Preparation And Photocatalytic H₂ Production Activity Of ZnO/ZnS Based Composite Photocatalysts

The rapid development of industry and the abuse of fossil fuels have led to energy crisis and environmental pollution.Photocatalytic water splitting to produce hydrogen is one of the effective ways to alleviate the energy and environmental crisis.ZnO has been widely concerned by researchers because of its high electron mobility and unique band structure.However,the low utilization rate of sunlight and high recombination rate of photogenerated carriers limit the development of pure ZnO in photocatalytic hydrogen production.Based on the above problems,ZnO is selected as the main research object in this paper.The heterojunctions are constructed by different experimental methods,which provide multi-path carriers transfer and improve the photocatalytic activity of ZnO.The structure,absorption capacity and photocatalytic activity of the composite photocatalysts are studied.The transport paths of carriers and the mechanism of the increase of photocatalytic performance are discussed.The details are as follows:?1?ZnO nanowires with a diameter of about 45nm were prepared by solid-state thermal decomposition method.A new core-shell nanowire photocatalyst ZnO/ZnS-X was prepared by two-step sulfuration of ZnO nanowires.The experimental results show that the photocatalytic hydrogen production rate of ZnO/ZnS-0.08 is nearly 680times?0.9522 mmol/h/g?,which is higher than that of pure ZnO.The hydrogen evolution efficiency of ZnO/ZnS-0.08 is significantly improved due to the type II heterostructure,which realizes the efficient transfer of e^-and h⁺.?2?ZnO/ZnS-SnS2 photocatalyst was successfully prepared by hydrothermal loading SnS2 with different quality on ZnO/ZnS-X core-shell nanowire.The ZnO/ZnS-SnS₂ composite photocatalysts were characterized by XRD,SEM,HRTEM and XPS.The results fully confirm the formation of heterojunction between SnS₂micro sphere and ZnO/ZnS-0.08 core-shell nanowire.The experimental results show that 20%ZnO/ZnS-SnS2 has excellent photocatalytic performance,and the hydrogen evolution efficiency is 2.1799 mmol/g/h.The hydrogen production rate of 20%ZnO/ZnS-SnS₂ is about 2.29 times of that of ZnO/ZnS-0.08.This significant improvement can be attributed to the construction of type II heterojunction and ternary heterojunction.A variety of carrier transfer paths are provided,which enable e-to aggregate effectively in ZnO and SnS₂,and h⁺to aggregate in SnS₂,thus achieving the purpose of separating photogenerated carriers.?3?A new semiconductor photocatalyst ZnO/ZnS-Mo S₂ was synthesized by loaded MoS2 on the basis of solid-state thermal decomposition method and ion exchange method.The experimental results show that 10%ZnO/ZnS-Mo S2 has excellent photocatalytic performance?4.411 mmol/g/h?,and the hydrogen production efficiency is much higher than that of pure ZnO?0.00140 mmol/g/h?and ZnO/ZnS-0.08?0.9522 mmol/h/g?.On the one hand,the enhancement of hydrogen production performance of 10%ZnO/ZnS-MoS₂ composite photocatalyst is attributed to the small band gap of MoS2,which effectively prolongs the response of photocatalyst to sunlight.On the other hand,two kinds of interface are constructed in ZnO/ZnS-MoS2,which correspond to type II heterojunction and ternary heterojunction respectively.The formation of two types of heterojunction can effectively promote the separation of photogenerated carriers.