Interactions between Zn2+ or ZnO with TiO2 to produce an efficient photocatalytic, superhydrophilic and aesthetic glass

Zinc was coupled with titanium dioxide using different methods. SiO2 and Zn-SiO2 doped TiO2 films, on the one hand, and Zn doped TiO2 on the other hand, have been produced using controlled sol-gel processes by alcoholic, cogelation and aqueous ways. From these syntheses, films were deposited on soda lime glass. These samples were compared to ZnO samples but also to bilayer samples constituting one layer of TiO2 and one layer of ZnO. The physico-chemical properties of the films were characterized by grazing-incidence X-ray diffraction, profilometry and UV-Vis absorption analyses. The photocatalytic activity has been evaluated from the degradation of methylene blue under UV-A light, from the degradation of p-nitrophenol under visible light and from the degradation of H2O2 under halogen light (UV-A + visible light). Superhydrophilicity was evaluated from contact angle measurement after UV exposition and also from hysteresis effects. Finally, a haze measurement was performed to evaluate the impact of the coating on the aesthetic property of the coated glass.
Aqueous films have better photocatalytic activity and superhydrophilicity than samples from alcoholic synthesis. The crystallization of the sample appears to be one key factor: alcoholic films required calcination to ensure the crystallization of TiO2, but the alkali migration from the glass support prevents this crystallisation, while aqueous synthesis promotes crystallized particles at low temperatures without alkali interference.
It appears that the relative activity from one sample to another depends on the nature of the illumination and on the nature of the molecule to be degraded. Nevertheless, the sample with ZnO layer deposited on first TiO2 layer (ZnO 500 Alc/TiO2 100 AQ) composite is found to be the best sample, maintaining a high hydrophilicity similar to TiO2 and a good activity.