Silica aerogels with tailored chemical functionality

Abstract

Silica aerogels are highly porous (~95%), predominantly mesoporous (20–50 nm) materials with very high surface area (~800 m2/g), but applications that valorize the chemical properties linked to the high surface area lag behind those that valorize the pore structure (thermal insulation). Here, we present widely applicable protocols to synthesize and characterize organo-functionalized silica aerogels with high surface area (356–1177 m2/g) and high mass loadings of surface functional groups (1.0–4.9 mmol/g, 0.9–3.9 molecules/nm2). Wet silica gels are soaked into dilute solutions containing pre-hydrolyzed organofunctional trialkoxysilanes, followed by supercritical CO2 drying. The retention of the various functional groups in the dry aerogels is confirmed by FTIR and their concentrations quantified by solid-state NMR spectroscopy. The mild reaction conditions are compatible with all tested functional groups (silanol, ethoxy, trimethylsilyl, amino, vinyl, methyl methacrylate, epoxy, phosphonate), without the need to optimize for each specific functional silane, making the synthesis of organofunctionalized aerogels a routine task.

Keywords

• Silica aerogels
• Chemical functionality
• Surface modification
• Solid-state NMR spectroscopy