Sol-gel synthesis and hydrothermal processing of anatase and rutile titania nanocrystals

The alkoxide sol-gel synthesis of nanostructured TiO₂ has been studied systematically to examine the processing parameters that control crystallite size and phase. Nonagglomerated, ultrafine anatase particles have been generated by hydrothermally treating the sol-gel-derived hydrous oxides. The degree of crystallinity and purity of the synthesized materials could affect their structural evolution during heat treatment. It was found that the 10-nm anatase TiO₂ sample derived by hydrothermal processing at 180 °C underwent neither phase change nor significant grain growth up to 800 °C. Nanocrystalline rutile TiO₂ particles have also been attained via hydrothermal treatment in an acidic medium. They possessed an ultrafine rutile grain size and a high surface area, which could not be achieved via phase transformation from thermal treatment of anatase particles.