Tuning crystallization and morphology of zinc oxide with polyvinylpyrrolidone: Formation mechanisms and antimicrobial activity.

Zinc oxide (ZnO) particles with different shapes and sizes have been previously reported to possess unique optical, electrical, photocatalytic, and antimicrobial properties. Capping agents are routinely used to control particle morphologies; however, few studies have evaluated the influence of capping agents on the growth kinetics of ZnO particles of different shapes. Herein, we report a simple water-based chemical precipitation method to produce unique bowtie-, flower-, and nest-shaped ZnO particles using zinc nitrate and urea in the presence of polyvinylpyrrolidone (PVP). Three distinct particle morphologies are obtained by adjusting polymer concentration during synthesis. This approach is simple and could enable large-scale production of ZnO particles with diverse shapes. We monitor the morphological evolution of ZnO particles and, at different polymer concentrations, uncover the preferable PVP adsorption onto different ZnO facets that controls the growth directions of ZnO. Previous reports have demonstrated the influence of particle shape on ZnO antibacterial activity. In this study, we show that ZnO particles with these three morphologies exhibit similar bacterial killing efficacy towards Escherichia coli and Staphylococcus aureus. Our detailed mechanistic studies suggest that the antibacterial mechanism of ZnO particles can be attributed to both Zn2+ release and oxidative stress, whereas shape plays only a minor role in the antibacterial activity of ZnO particles.