Bactericidal activity and mechanisms of BiOBr-AgBr under both dark and visible light irradiation conditions

BiOBr-AgBr hybrid photocatalysts were synthesized via a facile precipitation and in-situ ion exchange method at room temperature. The as-synthesized photocatalysts were well characterized with different techniques. The disinfection activities of BiOBr-AgBr towards model bacterial strain Gram-negative Escherichia coli (E. coli) were tested under both dark and visible light irradiation conditions. 1 × 10⁷ CFU/mL of E. coli cells could be completely inactivated by BiOBr-AgBr with the optimal silver amount (BiOBr-0.5AgBr) in 24 min under visible light irradiation, while 1.5 log CFU/mL decrease of viable cell density was achieved at the same experiment duration under dark condition. Obviously, with the visible light irradiation, the bactericidal efficiency BiOBr-0.5AgBr was significantly enhanced. The subsequent disinfection mechanism analysis showed that Ag⁺ released from BiOBr-0.5AgBr did not contribute to E. coli inactivation, while reactive oxygen species including h⁺, surfaced bounded OH, O₂^-, and H₂O₂ were found to play important roles in the disinfection process. The presence of dissolved O₂ and the direct contact of cells with photocatalysts was found to be essential for the disinfection process. The reactive species induced the destruction of cell membrane, thus led to the death of bacteria. In addition, BiOBr-0.5AgBr exhibited good bactericidal activity within a wide pH range (5-9) and contained effective antibacterial activity even in fifth consecutive reuse cycles.