ZnO nanoparticles formation by reactions of bulk Zn with H2O and CO2 at sub- and supercritical conditions: II. Morphology and properties of nanoparticles

Oxidation of solid and liquid zinc by water (temperature 335–648 °C, pressure 13.7–31.2 MPa, water density 0.045–0.420 g/cm3), supercritical CO2 (514–600 °C, 7.1–24.4 MPa, 0.041–0.158 g/cm3), mixture of H2O/CO2 (140–600 °C, 30 MPa, water density 0.026–0.569 g/cm3, initial ratio of [H2O]0/[CO2]0 = 0.46–2.75 mol/mol) has been studied. On the basis of scanning and transmission of electron microscopy data, we have demonstrated that depending on the process conditions nanoparticles with the size of 2–100 nm, nanorods and nanowhiskers with the diameter of 10–100 nm and length of up to 50 μm, mechanically solid nanostructured ceramics are synthesized. The presence of (Zn)n clusters with the size below 5 nm has been found in ZnO nanoparticles synthesized in supercritical water and H2O/CO2 mixture. Higher level perfection of nanocrystals formed at zinc oxidation by subcritical water has been revealed by means of room temperature photoluminescence study.