Levofloxacin (LVX), a widely used fluoroquinolone antibiotic, persists in aquatic environments due to low removal efficiency (53–78%) in wastewater treatment plants, posing ecological and human health risks via food chain bioaccumulation. Adsorption is a feasible removal technology, but developing low-cost, high-performance adsorbents with good regeneration ability remains challenging. Herein, KOH-modified magnetic rice husk biochar (Fe3O4@BC) was synthesized via KOH activation and one-step hydrothermal method for LVX adsorption. Saturated Fe3O4@BC was regenerated by calcination to form Fe2O3/Fe3O4@BC. Materials were characterized via XRD, SEM, XPS, BET, FT-IR, and zeta potential measurement. Batch experiments evaluated pH, concentration, and temperature effects; kinetics, isotherms, and thermodynamics were analyzed. Characterization confirmed successful Fe3O4 loading. Calcination at 800 °C for 1 h increased the specific surface area of Fe2O3/Fe3O4@BC by 14% with improved mesopores. Its maximum LVX adsorption capacity (99.032 mg/g at 323 K) exceeded Fe3O4@BC (65.030 mg/g at 323 K). Adsorption fitted both pseudo-first-order (R2 > 0.98) and pseudo-second-order (R2 > 0.99) kinetics, reflecting a mixed-control mechanism of physical and chemical adsorption, and Freundlich isotherm (R2 > 0.95) confirming multilayer adsorption consistent with the mixed adsorption nature. Thermodynamics showed positive ΔH (19.443, 22.916 kJ/mol for Fe3O4@BC and Fe2O3/Fe3O4@BC), negative ΔG, and positive ΔS, indicating endothermic, spontaneous, entropy-increasing adsorption. FT-IR/XPS identified the adsorption mechanism, mainly including pore filling, hydrogen bonding interactions between oxygen-containing groups of the adsorbent and nitrogen-containing groups of LVX, and π—π interactions between the graphite like structure of biochar and the aromatic ring of LVX. After five adsorption-regeneration cycles, Fe2O3/Fe3O4@BC retained high capacity, outperforming fresh Fe3O4@BC. This work provides a cost-effective biochar-based adsorbent preparation strategy. The excellent performance of Fe2O3/Fe3O4@BChighlights its potential for industrial LVX-contaminated wastewater treatment.

A Calcination Regeneration Method for KOH Modified Magnetic Rice Husk Biochar with Efficient Adsorption: Preparation, Adsorption Performance for Levofloxacin in Aqueous Solution, and Regeneration Adsorption Mechanism

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2026年2月23日

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Zhiqing Duan,
Xing Wang,
Ziru Li,
Lin Jia,
Yaxin Li,
Min Li,
Wenhao Jin,
Guojia Ji,
Zhi-wei Zhang

摘要

Levofloxacin (LVX), a widely used fluoroquinolone antibiotic, persists in aquatic environments due to low removal efficiency (53–78%) in wastewater treatment plants, posing ecological and human health risks via food chain bioaccumulation. Adsorption is a feasible removal technology, but developing low-cost, high-performance adsorbents with good regeneration ability remains challenging. Herein, KOH-modified magnetic rice husk biochar (Fe₃O₄@BC) was synthesized via KOH activation and one-step hydrothermal method for LVX adsorption. Saturated Fe₃O₄@BC was regenerated by calcination to form Fe₂O₃/Fe₃O₄@BC. Materials were characterized via XRD, SEM, XPS, BET, FT-IR, and zeta potential measurement. Batch experiments evaluated pH, concentration, and temperature effects; kinetics, isotherms, and thermodynamics were analyzed. Characterization confirmed successful Fe₃O₄ loading. Calcination at 800 °C for 1 h increased the specific surface area of Fe₂O₃/Fe₃O₄@BC by 14% with improved mesopores. Its maximum LVX adsorption capacity (99.032 mg/g at 323 K) exceeded Fe₃O₄@BC (65.030 mg/g at 323 K). Adsorption fitted both pseudo-first-order (R² > 0.98) and pseudo-second-order (R² > 0.99) kinetics, reflecting a mixed-control mechanism of physical and chemical adsorption, and Freundlich isotherm (R² > 0.95) confirming multilayer adsorption consistent with the mixed adsorption nature. Thermodynamics showed positive ΔH (19.443, 22.916 kJ/mol for Fe₃O₄@BC and Fe₂O₃/Fe₃O₄@BC), negative ΔG, and positive ΔS, indicating endothermic, spontaneous, entropy-increasing adsorption. FT-IR/XPS identified the adsorption mechanism, mainly including pore filling, hydrogen bonding interactions between oxygen-containing groups of the adsorbent and nitrogen-containing groups of LVX, and π—π interactions between the graphite like structure of biochar and the aromatic ring of LVX. After five adsorption-regeneration cycles, Fe₂O₃/Fe₃O₄@BC retained high capacity, outperforming fresh Fe₃O₄@BC. This work provides a cost-effective biochar-based adsorbent preparation strategy. The excellent performance of Fe₂O₃/Fe₃O₄@BChighlights its potential for industrial LVX-contaminated wastewater treatment.