What question did this study set out to answer?

This research aims to develop KOH modified magnetic rice husk biochar for effective levofloxacin adsorption and regeneration.

February 24, 2026

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

Key Points

This research aims to develop KOH modified magnetic rice husk biochar for effective levofloxacin adsorption and regeneration.
Synthesis of KOH-modified magnetic rice husk biochar via KOH activation and hydrothermal method.
Characterization of materials using XRD, SEM, XPS, BET, FT-IR, and zeta potential measurements.
Evaluation of adsorption kinetics and isotherms through batch experiments.
Maximum levofloxacin adsorption capacity of Fe 2 O 3 /Fe 3 O 4 @BC reached 99.032 mg/g at 323 K.
Regenerated biochar showed improved adsorption performance over five cycles, indicating longevity of the adsorbent.
Characterization indicated effective pore filling and interactions between biochar and levofloxacin.

Abstract

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 both pseudo-first-order (R 2 > 0.98) and pseudo-second-order (R 2 > 0.99) kinetics, reflecting a mixed-control mechanism of physical and chemical adsorption, and Freundlich isotherm (R 2 > 0.95) confirming multilayer adsorption consistent with the mixed adsorption nature. 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 @BChighlights its potential for industrial LVX-contaminated wastewater treatment.

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