Preparation And Visible-light Photocatalytic Activity Of Some Composite Catalysts

In recent years, the increasingly serious global environmental pollution and energy crisis are threatening the survival of mankind. Photodegradation of organic pollutants and photocatalytic water splitting under visible light are regarded as potentially effective solution to solve the energy shortage and environmental pollution. However, most of the photocatalysts take effect only under UV light irradiation due to their large band gap. So it is important to develop visible light photocatalysts, which will make full use of solar energy. In order to improve the visible light-driven photocatalytic properties of semiconductor photocatalysts, we prepare composite photocatalyst, based on semiconductor photocatalyst with different band gap. The main work is summarized as follows:1. Ag/AgCl microrods, aggregated by nanoparticles with a diameter ranging from 100 nm to 2 μm, were prepared by an ion-exchange reaction at 80 ℃ between Ag2WO4 template and NaCl solution. The existence of metallic Ag species was confirmed by XRD, DRS and XPS measurements. Ag/AgCl microrods showed excellent photocatalytic activity for the degradation of rhodamine B and methylene blue under visible light irradiation. The degradation rate constants of rhodamine B and methylene blue are 0.176 and 0.114 min-1, respectively. The cycling photodegradation experiments suggest that Ag/AgCl microds could be employed as stable plasmonic photocatalysts for the degradation of organic dyes under visible light irradiation.2. Hexagonal plate-like ZnS(en)o.5 precursor is first synthesized via solvothermal reaction in the presence of ethylenediamine and ethanol. Ag2S/ZnS hexagonal plates are then prepared through cation exchange reaction between ZnS(en)o.5 and AgNO3 solution. The synthesized Ag2S/ZnS composite exhibits efficient photocatalytic performance for hydrogen evolution from an aqueous Na2SO3 and Na2S solution without any cocatalysts under visible light irradiation. The content of Ag2S in the Ag2S/ZnS composite plays an important role on the photocatalytic performance, and the highest rate of H2 evolution reaches 199 μmol/g. The visible light-driven photocatalytic activity of Ag2S/ZnS composite hexagonal plates ought to be due to the direct interfacial charge transfer of the Ag2S/ZnS heterojunction.3. Dendritic g-C3N4 is first synthesized by calcination of HNO3 protonated melamine, then CdS nanoparticles are deposited on g-C3N4 to form heterostructure by in situ precipitation-deposition method. The dendritic CdS/g-C3N4 shows a high visible light catalytic performance for hydrogen evolution from aqueous triethanolamine solution, and the cyclic experiments confirm the stability of our photocatalyst. The highest rate of H2 evolution is 1490.9 μmol/h/g, which is 26.8 times that of pure g-C3N4.