Fe-doped kelp biochar-assisted peroxymonosulfate activation for ciprofloxacin degradation: Multiple active site-triggered radical and non-radical mechanisms

In this study, a novel iron-doped kelp-derived biochar (KBC) (Fe-KBC) was prepared via a combination of hydrothermal carbonization and pyrolysis, characterized, and tested for ciprofloxacin (CIP) degradation via peroxymonosulfate (PMS) activation. The CIP removal in KBC₈₀₀/PMS was remarkably improved in Fe-KBC₈₀₀/PMS from 63.38% to 97.48%, under optimised condition (CIP 10 mg L⁻¹, KBC₈₀₀/Fe-KBC₈₀₀ 0.1 g L⁻¹, PMS 0.5 mM). It was demonstrated that the CIP degradation in Fe-KBC₈₀₀/PMS was dominantly attributed to the enhanced electron transfer and the generation of radical (SO₄^[rad]−) and non-radical (¹O₂) species, on the surface reactive sites of Fe-KBC₈₀₀, such as defects, O−C=O in graphitic structures, and Fe-oxides, which were induced by the doped Fe. Those also suggest that the Fe was doped via substituting H⁺ in CH_x and K⁺, as well as bonding with O in C−O. The Fe-KBC₈₀₀/PMS showed an excellent degree of mineralization of CIP and the possible CIP degradation pathways were proposed based on identified intermediates. The performance of Fe-KBC₈₀₀/PMS was not significantly affected by reuses and co-existing ions, i.e., K⁺, Na⁺, Ca²⁺, Cl⁻, and SO₄²⁻, while it was inhibited by Mg²⁺, HCO₃⁻, H₂PO₄⁻, HA, and in natural groundwater, which may affect PMS activation. However, it was greatly enhanced by simply increasing PMS dose. The results in this study provides new insights into the reactions in metal-biochar composites and PMS activation thereby, emphasizing the great potential of Fe-KBC₈₀₀/PMS in the control of refractory organics in aqueous phase.