Bactericidal mechanism of BiOI–AgI under visible light irradiation

•BiOI–AgI contained strong bactericidal property under visible light irradiation.•h+, O2−, e− and H2O2 were found to play important roles.•e− indirectly kill bacteria through producing O2− and H2O2.•Surface contact between bacteria and BiOI–AgI was necessary for disinfection.•Good potential for repeated use in wide pH and ionic strength range.

The BiOI–AgI nanocomposites were synthesized by a solvothermal process, followed by an in-situ ion exchange reaction. The disinfection activities of BiOI–AgI on model cell type, Gram-negative Escherichia coli (E. coli), were examined under visible light irradiation conditions. BiOI–AgI could completely inactivate 5 × 107 CFU mL−1E. coli cells in 18 min under visible light irradiation (λ ⩾ 400 nm). The bactericidal mechanisms involved in this photocatalytic disinfection process were systematically investigated. Ag+ ions released from the nanocomposites did not contribute to the bactericidal activity of BiOI–AgI. Active species including h+, O2−, e−, and H2O2 generated by BiOI–AgI played important roles in the inactivation of bacteria. Direct contact of bacterial cells and nanoparticles was found to be essential for the disinfection processes. The destruction of cell membrane and emission of cytoplasm directly inactivated the cells. The influence of solution chemistry (pH and ionic strength) on disinfection process was also estimated. Low pH condition was found to be favorable for the inactivation process. High disinfection efficiencies were achieved at a wide range of solution ionic strength (0–1000 mM). The reusability of BiOI–AgI were also determined. BiOI–AgI exhibited strong antibacterial activity toward E. coli even in five consecutively reused cycles. This study indicated that the fabricated BiOI–AgI could be potentially utilized to disinfect bacteria in water (even with high salinity).

Graphical abstractBIOI–AgI nanocomposites contain strong bactericidal efficiency under visible light conditions due to the generation of reactive species.Figure optionsDownload full-size imageDownload as PowerPoint slide