Preparation And Photocatalytic Hydrogen Evolution Of Zn_xCd_1-xS-Based Photocatalysts

Photocatalytic hydrogen evolution as one of the methods for continuable carbon neutralization has received widespread attention.Among various photocatalysts,visible-light induced Zn_xCd_1-xS（ZCS）photocatalyst is widely studied due to its facile synthesis,abundant precursors and suitable band structure position.Nevertheless,the pure ZCS always suffers from low photocatalytic hydrogen evolution rate on account of its high recombination rate of photo-generated charge carriers,low photo-carrier transmission rate and a lack of active sites.In addition,ZCS photocatalyst also has the severe photo-corrosion,which inhibits its stable hydrogen production activity and hinders its development in the field of photocatalytic hydrogen production.Based on that,to promote the rate and stability of photocatalytic hydrogen production,a series of ZCS-based photocatalysts were prepared by loading oxidation catalysts and hydrogen-producing co-catalysts.The effects of electronic effects between the ZCS solid solution and the loaded components on the photogenerated carrier migration and hydrogen production process are systematically studied in this dissertation,which provides theoretical foundation for the construction of efficient and stable ZCS-based photocatalysts.The main contents of this paper are as follows:Using L-Cys capped Mo₂C（L-Mo₂C）nanosheets as the substrate,L-Mo₂C/ZCS heterojunction was constructed by self-assembly method and solvothermal method.Due to the anchoring effect of the L-Mo₂C nanosheets,the accumulation of ZCS solid solution in the solvothermal process is avoided,thus a more dispersed and stable heterojunction is synthesized.Moreover,due to the different work functions of Mo₂C and ZCS,more photogenerated holes are transferred into Mo₂C component.As a result,L-Mo₂C/ZCS heterojunction shows a good stability in the photocatalytic hydrogen production experiment.Under visible-light irradiation,Pt/L-Mo₂C/ZCS heterojunction exhibits an improved photocatalytic hydrogen production efficiency of 34.66 mmol h^-1 g^-1.After cyclic photocatalytic hydrogen evolution experiment for24 h,the hydrogen production rate of Pt/L-Mo₂C/ZCS heterojunction only declines by 10.0%of the initial hydrogen production rate.Polypyrrole-poly（sodium-p-styrenesulfonate）（PPy-PSS）were sectionally wrapped on the surface of ZCS nanorods via redox initiate polymerization to construct PPy-PSS-ZCS（PP-ZCS）heterojunction.Different from the multi-electron transfer channel of PPy-ZCS（P-ZCS）heterojunction,in the optimized PP-ZCS heterojunction,PP and ZCS components respectively act as oxidizing and reducing components,thus more photo-generated holes of ZCS are transferred into PP component.In addition,the optimized PP-ZCS heterojunction enhances the adsorption and the activation process of H₂O as well as the desorption process of hydrogen protons through a strong electronic interaction between PP and ZCS components,thus more hydrogen protons reduced into hydrogen molecules,which achieves effective photocatalytic hydrogen production activity.Consequently,under visible light,the hydrogen production efficiency of Pt/3-PP-ZCS heterojunction reaches 46.10 mmol h^-1 g^-1.After cyclic photocatalytic hydrogen evolution experiment,the hydrogen production rate only declines by 6.2%of the initial hydrogen production rate.In order to further enhance the utilization of photogenerated carriers in ZCS solid solution,through a defect-induced heterojunction constructing strategy,Ni₄Mo alloys were in-situ grown on the unsaturated coordinated sulfur atoms of sulfur vacancies-rich ZCS（Sv-ZCS）.Compared with Ni₄Mo/ZCS heterostructure,Ni₄Mo/Sv-ZCS composite is loaded with more Ni₄Mo nanoparticles and forms a number of Ni-S bonds due to the anchoring effect of Sv-ZCS component.At the same time,the dual built-in electric field of the Ni₄Mo/Sv-ZCS heterojunction cooperates with the Ni-S bonds as"electronic bridge"to further expedite the transfer of photo-carriers,the activation procedure of water molecules and the desorption procedure of hydrogen protons.Accordingly,the optimized Ni₄Mo/Sv-ZCS composite reaches an improved PHE rate of 94.69 mmol h^-1 g^-1,and the apparent quantum yield（AQY）of this composite achieves 18.23%under 420 nm irradiation.In order to further construct a highly active site for hydrogen production activity,Ni Mo P/ZCS（NMP/ZCS）,Ni Mo P/Ni Mo P₂/ZCS（NMPP₂/ZCS）and Ni Mo P₂/ZCS（NMP₂/ZCS）photocatalysts were synthesized by phosphating ZCS nanorods in a high-temperature reducing atmosphere by adding different amounts of red phosphorus.The experimental and theoretical results show that the NMPP₂/ZCS heterojunction accelerates the transfer of photogenerated electrons from the ZCS component to the outermost NMP₂ component through the middle layer of NMP driven by a strong electronic effect.At the same time,under the strong synergy between the NMP and NMP₂ components,the NMPP₂ dual-cocatalyst further promotes the dissociation of water and the desorption of hydrogen protons.Due to the construction of efficient hydrogen production sites and the rapid hydrogen evolution process on the surface of NMPP₂ dual-cocatalyst,under visible light irradiation,the photocatalytic hydrogen evolution rate of 15%NMPP₂/ZCS heterojunction achieves 85.85 mmol h^-1 g^-1,and the AQY of this heterojunction reaches 25.78%under 420 nm irradiation.