Synthesis And Photocatalytic Properties Of Novel Visible-Light-Driven Photocatalysts

In recent years, application of novel, efficient visible-light induced photocatalysts on solving environmental issues has become one of the most important research areas. In this work, several kinds of visible-light induced photocatalysts, Zn_xCd_1-xS, photocatalysts containing bismuth such as Bi₂MoO₆ and BiOX（X=Br, I） and InVO₄ were synthesized by hydrothermal method or solvothermal method. The prepared samples were characterized by XRD, SEM, TEM, UV-vis DRS, and nitrogen sorption/desorption to investigate the structure, morphology, photocatalytic activity and the photocatalytic mechanism of photocatalysts. The detailed works were summarized as follows.1. A series of monodisperse Zn_xCd_1-xS spheres composed of nanoparticles have been successfully fabricated in high yield by a facile hydrothermal route at a relatively low temperature. The positions of conduction band and valence band for the solid solution of Zn_xCd_1-xS were shifted toward more positive potential and more negative potential with the increase of Cd content, respectively. Among all the prepared samples, Zn_0.4Cd_0.6S exhibited the best photocatayltic activity. According to the information of the valence band and conduction band, the hVB⁺,·OH, HO_<sup>2·, and O_2·^- are regarded as the main active species during the photodegradation of RhB. In addition, we have also synthesized the Zn_xCd_1-xS solid solution via a simple one-pot solvothermal method. It was found that the morphologies of the products show a gradient evolution from hexagon to nanorods with decreasing the molar ratio of Zn/Cd.2. Bi₂MoO₆ nanoplates with different sizes have been controllably fabricated by citric acid （CA） assisted hydrothermal process and the mechanism for CA assisted hydrothermal synthesis of the Bi₂MoO₆ nanoplates is discussed. Moreover, the effect of pH values of the precursors on photocatayltic activity was investigated, the best photocatayltic activity was obtained at pH=3.08.3. Using polyvinylpyrrolidone （PVP） as surface modifier, we present a facile, one-step hydrothermal method for fabricating multilayered flower-like BiOX（X=Br, I） at a relatively low temperature of 120°C. Such three-dimensional （3D） BiOBr assemblies were constructed layer-by-layer from a large number of two-dimensional （2D） nanoplates and PVP plays an important role in the formation of flower-like structure. The morphology of the BiOBr sample can influence significantly on the photocatalytic properties, the BiOBr flowers exhibited higher visible-light photocatalytic activity than that of irregular BiOBr nanoplates due to its higher surface area.4. Self-assembled 3D BiOBr_xI_1-x microspheres composed of nanoplates have been successfully synthesized by a facile solvothermal method.The variation of molar ratio of Br/I leads to changes in their BET surface areas, porous structure, level of valence band and light absorption ability associated with the changes in band gap. It is shown that changes in optical and structural characteristics of BiOBr_xI_1-x solid solutions influence photocatalytic activity. Among all the prepared samples, the as-synthesized BiOBr_0.2I_0.8 microspheres possessed the best photocatalytic activity under visible light irradiation, which is ascribed to their energy band structure, high BET surface area, and porous structure. In addition, the photoinduced holes （hVB⁺） are regarded as the main active species during the photodegradation process based on analysis of the valence band and conduction band.5. InVO₄ was synthesized by hydrothermal method. Fe₂O₃/InVO₄, NiO/InVO₄ and CuO/InVO₄ were synthesized by impregnation method. The photocatalytic reduction of CO₂ experiments showed that the main production was methanol, Fe₂O₃/InVO₄ had the highest photocatalytic activity and the methanol concentration reached 191.45ppm after 8 hours’reaction. Fe₂O₃ and InVO₄ have matching band potentials, photoinduced electrons on the InVO₄ conduction band can transfer to the Fe₂O₃ conduction band, photoinduced holes Fe₂O₃ valence band can transfer to the InVO₄ valence band, which can promote the effective separation of photoinduced electron-hole pairs and enhace the ability to photoreduction CO₂ to yield methanol.