Visible-light-driven photocatalytic disinfection mechanism of Pb-BiFeO3/rGO photocatalyst

Abstract

While the visible-light-driven photocatalytic disinfection techniques for drinking water have recently attracted tremendous attentions, it is necessary to further improve the solar energy utilization efficiency. In this study, we synthesized Pb-BiFeO3 photocatalysts doped with different amounts of reduced graphene oxide (Pb-BiFeO3/rGO). The photocatalytic disinfection efficiencies toward gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) were evaluated under visible-light irradiation (λ ≥ 400 nm). The results indicated that Pb-BiFeO3 with 0.5 wt% rGO (Pb-BiFeO3/0.5% rGO) exhibited the highest disinfection efficiency. Complete inactivation was reached within 30 min and 90 min for E. coli and S. aureus, respectively. The transcriptomic analysis results indicated that Pb-BiFeO3/0.5% rGO deregulates the genes in E. coli cells that are involved in the cell membrane damage and oxidative stress responses. This was validated by the cell leakage of nucleic acids or proteins, transmission electron microscopy images of the bacteria, and the disinfection efficiency decrease caused by the introduction of scavenger of hydroxyl radical (HO•). Metal ions (Pb2+, Bi2+, and Fe3+) released from the photocatalysts did not contribute to the disinfection process. For the first time, our results elucidated that the photocatalytic disinfection mechanism of Pb-BiFeO3/rGO toward E. coli was mainly associated with oxidative stress due to HO• generation and the loss of membrane integrity from direct contact with the photocatalyst. After four consecutive cycles, the Pb-BiFeO3/0.5% rGO photocatalyst exhibited a strong antibacterial efficiency. The excellent disinfection efficiency and stability of Pb-BiFeO3/0.5% rGO suggests that this photocatalyst shows great potential for drinking water disinfection.