Precipitation of ZnO particles and their properties

The aqueous suspensions obtained from zinc acetate solution neutralized with varying amounts of NH4OH solution were hydrothermally aged at 160 °C. The precipitates were characterized by XRD, Raman, B.E.T. and TEM. ZnO particles were produced by dissolution/reprecipitation mechanism from the starting precipitate. The rate of this transformation increased with an increase in pH from 7 to 10. The sizes of these ZnO particles were in the micron range and their physical shape depended on pH. Ageing of the starting aqueous suspension for 7 months at pH 10 and room temperature yielded aggregates consisting of nanosize ZnO particles (∼ 20 to ∼ 60 nm). Nanosize ZnO particles were also synthesized by the sol–gel method based on fast hydrolysis of zinc 2-ethylhexanoate dissolved in 2-propanol. It was shown that nanosize particles induced distinct spectral changes in the standard Raman spectrum of ZnO.