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 micrometer 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.