Mn₃O₄/biochar catalyst for enhanced PMS activation and antibiotic degradation via radical and non-radical pathways

Metronidazole (MNZ) presents a significant threat to both human health and aquatic environments due to its environmental stability, antimicrobial properties, and capacity to promote drug resistance. Despite this, the effective and environmentally sound elimination of this compound remains a significant hurdle. This study introduces a hydrothermal and co-precipitation approach to synthesize a Mn₃O₄/biochar composite catalyst. This catalyst was engineered to activate peroxymonosulfate (PMS) and thereby expedite the removal of MNZ. The Mn₃O₄/biochar/PMS system exhibited outstanding catalytic efficacy, achieving a complete removal and a kinetic constant of 0.1402 min^-1 within a 30 minute timeframe under optimal conditions. The degradation of MNZ was consistently effective under various conditions, including different catalyst amounts, concentrations of PMS, initial pollutant concentrations, initial pH levels, the presence of inorganic anions, humic acid, and different water sources. The identification of reactive species through quenching experiments corroborated that sulfate (SO₄˙^-) and hydroxyl radicals (˙OH) were the main contributing factors in activating PMS for MNZ degradation, along with the minor contribution of singlet oxygen (¹O₂). Mechanistic studies also revealed that the efficient activation of PMS was facilitated by redox cycling between Mn²⁺/Mn³⁺/Mn⁴⁺. Additionally, possible MNZ degradation pathways were identified through UPLC-QTOF/MS analysis. Consequently, this study accomplished the development of highly stable, environmentally friendly, and efficient catalysts for PMS activation with lower metal leaching, thereby offering a promising method for effectively removing persistent organic pollutants from real-world water sources.