Synthesis and evaluation of a self-standing CuBi₂O₄/CuO/Fe₂O₃ electrode for arsenic removal via photoelectrocatalysis

Water contamination by arsenic (As) poses a significant threat to millions of people worldwide. The development of an effective, affordable, and decentralized system for As removal remains a critical need, particularly to treat As at environmentally relevant concentrations. In this study, a self-standing electrode composed of an engineered interface of CuBi₂O₄/CuO/Fe₂O₃ was synthesized on fluorine-doped tin oxide (FTO) substrate using electrodeposition and dip-coating techniques. Each layer Bi₂O₃, CuBi₂O₄, CuO, and Fe₂O₃ was characterized photochemically and electrochemically to identify their light harvesting and electron transfer capacities. The efficacy of the CuBi₂O₄/CuO/Fe₂O₃ electrode for removing 0.5 mg L⁻¹ As (III) was evaluated under various treatment conditions, including adsorption, photocatalysis (PC), electrocatalysis (EC), and photoelectrocatalysis (PEC). The PEC treatment at 1.0 V vs Ag/AgCl under visible light irradiation exhibited outstanding As removal efficiency of 96.8 %, surpassing PC (40.4 %) and EC (54.5 %). Fundamental evaluation of the removal mechanism revealed that CuBi₂O₄/CuO/Fe₂O₃ oxidizes As (III) to As (V) for enhanced adsorption onto iron oxide sites, as confirmed by X-ray photoelectron spectroscopy (XPS), which identified both As (III) and As (V) adsorbed on the surface. These findings underscore the importance of a rational design approach for photoanodes in As adsorption, highlighting the significant role of individual layers.