Performance and mechanism of sulfamethoxazole degradation on a Magnéli-phase Ti4O7 reactive electrochemical membrane

Abstract

Antibiotics have emerged as a new class of environmental contaminants of global concern due to their persistence and potential ecotoxicological impacts. In order to enhance antibiotic removal efficiency, it is necessary to develop cost-effective and environmentally friendly wastewater treatment technologies. Magnéli-phase titanium oxide (Ti₄O₇) presents a promising solution, combining excellent metallic-like conductivity with ceramic-like corrosion resistance. In this study, the electrochemical oxidation of sulfamethoxazole (SMX) with a Ti₄O₇ reactive electrochemical membrane (REM) as the anode and stainless steel as the cathode was systematically investigated. The effects of key operational parameters, including current density, initial pH, supporting electrolyte type and concentration, and the presence of humic acid (HA) on SMX degradation were evaluated. Under optimal conditions (current density of 0.08 mA cm⁻², pH of 7, supporting electrolyte of 0.1 mol L⁻¹ Na₂SO₄, no HA effect, and pump circulation), 99.7% SMX degradation was achieved within 2 hours. Quenching experiments and electron paramagnetic resonance (EPR) analysis confirmed that hydroxyl radicals (˙OH) played a dominant role in SMX degradation. High-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (HPLC-Q-TOF-MS/MS) identified key degradation intermediates, revealing three primary SMX degradation pathways: (1) ˙OH-mediated amino group oxidation, (2) S–N bond cleavage, and (3) –NH₂ hydroxylation. Additionally, Ecological Structure Activity Relationships (ECOSAR) software analysis demonstrated a significant reduction in overall toxicity following Ti₄O₇ oxidation. In summary, the Ti₄O₇ REM exhibits exceptional oxidation efficiency with low energy consumption, demonstrating strong practical feasibility and promising application potential for antibiotic-contaminated wastewater treatment.