Photocatalysis Technique Of The SiO₂/TiO₂ Nano-composite Film Coupled With A Pt Foil And Its Application

Nano-TiO2 photocatalyst has always attracted a great attention due to its high photocatalytic activity, chemical stability, low cost and nontoxicity. However, nano-TiO2 powder is easy to agglomerate and difficult to be separated for reusage. These fatal problems can be resolved through the immobility of the TiO2 on the substrate. Since the real surface area of immobile TiO2 film decreased greatly, the photocatalytic activity of the TiO2 film decreases dramatically compared with the nano-TiO2 powder. Therefore, great efforts have been devoted to improve the photocatalytic activity of TiO2 thin film.In this paper, the nano-SiO2 powder doped TiO2 thin film was electrically connected to a Pt foil to form a galvanic cell, which could improve the separation efficiency of the photogenerated holes and electrons, so as to accelerate the photocatalytic degradation of the organic pollutants over the SiO2/TiO2 composite film. The contents are as follows:(1) The uniform SiO2/TiO2 composite film was electrodeposited on the ITO glass with butyl titanate as precursor, ethyl alcohol as solvent, H2O2 as complexing agent, proper concentrated nitric acid to control the speed of reaction. The photocataytic activity of the SiO2/TiO2 composite film is higher than that of the nano-TiO2 thin film which is prepared by the same method.(2) The SiO2/TiO2 composite film and a Pt foil were electrically connected to form a galvanic cell, and then were immersed in the aqueous solutions of phenolic pollutants p-nitrophenol (4-NP) or azo dye methyl orange (MO). The concentration changes of 4-NP and MO were detected on a UV-vis spectrophotometer. Under the optimal coupling condition, the photocatalytic degradation rate constant of 4-NP and MO were 5.8 times and 7.5 times than that of uncoupling system, respectively. Moreover, the photocatalytic efficiency for the degradation of the organic pollutants in coupling system was found dependent on the initial solution pH, dissolved oxygen and the area ratio of the Pt plate. Furthermore, we investigated the catalytic mechanism of coupling photocatalysis technique.(3) Photoactivity of the TiO2/SiO2 composite film which has been worked in the coupling experiment was further studied: after 2 hours of working in the coupling system, the photocatalytic degradation rate constant of MO was 3.5 times of that over the new unmodified TiO2/SiO2 composite film. At last, the mechanism of coupling modification progress was discussed.