Underwater superoleophobic NaNbO3-based photocatalyst thin films prepared on bare soda-lime glass by sol–gel process

A self-cleaning flat transparent thin photocatalyst film was prepared on a bare soda-lime glass by a simple method using niobium alkoxide solution, which is a common coating solution for the sol–gel method. The film consisted of crystalline NaNbO3 and Na2Nb2O6·H2O phases. It was suggested that NaNbO3 and Na2Nb2O6·H2O were directly formed between the soda-lime glass and the niobium alkoxide coating solution during the heat treatment. Under UV irradiation, the film surface exhibited low photocatalytic oxidation activity and excellent photo-induced hydrophilicity. The hydrophilic state of the sample was maintained for 1 month in the dark, while the hydrophilicity of TiO2 sample prepared by a sol–gel method was decreased within 5 days in the dark. Additionally, the surface demonstrated excellent underwater oil repellency toward n-hexadecane and oleic acid and the ability to remove the adsorbed oily contaminant in water. These properties were also superior to those of the TiO2 surface.