Efficient Adsorption of Ionic Liquids in Water Using −SO₃H-Functionalized MIL-101(Cr): Adsorption Behavior and Mechanism

With the increasing application of ionic liquids (ILs) in industrial areas, the removal of ILs from aqueous media has attracted considerable attention due to their potential environmental impact. In this study, we investigated the adsorption behavior and removal mechanism of ILs in water using the metal-organic framework material MIL-101(Cr) and its sulfonated derivative MIL-101(Cr)-SO₃H. It was observed that MIL-101(Cr)-SO₃H exhibited notably elevated adsorption capacity (1.19 mmol/g) and rapid adsorption kinetics (1.66 g/mmol·min^-1) for [C₄mim]Cl in comparison to its unmodified form, underscoring the impact of strategic sulfonation on enhancing adsorption. Also, MIL-101(Cr)-SO₃H showcased the effective removal of various ILs featuring diverse cations and varying anions, highlighting its broad-spectrum capture capacities. The adsorption process is less influenced by the type of cations and anions. In contrast, enhanced adsorption of [C₁₆mim]Cl by MIL-101(Cr)-SO₃H demonstrated that the length of the alkyl chain of ILs' cation exerted a more significant influence on the adsorption than the type of head and tail group. This enhancement is attributed to a synergistic interplay of pore filling, electrostatic interactions, hydrophobic interactions, and micelle enrichment. These findings provided valuable insights into optimizing the design of metal-organic framework materials for the efficient removal of IL pollutants.