Photoelectrochemical Degradation of Diclofenac, Tetracycline, and Amoxicillin in an Aqueous Sulfate Medium: Analysis of Reactive Species

As the environment becomes increasingly polluted, there is a pressing need for the development of effective remediation technologies, particularly in the area of wastewater treatment. Recently, there has been growing interest in advanced oxidation systems (AOSs) based on renewable solar energy. This study focuses on the investigation of photoelectrochemical (PEC) AOSs using WO₃ and WO₃/BiVO₄ photoanodes and an environmentally friendly aqueous sulfate electrolyte for visible light-induced decomposition of pharmaceutical compounds, namely, diclofenac (DCF), amoxicillin (AMX), and tetracycline (TCC). It was demonstrated that in contrast to conventional persulfate-based advanced oxidation processes, where S₂O₈^2- is activated by UV, ultrasound, or thermal energy to generate highly reactive radical species, in photoelectrochemical systems reported here, radicals were generated by the interaction of photogenerated holes with H₂O molecules and SO₄^2- ions. These processes eventually led to the formation of S₂O₈^2- with an estimated Faradaic efficiency of 70-80%. Persulfate has also been shown to contribute to the degradation of pharmaceutical compounds, particularly diclofenac. The degradation efficiencies of AMX, TCC, and DCF were 10-14, 19-21, and 75-80%, respectively, in both PEC-AOSs studied. The formation of the WO₃/BiVO₄ heterojunction enhanced charge carrier separation and stability of the photoanode, but the effect on the pharmaceutical decomposition efficiency was not significant. The mechanism of visible light-induced generation of persulfate in the studied PEC systems was analyzed on the basis of thermodynamic considerations and experimental observations of pH variation during photoelectrolysis.