One-Step Coprecipitation Synthesis of BiOClxBr1–x Photocatalysts Decorated with CQDs at Room Temperature with Enhanced Visible-Light Response

BiOCl_xBr_1-x (0 ≤ x ≤ 1) solid solutions were synthesized at room temperature by one-step coprecipitation. Relative proportions of halogens in the anion layer were regulated, and thus, the band gap of BiOCl_xBr_1-x could be adjusted to suitable values to enhance the photocatalytic reaction. BiOCl_xBr_1-x exhibited enhanced visible-light response and higher photocatalytic activity in degrading rhodamine B (RhB) compared with individual BiOCl or BiOBr. Especially, BiOCl_0.5Br_0.5 showed the highest photocatalytic activity. Comparative tests showed that within 36 min the degradation rates of RhB upon BiOBr, BiOCl, and BiOCl_0.5Br_0.5 were 55.66, 24.03, and 94.91%, respectively. BiOCl_0.5Br_0.5 was further decorated with carbon quantum dots (CQDs) to promote the separation of photogenerated charge carriers. The photocatalytic activity was considerably enhanced by moderate doping of CQDs, and the degradation rate of RhB reached nearly 100% within 18 min upon 3CQDs-BiOCl_0.5Br_0.5 (the loading content of CQDs was 0.42 wt %). Active-species-trapping tests confirmed that h⁺ is the primary active species for photocatalytic degradation of RhB, whereas ^•O₂^- and e^- were the secondary ones. The synergistic effects of the band structure adjustment and CQD decoration on the photocatalytic activity were mainly expounded as the enhanced separation of photogenerated charge carriers and optimal redox potentials. In addition, the reuse and service life of the catalysts were analyzed. After five cycles, the photocatalytic activity still remained over 95%.