Construction And Properties Of Composite Photocatalysts Based On Heterojunction Enhanced Mechanism Tuning

The massive emission of greenhouse gases,environmental pollution,and excessive use of fossil fuels have become common problems facing the world.Photocatalysis is a technological method that can sustainably convert solar energy into chemical energy that can be stored and utilized with extremely low energy consumption.However,shortcomings such as high photo-generated carrier recombination rate and poor utilization of visible light still exist.Selecting suitable semiconductors to construct heterojunctions has been proven to be one of the efficient ways to solve the above problems.In this paper,based on the current theory of photocatalyst heterojunctions,different types of new photocatalysts are constructed and the mechanism of charge transport and separation in photocatalytic reactions is analyzed.The main research contents are as follows:（1）In this chapter,two new organic and inorganic semiconductors,Tp Pa-2-COF and Bi₂O₂S,were selected as raw materials,and the porous ordered framework of Tp Pa-2-COF was grown on Bi₂O₂S nanosheets by in-situ growth method.When the composite ratio of Bi₂O₂S is 15%of that of COF,the highest yield of CO can reach 58.4μmol·g^-1,and that of CH₄can reach 18.6μmol·g^-1.Compared with the monomer Tp Pa-2-COF and Bi₂O₂S,the activity of the composite catalyst was improved by 66.8 and 3.96 times,respectively.The photocatalytic activity enhancement mechanism follows the electron transport mode of the p-n junction,thereby realizing the fast and efficient transport and separation of photogenerated carriers,further improving the stability of the catalyst,and also improving the photocatalytic activity.（2）For the first time,Tp Pa-1-COF organic semiconductor and Ag₃PO₄metal compound semiconductor were selected to form a heterojunction composite photocatalyst.A related characterization project demonstrated the good activity and electron transport efficiency of the composite photocatalyst.Biochemical methods such as TOC and toxicity tests show the characteristics of non-toxic green degradation of the Tp Pa-1-COF/Ag₃PO₄（1:1）composite catalyst.A:C series composite photocatalysts are used in the photocatalytic degradation of organic pollutants"Pymetrozine"and"Rhodamine B".The A:C（1:1）photocatalysts can degrade both pollutants to more than97%.The band structures of Ag₃PO₄and Tp Pa-1-COF provide reasonable conditions for the construction of Z-type heterojunctions.（3）In this chapter,we changed the traditional semiconductor-semiconductor combination to form a heterojunction,and improved it in the form of conductor-semiconductor.On the outer layer of Cd_0.75Zn_0.25S nanorods,a Ni O layer with a uniform thickness of 5-7 nm was formed through multi-step in-situ self-assembly,forming a one-dimensional rod-like core-shell photocatalyst.Defect engineering increases S vacancies on the sulfide surface.The composite material has extremely high charge-hole separation efficiency and strong electron transport ability.The hydrogen yield of CN-0.15 sample can reach 149.1 mmol·g^-1·h^-1.Through the analysis of material work function,energy band structure and density of states,the type of heterojunction is determined to be Schottky junction.