Metal/Covalent Organic Framework-based Composites And Their Photocatalytic Hydrolysis Performance

Nowadays,energy and environmental problems are in urgent need of improvement,and photocatalytic hydrolysis has been called the most promising energy technology in recent years.In photoelectrochemical catalysis（PEC）or pure photocatalytic（PC）systems,Bi VO₄and nitrogen carbide（C₃N₄）have been highly favored by scientists as conventional semiconductor photocatalysts with excellent properties.However,their inherent defects such as high electron-hole complexation and poor interfacial kinetics have caused poor hydrolysis performance in practical applications.Metal/covalent organic frameworks have received much attention because of their large specific surface area,tunable chemical structure and good chemical stability,which can compensate for the shortcomings of conventional semiconductor photocatalysts.In this thesis,the photocatalytic carrier separation efficiency and enhanced interfacial interactions of Bi VO₄ and C₃N₄ were improved by constructing heterojunctions with in situ loaded metal/covalent organic frameworks.The details of the study are as follows:（1）Bi VO₄/Fe Co-LDH/Co-MOF ternary composite photoanodes were successfully prepared by electrodeposition and immersion in situ growth method,and their PEC hydrolysis performance was investigated.The experiments show that Bi VO₄/Fe Co-LDH/Co-MOF possesses a relatively excellent photocurrent density of 5.15 m A cm^-2（1.23 Vs.RHE）,the loading of Co-MOF improves the charge-hole separation efficiency,and the introduction of Fe Co-LDH increases not only the stability of Co-MOF in the reaction system,which also avoids the too rapid photocorrosion of Bi VO₄,thus exhibiting a higher activity of PEC.The actual H2 production was 112.75μmol and the actual O₂ production was 57.41μmol after 3 h of photodegradation water reaction,and the Faraday efficiencies were about 95%and 91%,respectively.Finally,the reaction mechanism was inferred from the characterization results,which confirmed that the Co-MOF and Fe Co-LDH on the Bi VO₄ surface enhanced the PEC hydrolysis performance by providing charge-hole transfer pathways,increasing the light absorption,and increasing the specific surface area of the chemical reaction.（2）Amino-rich graphitic nitrogen carbides were synthesized,which increased their dispersion in water and amino content,providing a design solution for further modification of COF.In the subsequent synthesis,the higher amount of amino groups provided more reaction sites for aldehyde amine condensation.COF-Tp Pa（hereafter referred to as TU-X）was successfully grown in situ on amino-rich graphitic nitrogen carbide（g-C₃N₄-NH₂）by a one-pot method,and the TU-X catalyzed water-resolving hydrogen performance was investigated.It can be concluded that TU-3 exhibits the best water-resolving hydrogen performance with the best hydrogen precipitation rate reaching 10.15 mmo L h^-1g^-1,which is nearly one hundred times higher than that of g-C₃N₄-NH₂.It can be inferred from the characterization of the interfacial charge transfer behavior that the excellent hydrogen precipitation performance is attributed to the increased charge transfer through the type II heterostructure connected by covalent bonds,which forms an effective pathway for electron-hole separation and retains a stronger redox capacity.