Preparation and characterization of transparent hydrophilic photocatalytic TiO2/SiO2 thin films on polycarbonate.

Transparent hydrophilic photocatalytic TiO2 coatings have been widely applied to endow the surfaces self-cleaning properties. A mixed metal oxide (TiO2/SiO2) can enhance the photocatalytic performance improving the ability of surface adsorption and increasing the amount of hydroxyl surface groups. The present work introduces a systematic study concerning the effect of the SiO2 addition to TiO2 films on the wettability, the photocatalytic activity, the adhesion strength, and the mechanical stability of the films. Transparent hydrophilic photocatalytic TiO2/SiO2 thin films were used to coat the polycarbonate (PC) substrate which was precoated by an intermediate SiO2 layer. The TiO2/SiO2 thin film was prepared employing a bulk TiO2 powder (Sachtleben Hombikat UV 100) and different molar ratios of tetraethoxysilane in acidic ethanol. A dip-coating process was used to deposit the films onto the polycarbonate substrate. The films were characterized by UV/vis spectrophotometry, FTIR spectroscopy, ellipsometry, BET, AFM, XRD, and water contact angle measurements. The mechanical stability and the UV resistance were examined. The photocatalytic activity of the coated surface was calculated from the kinetic analysis of methylene blue photodegradation measurements and compared with the photocatalytic activity of Pilkington Activ sheet glass. The coated surfaces displayed considerable photocatalytic activity and superhydrophilicity after exposure to UV light. The addition of SiO2 results in an improvement of the photocatalytic activity of the TiO2 film reaching the highest value at molar ratio TiO2/SiO2 equal to 1:0.9. The prepared films exhibit a good stability against UV(A) irradiation.