Effect of solvent species inside wet gel on fabrication of titania nanoparticle by supercritical carbon dioxide drying

Titania nanoparticles were fabricated by sol-gel reaction and supercritical carbon dioxide drying. The solvent inside wet gel obtained from sol-gel reaction was exchanged to organic solvents, acetone, 1-butanol and N-methylpyrrolidone before the supercritical drying. The wet gels exchanged by organic solvents were dried in supercritical carbon dioxide at 313 K and 10.0 and 20.0 MPa. It is found that the structures of the titania nanoparticles were like nano-needle. The minor-axis sizes of the nano-needle titania nanoparticles were measured by a scanning electron microscope observation. The wet gel exchanged by 1-butanol results in the smallest minor-axis of titania nanoparticles, 97 nm in the supercritical drying at 313 K and 20.0 MPa. The drying of the wet gel exchanged with N-methylpyrrolidone exhibit the reduction of the minor-axis of titania nanoparticle larger than those with acetone and 1-butanol, 181 to 103 nm by increase of pressure, 10.0 to 20.0 MPa. (C) 2016 Elsevier B.V. All rights reserved.