The Preparation Of Metal Sulfide Based Composite Photocatalysts And Their Photocatalytic Performance

With the exacerbation of the energy crisis and environmental deterioration,human society begins to seek green and sustainable energy to replace fossil energy.Using semiconductor materials to drive water splitting into hydrogen under sunlight is a promising method.Among the studied semiconductor materials,metal sulfide semiconductor materials are regarded as an important photocatalyst because of their suitable band gap and excellent photocatalytic performance in the visible region.However,due to its fast carrier recombination rate and serious photocorrosion,the material has a low utilization rate of light and poor cycling stability,which makes it difficult to efficiently achieve photocatalytic water splitting to hydrogen.Therefore,developing efficient and stable sulfide photocatalysts are still a hotspot.This paper focuses on the modification of cadmium sulfide（Cd S）photocatalytic materials.The main findings are as follows:（1）Construction of CoS/CdS composites and their photocatalytic performance for hydrogen production.The non-precious metal cobalt sulfide（Co S）cocatalyst was deposited onto the Cd S surface to construct composites using a solvothermal method.The fabricated structures were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,UV-visible diffuse-reflectance spectroscopy（UV-vis DRS）,photoluminescence（PL）,time-resolved PL spectra（TRPL）and photoelectrochemical measurements（PEC）.The composites were evaluated as photocatalysts using the hydrogen evolution reaction with lactic acid as a sacrificial agent.The photocatalytic H₂ production rate of the optimized Co S/Cd S sample reached 3193.7μmol·h^-1·g^-1 under visible light,which is 32 times higher than that of pure Cd S.The ohmic heterojunction formed by Co S and Cd S is deduced by DFT calculation,which greatly improves the separation efficiency of photogenerated electron-hole pairs and maintains high oxidation-reduction capacity of photogenerated electron-hole pairs.（2）Construction of CoS/Cd_0.5Zn_0.5S composites and their photocatalytic performance for hydrogen production.Co S/Cd_0.5Zn_0.5S composites were successfully constructed by a two-step solvothermal method.The Co S/Cd_0.5Zn_0.5S composites were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,UV-visible diffuse reflectance spectroscopy（UV-vis）and ultraviolet photoelectron spectroscopy（UPS）.The introduction of Co S can effectively improve the photocatalytic hydrogen evolution activity of Cd_0.5Zn_0.5S,and its content has an impact on the activity of the Co S/Cd_0.5Zn_0.5S composites.The hydrogen evolution rate of the optimized Co S/Cd_0.5Zn_0.5S composite reached 6916.7 mmol·g^-1·h^-1 in 3 vol%lactic acid aqueous solution with an optimal quantum efficiency of 9.32%,which is 5.1 times that of pure Cd_0.5Zn_0.5S.Moreover,the optimized Co S/Cd_0.5Zn_0.5S composite shows good photocatalytic hydrogen production stability.Meanwhile,the ohmic heterojunction is formed by Co S and Cd_0.5Zn_0.5S can effectively transfer and separate the photogenerated electrons and holes,thereby improving the photocatalytic hydrogen production.（3）Construction ofα-NiS-β-NiS/Cd_0.5Zn_0.5S composites and their photocatalytic performance for hydrogen production.Novelα-Ni S-β-Ni S nanosheet modified Cd_0.5Zn_0.5S nanoparticle have been successfully synthesized via a two-step solvothermal method.Theα-Ni S-β-Ni S/Cd_0.5Zn_0.5S composites were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,ultraviolet photoelectron spectroscopy（UPS）and UV-visible diffuse reflectance spectroscopy（UV-vis）.The results show that the morphology and structure ofα-Ni S-β-Ni S are complete.There is an interaction between Cd_0.5Zn_0.5S andα-Ni S-β-Ni S to form schottky heterojunction,which promotes the separation and transfer of photogenerated carriers.Theα-Ni S-β-Ni S/Cd_0.5Zn_0.5S composites demonstrated efficient photocatalytic hydrogen production and excellent stability,with hydrogen production reaching 3113 mmol·g^-1·h^-1 for optimized structures which is approximately 2.9 times higher than that of pure Cd_0.5Zn_0.5S.Moreover,the hydrogen production performance of Ni S/Cd_0.5Zn_0.5S was influenced by the Ni S crystal phase and the H₂ generation rate of the α-NiS-β-NiS/Cd_0.5Zn_0.5S is 1.3 times higher than that of β-NiS/Cd_0.5Zn_0.5S.