The synthesis of amide bond by a simple one-step method to connect ionic liquid and MIL-101-NH₂ firmly for efficient CO₂ cycloaddition

Finding robust combination modes between ionic liquids and MOFs is still a challenge. In this work, using a simple one step-synthesis method, the ionic liquid was grafted onto MOF without any additives, and the binding mode of the two was characterized by means of XPS, FT-IR, TGA, SEM etc. It was found that the carboxyl group in the ionic liquid bonded with the amino group in MOF to form an amide bond. Thus, a novel stable composite material MIL-101-NH₂-1-carboxypropyl-3-methylimidazolium bromine (1-C-3-M@MIL-101-NH₂) was synthesized. This composite employed as a catalyst for CO₂ cycloaddition demonstrated excellent catalytic activity, achieving a target product PC (Propylene carbonate) yield of 91.7 % under the conditions of 80 °C, 1.0 MPa, and a reaction time of 4 h, without the addition of any co-catalysts or solvents. The good catalytic activity was benefit from the synergistic effect of Lewis acidic Cr centers and nucleophilic Br^-, as well as the high specific surface area and good CO₂ affinity of 1-C-3-M@MIL-101-NH₂. In addition, owing to this robust bonding configuration, the catalyst can be recycled up to five times without losing activity. It is a potential catalyst for CO₂ capture and conversion.