| As a green and renewable energy,solar energy can be developed as a driving energy for different catalytic reactions,which can solve the increasingly serious problem of resource exhaustion and alleviate the urgent environmental problems.Compared with traditional organic synthesis methods,the reaction conditions of photocatalytic organic synthesis are usually mild,which not only avoids the poor selectivity caused by the harsh conditions of high temperature and pressure in traditional organic synthesis,but also prevents complicated and complicated reaction processes.Photocatalytic organic synthesis technology has become a research direction with great scientific research value.Researching out a new type of highefficiency photocatalytic material is the key of realizing light energy resource utilization.Metal-Organic Framworks(MOFs)is a porous crystalline material with semiconductor-like properties formed by self-assembly of metal ions or metal clusters and organic linkers through coordination bonds.The semiconductor properties of MOFs are due to the organic ligands in the framework that can generate excited state electrons under light radiation and transfer the ability on the framework.Meanwhile,MOFs usually have many advantages such as high specific surface area,controllable framework structure,high density of metal active sites,etc.,making it a photocatalyst with great potential for exploration.In this paper,a vanadium-based MOF material with good stability was prepared and applied to the photocatalytic oxidative coupling of benzylamine and the selective oxidation of thioether.The reaction mechanism of the two systems was further studied.The main research contents of the paper are as follows:(1)The V-MOF is prepared by a hydrothermal method,which could still maintain original structure after being immersed in different solvents for 12 hours.Acceptable thermal stability of BIT-66 is proved by TG/DSC that the temperature tolerance of the framework structure can reach 220 ℃.(2)In the photocatalytic reaction of benzylamine coupled oxidation under visible light irradiation with oxygen as the oxidant,BIT-66 can make the conversion rate of benzylamine reach 85% in 12 h,and it shows a good substrate derivative applicability.Free radical capture experiment results show that superoxide radicals,photogenerated electrons and holes participate in the reaction together.The interaction of photogenerated electrons and holes produces superoxide radical and intermediate state of benzylamine,which reacts with each other to remove a hydrogen peroxide molecule,then combines with a benzylamine substrate molecule,and finally transforms into imine.The signal of superoxide radical in the electron paramagnetic resonance test and the ultraviolet-visible absorption spectrum of hydrogen peroxide indicate the existence of superoxide radical in the system and the generation of hydrogen peroxide during the reaction,which further proves the predicted mechanism.(3)BIT-66 shows good catalytic activity in the selective oxidation of thioethers,and also shows good applicability to thioether derivatives.The experimental results of free radical trapping show that superoxide radical,hydroxyl radicals,photo-generated electrons and holes participate in the reaction.The photo-generated electrons are transferred to tertbutyl hydroperoxide molecules to generate hydroxyl radicals and superoxide radical.Benzyl sulfide is converted into intermediate state by the action of hole,and then the intermediate state reacts with hydroxyl radicals to be converted into product sulfoxide,and if it reacts further,sulfone is produced.The signal of hydroxyl radical andsuperoxide radical signal in the electron paramagnetic resonance test proves the reaction mechanism of the catalytic and selective oxidation of thioether that we speculated. |
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