Treating waste by waste: Cascade oxidation of Mn(II) and As(III) by PVDF@ Bi2WO6 composite

• Mn(II) was oxidized to amorphous manganese oxide (MnO x ) by PVDF@Bi 2 WO 6 under visible light for the first time. • O 2 − and h + play predominant roles in the visible light-induced formation of MnO x on PVDF@Bi 2 WO 6 . • The newly-generated MnO x on PVDF@Bi 2 WO 6 can transform As(III) to As(V) at pH 3 in the dark. • The cascade oxidation of Mn(II) and As(III) has been realized by PVDF@Bi 2 WO 6 . Polyvinylidene fluoride@Bi 2 WO 6 (PVDF@BWO) composite membranes were constructed to oxidize aqueous Mn(II) and As(III) by combining the BWO photocatalyst with the PVDF matrix material via non-solvent induced phase separation (NIPS) method. Characterization analysis confirmed the successful doping of BWO on PVDF, and the presence of BWO can effectively improve the mechanical properties and surface wettability of the obtained PVDF@BWO composite. Manganese oxides (MnO x ) produced via photocatalytic oxidation of Mn(II) by PVDF@BWO can form a heterostructure (PVDF@BWO-MnO x ), and superoxide and hole were further demonstrated as the main reactive oxidative species. Moreover, the conversion of As(III) (71.2%) in PVDF@BWO-MnO x system in the dark is higher than that (48.4%) in PVDF@BWO-Mn(II) system under visible light, and the removal percent of As(III) in the former system (80.6%) is also superior than that (62.6%) in the latter system. Therefore, the cascade oxidation of Mn(II) and As(III) has been realized by PVDF@BWO, achieving “treating waste by waste”. The present study provides a new avenue for treating reductive pollutants such as Mn(II) and As(III) coexisted in water environment.