Effect of Fe-N modification sequence on amoxicillin adsorption by lotus stalk biochar: Structure-activity
Shuangsheng Zhang1, Jing Qiang2, Junjie Zhou3
1College of Environmental Engineering, Xuzhou University of Technology, Xuzhou 221018, China.
Abstract:
Regarding the unclear influence of Fe-N modification sequences on biochar performance, this study systematically investigated the effects of Fe and N introduction sequences on biochar characteristics using lotus stalk as a precursor, urea as the nitrogen source, and FeCl3·6H2O as the iron source. The novelty of this work lies in revealing the synergistic mechanism of Fe-catalyzed carbon gasification coupled with N etching/cross-linking under simultaneous doping conditions, and establishing a clear structure-activity relationship correlating doping sequence with microstructure and adsorption performance. The optimal modified biochar was screened for AMOX adsorption from aqueous solution, and the adsorption mechanisms were elucidated through multi-scale characterization and batch adsorption experiments. The results show that simultaneous Fe-N doping combined with pyrolysis at 700 °C for 4 h (FeN-BC-4h) induced a synergistic effect of Fe-catalyzed carbon gasification and N etching, constructing a hierarchical pore structure with a specific surface area of 752.06 m2 g-1 and a total pore volume of 0.73 cm3 g-1. The equilibrium adsorption capacity for AMOX reached 130.92 mg g-1, surpassing samples with single or sequential doping and representing a 2.55-fold enhancement compared to raw biochar. The surface of FeN-BC-4h was highly heterogeneous, with chemisorption dominating the adsorption process. Intraparticle diffusion served as the rate-controlling step, and the adsorption was an endothermic spontaneous reaction that increased system disorder. The adsorption mechanisms included pore filling, π-π electron donor-acceptor interactions, hydrogen bonding, Fe-O/Fe-N coordination complexation, and electrostatic interactions. FeN-BC-4h maintained stable and efficient adsorption within the pH range of 4-9, exhibited magnetic responsiveness, and retained approximately 67.03% of its adsorption capacity after three regeneration cycles via HCl washing. This research provides theoretical insights and technical references for the high-value utilization of lotus stalk-based biochar and the efficient removal of antibiotic pollutants.
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