Formation and Characterization of Titania Nanosheet-Precipitated Coatings via Sol−Gel Process with Hot Water Treatment under Vibration

Vibrations were found to affect the nanostructure of titania crystallites formed on SiO 2 −TiO 2 gel coatings during hot water treatment. Granular anatase nanocrystals of 30−50 nm in size were formed on the coatings during hot water treatment without vibration, whereas the shape of the precipitates elongated to be sheetlike by applying a vibration to the substrate during hot water treatment. The sheetlike crystals mainly consisted of nanosheets with a spacing of about 0.6 nm, and were identified as a hydrated titania, m (TiO 2 )· n H 2 O, with the lepidocrocite-like layered structure. Titania nanosheets were characterized by a large surface-to-volume ratio, allowing the high photocatalytic reactivity comparable to that of anatase crystals. In addition, the coatings were highly transparent even after the formation of the nanosheets and thermally stable at around 500 °C. The hydrated titania nanosheet-precipitated coatings maintained an excellent wettability for water and antifogging properties even after being kept in dark for 2000 h due to their unique physicochemical properties. Processing temperatures for the coatings preparation are lower than 100 °C under atmospheric pressure, so that the coatings have a great potential for applications to various substrates including organic polymers with poor heat resistance.