Sorbitol cross-linked silica aerogels with improved textural and mechanical properties

It is well known that although organically modified silica aerogels have enhanced mechanical properties, the specific surface area decreases due to the larger pore size. However, cross-linking with sorbitol enhances the mechanical properties while maintaining the highly textural structure, low density, and the thermal conductivity of silica aerogel. Herein, we report the silica aerogels reinforced with sorbitol via facile sol-gel polymerization. The sorbitol improved mechanical properties while maintaining the textural structure of the silica aerogels. Sorbitol with surface hydroxyl groups was covalently cross-linked with either tetraethoxysilane (TEOS) or methyl trimethoxysilane (MTMS) precursor. The two possible combinations of sorbitol-TEOS or sorbitol-MTMS aerogels were systematically prepared by varying mol% of the precursor and aerogels to obtain different properties. The sorbitol-MTMS aerogel with a 90:1 M ratio of methanol to precursor attained a large surface area (1193 m²/g), good mechanical strength (205.9 kPa) during compression testing, a small pore volume (2.2 cm³/g), and low thermal conductivity (0.041 Wm⁻¹K⁻¹). The thermal stability of sorbitol-TEOS and sorbitol-MTMS cross-linked silica aerogels in air was up to ∼418 °C, as ascertained from their thermo-gravimetric profiles. The results indicate that using small linear organic molecules for cross-linking with an inorganic silica precursor is highly useful for obtaining aerogels with a high surface area and improved mechanical properties.