Syntheses,Characterization And Photocatalytic Hydrogen Production Properties Of Covalent Organic Frameworks Composite Catalysts

Covalent Organic Frameworks?COFs?are a new class of crystalline porous polymer formed by organic building blocks linked with covalent bonding.The unique set of features of COFs including their periodic networks,welldefined pores,tunable pore environments,large specific surface areas,good chemical and thermal stability,ability to harvest an extended range of visible-light wavelengths,and charge transfer facilitated by a?-conjugated architecture make them ideal candidates to load or encapsulate functional molecules into their pores or channels to obtain novel composites.In this thesis,our work mainly includes the following two parts:1.The homogeneous photocatalyst anion[Mo₃S₁₃]^2-cluster with high catalytic activity was encapsulated into a two-dimensional cationic EB-COF to obtain a highly efficient,stable and recyclable composite heterogeneous photocatalyst Mo₃S₁₃@EB-COF,which achieved the conversion of homogenous to heterogeneous catalyst.The structure of Mo₃S₁₃@EB-COF was demonstrated by various characterization methods,and the photocatalytic hydrogen evolution of Mo₃S₁₃@EB-COF was evaluated.In this part,the Ru?bpy?₃Cl₂/Mo₃S₁₃@EB-COF/L-Vc photocatalytic hydrogen evolution system was constructed and the experimental conditions of system was optimized.Finally,Mo₃S₁₃@EB-COF has remarkable photocatalytic hydrogen evolution rate of13215?mol g^-1 h^-1.Furthermore,the photocatalytic activity of Mo₃S₁₃@EB-COF remained after 4 hydrogen evolution reaction cycles.The steady-state fluorescence test proved that the photosensitizer was excited by visible light,and then the electrons were transferred to the catalyst by oxidative quenching for the catalytic hydrogen generation reaction.2.The post-modification of self-exfoliated covalent organic nanosheets TpTG-iCON was performed by using the strong coordination between the enriched nitrogen with lone pair electrons and the transition metal copper ions to obtain an efficient,stable and recyclable heterogeneous photocatalyst Cu@TpTG-iCON,which the thin layer structure of iCON exposed more catalytic sites and accelerate electrons in interface transport.The structure,morphology,composition and valence state of Cu@TpTG-iCON were demonstrated by various characterization methods,and the photocatalytic hydrogen evolution of Cu@TpTG-iCON was evaluated.In this part,the Fluorescein/Cu@TpTG-iCON/TEA photocatalytic hydrogen evolution system was constructed and optimized.Finally,Cu@TpTG-iCON has remarkable photocatalytic hydrogen evolution rate of 8484?mol g^-1 h^-1.Furthermore,the photocatalytic activity of Cu@TpTG-iCON remained after three hydrogen evolution reaction cycles.The steady-state fluorescence test proved that the photosensitizer was excited by visible light,and then the electrons were transferred to the catalyst by oxidative quenching for the catalytic hydrogen generation reaction.