Time-dependent synthesis of BiO2-x/Bi composites with efficient visible-light induced photocatalytic activity.

A series of BiO2-x/Bi nanocomposites were prepared via a time-dependent aqueous method, with the induction of lactic acid. The interaction of Bi3+ and C3H6O3 in stock solution determined the formation of nonstoichiometric BiO2-x as the precursor, subsequent reduction reaction at acid circumstance (pH = 3) produced combined composition of BiO2-x nanosheets and Bi particles. Multiple valence states of Bi element (Bi0, Bi3+ and Bi5+) in the composite sample make it possible to manipulate the band structures of photocatalysts. The BiO2-x/Bi composites with appropriate composition exhibited superior photocatalytic performance in the degradation of colorless bisphenol A (BPA) under visible-light irradiation. The O2- and OH radicals were detected as valid active species in the degradation process from ESR analysis. The photocatalytic mechanism over BiO2-x/Bi composites was proposed on the consideration of electron-hole separation and the interfacial charge transfer.