Effect of CaO Doping on Antibacterial Activity of ZnO Powders

Abstract

Effect of doping amount of CaO on the antibacterial activity of ZnO powders was studied by conductance method and colony count method under the condition of enabling and not enabling bacterial growth, respectively. ZnO-CaO solid solution powders when CaO was added in a molar ratio (CaO/ZnO)<10mol%, ZnO-CaO solid-solution powders were synthesized by heating at 1400°C for 6h in air, but ratios>10mol% resulted in a residual CaO phase in addition to ZnO-CaO solid solution. After milling the powders by planetary ball mill, the average particle size of the obtained powders was 0.5μm and used in the test of growth-inhibition of bacteria. Evaluation by the conductance method revealed that the increase of CaO in ZnO-CaO powders resulted in a decrease of the growth inhibitory effect against Escherichia coli and Staphylococcus aureus. In addition, the inhibitory effect against S. aureus was found to be stronger than that against E. coli in ZnO-CaO powder slurries. On the other hand, in the case of the colony count method, the killing effect of ZnO-CaO powders on S. aureus markedly increased with increasing the excess CaO in ZnO-CaO powders, i.e., the deposition of CaO from ZnO-CaO solid solution.