Peroxymonosulfate activated by Co-doped lignin-based biochar for efficient degradation of norfloxacin: singlet oxygen plays a dominant role

Abstract

Norfloxacin (NOR) is a common fluoroquinolone antibiotic which is difficult to completely remove through traditional water treatment methods. In this study, a cobalt-doped lignin-based biochar catalyst (CoBC700) was prepared through impregnation and one-step pyrolysis. CoBC700 was coated with well-dispersed multivalent cobalt species, which activated PMS to achieve 95.98% removal of NOR within 30 minutes, with a rate constant reaching 0.3642 min⁻¹, which was significantly higher than that for CoBC550 and CoBC850. Quenching experiments and EPR analysis indicated that NOR was mainly removed by a non-free radical pathway (¹O₂), with the SO₄˙⁻ playing a minor role. The redox cycling of Co⁰/Co²⁺/Co³⁺, in synergy with carbon defects, promoted interfacial electron transfer and selective PMS activation. The system exhibited good stability in the pH range of 3–9, and maintained a removal efficiency of 81.98% after five cycles. Combining DFT calculations and LC–MS, the possible degradation pathways of NOR were proposed. Toxicity assessment showed that the toxicity of most intermediates was lower than that of NOR. This Co-defect synergy strategy provides a pathway to design efficient and environmentally friendly PMS activators.