Study On Hydrogen Production Via Visible-light-driven Water Splitting Over Transition Metal Sulfide （MS_x）/g-C₃N₄ Catalyst And Its Mechanism

Because of the global energy crisis as well as the worsening environmental pollution and greenhouse effect, the exploration to discover new energies, including solar energy, biomass energy and wind power, etc. is imminent. Using direct solar-to-hydrogen conversion by photocatalytic decomposition of water is an ideal way to get new energy. Since Fujishima and Honda discovered the photocatalytic splitting of water on TiO2 electrodes in 1972, photocatalytic water splitting for hydrogen production has been receiving great attention and substantial progress has been made. However, the utilization of solar energy and the quantum efficiency of traditional semiconductor TiO2 are still low, which limits its practical application. Therefore, it is very important to develop the novel photoctalysts with high light utilization rate and quantum yield.Graphite carbon nitride (g-C3N4) is a recently discovered polymer semiconductor as a visible-light-driven catalyst rich in resources, with stable structure and good photocatalytic performance for hydrogen production. It is worthy of further research in the field of photocatalysis. However, pure g-C3N4 has poor hydrogen production kinetics, thus the electrons on the surface of g-C3N4 can not effectively transfer to the reactants. The photocatalytic performance for hydrogen production over g-C3N4 has been improved obviously after loading cocatalyst. Unluckily, the overall efficiency of hydrogen production in g-CsN4 photocatalytic system is still low and the used cocatalysts are mainly composed of at least one noble metal by the noble metal. In this study, we developed new and cheap metal sulfides on the surface of mesoporous graphite carbon nitride (mpg-CN) as cocatalysts.This study mainly includes the following works:(1) On the basis of the structural similarity of both mpg-CN4 and MoS2, the ultra-thin surface junctions (MoS2/mpg-CN) were constructed with an impregnation-sulfidation approach, and the photocatalytic hydrogen production over the obtained catalysts and its mechanism were studied in detail. (2) Since WS2 has similar crystal structure and chemical properties as MoS2, we also investigated the photocatalytic hydrogen production over WS2/mpg-CN. (3) Other transition metal sulfides were also loaded onto mpg-CN with similar approach and the obtained catalyst were applied in the phocatalytic system for hydrogen production under visible light irradiation.The novelties and innovations of this study are as follows:(1) The photocatalytic water splitting performance for hydrogen production over mpg-CN was improved by optimizing the composition of a catalyst and controlling its structure. (2) On the basis of the graphite-like structure of both mpg-CN and M0S2, the ultra-thin surface junctions (MS2/mpg-CN, M=Mo, W) were constructed, and the obtained junctions showed enhanced photocatalytic performances for hydrogen production (3) The abundant and cheap transition metal sulfides instead of precious metals were used as cocatalysts, which would promote the wide applications of photocatalysis.