| The multi-metal sulfide solid solution or composite semiconductor photocatalysts with excellent optical absorption ability and controllable energy band gap have been extensively investigated. Compared with surfactant or polymer assisted hydrothermal or solvothermal method to prepare semiconductor photocatalysts with controllable size and shape, inorganic salt-assisted hydrothermal method is more promising. In this thesis, Zn-In-S, ZnS-CdS composites and ZnS-In2S3-CdS solid solution were synthesized by simple hydrothermal or low temperature water-solution method and their activities for photocatalytic hydrogen evolution are evaluated. The thesis is composed of the following five parts.1. In the absence of template agent and surfactant, Zn-In-S composites were prepared by a NaCl-assisted hydrothermal method. The as-prepared samples were characterized by X-ray diffractometer (XRD), scan electron microscope/energy dispersive spectrometer (SEM/EDS), transmission electron microscope and high-resolution TEM (TEM/HRTEM), BET, UV-Vis absorption spectrometer and inductively coupled plasma-atomic emission spectrometer (ICP-AES). The results show the composition of the products changes with NaCl concentration, including ZnIn2S4, ZnmIn2Sm+3, ZnS and In2S3. When the concentration of NaCl is 0.20 mol L the product is composed of single Znln2S4 The samples are consisted of microspheres and sheet-like grains with marigold-like superstructure. The grain size of the products increases and the specific surface area decreases with an increase of the NaCl concentration. Their photoactivities were evaluated by hydrogen evolution from an aqueous triethanolamine solution under visible light (λ≥420 nm) irradiation.0.50 wt% Pt was deposited on the samples for the photocatalytic hydrogen evolution by in situ photoreduction. The sample obtained in the presence of 0.20 mol L-1 NaCl exhibits the highest activity for hydrogen evolution, ca.4 times as high as that of the sample prepared without NaCl. A possible formation mechanism was discussed.2. The single ZnIn2S4 or Zn-ln-S composites were synthesized by changing hydrothermal treatment parameters in the presence of 0.20 mol L-1 NaCl. The samples obtained under the different treatment conditions, such as the hydrothermal treatment time, the temperature. pH value in the reaction system and different kinds of halogen ions, were characterized by XRD, SEM. UV-Vis DRS and BET. The nanosheets consisting of microspheres grow up and the photoactivities of the products are almost not influenced with increase of hydrothermal treatment time. When hydrothermal temperature reached to 120℃, the prepared sample has the highest photoactivity When the pH value was 3.5 or radius of the added halogen ions was bigger than that of Cl- in the hydrothermal system, the samples are composed of ZnIn2S4 and ZnS and In2S3. The bigger radius of halogen ion is. the higher content of In2S3 in the product i The product obtained with pH 2.1 and 0.20 mol L-1 Cl- exhibits the highest photocatalytic activity for hydrogen evolution.3. The single Znln2S4 or Zn-In-S composites were synthesized at low temperature with assistance of NaCI. The products were characterized by XRD. SEM. TEM/HRTEM, XPS, ICP-AES, BET, UV-Vis absorption spectrometer, and the decomposition of thioacetamide (TAA) at low temperature was investigated. At low temperature, the decomposition rate of TAA influences the composition and morphology and grain size of the products. The composition and size and shape and crystal structure of products change with the NaCl concentration. The obtained samples are marlgold-like microshperes formed by self-organized of nanosheets. The nanosheets grow up and the specific surface area of the samples decreases with the increase of treatment temperature and extension of treatment time. Using the triethanolamine as electron donor and loading 0.10 wt% Pt on the samples by in situ photoreduction. the photocatalytic activity for hydrogen evolution under visible light (λ≥420 nm) of the sample obtained in the presence of 0.50 mol L-1 NaCl is cu. times as high as that of the sample obtained without NaCl. Too high or low treatment temperature is disadvantageous to the hydrogen evolution. The treatment time at low temperature has little effect on hydrogen production. The photocatalyst obtained in the presence of 0.50 mol L-1 NaCl has good stability during 20 h visible light irradiation. The effect of percentage of loaded Pt on photoactivity of the sample was investigated. It is found that the photocatalyst has the highest activity when Pt loaded content is 0.10 wt%; and the photoactivity keeps almost constant when it is beyond 0.10wt%.4. A series of ZnS-CdS composite nanoparticles were synthesized by sulfidizing the binary metal hydroxide precursors at room temperature. The effects of different preparation methods, Zn/Cd molar ratios, and treatment temperatures on the composition and optical absorption property of the obtained samples were investigated. Photocatalytic activity of the samples for hydrogen evolution under visible light (λ≥420 nm) were evaluated from S2-/SO32- solution (electron donor) when 0.50 vvt% Pt was loaded on the samples by in situ photoreduction. The final product is composed of Cd(OH)2 and ZnO and CdS when zinc and cadmium salts was precipitated by NaOH respectively, the two precipitates were mixed and then the mixture was sulfidized by adding Na2S (method 1). However, the product is consisted of a mixture of two sulphide solid solutions, namely a Zn-rich solid solution and a Cd-rich solid solution, when zinc and cadmium salts were simultaneously precipitated by NaOH and then Na2S was added (method 2). The photoactivity of the product obtained by method 2 is 9 times as high as that of the product obtained by method 1. The molar ratio of Zn/Cd is 2:1, the obtained sample has the highest activity and good stability. Increase of reaction temperature is harmful to hydrogen evolution. The sample obtained at room temperature has higher activity.5. ZnS-In2S3-CdS compound photocatalysts were synthesized by hydrothermal method. Effects of different molar ratios of Zn/In/Cd and pH values in hydrothermal system on the composition and optical absorption property of the obtained samples were investigated. Photoactivities of the samples were evaluated by hydrogen evolution under visible light (λ≥420 nm), applying the triethanolamine as the electron donor and loading 0.50 wt% Pt on the samples by in situ photoreduction. When the molar ratio of Zn/ln/Cd is 1:0.5:0.1 and pH value in the hydrothermal system is 1.75, the obtained sample has the highest photoactivity for hydrogen evolution and its stability decreases a little during 10 h irradiation. The effect of loaded Pt content on the photoactivity was investigated, and the sample loaded with 0.50 wt% Pt shows the highest activity for hydrogen evolution, and when the loaded Pt content is beyond 0.50 wt%, it does not basically influence the photoactivity of the sample.
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