[en] Supercritical carbon dioxide is beneficial to the synthesis of superior ultrafine and uniform materials due to its high chemical stability, low viscosity, high diffusivity, and 'zero' surface tension. γ-Alumina nano-sheets were obtained by a simple hydrothermal route in the presence of supercritical carbon dioxide. XRD, FTIR, SEM, TEM and nitrogen sorption isotherm were employed to characterize the samples. Alumina as-prepared has a high specific surface area of up to 200 ± 6 m² g^-1, which presents a high adsorption capacity (4.66 ± 0.02 mg g^-1) for uranyl ions from aqueous solution. Furthermore, the adsorption process was found to be endothermic and spontaneous in nature. (authors)