Citric acid and polyethylene glycol modified Na-cyclodextrin MOFs for efficient antibiotic removal and in-depth investigation of adsorption mechanisms.

Antibiotics in wastewater have a significant threat to human health and ecosystems. Metal-organic frameworks (MOFs) are among the most promising adsorbents for removing antibiotics from wastewater. In the present study, an environmentally friendly sodium-based cyclodextrin metal organic framework (CD-MOF) was synthesized and further modified with citric acid (CA) and polyethylene glycol (PEG) to enhance its water stability and adsorption capacity. The resulting PEG-CA-β-CD-MOF exhibited good water stability and sedimentation properties. The morphology, chemical structure, and physical properties of the resulting PEG-CA-β-CD-MOF was characterized by FT-IR, XRD, zeta potential and TGA. The optimum conditions for removal were obtained at 318 K under neutral conditions, with the actual maximum adsorption capacities for ciprofloxacin hydrochloride (CIP·HCl) and tetracycline hydrochloride (TCH) being 503 mg/g and 326 mg/g, respectively. Adsorption followed the Freundlich model, indicating multilayer adsorption (R2 CIP·HCl = 0.9992, R2 TCH = 0.9901). Kinetic studies showed chemisorption as the dominant mechanism (R2 CIP·HCl = 0.9976, R2 TCH = 0.9997), while thermodynamic parameters revealed an endothermic and spontaneous process (R2 CIP·HCl = 0.9388, R2 TCH = 0.9805). After five regeneration cycles, the removal efficiencies for CIP·HCl and TCH remained at 81 % and 84 %, respectively. Adsorption in simulated wastewater also showed excellent adsorption capacity and selectivity for CIP·HCl and TCH. Mechanism studies indicated that PEG modification, β-CD cavity inclusion, hydrogen bonding, and electrostatic attraction were key to the adsorption process. The environmental-friendly, low-cost sodium based PEG-CA-β-CD-MOF showed good water stability, fast sedimentation, good recyclability and high selectivity, indicating its potential for antibiotic removement in aquatic environment.