Bi25VO40 microcube with step surface for visible light photocatalytic reduction of Cr(VI): Enhanced activity and ultrasound assisted regeneration.

In this study, a kind of bismuth vanadium (Bi25VO40) microcube with step surface was successfully synthesized by a fast and mild hydrothermal method. The reaction time and hydrothermal temperature are the key factors which are accounted for the formation of this unique structure. The as-prepared Bi25VO40 microcube exhibited considerably higher visible light photocatalytic activity compared with the smooth one, revealing that fabrication of Bi25VO40 with step surface was an effective method to improve the photocatalytic activity. The enhanced photocatalytic activity over this Bi25VO40 could be attributed to its enhanced separation efficiency of photo-generated holes and electrons. In addition, the XPS analysis of the Bi25VO40 after photo-reduction showed that most of highly toxic Cr(VI) were reduced into less dangerous Cr(III). The XRD results indicated the reduced Cr(III) existed in the form of Cr2O3 and Cr3O8 on the catalyst surface and occupied the active site, counting for the decreased activity after multiple use. A facile ultrasound treatment facilitated the regeneration of deactivated photocatalyst by removing the adsorbed Cr2O3 and Cr3O8, improving the removal ratio of Cr(VI) over the photocatalyst from 74.0% to 85.6% after four recycling use, which make it applicable for the photocatalytic removal of a typical Cr(VI) pollutant continuously.