Multilayer TiO2/SiO2 thin sol–gel films: Effect of calcination temperature and Na+ diffusion

The detrimental effect of Na+ ion diffusion originating from soda-lime glass substrate during calcination on the properties of TiO2 thin sol–gel films can be eliminated by a barrier layer between the glass substrate and the final TiO2 film. This work deals with two layer films consisting of a barrier layer (SiO2 or TiO2) and a final layer (TiO2) deposited on soda-lime glass as a substrate. Particular emphasis was given to the effect of calcination temperature on both barrier and final layer.It was found that photocatalytic properties of titania thin films depend directly on the amount of crystalline anatase which is produced during calcination. It was proved that the SiO2 layer is a much better barrier against Na+ ion diffusion than the TiO2 layer. Furthermore using a SiO2 barrier the final titania layers are active even when calcined at 300 °C. With the application of a SiO2 barrier we can increase the activity of titania layers more than 20 times and moreover 200 °C is sufficient to form a stable and functional SiO2 barrier. It was also shown that when SiO2 barrier is used, no Na+ ion diffusion is possible.