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RESEARCH PRODUCT

Hydrothermal growth of ZnO nanostructures in supercritical domain: Effect of the metal salt concentration (Zn(NO3)2) in alkali medium (KOH)

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Abstract The metal salt concentration effect on the size and morphology of ZnO NPs was highlighted through its synthesis thanks to a continuous one-step method at 401 ± 15 °C and 306 ± 8 bar. Experiments were performed from Zn(NO3)2 and KOH as reactants in concentration ranges of 10–480 mM and 40–1920 mM, respectively. A constant [KOH]/[Zn(NO3)2] ratio of 4 was fixed in order to maintain a constant pH value between 12.5 and 13.0. The as-prepared NPs were characterized by X-ray diffraction and (high-resolution) transmission electron microscopy. Based on Louer's method, ZnO crystal exhibiting a hexagonal structure was considered as cylinder with a diameter D and a height H. The D/H parameter has already been used to observe the change of ZnO crystallite shape and correlated with (HR)TEM observations. The evolutions of crystal size and morphology according to [Zn(NO3)2] in alkali medium are investigated and the particle growth mechanisms in supercritical water are discussed.