→Pd(I)→Pd(0).The synthesized Pd-SAC/MOF as photocatalyst to carry out the Heck reaction under visible light,result shows that the single-atom catalyst can effectively activate aryl iodid to generate aryl radical,thereby initiating the Heck reaction.Mechanistic studies show that the photocatalytic reaction is different from the traditional Pd-catalyzed thermal reaction.Although the Pd(0)as the catalytically active center,the reaction undergoes radical and carbocation intermediate to generate Heck product.This study demonstrates that photoactive MOF can easily control the electronic state of single-atom catalyst to realize novel photocatalytic reaction.4.A novel Mn-MOF with broad visible-light adsorption was synthesized using anthracene-based tetracarboxylic acid ligand.For the first time,the application of dual-catalytic system composed of MOF photocatalyst and Pd(OAc)2 co-catalyst in the cross-coupling reaction of aryl diazonium salt with olefin was explored.The dual-catalytic system can efficiently generate target products with the advantages of short reaction time,high selectivity,and high yield.And the dual-catalytic system can prepare different cross-coupling products from a variety of substrates.Mechanistic studies show that the MOF photocatalyst reduces diazonium substrate to generate active radical,meanwhile,the interface electrons transfer of MOF generates Pd(0)catalytically active species.The synergistic effect of the two catalysts leads to the efficient cross-coupling reaction.This study demonstrates that developing suitable catalytic strategy can effectively expand the MOF-modulated photocatalytic reaction.5.A series of Zr-MOF with different structural defect were synthesized by acid-regulated "defect engineering".It is found that structural defect in these compounds can effectively tune their photocatalytic properties.Experiments show that the defective Zr-MOF exhibits better photocatalytic performance for CO2 reduction than the defect-free Zr-MOF.Transient spectroscopy and EPR measurements demonstrate that structural defect in Zr-MOF can effectively promote the photogenerated charges separation,thereby enhancing their photocatalytic performance.This study provides experimental data for in-depth understanding the photocatalytic properties of defective MOF.