Mechanistic insights into selective and pH-independent removal of sulfamethazine by Fe₂O₃-functionalized lignin-derived biochar

Abstract

In this study, a novel recycling strategy was developed to convert lignin waste into magnetic Fe₂O₃-functionalized biochar (Fe@LBC) for selective sulfonamide removal. A high adsorption capacity for sulfamethazine of 39.92 ± 0.14 mg/g was achieved within 360 min using Fe@LBC prepared by impregnation with 0.125 mol/L FeCl₃ followed by calcination at 800 °C, which was approximately 2.6 times that of LBC. Kinetic, isotherm, and thermodynamic analyses revealed that sulfamethazine adsorption on Fe@LBC was dominated by chemisorption-related surface interactions, with intraparticle diffusion also contributing to the overall adsorption process. In addition, Fe@LBC showed superior tolerance to the interference from coexisting salts and organic matter during the adsorption process. Notably, in contrast to LBC, Fe@LBC exhibited enhanced adsorption performance, stable adsorption over a broad pH range (3−9), and preferential selectivity toward sulfonamide antibiotics. According to the regeneration tests, Fe@LBC further exhibited satisfactory reproducibility and recyclability. Moreover, density functional theory calculations and X-ray photoelectron spectroscopy analyses confirmed that Fe₂O₃ coordination was the dominant mechanism responsible for selective sulfonamide binding. This study highlights a viable pathway for lignin valorization and provides a cost-effective, high-performance adsorbent for antibiotic-contaminated wastewater.

Graphical abstract

Keywords

Lignin / Fe₂O₃ / Sulfamethazine / pH adaptability / Preferential selectivity

Highlight

	● Lignin waste was upcycled into magnetic Fe2O3-functionalized biochar.
	● Fe@LBC exhibited high and pH-tolerant adsorption of sulfonamide antibiotics.
	● Fe@LBC showed strong anti-interference ability and selective sulfonamide uptake.
	● Fe2O3 complexation dominated selective sulfonamide adsorption mechanisms.

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