Mediation of band structure for BiOBrxI1-x hierarchical microspheres of multiple defects with enhanced visible-light photocatalytic activity

The band edge positions are of vital importance due to their direct effect on the redox reactions occurring at the surface of the samples. Herein, BiOBrxI1-x solid solutions having tunable band structures with multiple defects of oxygen vacancies (OVs), Bi5+ and Bi(3-x)+ have been successfully synthesized by varying the Br/I molar ratios via a simple method at room temperature. Based on the results of the XPS analysis, Bi5+, Bi(3-x)+ and OVs exist on the surface of the samples, which can influence their band structures and further improve the photocatalytic activity for rhodamine B under visible light irradiation (lambda > 420 nm). Furthermore, the locations of the conduction bands (CB) and valence bands (VB) of the samples are investigated by an electrochemical method. It is found that the CB and VB positions of the samples significantly shift up with the decrease in the Br/I molar ratio. The findings of this study not only provide a new insight into the role of defects but also open up a new way for band structure engineering for promoting photocatalytic activity.