Dynamic Bromine Vacancy-Mediated Photocatalytic Three-Step Three-Electron Oxygen Reduction to Hydroxyl Radicals

Hydroxyl radicals (•OH), recognized for their strong oxidizing ability, have garnered extensive attention in the field of photocatalysis. However, as a two-dimensional layered material widely employed in the field of environmental photocatalysis, BiOBr is incapable of catalyzing the generation of •OH, severely impeding its efficient degradation of organic pollutants. In this paper, we propose an efficient approach to generate •OH by expanding the spacing between crystal faces. Through the expansion of the {001} crystal face spacing of BiOBr, we synthesized ultrathin BiOBr-3 nanosheets with reduced bond energy of the Bi–Br bond, which favored the precipitation of Br^– and the formation of bromine vacancies (Br_V) under photocatalytic conditions, thereby promoting the efficient activation of molecular oxygen to generate •OH. The mechanism of photocatalytic reduction of molecular oxygen to hydroxyl radicals by three steps and three electrons was elucidated by in situ infrared spectroscopy and free radical probe experiments. Density functional theory calculations indicated that BiOBr-3 containing bromine vacancies significantly reduced the free energy barrier of *OOH, facilitating the formation of H₂O₂ and the reduction to •OH. In comparison to BiOBr without Br_V, BiOBr-3 containing Br_V demonstrated higher photoactivity toward degradation of triazine organic pollutants. The toxicity of the atrazine degradation solution was significantly reduced through the use of the toxicity estimation software tool and quantitative structure–activity relationship-based methods, as well as HepG2 cell viability detection.