Influence Of Metal Modified And Semiconductor Coupled Effects On The Photocatalytic Activity For H₂Production From Glycerol Solution Over Cd_1-xZn_xS/SiO₂

In this paper, Cd_1-xZn_xS/SiO₂series coupled semiconductors with differentcomposition and different calcination temperature were prepared by isometricimpregnation, and the metal modified series coupled semiconductorsM/Cd_0.8Zn_0.2S/SiO₂（M=Cu、Ag、Pd） were prepared by impregnation-H2reduction.Their crystal structure, surface compositions, photo-absorption properties wereinvestigated by techniques of XRD，TPR，XPS，UV-Vis. The as-prepared coupledsemiconductors were used as photocatalysts for photocatalytic H2production fromglycerol solution. The effects of CdS/ZnS ratio, thermal treatment, composite andmetals modifidy on the coupled semiconductors’ crystalline phase composition,structure, optical properties, energy levels and photo-activity was discussed.The experiment results of Cd_1-xZn_xS/SiO₂series show that the solid solutions ofCdS and ZnS have formed instead of simply being coupled; Both the compositon andcalcination temperature have great effects on the coupled semiconductors’ structure,amount of solid solution, optical properties, energy levels; Cd_0.8Zn_0.2S/SiO₂calcinatedat450℃have a highest H2production rate of550μmol/h under UV irradiation and210μmol/h under simulated solar irradiation, which can be attribute to the strongcomposite effect of semiconductors, the largest amount of solid solution, and the highlight absorption efficiency.The study results of M/Cd_0.8Zn_0.2S/SiO₂series show the structure of solid solutiondidn’t change after doping metal, and the metal just finely dispersed on the solidsolution, and there is not strong interation between metal and solid solution; After themodification of meatl, the M/Cd_0.8Zn_0.2S/SiO₂series showed better photo-activty onH2production from glycerol and water mixture;0.5wt%Pd/Cd_0.8Zn_0.2S/SiO₂have ahighest H2production rate of2767μmol/h under UV irradiation,5times of that ofCd_0.8Zn_0.2S/SiO₂;611μmol/h under simulated solar irradiation,3t imes of that ofCd_0.8Zn_0.2S/SiO₂; This can be attribute to:1) The better separation of electrons andholes because of the Schottky effect;2) Better light response ablity and more effectiveuse of electrons;3) the improvement of the absorption and activation of water.We have studied the effects of operation conditions on the rates of H2production,and found that the reaction temperature, flow rate of carrier gas, the concentration of glycerol, and the reaction time all have an optimum condition.