Study On Photocatalytic Hydrogen Production Performance And Photo-generated Charge Transport Mechanism In A Novel Transition Metal Sulfide Composite Photocatalyst

As a clean renewable energy source,hydrogen energy has been a research hotspot in the field of the environment.The use of semiconductor photocatalytic water-splitting to produce hydrogen is a promising strategy for solving global energy and environmental problems.However,many catalyst materials have disadvantages such as large band gap and high electron-hole recombination rate,which limit hydrogen production activity.Therefore,we need to improve the separation efficiency of photogenerated electrons and holes in semiconductor materials.The main content of this paper:the modification of the catalyst,the optimization of hydrogen production conditions.Morphology,surface element chemical state,optical properties,physical properties and separation of electrons and holes have been characterized.Finally,the mechanism of electron transfer in hydrogen production is studied.The main work is as follows:1.Study on photocatalytic water-splitting to produce hydrogen system based on sulfur-cobalt compound system by dye sensitization?1?First,oxygen vacancy zinc oxide?ZnO?was prepared,and amorphous CoS_x was loaded on OV-ZnO.The obtained novel composite photocatalyst CoS_x/OV-ZnO has high photocatalytic activity and is increased about 30%compared with CoS_x/ZnO.The morphology,crystal structure,valence state and active sites of the catalyst were studied by SEM,TEM,XRD,XPS and BET.Fluorescence and electrochemistry have analyzed the amorphous CoS_x and oxygen vacancies to improve the separation efficiency of ZnO photo-generated charges.In addition,dye sensitization also extends the absorption range of visible light,so the hydrogen production activity of the system is improved.?2?The Co₃S₄/CuWO₄·2H₂O composite photocatalyst was successfully synthesized by hydrothermal method.The hydrogen production of 20%Co₃S₄/CuWO₄·2H₂O composite photocatalyst was 169?mol and 148.92?mol higher than that of CuWO₄·2H₂O and Co₃S₄,respectively.Through a series of characterizations,it is known that Co₃S₄ provides more active sites for CuWO₄·2H₂O photocatalyst,which is beneficial to the adsorption of dye molecules.The synergistic effect of Co₃S₄/CuWO₄·2H₂O and Co₃S₄ can improve the hydrogen evolution performance.The introduction of Co₃S₄ accelerates the photogenerated electron transfer efficiency and improves the photoelectric characteristics of the semiconductor,that is,promotes the separation efficiency of photogenerated electrons and photogenerated holes,thereby improving the photocatalytic hydrogen production activity.?3?In this system,the catalyst Co₃S₄ was used as a carrier,and Ni₁₂P₅ was successfully loaded on the prepared Co₃S₄ for modification.Ni₁₂P₅/Co₃S₄ composite catalytic materials have high solar energy utilization efficiency,benefiting from the structural advantages of the catalyst and the improvement of light-capturing ability of sensitizing dyes.The close contact interface of Ni₁₂P₅ and Co₃S₄ effectively accelerates the separation and transfer of photogenerated electrons.The optimized Ni₁₂P₅/Co₃S₄ has excellent hydrogen production performance,and its hydrogen production rate reaches 4922.4?mol·g^-1·h^-1,which is 4.8times that of pure Co₃S₄.The above work will provide a strategy for developing a highly efficient and low cost Co₃S₄ based composite photocatalytic system.2.Dye sensitization based on MoS₂ composite material photocatalytic water-splitting hydrogen production systemIn this study,a novel composite photocatalyst MoS₂/NiTiO₃ was synthesized by a simple hydrothermal method.The composite catalyst MoS₂/NiTiO₃ has high dispersibility and high specific surface area,which provides a rich reaction site for hydrogen evolution reaction.The photogenerated electrons of the composite catalyst MoS₂/NiTiO₃ have high transfer efficiency,so the photocatalytic performance of the obtained composite catalyst has great potential.The hydrogen evolution amount of MoS₂/NiTiO₃ was 300.43?mol,which was 5.3 times higher than that of pure NiTiO₃.In addition,the catalyst 7%MoS₂/NiTiO₃ has good photocatalytic stability.We also proposed the charge transfer mechanism of MoS₂/NiTiO₃ composite catalyst.This work provides a cornerstone for the rational construction of NiTiO₃ based composites for photocatalytic hydrogen evolution.