Enhanced Carbamazepine Degradation by Electrochemical Activation of Sulfite on a Metal-free Anode

Abstract

This study developed a metal-free electrosulfite (ES) system using active graphite felt (GF-400) anode to overcome persistent challenges of metal secondary pollution in activated sulfite [S(IV)] procedures. The GF-400 anode demonstrated excellent performance in activating sulfite (S(IV)) to degradation of carbamazepine (CBZ) with a rate constant of 0.056 min^–1, which was 50-fold higher than conventional electro-oxidation (0.001 min^–1) at neutral pH. Quenching experiments and electron spin resonance (ESR) spectroscopy verified SO₄^•– and •OH as dominant reactive species, contributing to 93.1% CBZ removal within 60 min. DFT calculations identified carboxyl groups (−COOH) as the primary active sites (adsorption energy: −1.78 eV), enabling efficient S(IV) activation through a low-energy pathway: SO₃^2– → SO₃^•–→ SO₅^•–/H SO₅^•–→ SO₄^•– (ΔG = −3.9424 eV). Real wastewater tests with more than 83.6% CBZ removal further demonstrated the superiority of the ES system. The ES system maintained stable performance for CBZ degradation over 18 cycles while converting waste SO₂ into value-added oxidants. This technology offers a sustainable dual approach for simultaneous flue gas purification and water treatment.