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

Abstract

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. 5nm in diameter and anatase nanoparticles of 14.8–24nm. 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 0.1M 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.