Preparation of mesoporous SiO2/Bi2O3/TiO2 superhydrophilic thin films and their surface self-cleaning properties

Mesoporous SiO2/Bi2O3/TiO2 triple-layered thin films were prepared on glass slides using a simple sol-gel/spin-coating method. For comparison, double-layered Bi2O3/TiO2 and mixed Bi2O3-TiO2 thin films were prepared using the same method. The obtained samples were characterized by X-ray diffraction (XRD), UV-vis spectrophotometry (UV-vis), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Methyl orange was used as a model pollutant to evaluate the photocatalytic properties of the thin films. The self-cleaning properties of the thin films were investigated by tracking the photocatalytic removal of stearic acid. The mesoporous SiO2/Bi2O3/ TiO2 multi-layered thin films retained the mesoporous structure of SiO2, demonstrating superhydrophilicity and antifogging ability even in the dark, as well as more efficient photocatalytic behavior than double-layered Bi2O3/TiO2 and mixed Bi2O3-TiO2 thin films when illuminated with weak UV light irradiation. Moreover, the thin films resisted both acidic and alkali corrosion of the type they might encounter in the natural environment.