Photocatalytic activity of sol–gel TiO2 thin films deposited on soda lime glass and soda lime glass precoated with a SiO2 layer

This paper reports the preparation and characterization of thin transparent TiO2 films with special focus on the role of the support (soda lime glass vs. soda lime glass covered with a SiO2 layer). The TiO2 films and the SiO2 layer were prepared by the sol–gel method and the final treatment was carried out at an elevated temperature of 500 °C for 2 h. The films were characterised with help of XRD, UV–VIS spectroscopy, TG/DTA thermal analysis, contact angle measurements, profilometry, SEM and AFM microscopy. Surprisingly the TiO2 films deposited on soda lime glass revealed only the brookite crystal phase structure. For the layers deposited onto the glass pre-covered with the SiO2 layer the anatase structure dominated. The role of sodium ions freely diffusing from the support was clearly identified by means of glow discharge atomic emission spectrometry. The photoinduced activity of the films was determined using two model compounds: anionic dye Acid Orange 7 (AO7) and 4-chlorophenol (4-CP). As expected the anatase films exhibited much better activity than the films with the brookite structure. On the other hand the brookite films possessed superhydrophilic properties, even in dark conditions.