Construction Of A New Type Ⅱ Heterojunction Photocatalyst And Study On Its Hydrogen Production Performance

Nowadays,owing to serious lack of energy and harsh environment,people are looking for new alternative energy materials to solve the current problems.Among them,solar energy and hydrogen energy are attracting much attention.Since hydrogen energy is cheap and available,solar energy can provide light,which are pollution-free renewable energy sources.The photocatalytic hydrogen production technology is using sunlight to drive the splitting of water to obtain clean energy-hydrogen energy,so the energy conversion between solar energy and hydrogen energy can be realized.This technology has unlimited prospects in future energy development.In this thesis,a series of semiconductor-based composite typeⅡheterojunction photocatalysts were prepared,the main research objects were metal sulfide and non-metallic nitride.The separation rate and transfer rate of photocarriers were improved by constructing semiconductor heterojunction interface with excellent performance and good stability,so the hydrogen production performance of photocatalyst was improved.The research content of this thesis mainly includes the following four chapters:1.Bi₂O₃ nanomaterials were synthesized by solvothermal method and calcination method,and then using cadmium acetate and thioacetamide as cadmium source and sulfur source respectively,Cd S nanoparticles with uniform size were synthesized by solvothermal method and loaded on Bi₂O₃ nanoparticles.A series of Bi₂O₃/Cd S typeⅡheterojunction composite photocatalysts with different proportions were prepared.Due to the natural growth of Cd S on Bi₂O₃,the specific surface area was increased and more active sites were generated.Compared with the single semiconductor photocatalyst,these composite photocatalyst materials obviously showed better activity of hydrogen evolution.Through the online hydrogen detection experiment,the composite photocatalyst of 5%Bi₂O₃/Cd S had the best hydrogen production performance.After three hours of detection,the hydrogen production rate reached 2961.2μmol g^-1.2.Firstly,the flower-like ZnIn₂S₄ nanoparticles were synthesized by hydrothermal method,and then the Cd Se nanosheets were prepared by hydrothermal method and coated on ZnIn₂S₄ nanoflowers at a certain ratio,so a series of Cd Se/ZnIn₂S₄ typeⅡheterojunction composite materials were constructed.The core-shell composite photocatalyst had a close contact interface between the two,which accelerated the transfer of photogenerated charge.At the same time,the appropriate band structure was conducive to hydrogen reduction,which could produce more hydrogen.The optimal hydrogen yield of 5%Cd Se/Znln₂S₄ catalyst was 620μmol g^-1 in three hours.The catalyst maintained good stability under continuous illumination for 9 hours,and the final hydrogen yield reached 555.8μmol g^-1.The research provided a new idea for photocatalytic materials based on ZnIn₂S₄ in this chapter.3.Based on the research content of the previous chapter,the photocatalytic materials based on ZnIn₂S₄ were further explored.In this chapter,Mo-W₁₈O₄₉nanostructure was synthesized using WCl₆ and Mo Cl₅ as raw materials,and then the nanostructured ZnIn₂S₄ was prepared by solvothermal method,Mo-W₁₈O₄₉/ZnIn₂S₄typeⅡheterojunction composite structure was formed by in-situ modification of the ZnIn₂S₄ structure with Mo-W₁₈O₄₉.In addition,a series of composite photocatalyst structures were synthesized by adjusting different proportions of the loading capacity.The water splitting test showed that 10%Mo-W₁₈O₄₉/ZnIn₂S₄ had the best hydrogen production performance,the hydrogen production reached 2592.8μmol g^-1.Multiple characterization methods were used to prove that the photocatalyst had high stability and charge separation performance.4.In this chapter,P-doped g-C₃N₄ was synthesized by calcination method,and P-doped g-C₃N₄ was used as the research object to construct Ui O-66-NH₂/P-g-C₃N₄ typeⅡheterojunction structure with Zr-based MOF（Metal Organic Framework）-Ui O-66-NH₂,which promoted the effective separation of charge.Under the excitation of visible light,composite semiconductor nanomaterials showed higher photocatalytic hydrogen production than single semiconductor materials.The cumulative hydrogen production of P-g-C₃N₄ and Ui O-66-NH₂/P-g-C₃N₄ over three hours were 56.2μmol g^-1 and 180.9μmol g^-1,respectively.