Determining the structure-antibacterial properties relationship and bacterial inactivation kinetics in different morphological-controlled ZnO nanoarchitectures for wastewater applications

This study aimed to systematically evaluate and determine the specific roles of reactive oxygen species (ROS) and Zn²⁺ ions in governing the antibacterial properties of different ZnO nanoarchitectures. This could differ greatly on model bacteria under different irradiation conditions and affects on the design and scale-up of ZnO-based photocatalytic system for wastewater applications. Various ZnO nanostructures were synthesized, characterised and systematically evaluated for their antibacterial properties on both Gram-positive and Gram-negative bacteria under dark, UV-light, and simulated solar irradiation conditions. Results showed that the 1D-ZnO nanorods possessed the highest photo-deactivation ability with a 3.5-log reduction for B. subtilis and a 4.2-log reduction for E. coli under UV light conditions. This is precisely linked to the 1D rod-like ZnO nanostructures with a higher exposed polar surface that favours the dissolution kinetics of Zn²⁺ ions. Besides, the surface oxygen vacancies were found to be strongly correlated to the intracellular ROS concentration that imparts bactericidal effect at different extents depending on the ZnO nanostructures used. The photo-deactivation kinetics were found to be best-fitted using the empirical Hom model, as it could represent the non-linear bacterial inactivation kinetics profile with a prolonged tailing characteristic. Finally, the Friedman non-parametric test showed that all experimental datasets for B. subtilis and E. coli surviving cases were significantly different (p-value < 0.05). The post-hoc approach indicated that the Zn²⁺ ions dissolution was the fundamental factor in dictating the antibacterial properties in different ZnO nanostructures.