Synthesis And Characterization Of Visible-light-Responsive Coordination Polymers For Photocatalytic Oxidation Of Organics

In recent years,the study of converting sustainable clean solar energy into chemical energy through photocatalytic technology under mild conditions have been made a great progress.It greatly depends on the development and exploration of various types of photocatalysts.Coordination polymer?CP?materials,also referred as metal organic framework?MOF?compounds,serving as a new multifunctional crystalline material exhibits unique photocatalytic performance due to the unique combination of properties,such as their rich chemical composition,tunable structure and predesignable functionality,and the existence of a large number of accessible catalytic sites.Therefore,the design and synthesis of CPs with novel compositions and structures,as well as the exploration of their photocatalytic property,has become one of the hot topics in this field.In this thesis,two novel CPs with different structures and physicochemical properties were successfully constructed by using the ligand of conjugated carboxylic acid with visible-light absorption property to coordinate with different types of metal ions under solvothermal conditions.The synthesized CPs were well studied by single-crystal structure analysis,X-ray diffraction,ultraviolet spectrum,fourier transform infrared spectrum,thermogravimetric characterization techniques.Furthermore,the photocatalytic properties and possible reaction mechanisms for the transformation of simple organic substrates of CPs were also explored.The detailed studies are summarized as follows:1.A new type of CP 1 in the formula of Mn?ADBEB?₂?DMF?₂was synthesized from conjugated dicarboxylic acid ligands and transition metal Mn²⁺ions under solvothermal condition.The crystal structure analysis shows that compound 1 has a one-dimensional chain structure,and there are two kinds of ?-? interactions between the conjugated ligands in the structure,that is,intra-chain and inter-chain interactions.In this case,the compound exhibits a three-dimensional supramolecular structure.Physicochemical property tests show that 1 has good thermal and chemical stability.More importantly,Compound 1 has a broad absorption band in the visible range with the absorption edge at 560 nm.We have studied the use of compound 1 as a visible-light photocatalyst to oxidize different organic amines to synthesize imine products with molecular oxygen as the oxidant.The mechanism studies show that in these photocatalytic systems,superoxide radical(O₂^?-)and singlet oxygen?¹O₂?act together as reactive oxygen species to promote the reaction.2.The conjugated ligand reacts with Pb²⁺ion was used to construct a new type of CP 2 with a formula of Pb?ADBEB??DMA?under solvothermal condition.Crystal structure analysis shows that compound 2 also has a one-dimensional skeleton structure,and there is a ?-? interaction between adjacent organic ligands in the structure.Compound 2 with good chemical stability and visible-light absorption was used as a visible-light photocatalyst to carry out the aerobic oxidation of organic sulfides.The experimental results show that compound 2 can oxidize sulfide into sulfoxide products efficiently and selectively under oxygen atmosphere.Under optimized conditions,compound 2 can convert anisole substrate into methylphenylsulfoxide almost completely.Experiment results also show that the reaction is due to the photoexcited CP energy transfer to the molecular oxygen in the system after being excited by visible light,generating singlet oxygen?¹O₂?which is a highly active oxygen,and then oxidizing sulfide to form sulfoxide.