Photoelectrocatalytic degradation of emerging contaminants at WO3/BiVO4 photoanodes in aqueous solution

Abstract

WO₃/BiVO₄ films obtained by electrochemical deposition of BiVO₄ over mesoporous WO₃ were applied to the photoelectrochemical degradation of selected emerging contaminants (ketoprofen and levofloxacine) in aqueous solutions. The WO₃/BiVO₄ films in this work are characterized by a mesoporous morphology with a maximum photoconversion efficiency >40% extending beyond 500 nm in Na₂SO₄ electrolytes. Oxygen was found to be the dominant water oxidation product (ca. 90% faradaic yield) and no evidence for the photogeneration of OH radicals was obtained. Nevertheless, both 10 ppm levofloxacine and ketoprofen could be degraded at WO₃/BiVO₄ junctions upon a few hours of illumination under visible light. However, while levofloxacine degradation intermediates were progressively consumed by further oxidation at the WO₃/BiVO₄ interface, ketoprofen oxidation byproducts, being stable aromatic species, were found to be persistent in aqueous solution even after 15 hours of solar simulated illumination. This indicates that, due to the lower oxidizing power of photogenerated holes in BiVO₄ and a different water oxidation mechanism, the employment of WO₃/BiVO₄ in photoelectrochemical environmental remediation processes is much less universal than that possible with wider band gap semiconductors such as TiO₂ and WO₃.