Enhanced photoactive and photoelectrochemical properties of TiO sub(2) sol-gel coated steel by the application of SiO sub(2) 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 TiO sub(2) films by applying an intermediate SiO sub(2) film between the TiO sub(2) film and the stainless steel substrate. TiO sub(2) and SiO sub(2) coatings are synthesized by a sol-gel method and the thickness of TiO sub(2) 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 TiO sub(2) films. The enhanced photocatalytic properties of SiO sub(2)/TiO sub(2) coatings as compared to TiO sub(2) films are verified using methylene blue (MB) discoloration tests, while the improved photoelectro-chemical 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 SiO sub(2) film on the photocatalytic and photoelectrochemical performance to the high electrical resistance of the SiO sub(2) that imposes a high-energy barrier for electron transfer and, therefore, (partly) insulates the TiO sub(2) 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 TiO sub(2) films.