Photo-electrochemical and interfacial-process analysis of WO3 nanostructures supported on TiO2: An approach to BPA oxidation

The photo-electrooxidation of bisphenol A (BPA) at the interface of nanostructured materials of TiO2 and WO3-TiO2 was studied under neutral conditions. The tested materials were synthesized via the sol-gel method, and characterized by X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS); as well as electrochemical techniques. X-ray diffraction indicated the formation of pure anatase phase and the presence of monoclinic WO3. XRD-HRTEM revealed WO3 nanoparticles of ca. 5 nm in diameter and anatase nanoparticles of 14.8-24 nm. The XPS analysis confirmed the predominance of WO3 (W6+) and TiO2 (Ti4+) as an heterostructured couple. The semiconductor properties of the synthesized composites were evaluated in 0.1 M KCl using cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The electrochemical analysis confirmed the formation of the tungsten-oxide bronze sites, and it is proposed that WO3-(OH)ads species are responsible of BPA oxidation. The assays using frequency variation demonstrated that both the flat-band potential and the electrical resistance decrease in the presence of WO3. The evaluation from linear voltammetry during illumination in visible-light region confirmed that the better performance for BPA oxidation was with nanostructured WO3-TiO2 obtaining a faster rate of interfacial electron transfer.