Evidence of the formation mechanism of ZnO in aqueous solution

Using a combination of scanning electron microscopy and X-ray diffraction techniques, the mechanism for ZnO formation was studied by simply heating an aqueous solution containing zinc salts and ammonium hydroxide to 85 °C. Growth of ZnO occurred via the initial precipitation of stable e-Zn(OH)2 microcrystals and subsequent formation of ZnO under these conditions. By monitoring an intermediate growth stage, phase transformation from e-Zn(OH)2 to ZnO was found to take place either via a dissolution–reprecipitation mechanism or via an in situ crystallization transformation mechanism that involves dehydration and internal atomic rearrangements. These findings may contribute to control the synthesis of ZnO in liquid media.