Preparation of ZnO Powders with Strong Antibacterial Activity under Dark Conditions

Abstract

Fine ZnO powders have been prepared from plate-like ZnO particles by hydrothermal-treatment in 3 mol/L Zn(NO₃)₂ aqueous solution at 170°C for 7 h (443 K for 25.2 × 10³ s), followed by the heating at 400~700°C for 1 h (673~973 K for 3.6 × 10³ s) in air. They show strong antimicrobial activity in the sunshade; those disinfect many kinds of bacteria even MRSA. The origin of antibacterial activity might be explained in terms of the generation of most powerful reactive oxygen species (ROS) of hydroxyl radical (OH·). As the intensity of chemiluminescence (CL) reflects the amount of ROS, the antibacterial activity has been estimated by measuring the CL emitted from the surface of ZnO in the luminol solution. Both electron spin resonance (ESR) spectroscopy and CL detection were used for identification of ROS. Furthermore, in order to increase the CL values, the ZnO powders have been ball-milled (BM) under the various conditions. It is cleared that the suitable BM conditions, such as BM time and ball size, can improve CL values greatly in comparison with those of ZnO without BM. This effect might be brought by both increasing surface area of ZnO powder and the lattice strain from “Debye effect”.