Recovery and Reutilization of the Solvents and Catalyst Used in the Sol–Gel Synthesis of Silica Xerogel

Silica xerogels were synthesized via the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under the catalysis of n-butylamine (BA), followed by drying the formed wet gel under ambient pressure at 120 °C. The solvents (water and ethanol) and catalyst enclosed in wet gels were recovered during the drying process. It was found that the relative percentage of ethanol in the recovered liquids increased, while those of water and butylamine decreased. The recovered liquids were directly used for four runs, and then the contents of BA, H2O, and TEOS were adjusted to maintain the reactant ratios to be the same as those in the first run, facilitating a fast sol and gel formation. Totally 12 silica xerogels with high degree of three-dimensional Si–O–Si network were synthesized. The results indicate that all the silica xerogels are composed of aggregated particles sized 20–250 nm, resulting in porous networks with specific area, pore volume, and pore diameter in the range of 290–690 m2/g, 1.54–2.40 cm3/g, and 17.4–68.2 nm, respectively. The compositional change in the recovered liquids, the drying time, and the volume of wet gel had influence on the aggregation, degree of condensation, and surface area of the cyclically synthesized xerogels. The synthesis route not only saves resources but also does not generate any waste, providing a sustainable sol−gel way to synthesize materials.