Underwater superoleophobic NaNbO<sub>3</sub>-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 Na2Nb2O6H2O phases.It was suggested that NaNbO3 and Na2Nb2O6H2O 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.