Poly(ionic liquids-acrylic acid)-modified MIL-101(Cr) metal−organic frameworks: Preparation and efficient adsorption of europium

A novel composite material, Poly(IL-AA)@MIL-101(Cr), combining metal–organic framework, polymeric ionic liquid and acrylic acid, was synthesized for the selective and efficient adsorption of rare earths europium(III) (Eu³⁺). Characterization of the materials was carried out using techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET). The results demonstrate successful incorporation of the polymeric ionic liquid onto the material surface while preserving the crystal structure and morphology of MIL-101(Cr). Adsorption experiments were conducted to explore parameters including equilibrium pH, initial Eu³⁺ concentration, and duration, with comprehensive analyses of adsorption kinetics, isotherms, and mechanisms. Findings reveal that Poly(IL1-AA)@MIL-101(Cr), Poly(IL3-AA)@MIL-101(Cr), and Poly(IL5-AA)@MIL-101(Cr) achieve adsorption equilibrium for Eu³⁺ at approximately 9 h with an equilibrium pH of 6.2. The adsorption of Eu³⁺ predominantly follows a pseudo-second-order kinetic model and Langmuir isotherm adsorption model. Moreover, the prepared composite material exhibits superior adsorption selectivity for Eu³⁺ over other metal ions in the mixture (K⁺, Mg²⁺, Ni²⁺, Co²⁺, Zn²⁺, La³⁺, and Nd³⁺). Even after five adsorption–desorption cycles, the composite material maintains satisfactory adsorption performance.