In-situ sunlight-driven tuning of photo-induced electron-hole generation and separation rates in bismuth oxychlorobromide for highly efficient water decontamination under visible light irradiation

Photocatalytic materials have received great interest due to their capability for remediating environmental pollution especially water pollution. However, the scalable application of the current photocatalytic materials is still limited by their poor visible-light absorption and low separation efficiency of charge carriers. Here, we report in-situ sunlight-driven tuning of photo-induced electron-hole generation and separation rates in bismuth oxychlorobromide (BiOCl_0.8Br_0.2) nanoflowers. It shows photochromic response under 10-minute natural sunlight irradiation changing color from white to black. The characterization reveals the presence of hydroxyl groups on the surface of the pristine BiOCl_0.8Br_0.2 nanoflowers and abundant oxygen vacancies for the sunlight-irradiated BiOCl_0.8Br_0.2 nanoflowers which narrow the bandgap and serve as electron trapping centers, thus effectively enhancing the generation and separation rates of electron-hole pairs. As a result, the sunlight-irradiated BiOCl_0.8Br_0.2 film demonstrates outstanding photocatalytic performance in water purification such as degrading Rhodamine B (RhB) dye under visible light irradiation with 2-fold higher than its pristine state.