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

•Nano-needle of TiO2 is fabricated from sol–gel reaction and supercritical drying.•Minor-axis size of the nano-needle can be designed by solvent species inside wet gel.•The smaller minor-axis size leads to the larger surface roughness of TiO2 thin film.

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.

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