Optimization and mechanism exploration of NH2-functionalized MIL-101(Fe) for enhanced adsorption of antibiotics in single and binary systems: Experimental analysis and DFT calculations

Antibiotic pollution and resistance spread pose urgent environmental risks, compounded by coexisting multiple antibiotics. To address this, this study aims to enhance the adsorption of typical antibiotics (tetracycline, TC; ciprofloxacin, CIP) through structural and functional modulation of metal-organic frameworks (MOFs). Focusing on MIL-101(Fe), a series of NH 2 -MIL-101(Fe) materials with tunable amination degrees were prepared via a mixed-ligand strategy, which involves adjusting the molar ratio of terephthalic acid (H 2 BDC) to 2-amino terephthalic acid (NH 2 -H 2 BDC). This strategy breaks through the limitations of traditional single-ligand systems. Results revealed that the NH 2 -MIL-101(Fe)-3 (H 2 BDC: NH 2 -H 2 BDC = 1:3) exhibited remarkable adsorption performance in both single and binary systems. The maximum adsorption capacities for TC and CIP reached 827.75 mg/g and 806.26 mg/g, respectively, representing significant increases of 46.34 % and 52.44 % compared to pristine MIL-101(Fe). Although the adsorption capacities decreased in the competitive binary system, they still achieved 641.17 mg/g and 588.43 mg/g for TC and CIP, respectively, outperforming most reported adsorbents. Additionally, NH 2 -MIL-101(Fe)-3 demonstrated robust tolerance to interference from inorganic ions and natural organic matter, along with excellent cyclic regeneration performance. FTIR, XPS, and density functional theory (DFT) calculations clarified mechanisms: -NH 2 groups enhanced the material's polarity and hydrophilicity, facilitating hydrogen bonding; Fe 3 + -antibiotic chelation dominated, supplemented by π-π stacking and pore-filling effects. This multi-mechanism synergy, quantified by DFT-derived binding energies (coordination > hydrogen bonding > π-π interactions). Overall, this study underscores the potential of mixed-ligand functionalized MOFs in addressing complex pollution systems, providing a theoretical foundation for high-performance adsorbent design and antibiotic pollution control.