Experimental study on the morphology and porosity of TiO2 aerogels synthesized in supercritical carbon dioxide

Supercritical CO2 (scCO2) 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. ScCO2 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 TiO2 aerogels prepared in scCO2 under varying temperature, pressure and acetic acid/Ti alkoxide ratios (R values) were examined using electron microscopy and N2 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 TiO2 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.

Graphical abstractTiO2 aerogels can be produced in supercritical CO2 solvent using hexamer building blocks withthe morphology and porosity of the products found to be functions of reactant ratios and reactor temperature and pressure..Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Supercritical carbon dioxide (scCO2) led to formation of mesoporous nanostructured titania aerogels. ► Alkoxide/acetic acid (R) ratio had a significant effect on morphology and pore size distribution. ► Reaction temperature and pressure controlled the particle/pore size distribution. ► By tuning the R ratio with TTIP, the aerogels morphology can be changed to fibers. ► By tuning the R ratio with TTBO, the aerogels morphology can be changed to ribbons to curled or straight fibers.