High performance of Fe(III)-modified maize stover biochar for adsorptive removal of sulfamethoxazole from aqueous solutions.

The increasing occurrence of antibiotics in the aquatic environment and the associated risks of antibiotic resistance have raised interest in the development of effective remediation technologies. In this study, a magnetic biochar (MSB-Fe) was fabricated from maize stover through Fe(III) impregnation followed by pyrolysis for the adsorption of sulfamethoxazole (SMX) from aqueous solutions. The physicochemical properties, adsorption performance, mechanisms, and reusability of the adsorbent were systematically investigated. Characterization by SEM, BET, FTIR, XPS, and XRD confirmed that Fe modification coupled with pyrolysis significantly improved the surface area, pore structure, and surface chemistry of the biochar, resulting in a high maximum adsorption capacity of 183.19 mg/g, outperforming many lignocellulosic biochars. The adsorption process was well described by the Langmuir isotherm and Pseudo-second-order kinetic models and was found to be spontaneous and endothermic. Mechanistic study indicated that pore filling, hydrogen bonding, Fe-mediated surface complexation, and π-π EDA interactions synergistically governed SMX adsorption. Regeneration tests showed that although a mixture of 0.15 M NaOH and 60% ethanol achieved relatively high desorption efficiency, the adsorption capacity declined after three consecutive cycles, necessitating the search for more effective regeneration strategies. Further studies should evaluate the long-term stability and practical applicability of MSB-Fe in continuous, pilot-scale, real wastewater systems.