Construction Of Metal Sulfide Based Heterojunction Catalysts And Their Performance Of Hydrogen Production By Photolysis Of Water

In recent years,the problems of resource scarcity and environmental degradation have become increasingly serious,and the development of clean and environmentally friendly renewable energy sources has received widespread attention.Among them,hydrogen energy is a renewable clean energy with high energy density and environmental friendliness,and is considered as one of the most promising clean energy sources.Photocatalytic technology based on semiconductors and their derivatives as media can convert inexhaustible solar energy into hydrogen,which is an effective way to achieve sustainable development.Among them,the key to photocatalytic decomposition of water for hydrogen production is to find suitable photocatalytic materials.Metal sulfide semiconductors with suitable band gaps and excellent optoelectronic properties are a hot topic in the field of photocatalytic materials.However,high photogenerated charge complex rates and photocorrosion severely limit their practical applications.Based on this,this thesis takes metal sulfides（ZnIn₂S₄,ReS₂,1T/2H-MoS₂）as the entry point to effectively enhance the light absorption performance,built-in electric field strength and carrier separation rate of photocatalytic materials through defect modulation,crystal phase engineering and heterostructure building strategies.The constitutive relationships between the enhanced decomposing water hydrogen production activity and the interactions between surface defects,charge transfer pathways and heterojunction interfaces are systematically investigated.The main contents and results of this thesis are as follows:（1）Hollow Ce O₂ microspheres were prepared by a template-free method with a mild hydrothermal treatment,and then ZnIn₂S₄ nanoribbons were grown in situ on the surface of Ce O₂ microspheres using an oil bath method,thus constructing Ce O₂@ZnIn₂S₄ S-scheme heterojunctions.The morphological structure,charge transfer and active species produced in the decomposition of water to hydrogen reaction of the composites were systematically investigated.The results show that the best hydrogen production performance of Ce O₂@ZnIn₂S₄ heterojunction is achieved at a Ce O₂ to ZnIn₂S₄ mass ratio of 1 to 7,up to 69μmol/h,which is 11.5 and 4.9 times higher than that of Ce O₂（6μmol/h）and ZnIn₂S₄（14μmol/h）,respectively.The combined effects of multiple light reflections inside the hollow microspheres and the 3D/2D heterojunction structure result in good photolytic water activity as well as stability of Ce O₂@ZnIn₂S₄ composites.（2）S-scheme heterojunctions of ReS₂（S_v-ReS₂）/2H-MoSe₂ rich in S vacancies were prepared using a defect-induced strategy combined with hydrothermal method.Reduced hydrazine hydrate provides a key prerequisite for the generation of coordinated unsaturated S atoms,which enables the in situ growth of 2H-MoSe₂ on the surface of S_v-ReS₂ through Mo-S bonds,and the S vacancies can become traps for electron-hole pairs,thus extending the carrier lifetime.Contact angle measurements combined with density flooding theory（DFT）calculations indicate that the introduction of S vacancies can reduce the adsorption/dissociation energy of the reactant water molecules.The photovoltaic and hydrogen photolysis properties of S_v-ReS₂/2H-MoSe₂ were greatly enhanced,and the maximum hydrogen photolysis rate of S_v-ReS₂/2H-MoSe₂ reached 78.2μmol/h,which is about 5.9,3.2 and 2.5 times higher than that of ReS₂,S_v-ReS₂ and ReS₂/2H-MoSe₂,respectively,and has a better stability.In addition,the S_v-ReS₂/2H-MoSe₂ was further revealed to be an S-scheme heterostructure by energy band structure,radical trapping,ESR measurements combined with DFT calculations.（3）An all-solid tate Z-scheme heterojunction consisting of edge-rich bicrystalline ultrathin 1T/2H-MoS₂ nanosheets and{110}-faceted Ce O₂nanorods was prepared using crystallographic phase engineering combined with hydrothermal method.In which the 2H-semiconductor phase MoS₂ acts as a photosensitizer,while the conductive 1T-metal phase MoS₂ acts as an electron conduction medium in the heterostructure.The composite catalyst was characterized in various ways,and the synergistic effect of each component on the photolytic hydrogen production activity under visible light irradiation was investigated.The contact angle test results showed that the heterojunction possesses better hydrophilicity,which makes it easier for water molecules to adsorb to its surface.The photolytic hydrogen production efficiency of 1T/2H-MoS₂@Ce O₂ under visible light irradiation（288.7μmol）is7.8 and 4.9 times higher than that of pure Ce O₂ nanorods and physical mixtures of the two molecules,respectively.The broadened visible light absorption range,short electron diffusion distance,and abundant Ce³⁺/Ce⁴⁺redox pairs of 1T/2H-MoS₂@Ce O₂ endow the composite photocatalyst with efficient photocatalytic hydrogen production efficiency and cycling stability.These factors give the composite photocatalyst high efficiency and cycling stability for hydrogen production by photolysis of water.In addition,the electron density distribution and adsorption/dissociation ability on the 1T/2H-MoS₂@Ce O₂ heterojunction were explored based on the changes of energy band positions,XPS binding energy combined with DFT calculations,and a reasonable Z-scheme reaction mechanism was proposed.