Construction of rice husk-derived magnetic biochar and its synergistic roles in adsorption and visible-light-driven photocatalytic degradation of levofloxacin: performance evaluation and mechanistic insights

Abstract

Rice husk-derived magnetic biochar (Fe₃O₄@BC) was fabricated via KOH activation and one-step hydrothermal Fe₃O₄ loading. The composite possessed a specific surface area of 73.99 m² g⁻¹, an average pore diameter of 3.94 nm, and a saturation magnetization of 6.66 emu g⁻¹ enabling efficient magnetic separation. Adsorption experiments showed that Fe₃O₄@BC exhibited a maximum LVX adsorption capacity of 57.83 mg g⁻¹, following pseudo-second-order kinetics and Freundlich isotherm models. Thermodynamic results confirmed spontaneous (ΔG < 0) and endothermic (ΔH = 19.443 kJ mol⁻¹) adsorption, driven by a mixed mechanism of chemisorption (electrostatic interactions, hydrogen bonding, and π–π interactions) and auxiliary physical adsorption (pore filling). In the Fe₃O₄@BC/PMS/visible light system, 95.34% of LVX was degraded. Based on ESR characterization and radical capture experiments, ˙O₂⁻ is the reactive species with the highest relative contribution, while h⁺, ˙OH, and SO₄˙⁻ also participate in the degradation process. Three degradation pathways involving hydroxylation, decarboxylation, and defluorination were proposed. After five consecutive cycles, the degradation efficiency remained 79.66% with a stable structure. This work realizes agricultural waste valorization and provides a synergistic adsorption–photocatalysis strategy for efficient LVX removal, offering technical support for antibiotic-contaminated water remediation.