Improved photocatalytic activity of polymer-modified TiO₂ films obtained by a wet chemical route

Porous TiO₂ films, exhibiting improved photocatalytic activity compared with commercial materials, have been deposited on glass. The films were dipcoated from a polymer-modified TiO₂ precursor solution, containing about 90 vol% water as solvent. The addition of water-soluble polymers such as polyethyleneglycol and polyvinylalcohol has produced TiO₂ films with different morphologies, exhibiting RMS roughnesses of up to 60 nm and increased porosity. We studied the effect of the polymers on the morphology and surface topography of a series of polymer-modified TiO₂ films and evaluated how their presence in the precursor influences the crystallinity, optical transmittance and most importantly, the photocatalytic activity of the films. X-ray diffraction analysis shows that all films exhibit the anatase crystal structure after calcining for 2 h at 500 °C. We find that the presence of polyethyleneglycol inhibits the crystallization of the TiO₂ films. Transmittance spectra show that most of the polymer-modified TiO₂ films obtained in this work are transparent although high polymer content can lead to opaque films because of increased porosity and surface roughness. The surface morphology of the films was studied by scanning electron microscopy and atomic force microscopy. Their photocatalytic efficiency was studied by following the decomposition of methylene blue under UV irradiation. The activity of the reference TiO₂ film obtained from a precursor without polymers is comparable to that of Saint-Gobain (SG) self-cleaning Bioclean glass, while some of the polymer-modified films show efficiencies that can be up to seven times higher.