Insight into peroxydisulfate activation by N-BC@Fe3S4 for enrofloxacin degradation through radical and non-radical pathway

Abstract

Nitrogen-doped biochar loaded with Fe₃S₄ (N-BC@Fe₃S₄) was synthesized for peroxydisulfate (PDS) activation to remove antibiotics of enrofloxacin (ENR). Physical and chemical characteristics of N-BC@Fe₃S₄ were examined using scanning electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and X-ray photoelectron spectroscopy (XPS), individually. A comprehensive assessment of operating variables on ENR degradation efficiency was conducted, including PDS concentration, catalyst dosage, initial pH, inorganic anions, humic acid (HA) and diverse water matrices. Under the optimal reaction conditions, N-BC@Fe₃S₄/PDS system exhibited a notably high degradation rate constant for ENR, reaching 0.0538 min⁻¹, which was 1.51 and 22.42 times greater than that in BC@Fe₃S₄/PDS and BC/PDS systems. Quenching experiments and electron paramagnetic resonance (EPR) measurements confirmed the involvement of SO₄•⁻, •OH, and •O₂⁻ in both N-BC@Fe₃S₄/PDS and BC@Fe₃S₄/PDS systems, while ¹O₂ was only appeared in N-BC@Fe₃S₄/PDS system. These observations demonstrated that radical species were produced via PDS activation by Fe²⁺ released from Fe₃S₄, whereas non-radical oxidant of ¹O₂ originated from PDS activation mediated by nitrogen functional groups on BC. In addition, degradation pathway was proposed combined active sites identified by DFT calculation and intermediates analyzed by LC-MS detection. Results showed that piperazine ring cleavage and quinolone moieties transformation were two dominate pathway for ENR degradation. These results demonstrated that N-BC@Fe₃S₄ was a high-performance catalyst for antibiotics degradation, with great potential for practical application.