Effects of electric field on the formation of titania nanocrystals on SiO2-TiO2 gel coatings during hot water treatment

Abstract

Sol-gel derived SiO2-TiO2 coatings on indium tin oxide (ITO)-coated glass substrates were treated with hot water at 90°C under electric field aiming at the control of morphology and crystalline phase of the titania precipitates. The shape of the precipitates on 75SiO 2· 25TiO2 (mol%) coating at the negative electrode changed from granular to ramiform by applying an electric field to the substrates during the treatment, whereas such changes in the shape of titania nanocrystals with the electric field were not observed at the positive electrode. The granular and ramiform precipitates were identified as anatase (TiO2) and hydrated titania (n(TiO2) ·mH 2O), respectively. The ramiform shape of the titania precipitates became significant with increasing the applied voltage, while the coatings gradually dark-colored due to the reduction of Ti4+ to Ti 3+.