Bi_2.15WO₆ And PVDF@Bi_2.15WO₆ Cascade Oxidation Of Mn(Ⅱ) And As(Ⅲ) )Research

Mn（Ⅱ）and As（Ⅲ）pollutants in water pose a great threat to the environment and human health.In this study,the bismuth self-doped bismuth tungstate Bi_2.15WO₆（BWO）will be synthesized and used as the photocatalyst for cascade oxidation of aqueous Mn（Ⅱ）and As（Ⅲ）under visible light.In addition,in view of the shortcomings of easy agglomeration and difficult recycling during photocatalysis process by BWO,PVDF@BWO composite membrane was prepared by nonsolvent induced phase separation method（NIPS）.Our results show that BWO can oxidize Mn（Ⅱ）via abiotic pathways to amorphous manganese oxide（MnO_x）in two steps under visible light[the formed Mn（IV）after exposure to visible light for 4 h was as high as 2.1 mg L^-1at p H 8.9],with Mn（Ⅲ）as an intermediate in the system of BWO-Mn（Ⅱ）.Quenching experiments revealed that O₂^·-and h⁺play predominant roles in the visible light-induced formation of MnO_x on BWO.Subsequently,oxidation of As（Ⅲ）under alkaline conditions was realized by BWO-MnO_xin the dark and the conversion（71.2%）was higher than that（61.7%）obtained in the simultaneous photo-oxidation system of Mn（Ⅱ）and As（Ⅲ）by BWO.The cascade oxidation of Mn（Ⅱ）and As（Ⅲ）by BWO system[Mn（Ⅱ）was first oxidized to MnO_x,and the newly-generated MnO_x can further transform As（Ⅲ）to As（V）]achieved the purpose of treating waste by waste.In order to improve the recyclability of BWO,we prepared PVDF@BWO by NIPS method via coupling of BWO and PVDF matrix material.When the content of BWO was 1.0%,the results showed that PVDF@BWO exhibited the best photocatalytic activity,and the oxidation percentage of As（Ⅲ）was 62.6%after 2 h visible light irradiation.Subsequently,the doping of BWO and formation of MnO_x could effectively improve the mechanical properties and surface wettability of the composite membrane.The results showed that the removal of As（Ⅲ）by PVDF@BWO-MnO_x system in the dark（84.1%）exhibited better reactivity than that（68.3%）obtained in the PVDF@BWO-Mn（Ⅱ）system under visible light irradiation at p H 3.0.In addition,PVDF@BWO-MnO_x can retain 47.8%of the original As（Ⅲ）oxidation activity after repeating four cycles.This study provides new insights for removal of Mn（Ⅱ）and As（Ⅲ）by the method of treating waste by waste via cascade oxidation of aqueous Mn（Ⅱ）and As（Ⅲ）on BWO.