Enhanced photoactive and photoelectrochemical properties of TiO2 sol-gel coated steel by the application of SiO2 intermediate layer

Photocatalysis is a promising solution for purifying air and water from pollutants, yet more efficient photocatalytic materials are needed. A new approach is proposed in this paper for enhancing the photoactive and photoelectrical properties of anatase TiO₂ films by applying an intermediate SiO₂ film between the TiO₂ film and the stainless steel substrate. TiO₂ and SiO₂ coatings are synthesized by a sol-gel method and the thickness of TiO₂ film is varied in order to obtain improved understanding on the role of thickness in photocatalytic and electrochemical performance. The obtained coatings are systematically characterized in terms of microstructure using such techniques as field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and X-ray diffraction (XRD), that demonstrate, e.g., the anatase phase structure of the TiO₂ films. The enhanced photocatalytic properties of SiO₂/TiO₂ coatings as compared to TiO₂ films are verified using methylene blue (MB) discoloration tests, while the improved photoelectrochemical properties are shown by potentiodynamic i-V scans, open circuit potential (OCP) monitoring and electrochemical impedance spectroscopy (EIS). We attribute the beneficial effect of the intermediate SiO₂ film on the photocatalytic and photoelectrochemical performance to the high electrical resistance of the SiO₂ that imposes a high-energy barrier for electron transfer and, therefore, (partly) insulates the TiO₂ film from the substrate and acts as a capacitor for photo-generated electrons under illumination. The presented results show an effective way of enhancing the photocatalytic performance of anatase TiO₂ films.