Controllable synthesis of Bi4O5Br2 ultrathin nanosheets for photocatalytic removal of ciprofloxacin and mechanism insight

A novel Bi4O5Br2 photocatalyst was prepared via a reactable ionic liquids-assisted solvothermal method accompanied with facile pH control. A Bi4O5Br2 ultrathin nanosheets material with 8 nm thickness could be obtained. The photocatalytic activity of the Bi4O5Br2 ultrathin nanosheets was evaluated with respect to the photo-degradation of colourless antibiotic agent ciprofloxacin (CIP) under visible light irradiation. The results revealed that the Bi-rich Bi4O5Br2 ultrathin nanosheets exhibited higher photocatalytic activity than BiOBr ultrathin nanosheets for the photo-degradation of CIP. The O-2(center dot-) anion was determined to be the main active species for the photo-degradation process by ESR. After multiple characterizations, the variable energy band structure was confirmed to be responsible for the enhanced photocatalytic activity. The more negative conduction band (CB) value of Bi4O5Br2 facilitated the formation of more active species, O-2(center dot-). The upshifting of the CB and the wider valence band favor the higher separation efficiency of electron-hole pairs. It was hoped that this architecture of ultrathin 2D inorganic materials with a suitable band gap can be extended to other systems for high-performance photocatalysis applications.