Post-illumination activity of Bi₂WO₆ in the dark from the photocatalytic "memory" effect

Photocatalysts with the photocatalytic "memory" effect could resolve the intrinsic activity loss of traditional photocatalysts when the light illumination is turned off. Due to the dual requirements of light absorption and energy storage/release functions, most previously reported photocatalysts with the photocatalytic "memory" effect were composite photocatalysts of two phase components, which may lose their performance due to gradually deteriorated interface conditions during their applications. In this work, a simple solvothermal process was developed to synthesize Bi₂WO₆ microspheres constructed by aggregated nanoflakes. The pure phase Bi₂WO₆ was found to possess the photocatalytic "memory" effect through the trapping and release of photogenerated electrons by the reversible chemical state change of W component in the (WO₄)^2- layers. When the illumination was switched off, Bi₂WO₆ microspheres continuously produced H₂O₂ in the dark as those trapped photogenerated electrons were gradually released to react with O₂ through the two-electron O₂ reduction process, resulting in the continuous disinfection of Escherichia coli bacteria in the dark through the photocatalytic "memory" effect. No deterioration of their cycling H₂O₂ production performance in the dark was observed, which verified their stable photocatalytic "memory" effect.