Anodized BiOI coatings and their photocatalytic activity of organic dye degradation

•BiOI coatings consisted of flower-like particles were prepared by anodization.•The coatings showed a good photocatalytic activity in the degradation of MB dye.•Band position shift of BiOI made it possible to form superoxide species.••O2 rather than •OH or holes played the key role in MB degradation. Pure tetragonal BiOI coatings of nano-sized flower-like structure were prepared on the substrate of Bismuth foil by anodic oxidation. The combined results of XRD, Raman and SEM show that the BiOI crystal grains with an average size of 23.2nm preferentially grew along crystal face (102) and (110). The thickness of the as-prepared BiOI coatings was estimated to vary from 5 to 10 μm. The great thickness made the substrate of Bismuth foil had no effect on the photocatalytic activity of the BiOI coatings. Although the band gap (1.75 eV) of the anodized BiOI coatings is close to those prepared by other methods, the overall shift of the valence maximum (VBM) and the conduction band minimum (CBM) to a more negative potential position was observed. The shift made the formation of •O2¯ radicals possible. •O2¯ radicals played the key role in the photocatalytic degradation of MB organic dye under visible light irradiation. Meanwhile, photo-generated holes and •OH radicals were also helpful to the photocatalytic reaction. Compared with those prepared by other methods, anodized BiOI coatings showed a higher photocatalytic activity.