Facile synthesis of flower-like CQDs/S-Bi4O5Br2 composites as a highly efficient visible-light response photocatalyst for ciprofloxacin degradation

The flower-like CQDs/S-Bi4O5Br2 composites photocatalyst with high visible-light response is prepared by adjusting bismuth-rich, S-doped, and introducing carbon quantum dots (CQDs) into the bismuth oxybromide (BiOBr). Particularly, the prepared C10/S6–Bi4O5Br2 composite shows the highest degradation efficiency for the ciprofloxacin (CIP) under visible-light irradiation with the apparent rate constants k of 0.03798 min−1, which is 26.3 times and 10.1 times higher than that of BiOBr and Bi4O5Br2, respectively. The sulfur doping leads to the increase of the specific surface area and decreases of the band gap but retains the original flower-like morphology of Bi4O5Br2. Compared to the pure Bi4O5Br2, CQDs/Bi4O5Br2, and S-Bi4O5Br2, the CQDs introduction and S-doping can improve both of the light absorption range and intensity, as well as the charge transfer efficiency for the C10/S6–Bi4O5Br2 composites. Furthermore, because of the combination of the CQDs and S doped for the Bi4O5Br2 composites, the separation efficiency of photo-generated carriers is improved with the recombination rate greatly reduced.Graphical Abstract