Design of nano-needle titania and surface roughness of its film by processing sol⿿gel reaction and supercritical drying

Abstract

Nano-needle titania was fabricated from sol⿿gel reaction using titanium butoxide (TBO) as titania precursor and acetic acid (HAc). The wet gel after the sol⿿gel reaction was dried in supercritical carbon dioxide at 313K and 10.4MPa for the production of titania powder. The minor-axis of the nano-needles were measured by a scanning electron microscope and evaluated with respect to the effect of the initial molar ratios of HAc to TBO and reaction time in the sol⿿gel reaction process. A higher molar ratio of HAc in the sol⿿gel reaction results in a smaller minor axis of the nano-needle. The minor-axis of the titania nano-needle increases with increasing sol⿿gel reaction time. From these results, the minor-axis size of titania nano-needle could be controlled by the molar ratios of HAc to TBO and reaction time in the sol⿿gel reaction. The nano-needle titania was also applied to the fabrication of a thin film by a casting and solvent evaporation method. The surface roughness of the titania thin film from the nano-needle with various minor-axis was evaluated and compared with that from the nano-sphere titania. A smaller minor-axis of the nano-needle titania results in a larger roughness of the surface on the thin film. It is found that the roughness of the nano-needle film was larger than that using the nano-sphere.