Experimental study on the morphology and porosity of TiO 2 aerogels synthesized in supercritical carbon dioxide

Abstract

Supercritical CO 2 (scCO 2) has emerged as a viable reaction medium for producing nanomaterials with unique features, while maintaining delicate nanoarchitectures, pore structures, and high surface areas that are difficult to obtain using conventional organic solvents. ScCO 2 has tuneable properties allowing for controlling the morphology and the pore size of the resulting materials. In this study, the morphology and pore size of TiO 2 aerogels prepared in scCO 2 under varying temperature, pressure and acetic acid/Ti alkoxide ratios ( R values) were examined using electron microscopy and N 2 physisorption for characterization. It was found that the formation of monodisperse spherical particles with mesoporous structure was favored by high reaction temperatures and pressures. The microstructures of TiO 2 aerogels derived via the sol–gel reactions of Ti butoxide and acetic acid changed from precipitate-like to micron-size rods to nanofibers when the R value was increased from 4.0 to 5.5. In addition, the pore size was also found to be related to the temperature, pressure and the R value.