Supercritical carbon dioxide and imidazolium based ionic liquids applied during the sol-gel process as suitable candidates for the replacement of classical organic solvents

In the present work, a sol-gel process with the precursor tetramethyl orthosilicate (TMOS) is investigated. The gelation was carried out in three different organic solvents. In addition the organic solvents were substituted by six different ionic liquids (ILs). By adding the ILs during the sol-gel process, so called ionogels are formed. The synthesis of such ionogels in supercritical CO2 atmosphere, and its influence on gelation time and the properties of the final ionogels were determined. For the characterization of the ionogels, BET and TGA analysis were carried out. In presence of supercritical carbon dioxide and ionic liquids, the gelation time of silica gels can be decreased significantly. The results illustrate, that organic solvents, typically used in aerogel synthesis, can be replaced completely and that, in presence of CO2, no further catalyst is necessary to promote the gel formation. The results further show that the porous characteristics of the so formed gels can be improved, compared to the classical sol-gel process in presence of organic solvents.