Photocatalytic Oxidation Of As（Ⅲ） And Benzyl Alcohol By Bismuth Self-doped Bi₂WO₆(Bi_2.15WO₆) Under Visible Light

In the recent years,photocatalytic technology driven by solar light attracts more attention due to its advantages in energy saving and environmentally friendly properties.Bismuth tungstate（Bi₂WO₆）has been widely investigated in the oxidation of environmental contaminants due to its high photocatalytic activity under visible light.However,to the best of our knowledge,oxidation of environmental contaminants or chemical materials by Bi₂WO₆ under alkaline conditions has been rarely investigated.In this study,bismuth self-doped bismuth tungstate(Bi_2.15WO₆)will be synthesized and used for the oxidation of As（Ⅲ）contaminant and organic matters（benzyl alcohol,cinnamyl alcohol,cyclobutanol and ethyl lactate）under alkaline conditions and visible light.The photocatalytic activities of Bi_2.15WO₆ toward these substrates will be investigated,the reactive oxidative species（ROS）as well as the mechanism involved in the oxidation of As（Ⅲ）will be elucidated,and the conversion yields as well as the oxidation selectivity in the selective oxidation of organic matters will be explored.In Chapter Ⅱ,the photocatalytic activity of Bi_2.15WO₆ in the oxidation of As（Ⅲ）was investigated under alkaline conditions and visible light.The kinetic results show that the oxidation rates of As（Ⅲ）increase with increasing p H values in the Bi_2.15WO₆system,and 20 mg L^-1 As（Ⅲ）was completely oxidized in 20 min at p H 11.6 with the rate constant of(k_obs)3.5×10^-1 mg^0.4 L^-0.4 min^-1.Photoluminescence（PL）and the Mott-Schottky analyses confirm that OH^-promotes the separation and transfer of photogenerated electron-hole pairs over Bi_2.15WO₆,thus facilitating oxidation of As（Ⅲ）.Electron paramagnetic resonance（EPR）analysis and quenching experiments indicate that surface-OOH and/or H₂O₂are indeed the predominant species under alkaline conditions.The F^--pretreatment experiment and the improved production of H₂O₂by H-donators such as glucose and phenol,as well as the analyses of UV-vis diffuse reflectance（DRS）and Raman spectroscopy,further confirm the formation of the-OOH peroxo on the Bi_2.15WO₆ surface under alkaline conditions.Under visible light,dissolved oxygen was transformed to-OOH on the surface via a direct 2e pathway,instead of forming a superoxo intermediate(O₂^·-).Given the high photocatalytic activity toward As（Ⅲ）oxidation,Bi_2.15WO₆ shows a potential in the treatment of As（Ⅲ）wastewater under alkaline conditions.In Chapter Ⅲ,the oxidation of benzyl alcohol by Bi_2.15WO₆ under visible light and alkaline conditions was investigated.Under the optimal conditions(p H 14.0,2 h and 2 g L^-1 Bi_2.15WO₆),100 mg L^-1benzyl alcohol could be completely oxidized to benzaldehyde under visible light within 2 h,with the selectivity of 99.0%toward benzaldehyde,indicating the high photocatalytic selectivity of the Bi_2.15WO₆ system under alkaline conditions.The selective oxidation of cinnamyl alcohol,cyclobutanol and ethyl lactate was also investigated.Although cinnamyl alcohol and cyclobutanol can be selectively oxidized at p H 11.6,ethyl lactate cannot.This study confirms the oxidation activity and selectivity of surface-OOH in the Bi_2.15WO₆system under alkaline condition,and provides important guidance in the oxidation of organic contaminants or selective oxidation of chemical materials for chemical industries.