Differential adsorption mechanism of norfloxacin and tylosin by potassium salt modified biochar: Experimental and DFT studies

Developing efficient and low-cost adsorbents is essential for removing antibiotics of different molecular sizes from water. This study prepared potassium-modified biochar (K-NBC) from waste peanut meal using potassium formate as an activation agent. Innovatively and simultaneously selects the polar small-molecule antibiotic norfloxacin (NOX) and the lipophilic macromolecular antibiotic tylosin (TY) as target contaminants, and systematically investigates their adsorption behaviors. The results demonstrate that K-NBC exhibits a high specific surface area (2215.78 m²·g −1 ), rich micropores, and abundant oxygen-containing groups. showing maximum capacities of 1275.64 and 730.31 mg·g −1 at 45°C, respectively. NOX adsorption followed pseudo-second-order kinetics, while TY adsorption fitted the Elovich model; both isotherms matched the Freundlich model. Optimal NOX adsorption occurred at pH 5–8, whereas TY adsorption was less pH-sensitive. Multivalent cations significantly inhibited adsorption. Combined experiments and DFT simulations revealed the primary mechanisms as micropore filling, hydrogen bonding, and π-π interactions, highlighting a molecular sieving effect: the microporous structure favored NOX, while TY was limited by size. DFT confirmed the strongest interaction and highest adsorption energy (-228.28 kJ·mol −1 ) for neutral NOX. This study presents a feasible strategy for waste biomass resource utilization. More importantly, it elucidates for the first time the matching mechanism between biochar microporous structure and antibiotics with different molecular sizes, and offers a solid theoretical basis and rational material design guidelines for the precision adsorption remediation of antibiotics in aqueous solutions. Download: Download high-res image (226KB) Download: Download full-size image