Ti(OBu)4 diluted with PrOH was added drop wise
into water under vigorous stirring, whose
acidity was adjusted with HNO3. The molar ratios
of PrOH and water to Ti(OBu)4 were 1.42 and 151,
respectively. Then, the solution was kept under
reflux condition (around 75 1C) for 24 h. Finally,
pure TiO2 sol was obtained, which was used to
prepare thin films and equivalent powders, after
PrOH and n-butyl alcohol were removed from the
solution in a rotatory evaporator under vacuum.