Facile synthesis of flower-like CQDs/S-Bi 4 O 5 Br 2 composites as a highly efficient visible-light response photocatalyst for ciprofloxacin degradation

The flower-like CQDs/ S -Bi 4 O 5 Br 2 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 C 10 /S 6 –Bi 4 O 5 Br 2 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 Bi 4 O 5 Br 2 , 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 Bi 4 O 5 Br 2 . Compared to the pure Bi 4 O 5 Br 2 , CQDs/Bi 4 O 5 Br 2 , and S -Bi 4 O 5 Br 2 , 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 C 10 /S 6 –Bi 4 O 5 Br 2 composites. Furthermore, because of the combination of the CQDs and S doped for the Bi 4 O 5 Br 2 composites, the separation efficiency of photo-generated carriers is improved with the recombination rate greatly reduced. Graphical Abstract