Influence of the pH on the ZnO nanoparticle growth in supercritical water: Experimental and simulation approaches

Abstract In order to improve the knowledge on the nucleation and the growth mechanisms of metal oxides nanoparticles produced in supercritical water domain, ZnO was used as a “model” material. A continuous process of hydrothermal synthesis was employed to synthesize ZnO nanopowders ( T  = 410 °C and P  = 305 bar) from Zn(NO 3 ) 2 and KOH solutions with different values of [KOH]/[Zn(II)] ratio from 0 to 8 in order to investigate the pH effect on the growth of ZnO nanocrystallite in terms of size and morphology. The samples were characterized by X-Ray Diffraction and Transmission Electronic Microscopy. ZnO crystal was considered as a cylindrical crystallite with a diameter D and height H . Especially, the aspect ratio D / H was already used to observe the change of ZnO nanoparticle shape correlated with TEM observations and results from a CFD simulation model. A schematic synoptic of the ZnO growth in supercritical domain is also presented.