Exploration of adsorption behavior and mechanism of ciprofloxacin on sediments of the Weihe River

The presence of antibiotic residues in aquatic environments has become a matter of significant concern in the fields of environmental science and global public health. However, research on the adsorption behavior of antibiotics in aquatic environments remains relatively limited. In this study, ciprofloxacin (CIP) was selected as the target contaminant, and sediments from the Wei River were used as the study subject. Through batch equilibrium experiments, combined with kinetic and isotherm models, microscopic representation and density functional theory (DFT) calculation, the adsorption behavior and mechanisms of CIP by sediments were elucidated. The results indicated that the kinetics is consistent with the pseudo-second-order kinetic model (R²>0.999), and the adsorption and desorption behaviors were jointly regulated by multiple mechanisms, with significant hysteresis in desorption. The thermodynamic fitting results showed that the Freundlich model had the best results (R²>0.968), indicating that the adsorption process of CIP on sediments was simultaneously affected by the multi molecular layer adsorption and hydrophobic distribution on heterogeneous surfaces, and that increasing the temperature had an inhibitory effect on the adsorption process. Characterization analysis demonstrated that pore filling, surface complexation, π-π interactions, and hydrogen bonding collectively contributed to the adsorption process. Among them, mineral components (SiO₂, Al₂O₃, and Fe₂O₃) served as the primary active sites, and the contribution of Fe₂O₃ being particularly prominent (70.2%). DFT calculations revealed the differences in different components at the molecular level: SiO₂ is mainly bound by hydrogen bonds, while Fe₂O₃ and Al₂O₃ are mainly surface complexed. Among them, Fe₂O₃ has the highest adsorption energy (-9.722 eV). This study elucidates the multi mechanism synergistic process of sediment adsorption of CIP, providing a theoretical basis for accurately predicting the migration and fate of antibiotics in the environment.