Synthesis of SiO₂-Aerogel Inverse Opals in Supercritical Carbon Dioxide

SiO 2 -aerogel inverse opals were produced for the first time in supercritical carbon dioxide (scCO 2 ) with three-dimensional (3D) latex arrays as templates. The polymeric templates were reacted with tetraethyl orthosilicate in humidified scCO 2 at 40 °C and 85 bar. After calcination of the template, highly porous materials replicating the structure of the original template were obtained. Polystyrene latex particles decorated with different hydrophilic groups were organized in 3D ordered arrays and used as templates. Particles were impregnated with benzenesulfonic acid, which activates the condensation process of silica precursors. Scanning and transmission electron microscopy (SEM and TEM) images showed that the reaction in scCO 2 takes place only on the particle surface and that the octahedral and tetrahedral holes in the original fcc packing of latex spheres are empty. N 2 adsorption isotherms showed broad adsorption−desorption loops characteristic of mesopores. Brunauer−Emmett−Teller (BET) surface areas are large and range from 270 to 594 m 2 /g, since these materials are structured aerogels produced directly in scCO 2 . Analysis of the desorption branch revealed the presence of an extremely large mesoporosity that is located in the macropore walls. The porosity of the materials obtained for each template is different. Furthermore, shrinkage of the network upon condensation in scCO 2 was small. The synthesis of inverse opals in scCO 2 overcomes some of the limitations of the liquid-phase techniques, being a faster method of synthesis and, at the same time, rendering materials of unique properties.