Self-cleaning performance of sol–gel-derived TiO₂/SiO₂ double-layer thin films

The self-cleaning properties of the TiO₂/SiO₂ double-layer films prepared by sol–gel method were investigated. Thin films were prepared by spin coating onto glass and then thermally treated at different temperatures, and characterized using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and UV–visible spectroscopy. The cross-sectional structure of the films was observed by FESEM. The surface roughness of the films was characterized by AFM. The root mean square surface roughness of the thin films was below 2 nm, which should enhance their optical transparency. The photo-induced hydrophilicity of the films was evaluated by water contact angle measurement in air. The photocatalytic activity of the films was studied by the photocatalytic degradation of methylene blue under UV light irradiations. The TiO₂/SiO₂ double-layer thin films are plausibly applicable to developing self-cleaning materials in various applications such as windows, solar panels, cement, and paints.