Exploring the mechanism of norfloxacin removal and active species evolution by coupling persulfate activation with biochar hybridized Fe₃O₄ composites

In situ growth of dispersed active sites on substrates is a strategy for designing highly efficient catalysts for sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs). Here, magnetic biochar composite (Fe₃O₄/BC) was fabricated as an activator to trigger PDS (peroxydisulfate) for norfloxacin (NOR) removal, achieving reliable NOR removal efficiency (>90%) within 10 min. Based on the synergistic effect between Fe₃O₄ and BC, the removal rate increases to 0.0265 L mg^-1 min^-1. Fe₃O₄/BC exhibited decent adaptability, stability, and recyclability toward affecting factors variation during PDS activation, attributed to the synergistic effect between Fe₃O₄ and BC. The electron transfer of magnetic Fe₃O₄ coupled with the adsorption and conduction function of carbon skeleton, which overcomes typical problems as crystal agglomeration, metal leaching, and catalysts recovery etc. The electron-rich Fe(II) sites promote the radical pathway by generating reactive oxygen species (ROS, ^•OH, SO₄^•- and O₂^•-), and radicals evolution contributing to the form of ¹O₂ in non-radical pathway. Under the effect of multipath in NOR degradation, HPLC-QTOF-MS spectroscopy and DFT calculation revealed the possible degradation pathway of NOR. In addition, according to toxicity prediction, the overall NOR contamination toxicity of NOR was effectively alleviated by Fe₃O₄/BC + PDS system. Overall, this study presents a promising composite in PDS activation and views the active species evolution in the NOR removal system, which is crucial for mechanism study in relevant research in the future.