Silica xerogels and aerogels synthesized with ionic liquids

The synthesis of silica gels with ionic liquids (IL) as either additives or co-solvents is described. The wet gels were either dried by supercritical CO₂ or by evaporation to obtain aerogels or xerogels, respectively. The effects of two ionic liquids: 1-butyl-3-methyl imidazolium tetrafluororate (IL1) and 1-butyl-4-methyl pyridinium tetrafluoroborate (IL2), on the structural and textural characteristics of gels were investigated. IL2 showed a more important influence than IL1, on the gelation time and gel structure, according to solid state NMR investigations. With both types of ionic liquids, the average pore radius of xerogels increased from ≈2 nm at an IL to Si molar ratio n_IL/n_Si = 0.07, to ≈4 nm at n_IL/n_Si ≈ 1.5 and the size distributions were rather well centered about each mean radius. Hence, ionic liquids appeared as interesting additives to target gels with a given pore size.