Competitive adsorption of oxytetracycline and ciprofloxacin on K2CO3-activated sycamore flocculent biochar

This study investigated the competitive adsorption behavior and underlying mechanism of a potassium carbonate-activated sycamore flocculent biochar (KBC-SF) for the simultaneous removal of oxytetracycline hydrochloride (OTC-HCl) and ciprofloxacin (CIP) from aqueous environments. The structural and surface properties of KBC-SF were comprehensively characterized using SEM, FTIR, Raman spectroscopy, XPS, and N 2 adsorption–desorption analysis (BET). OTC-HCl and CIP concentrations quantified by validated UV–Vis spectrophotometry. The biochar exhibited a high specific surface area (1651 m 2 /g) and abundant oxygen-containing functional groups. In binary systems, maximum adsorption capacities at 45 °C reached 533 mg/g for OTC-HCl and 366 mg/g for CIP, which were substantially lower than those in single-solute systems, indicating significant competitive antagonism with OTC-HCl showing stronger affinity. The adsorption followed pseudo-second-order kinetics and was best described by the Freundlich isotherm, suggesting multilayer chemisorption. Thermodynamic parameters confirmed that the process was spontaneous and endothermic. Despite moderate interference from coexisting ions (e.g., Al 3+ , CO 3 2− ) and various real water matrices, KBC-SF maintained nearly complete removal efficiency. The adsorption process was dominated by π–π electron donor–acceptor (EDA) interactions, hydrogen bonding, and pore filling. These findings highlighted the excellent applicability and robustness of KBC-SF for removing coexisting antibiotics in complex aquatic environments.