Preparation of zinc oxide ceramics with a sustainable antibacterial activity under dark conditions

Fabrication of ZnO ceramics with a sustainable antibacterial activity even in the dark has been conducted. Fine ZnO powders were hydrothermally treated in 0.5–3 mol ml−1 Zn(NO3)2 aqueous solutions at 110–180 °C for 3–20 h. After an uniaxial pressing of the ZnO powders thus prepared, they were sintered at 400–600 °C for 1 h in air. Sustainability in antibacterial activity was evaluated using a colony count method with Escherichia coli bacteria on nutrient agar medium (36 °C/24 h) in a Na–P-buffer solution. The best data was attained for the ZnO ceramics prepared from the following conditions: a 3 mol ml−1 zinc nitrate solution for the hydrothermal treatment at 120 °C for 7 h and sintering in air with a step-by-step pattern (470 °C/1 h–485 °C/1 h–500 °C/1 h). ESR and chemical photoluminescence analyses have cleared that radical oxygen of super-oxide (O2−) originated from the surface of ZnO might exhibit an antibacterial activity even under the dark condition.