Microwave-assisted Synthesis Of Efficient Nanocomposites For Photocatalysis

Semiconductor photocatalysis as a novel and environmentally-friendly technology has attracted considerable attention due to its wide applications such as in the degradation of organic pollutants, reduction of heavy metals, air purification, and hydrogen production. Based on the working mechanism of photocatalysis, the crucial factors for the photocatalytic activity are the adsorption of pollutants, the light absorption and the charge transportation and separation. In the thesis, we explored and synthesized the novel photocatalysts to improve the adsorption of pollutants and the visible light absorption as well as the reduction of electron-hole pair recombination, and the major contents of the thesis is summarized as follows:1. ZnO, Bi2O3and SnO2were fabricated via microwave-assisted method for photocatalysis. ZnO synthesized in5min achieves a highest Cr(VI) removal efficiency of81%under UV light irradiation; Bi2O3synthesized at pH value of7and SnO2QDs synthesized at pH value of5achieve the highest MB degradation rate of76%and90%under visible light irradiation.2. ZnO-Y3Al5O12:Ce3+, ZnO-Y2O2S:Eu3+and ZnO-NaSrBO3:Eu3+composites were synthesized via a microwave-assisted method for visible light photocatalysis. When phosphors are doped into ZnO, they can absorb the high energy photons well and emit the low energy photons, which can be easily absorbed by the dye and thus effectively excite the dye to generate more electron-hole pairs, resulting in the obvious improvement of the self-sensitized degradation of dye. ZnO-Y3Al5O12:Ce3+composite with3wt.%Y3Al5O12:Ce3+, ZnO-Y2O2S:Eu3+composite with0.5wt.%Y2O2S:Eu3+, and ZnO-NaSrBO3:Eu3+composite with1wt.%NaSrBO3:Eu3+achieve the highest MB degradation rate of93%,95%, and97%under visible light irradiation.3. ZnO-reduced grapheme oxide (RGO), TiO2-RGO, ZnO-TiO2-RGO, CdS-RGO, Bi2O3-RGO and ZnO-TiO2-CNTs composites were synthesized via microwave-assisted method and UV-assisted photocatalytic synthesis for photocatalysis. The RGO or CNTs can act as an excellent electron-acceptor/transport material to effectively facilitate the migration of photo-induced electrons and hinder the charge recombination, which is beneficial for the photocatalytic performance. ZnO-graphene composite fabricated by microwave-assisted method and UV-assisted photocatalytic synthesis with1.0wt.%RGO achieve the highest Cr(VI) removal rate of98%and96%under UV light irradiation; TiO2-graphene composite with0.8wt.%RGO, ZnO-TiO2-RGO composite with10wt.%TiO2, and ZnO-TiO2-CNTs composite with3wt.%CNTs achieve the highest Cr(VI) removal rate of91%,99.4%, and90%under UV light irradiation; CdS-graphene composite with1.5wt.%RGO achieves a highest Cr(VI) removal rate of92%under visible light irradiation; Bi2O3-RGO composite with2wt.%RGO achieves a highest MO degradation rate of93%and a MB degradation rate of96%under visible light irradiation.4. Au-TiO2and AU/N-T1O2composites were synthesized via a simple sol-gel method for photocatalysis. In the photocatalysis process, Au can act as excellent electron-acceptor/transport materials to effectively facilitate the migration of photo-induced electrons and hinder the charge recombination, which enhances the photocatalytic performance, while N elements can tune the band gap and extend the photo-response of TiO2into the visible light region. Au-TiO2composite with0.5wt.%Au achieves a highest Cr(VI) reduction rate of91%under UV light irradiation; Au/N-TiO2composite with0.3wt.%Au achieves a highest Cr(VI) reduction rate of90%under visible light irradiation.