Surfactant-templated silica aerogels

By combining the molecular silica precursor tetramethoxysilane (TMOS) with an alkaline, micellar, water:methanol solution, we form surfactant-templated silica gel (STSG) monoliths. The wet monoliths can be exchanged with ethanol and then supercritically extracted with carbon dioxide to produce surfactant-templated silica aerogels (STSAs). STSAs represent a new class of aerogels that are composed of aggregated submicron porous particles that have tunable intraparticle nanoporosity. STSAs catalyzed with NH,OH experience no measurable shrinkage upon extraction and have bulk densities less than similar to 0.15 g/cc. The STSAs can then be calcined to remove the remainder of the surfactant. The calcination process leads to minimal shrinkage (< 8%), high surface area (similar to 700 m(2)/g), uncracked monoliths with hierarchical inter- and intraparticle porosities, and bulk densities less than 0.08 g/cc. We use XRD, SAXS, SEM, Si-29 NMR, and N-2 sorption to characterize the structure and porosity of these novel aerogels. (C) 1998 Elsevier Science B.V.