Zinc oxide is a useful material for various products. ZnO crystals usually grow in the c-axis direction, on the less exposed (001) plane. However, the (001) plane has high chemical reactivity, and plate-like ZnO crystals on large (001) planes have superior UV-lasing and other properties. In this study, layered zinc hydroxide acetate (ZHA), a precursor of ZnO, was aged in deionized water and Zn(OCOCH 3) 2 or CH 3 COONa aqueous solutions of various concentrations under hydrothermal conditions at 90 and 120°C. Aging at above 90°C yielded ZnO in all the solutions, and the concentrations of the CH 3 COONa aqueous solutions did not affect the form of the ZnO particles. On the other hand, when ZHA was aged in Zn(OCOCH 3) 2 aqueous solution, the crystal growth of ZnO in the c-axis direction was suppressed as the Zn(OCOCH 3) 2 concentration increased. In the case of aging in 1 molL −1 Zn(OCOCH 3) 2 aqueous solution, plate-like ZnO was obtained, but the yield was about 10% and a large amount of ZHA remained. When the obtained mixture of plate-like ZnO and ZHA was aged again in deionized water at 90 and 120°C after washing, most of the ZHA was transformed into plate-like ZnO after aging for over 72 hours.

ZnO is widely used as a raw material of various electronic parts and cosmetics. The properties of ZnO particles depend on the morphologies of the crystals. So, it is important to control the morphology of ZnO particles to obtain desired properties. Layered zinc hydroxides are known as the precursor of ZnO because it can be easily synthesized and transformed to ZnO by aging in aqueous solution at relatively low temperature. Moreover, ZnO particles derived from the layered zinc hydroxides by aging in aqueous solutions show various forms which in difficult to obtain by the direct thermal decomposition of zinc hydroxides at a high temperature. In this report, ZnO was synthesized from a layered zinc hydroxide containing nitrate ions between layers, Zn5(OH)8(NO3)2 •2H2O (ZHN), as a precursor by aging under various conditions. Effects of the amount of deionized water, the concentrations of NaNO3 aqueous solutions and the temperature were investigated on the transition of ZHN to ZnO during aging. The formation ratio of ZnO increased with increasing the amount of deionized water and aging temperature. When the ZHN was aged in 200 mL deionized water, the formation ratio of ZnO was 70% even at 60℃ and increased to 95% at 90℃ and 120℃. The aging in NaNO3 aqueous solutions enhanced the formation of ZnO but the formation ratio largely decreased by aging in a 0.1 mol/L NaNO3 aqueous solution. When aging was carried out in NaNO3 aqueous solutions of 1×10-2 to 1×10-6 mol/L at 90℃ and 120℃, the ZnO formation ratio was almost above 95%. In the case of high formation ratio of ZnO, well crystalized rod-shaped particles, which is characteristic shape of ZnO, was obtained and the aspect ratios of ZnO particles decreased with increasing NaNO3 concentrations.