Influence of the mixing ratio on antibacterial characteristics of MgO-ZnO solid solution in two phase coexistence region

Though occurrence of the antibacterial activity on some oxides, MgO and ZnO, is well-known, it is not clear what the mixing ratio among solid solutions affects antibacterial activity. In present work, change in antibacterial activity with the mixing ratio of two-type solid solutions, Mg1-XZnXO with cubic structure and Zn1-XMgXO with hexagonal structure, was studied. After MgO and ZnO powders were mixed with the molar ratio (MgO/ZnO) of 0.44, 1.22 and 1.86, the solid solutions were obtained by heating at 1200°C for 5 h in air. By X-ray diffraction measurement, it was found that two-type solid solutions of cubic and hexagonal structure were formed at the molar ratio of 1.22-0.44. The formation amount of cubic-type solid solution increased with increasing the molar ratio. At the molar ratio of 1.86, cubic-type solid solution was formed without any hexagonal-type. In three powder samples of the obtained solid solutions, antibacterial characteristics were examined by colony count method, using Staphylococcus aureus and Escherichia coli. In the case of the mixture of cubic- and hexagonal-type solid solutions, antibacterial activity enhanced with increasing the formation amount of cubic-type solid solution. The powder sample with a single phase of cubic-type solid solution showed strongest antibacterial activity in three powder samples. As mentioned above, the mixing ratio of two-type solid solutions with cubic and hexagonal structure was found to affect antibacterial activity.