Excellent antibacterial activities in the dark of ZnO nanoflakes with oxygen vacancies on exposed {2(1)over-bar(1)over-bar0} facets

The rapidly evolving threat of antibiotic resistance around the globe urges materials scientists to find alternative solutions to kill bacteria in the dark when illumination for photocatalyst based antibacterials is not available. Here we show that {2 (1) over bar(1) over bar0}-ZnO exhibits excellent antibacterial activities in the dark against both E. coli and S. aureus, which is attributed to the reactive oxygen species (ROS) generated in the dark. Interestingly, different from the previously reported mechanism involving single ionized oxygen vacancy-mediated O-center dot(2), the oxygen vacancies on the exposed {2 (1) over bar(1) over bar0} facets are able to generate both O-center dot(2)- by single-electron transfer and O-2(2-) by two-electron transfer. This work highlights the oxygen activation on oxygen vacancies for the generation of ROS in the dark and may enlighten the rational design of novel antibacterials in the dark via surface engineering.