The {101}-{001} surface heterojunction constructed on polyhedral titanium dioxide (TiO2) nanocrystals has recently been proposed to be favorable for the efficient electron-hole spatial separation due to the preferential accumulation of electron and hole on {101} and {001} facets, respectively. The formed free electron and hole can promote reactive oxygen species (ROS) production, which potentially can be used for inactivation of bacteria. In the present study, a series of truncated octahedral bipyramid TiO2 nanocrystals (T1, T2, T3, and T4) coexposed with {101} and {001} facets were prepared to form various ratios of {101} to {001} facet for optimization of electron-hole spatial separation efficiency. All these polyhedral TiO2 nanocrystals could more significantly produce ROS than spherical TiO2 nanocrystals (Ts), exhibiting the higher antibacterial activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria under simulated sunlight irradiation. Among these polyhedral TiO2 nanocrystals, T3 with a {101}/{001} ratio of 1.78 was found to be the best one showing the highest ROS and the most potent antibacterial performance. Scanning electron microscope images of bacteria displayed that the surface membrane structure of both E. coli and S. aureus bacteria was influenced to different extents by these TiO2 nanocrystals, where T3 caused the most severe membrane damage. The molecular mechanism underlying the high antibacterial activity of TiO2 nanocrystals was ascribed to activation of oxidative stress as evidenced by intracellular ROS production, glutathione depletion, and membrane lipid peroxidation in bacteria. The surface heterojunction as a completely new strategy holds great promise to develop effective antibacterial nanomaterials.
Keywords: ROS production; antibacterial activity; nanocrystals; surface heterojunction; titanium dioxide.