Multiscale investigation of pefloxacin adsorption on CMCS/MIL-101(Cr)-NH2: synergistic experiments and molecular simulations

This study developed a novel carboxymethyl chitosan/MIL-101(Cr)-NH 2 (CMCS/MIL-101(Cr)-NH 2 ) composite material for the efficient removal of pefloxacin (PEF) from aqueous environments. Experimental results show that the composite possesses a high specific surface area (466.3 m 2 /g) and a hierarchical pore structure, achieving a maximum adsorption capacity of 339.7 mg/g for PEF under optimal conditions (pH = 6, 298 K). The adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm model. Experimental characterization (FT-IR, XPS) suggests that the adsorption involves electrostatic interactions, hydrogen bonding, and π-π stacking. To elucidate the dominant mechanisms at the atomic scale, density functional theory (DFT) calculations were further conducted. DFT calculations revealed multiple interactions between PEF and the MIL-101(Cr)-NH 2 ligand at the electronic level: van der Waals surface penetration analysis confirmed the electrostatic attraction nature of hydrogen bonding; π-electron analysis demonstrated continuous π-electron isosurfaces between aromatic rings, confirming π-π stacking; lone pair electron analysis identified hydrogen bond donor/acceptor sites; Independent Gradient Model (IGM) analysis visually displayed the coexistence of hydrogen bonding and π-π stacking; Hirshfeld surface analysis quantitatively evaluated the contributions of different interaction pairs, indicating that carboxyl-carboxyl interactions are strongest, followed by carboxyl-piperazine, amino-ketone, and amino-piperazine interactions. The key novelties of this work are: (1) the first combination of IGM, Hirshfeld, and van der Waals penetration analysis with experimental characterization for a CMCS–MOF/PEF system; (2) explicit demonstration of a triple–synergistic mechanism (electrostatic–driven, hydrogen–bond–anchored, π–π–stacking–reinforced); and (3) direct mutual validation between DFT predictions and spectroscopic evidence. The theoretical calculations are in excellent agreement with experimental findings, collectively clarifying a multi-mechanism synergistic adsorption process. Furthermore, cycling experiments confirm the good reusability of the material. This work, through a multi-scale strategy, provides a solid theoretical and experimental foundation for the rational design of efficient MOF-based adsorbents for antibiotic removal.