Research On Silica Aerogels Synthesized With Ionic Liquids At Ambient Pressure

Silica aerogels have attracted increasingly more attention due to their extraordinaryproperties and their existing and potential applications in wide variety technological areas.Silica aerogel is a nanostructured material with high specific surface area, high porosity, lowdensity, and excellent heat insulation properties.However the traditional preparation ofaerogels by supercritical drying is expensive, complicated and unsafe to a center extent,research on preparation of silica aerogels via ambient pressure drying at a reasonable cost isconsidered necessary and significant. Especially in recent years, ionic liquids has receivedsignificant attention and a few report about synthesis of silica aerogels with ionic liquidswere pulished, which offer a new method for synthesis of silica aerogels at ambient pressure.Mading silica aerogels with ionic liquids show the great advantage, so the mechanism andreaction laws deserve further exploration.The synthesis of silica aerogels based TEOS with high surface area using ionic liquidsas catalyst, co-solvents and aging agent at ambient pressure was described.The effection ofvarious parameters on the gel properties was studied and we focused on the mechanism andreaction laws of type and concentration ratio of ionic liquids, the consequence shows that:(1)Effects of water, ethanol and temperature on gel time and properties following aregulation. gelation time decreases with water increased until nWATER:nTEOS=7,and thengelation time increase with water increased. The density decreases rapidly with waterincreased as nWATER:nTEOS<4, and the density increasing gradually with water increased whennWATER:nTEOS>4. Gelation time increased with amount of ethanol increased; The density ofaerogel was lowest and porosity was highest as nEtOH:nTEOS=7~10. gelation time decreasedrapidly with the reaction temperature raise. Aging temperature also had a certain impact onthe aerogels properties, The density of aerogel was lowest and porosity was highest whenaging temperature was50~60℃. The density of aerogel decreased and porosity increasedwith aging time increased.(2)Silica aerogels based TEOS was synthetized with ionic liquids [HMIM]Br as catalyst,co-solvents and aging agent at ambient pressure. The BET and SEM of aerohel showed that the silica aerogel has high surface area, open nano-porous structure and uniform pore sizedistribution (surface area up to992m2/g, average pore size of21.68nm).With the molar ratioof IL to Si atoms, nIL/nSiincreased，The gelation time increased; specific surface areagradually increased; pore size distribution was increasingly narrow and average pore sizebecame smaller.[HMIM]BF4shows better catalytic performance than [HMIM]Br, becausethe gel time was much shorter with [HMIM]BF4as catalyst.and density of aerogels was lowerwith [HMIM]BF4than [HMIM]Br.