Effect of Fe-N modification sequence on amoxicillin adsorption by lotus stalk biochar: Structure-activity relationship and dominant mechanisms.

, 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.