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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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 (Fe 3 O 4 @BC) was synthesized via KOH activation and one-step hydrothermal method for LVX adsorption. Saturated Fe 3 O 4 @BC was regenerated by calcination to form Fe 2 O 3 /Fe 3 O 4 @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 Fe 3 O 4 loading. Calcination at 800°C for 1 h increased the specific surface area of Fe 2 O 3 /Fe 3 O 4 @BC by 14% with improved mesopores. Its maximum LVX adsorption capacity (99.032 mg/g at 323 K) exceeded Fe 3 O 4 @BC (65.030 mg/g at 323 K). Adsorption fitted pseudo-second-order kinetics (R 2 > 0.99, chemical adsorption dominant) and Freundlich isotherm (R 2 > 0.95, multilayer adsorption). Thermodynamics showed positive ΔH (19.443, 22.916 kJ/mol for Fe 3 O 4 @BC and Fe 2 O 3 /Fe 3 O 4 @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, Fe 2 O 3 /Fe 3 O 4 @BC retained high capacity, outperforming fresh Fe 3 O 4 @BC. This work provides a cost-effective biochar-based adsorbent preparation strategy. The excellent performance of Fe 2 O 3 /Fe 3 O 4 @BC highlights its potential for industrial LVX-contaminated wastewater treatment.
