| With the accelerating consumption of fossil fuels and the increasingly severe environmental pollution,promoting the use of clean energy has increasingly become an important engine to drive the economic development of all countries.Due to its high combustion value,low density,zero emission and other advantages,hydrogen has established its"dominant position"in the clean energy family.Photocatalytic water splitting to produce hydrogen is an effective way to convert solar energy to hydrogen energy.Preparation of photocatalytic materials with high efficiency,high stability and low cost is a key step in the hydrogen production from photocatalytic water splitting.Among many photocatalysts,hexagonal Zn In2S4（ZIS）has the characteristics of visible light response,tunable band gap（2.02～2.59 e V）,low preparation cost and environmentally friendliness,which makes it a promising material for photocatalysis.However,the narrow absorption range of visible light and the fast recombination rate of photogenerated electrons and holes lead to the extremely low efficiency of ZIS for photocatalytic hydrogen production.Therefore,it is of great significance to find an effective modification strategy to broaden the range of visible light absorption and inhibit the recombination of the electron/hole pair to improve the photocatalytic hydrogen production of ZIS.This paper explores the modifications of ZIS from two aspects:（1）Sulfur vacancies and nickel dopants were both introduced to enhance the photocatalytic performance of ZIS ultrathin nanosheets.In this paper,a one-step hydrothermal method was used to synthesize ZIS ultrathin nanosheets with sulfur vacancies and nickel dopants.The existence of sulfur vacancies in ZIS ultrathin nanosheets was confirmed by photoelectron spectroscopy and electron quasi-magnetic resonance spectroscopy.The results of ICP,EDS and X-ray diffraction showed that nickel ions had been successfully incorporated into ZIS ultrathin nanosheets.The band structure and Fermi level positions obtained by Mott-Schottky plots,X-ray valence band spectrum and Tauc’s band gap plots analysis indicated that the sulfur vacancies cause the position of the conduction band to move up,and the introduction of nickel dopants makes the Fermi level increase,which helps the electrons in the conduction band improve reducing ability and generate more photogenerated electrons.The results of photocurrent,steady-state fluorescence,fluorescence lifetime and impedance tests showed that sulfur vacancies and nickel dopants can synergically promote carrier separation,inhibit carrier recombination,increase electron transport life and reduce electron transport resistance.Under visible light,the hydrogen production rate of nickel doped ZIS ultrathin nanosheets with rich sulfur vacancies with triethanolamine as sacrificial agent reached 8.91 mmol g-1 h-1,which was about 4.5 and 2.5 times that of ZIS ultrathin nanosheets with poor sulfur vacancies and ZIS ultrathin nanosheets with rich sulfur vacancies without nickle,respectively.（2）Constructing Co9S8@ZIS nanosheet heterojunction composite material to improve the photocatalytic performance.In this paper,Co（CO3）0.35Cl0.20（OH）1.10nanoneedles were synthesized by hydrothermal method,and the effect of heating rate on the uniformity of nanoneedles was explored.Co9S8 nanotubes were prepared by curing Co（CO3）0.35Cl0.20（OH）1.10nanoneedles with Na2S,and the effects of Na2S concentration on the thickness of nanotubes under the condition of complete vulcanization and the thickness of the tube wall on the photocatalytic performance were investigated.0.5 M HCl was used to regulate the p H of the deionized water/glycerol mixture of dispersed Co9S8,and the influence of p H and the moral ratio of Co9S8 on the photocatalytic performance of Co9S8@ZIS was investigated.Under visible light,the hydrogen evolution rate of Co9S8@ZIS with thinner tube wall and Co9S8 component ratio at 15%reached 5.443 mmol g-1 h-1,which is 12.8 times that of pure ZIS when p H=5,and triethanolamine as sacrificial agent. |
