Langmuir, 2019, vol 35, 36, pp. 11702-11709
DOI:10.1021/acs.langmuir.9b01149
Abstract
The synthesis of ZnO nanoparticles proceeds through a complex sequence of precursor reactions, nucleation, and growth processes. For further advancement and control of nanoparticle synthesis, a detailed understanding of the mechanisms and kinetics is essential. With the recent advancement in X-ray scattering and spectroscopy methods, in situ experiments during nanoparticle synthesis can be performed, which provide important new insights into reaction and growth mechanisms. Here we use in situ small- and wide-angle X-ray scattering (SAXS, WAXS) coupled with UVvis spectroscopy to investigate the nucleation and growth process of an oleate-based ZnO nanoparticle synthesis yielding narrowly disperse nanoparticles over the complete time scale from 30 s to 18 h. We find that the nucleation and early growth period during the first 1000 s can be quantitatively described by a classical homogeneous nucleation and growth mechanism. Furthermore, we identified a second growth phase where nanoparticle crystallization occurs, as indicated by the appearance of higher-order Bragg peaks and a pronounced shift of the absorption edge in the UVvis spectra. The results are in very good agreement with recent studies on the use of the ZnO alkali hydroxide hydrolysis route. Thus, a very good understanding of the nucleation and growth mechanisms and kinetics of the most important ZnO synthesis routes has been established.
