Preparation And Photocatalysis Of Polyoxometalates/Semiconductor Composite

How to use solar energy has become a worldwide research to solve the problem of the energy crisis and environmental pollution. It is an important research direction to improve the photocatalytic efficiency of the semiconductor materials. Polyoxometalates ?POMs?, as a kind of good electron acceptor, which can capture photogenerated electrons from the conduction band of the semiconductor to suppress the electron-hole recombination, are able to enhance the photocatalytic and photoconductive performances of the semiconductor. In this paper, we prepared a series of POMs/g-CsN4 and POMs/ZnO composites. POMs/g-C₃N₄ were investigated about their photocatalytic performance to oxide styrene to benzaldehyde and to degrade methyl orange ?MO?. POMs/ZnO were investigated about their photoconductive performances.1. We fabricated the K₃PW₁₂/C₃N₄ composite with K₃PW₁₂O40 and g-C₃N₄ by the direct-precipitating-evaporate treatment method. The K₃PW₁₂/C₃N₄ and g-C₃N₄ were used to photocatalyze the selective oxidation of styrene to benzaldehyde with H2O2 as oxidant at room temperature. It's shown that K₃PW₁₂/C₃N₄ have a higher conversion of styrene and selectivity to benzaldehyde than pure g-C₃N₄.2. The PW₁₂/C₃N₄ and PMo12/C₃N₄ composites were successfully prepared with H3PW₁₂O40, H3PMo12O40 and g-C₃N₄ by the mixing-evaporate treatment method. We investigated their degradation efficiency and also simply explored the photocatalytic mechanism of degradation of MO under visible light. The results show that O2·-radicals are the main active species and h+ species are also responsible for the degradation of MO in current g-C₃N₄-based photocatalytic systems. The PW₁₂/C₃N₄ exhibits the enhanced photocatalytic activity under visible-light irradiation compared with PMo12/C₃N₄ and pristine g-C₃N₄.3. A series of ZnO-PW₁₂ composite thin films with different mass of H3PW₁₂O40 ?0,1 and 10 wt%? were prepared by a facile mixing-heat treatment method. The photoconductive performance of ZnO-PW₁₂ has been explored by photocurrent response measurements. ZnO-PW₁₂?1? exhibits the enhanced photoconductive activity under UV-light irradiation compared with ZnO and ZnO-PW 12?10?. The results show that an appropriate combination of POMs with ZnO could effectively improve the photoconductivity, but an excess of POMs could inhibit the ability of photoconductivity.All in all, these results suggest that the POMs could improve the photocatalytic performance of g-C₃N₄ and enhance light-to-electricity conversion ability of ZnO by effectively suppress electron-hole recombination. The results also show POMs have an broad application prospects in enhancing photocatalytic activity and photoelectric conversion performance of the semiconductor.