New synthesis, characterization and antibacterial properties of porous ZnO and C-ZnO micrometre-sized particles of narrow size distribution

Zinc oxide has photocatalytic properties that make it both a physical UV blocker and an antibacterial agent, thereby contributing to the widespread commercial use of ZnO particles for various dermatological and cosmetic applications. This photocatalytic activity is surface-area dependent: it increases with increasing surface area of the ZnO particles. ZnO nanoparticles are characterized by a large surface area due to their small size. However, the use of ZnO nanoparticles has created health concerns for both consumers and governing bodies due to the risk of penetration of the small nanoparticles through the skin, thereby damaging inner organs. In this study, in order to overcome this safety risk, porous micrometre-sized ZnO and C-ZnO particles of narrow size distribution have been synthesized and characterized. These porous microparticles were prepared by entrapping a ZnO precursor in porous poly(divinylbenzene) template particles, followed by calcination at several temperatures in either an air or inert atmosphere. The effect of the calcination temperature and atmosphere on the particle size, morphology, crystallinity and fluorescence properties of the obtained microparticles has been investigated. The antibacterial activity of the ZnO and C-ZnO microparticles was tested against Staphylococcus aureus and Escherichia coli. The antibacterial activity of the C-ZnO particles was significantly lower than that of the ZnO particles. In addition, the antibacterial activity increased as the surface area of the particles increased and was significantly higher against Staphylococcus aureus compared to Escherichia coli.