Hexagon γ-alumina nanosheets produced with the assistance of supercritical ethanol drying

Well-defined hexagon γ-alumina (γ-Al2O3) nanosheets were successfully obtained with a sol–gel process under supercritical ethanol drying condition. The sol–gel of alumina precursors was carried out in refluxing aqueous solutions that contained excess urea and 0.1–0.4 M Al3+, always kept the [urea]/[Al3+] ratio constant at a value of 3.0. The obtained precursor precipitates were calcined at different temperatures in a muffle furnace in order to compare with supercritical ethanol drying. The effects of reactant original concentrations in the sol–gel solution, sol–gel precursor concentrations in the supercritical ethanol solution and time for removal supercritical ethanol vapour have been studied. Nano-γ-alumina particles obtained by supercritical ethanol drying exhibited hexagon sheet characteristics with the diameter of 5–10 nm and always had the γ-alumina phase. The formation mechanism of nanosheets γ-alumina was also discussed.