Light-Induced Assembly of Metal Nanoparticles on ZnO Enhances the Generation of Charge Carriers, Reactive Oxygen Species, and Antibacterial Activity

Increasing the photocatalytic activity of semiconductors by forming heterojunctions with metal improves their energy transfer efficiency and environmental remediation capabilities. However, our knowledge regarding the structure-activity relationship of semiconductor/metal hybrid nanostructures is lacking due to poor control over their physicochemical properties. Here, we report a facile way to make ZnO/metal hetero-nanoparticles by the mixing/irradiation process of ZnO and metal nanoparticles. The resultant products provide an expedient model to explore the effects of various metal NPs on light-induced electron/hole separation, reactive oxygen species (ROS) production, and antibacterial activities of ZnO NPs. Electron spin resonance spectroscopy was used to compare the effect of mixing Pt, Au, or Ag NPs at different sizes and concentrations with ZnO NPs on light-induced electron-hole separation and ROS production. The enhancing effect of metal NPs depends on particle size, composition, and mass ratio of the metal NPs to the ZnO NPs. Smaller-sized Pt NPs are more efficient in promoting charge carrier generation and ROS production. At 5 nm, Ag NPs promoted charge carrier generation more efficiently than Pt and Au NPs, but Pt NPs promoted ROS generation more efficiently than Au and Ag NPs. These results provide valuable strategy to design the synthesis of semiconductor/metal hybrid nanostructures and easy tailoring of ROS and charge carrier production.