The Effect of the Water–Precursor Ratio on the Structural Characteristics of Alumina Aerogels

Alumina aerogels are obtained by the sol–gel synthesis and subsequent supercritical drying. The sol–gel synthesis is carried out by adding epichlorohydrin to aluminum chloride dissolved in water and ethanol. The supercritical drying (SCD) of the gels is carried out in a medium of supercritical carbon dioxide SC-CO2 at 40°C and 12.0 MPa for 8 h. The structural characteristics of the aerogels are studied by low-temperature adsorption of nitrogen, helium pycnometry, and scanning electron microscopy. The obtained aerogels have a high specific surface area (up to 764 m2/g) and a high level of porosity (up to 96.2%, with the pore volume of up to 4.9 cm3/g), as well as a low density (up to 0.066 g/cm3). It is found that the structural characteristics of the alumina aerogels can be controlled by varying the water : precursor ratio. In particular, increasing this ratio leads to an increase in the specific surface area and pore volume.