Preparation and Characterization of Transparent Hydrophilic Photocatalytic TiO2/SiO2 Thin Films on Polycarbonate

Transparent hydrophilic photocatalytic TiO2 coatingshave been widely applied to endow the surfaces self-cleaningproperties. A mixed metal oxide (TiO2/SiO2) can enhance thephotocatalytic performance improving the ability of surface adsorptionand increasing the amount of hydroxyl surface groups. The presentwork introduces a systematic study concerning the effect of the SiO2addition to TiO2films on the wettability, the photocatalytic activity,the adhesion strength, and the mechanical stability of the films.Transparent hydrophilic photocatalytic TiO2/SiO2 thin films were usedto coat the polycarbonate (PC) substrate which was precoated by anintermediate SiO2 layer. The TiO2/SiO2 thin film was preparedemploying a bulk TiO2 powder (Sachtleben Hombikat UV 100) anddifferent molar ratios of tetraethoxysilane in acidic ethanol. A dipcoatingprocess was used to deposit the films onto the polycarbonatesubstrate. The films were characterized by UV/vis spectrophotometry, FTIR spectroscopy, ellipsometry, BET, AFM, XRD, andwater contact angle measurements. The mechanical stability and the UV resistance were examined. The photocatalytic activity ofthe coated surface was calculated from the kinetic analysis of methylene blue photodegradation measurements and comparedwith the photocatalytic activity of Pilkington Activ sheet glass. The coated surfaces displayed considerable photocatalytic activityand superhydrophilicity after exposure to UV light. The addition of SiO2 results in an improvement of the photocatalytic activityof the TiO2 film reaching the highest value at molar ratio TiO2/SiO2 equal to 1:0.9. The prepared films exhibit a good stabilityagainst UV(A) irradiation.