Effect of surface microstructure on the photoinduced hydrophilicity of porous TiO2 thin films

The relationship between photoinduced hydrophilicity and surface microstructure of porous TiO2 thin films has been investigated. Porous TiO2 thin films on soda-lime glass were prepared by the sol–gel method from alkoxide solutions containing polyethylene glycol (PEG). These materials were characterised by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV-Vis transmittance measurements. The larger the amount of PEG used in preparing the thin films, the larger was the pore size produced from the thermal decomposition of PEG. This generated also a relatively rough thin film surface with a strong affinity for hydroxyl groups. This study proves that suitable surface microstructures can enhance the photoinduced super-hydrophilic properties of porous TiO2 thin films and hinder the conversion from a hydrophilic to a hydrophobic state. Among the porous TiO2 thin films tested, the one with a PEG to TiO2 mass ratio of 12.5% exhibited the best photoinduced super-hydrophilic property and the slowest conversion rate from the hydrophilic to a hydrophobic state.