Degradation of sulfamethazine by cerium mediated photoelectrochemical oxidation with hydroxyl radical oxidation effect

A cerium (Ce) mediated photoelectrochemical oxidation (MPEO)/H₂O₂ system, integrating UV photocatalysis and hydroxyl radical (⋅OH) oxidation, was developed to improve the degradation of sulfamethazine (SMT). SMT is an emerging contaminant with medical toxicity in environmental matrices. In the study of electrolytic production of Ce(IV), the Ce(III)/Ce(IV) redox reaction was found to have good reversibility at high HNO₃ concentrations above 0.5 M, due to more cerium ions being trapped by NO₃^- ions near the anode. In addition, optimum current density of 8 mA cm⁻² and reaction temperature of 313 K, for Ce(IV) production, are determined by considering specific energy consumption (SEC) and Ce(IV) percent yield. The MPEO/H₂O₂ system demonstrates favorable SMT removal efficiencies of 76% and 98%, at treatment times of 60 and 120 min, respectively. This system outperforms the mediated electrochemical oxidation (MEO) and MPEO systems, for SMT degradation. In addition, the kinetics of SMT degradation, using the MPEO/H₂O₂ system, was found to follow a proposed pseudo-first order model, rather than a pseudo-second order model, and exhibit a higher rate constant than those of the MEO and MPEO systems. Moreover, the concentration of ⋅OH during SMT treatment can be estimated by measuring the concentrations of 4-Hydroxybenzoic acid (4-HBA) and 3,4-Dihydroxybenzoic acid (3,4-DHBA), over time. Our findings reveal that introducing UV irradiation and H₂O₂ into the MEO system can induce a higher production of ⋅OH in addition to the Ce(IV) ions, thus leading to improved SMT removal efficiency.