Influence of hydrothermal conditions on the morphology and particle size of zinc oxide powder

Crystalline zinc oxide powder has been successfully prepared by adopting ammonia as the base source via the hydrothermal process at temperature ⩾100°C. The temperature for synthesizing ZnO powder is around 200°C lower than that of conventional heating process. The formation and growth ZnO powder under hydrothermal environment progress rapidly as soon as the temperature reaches 100°C. Prolonging the reaction time at 100°C does not significantly influence the characteristics of obtained powder; however, raising the reaction temperature slightly reduces the particle size and the production yield of ZnO powder. On the other hand, as the pH of the starting solution increases from 9 to 12, the morphology of ZnO powder markedly varies from an ellipsoidal shape to a rod-like shape. In addition, the crystallinity and particle size of ZnO powder increase with rise in the pH of solutions, but the yield of production decreases. The reason for the variation of morphology and characteristics of obtained powder with pH mainly depends on the nucleation states occurring in the hydrothermal reaction.