Titanium dioxide and composite metal/metal oxide titania thin films on glass: A comparative study of photocatalytic activity

Titania and composite (Ag, Au, W) titania coatings were prepared on glass microscope slides via a sol–gel dip-coating method. The resulting coatings were characterised by X-ray diffraction, Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX), Brunauer–Emmett–Teller (BET) surface area analysis, atomic force microscopy (AFM) and UV–visible absorption techniques. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid under 254, 365 nm and white light sources monitored by FT-IR spectroscopy. These activities at 254 and 365 nm light were represented as formal quantum efficiencies (FQEs) after determination of photon flux. Water contact angle measurements were made before and after irradiation with monochromatic 254 or 365 nm light; all films demonstrated photo-assisted super hydrophilicity (PSH). A Ag:Au titania composite coating was found to be the most significant photoactive film. The mode of improved photocatalytic activity was postulated in terms of a charge separation model. The Ag:Au TiO2 coating showed potential as a useful coating for hard self-cleaning surfaces due to its robustness, stability to cleaning and reuse and its photoactive response to indoor lighting conditions.