Superhydrophilic and Highly Transparent TiO2 Films Prepared by Dip Coating for Photocatalytic Degradation of Methylene Blue.

Nanocrystalline TiO2 films were prepared on slide glass by sol-gel and dip-coating methods, and the samples were then annealed at 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C and 500 °C for 2 h. The samples' crystal structures, morphology, water contact angle, transmission spectra, and photocatalytic performance with respect to the degradation of methylene blue (MB) under UV light irradiation were characterized by X-ray diffraction spectroscopy, scanning electron microscopy, contact angle measurement, and UV-vis spectrophotometry. The results obtained indicate that all of the films were highly transparent to the visible spectrum, but with an increase in the annealing temperature, the optical band-gap and the water contact angle both reduced. Samples annealed at 450 °C and 500 °C exhibited superhydrophilic properties, with the hydrophilicity of the films remaining stable for at least 6 months without UV light irradiation. Among all the samples, the one annealed at 450 °C was found to have the highest maximum MB degradation rate of 71.1%.