Synergistic antibacterial properties of ZnO–SnO2 composite under both light and dark conditions

Antibacterial performance of photocatalytic materials is limited by their low utilization of visible light, rapid recombination of photocarriers, and dependence on light irradiation. ZnO–SnO2 composite photocatalytic antibacterial materials were synthesized by hydrothermal method with different molar ratios. Results showed that heterojunction structure was formed between ZnO and SnO2, improving lifetime of photocarriers and enhancing photocatalytic antibacterial performance. Meanwhile, dissolution of Zn2+ ensured strong antibacterial effect in the dark. When the addition amount of ZnO in the composite material was 40%, the best antibacterial effect was achieved, with bactericidal rate of Escherichia coli (E. coli) reaching more than 99% after 15 min illumination. Antibacterial mechanism of this photocatalyst was studied by inductively coupled plasma optical emission spectrometry (ICP-OES), electron paramagnetic resonance (EPR), fluorescence spectroscopy, and scavenger experiments. Results demonstrated that Zn2+ and reactive oxygen species (ROS) played vital role in antibacterial process. Moreover, ·OH was the most significant ROS. Compared with single-component photocatalytic antibacterial agents, ZnO–SnO2 composite demonstrated enhanced photocatalytic antibacterial performance as well as improved light utilization through synergistic sterilization effect of Zn2+ ions and enhanced ROS. These results have significant practical value for development of antibacterial photocatalysts.