Study On The Mechanism Of Photocatalytic Oxidation Of Mn(Ⅱ) By Bismuth Tungstate And Anthraquinone Syste

Manganese is an important element in nature,and the biotic and abiotic oxidation of Mn（Ⅱ）in the water environment are important processes in the cycling of many elements.However,the process of oxidation of Mn（Ⅱ）and the formation of Mn（ⅡI/IV）oxides in nature and its reaction mechanism have not been clearly elucidated.By means of kinetic experiments and various characterizations,we investigated catalytic oxidation of Mn（Ⅱ）on the surface of Bi_2+xWO₆(Bi_2.15WO₆)and the mechanism.In addition,we explored the effects of anthraquinone compounds（such as anthraquinone-2-sulfonate）on the redox process of manganese under visible light and homogeneous conditions.In this study,it was find that adsorbed Mn（Ⅱ）on the surface of Bi_2.15WO₆ was oxidized to Mn（ⅡI,IV）oxides rapidly under visible light irradiation,and the ligand-metal charge transfer（LMCT）pathway was involved in the oxidation process.Kinetic results and XPS characterization results showed that the oxidation of Mn（Ⅱ）to Mn（ⅡI/IV）oxides on Bi_2.15WO₆ was accelerated significantly under visible light.The results of FT-IR and Raman characterization showed that Bi（ⅡI）-O-Mn（Ⅱ）surface complexes were formed on the surface of Bi_2.15WO₆.DRS,PL and electrochemical analysis proved that the band gaps of[Bi_2.15WO₆+Mn（Ⅱ）]_dark（E_g=2.72e V）and[Bi_2.15WO₆+Mn（Ⅱ）]_light（E_g=2.53e V）materials were lower than the pure Bi_2.15WO₆（E_g=2.86e V）material,which also indicate that the LMCT pathway has an important contribution to the photocatalytic oxidation of Mn（Ⅱ）.In addition,the inorganic oxidants with strong oxidizing ability(such as Cr₂O₇^2-,NO₃^-or NO₂^-)significantly accelerated the oxidation of Mn（Ⅱ）,which further validated the contribution of the LMCT pathway to the oxidation of Mn（Ⅱ）.Therefore,we consider the LMCT pathway have an important role to Mn（Ⅱ）oxidation on Bi_2.15WO₆ under visible light.This study also find that anthraquinone-2-sulfonate（AQS）have significant impact on redox process of manganese in a homogeneous system under visible light irradiation.The results of kinetic experiments and solid characterization analysis proved that AQS oxidize the dissolved Mn（Ⅱ）in the system to Mn（ⅡI/IV）oxides under visible light irradiation,and then part of the manganese oxides in the system were reduced to Mn（Ⅱ）gradually.Quenching experiments showed that·OH and O₂^·-played certain roles in the oxidation of Mn（Ⅱ）.This result is also of great significance for our understanding of the abiotic oxidation process of manganese and the recycling of manganese elements.