Permanent cavities in ionic liquids created by metal–organic polyhedra

Abstract

As an emerging type of material, porous liquids combine the fluidity of liquids with the permanent porosity of porous solids, which makes them promising for various applications. Despite several significant attempts earlier, the porous liquid system still requires the novel entries of porous hosts and bulky liquids. Here, we report a new porous liquid system based on the coalition of metal–organic polyhedra and well-designed bulky ionic liquids. As a proof of concept, the typical metal–organic polyhedra, Pd₁₂L₂₄ where L represents the ligands, are employed as porous hosts. Also, a polyethylene glycol-linked bis-imidazolium-based bulky ionic liquid with a molecular size larger than the pore aperture of Pd₁₂L₂₄ is designed as a solvent, yielding type II porous ionic liquids. These liquid materials possessing permanent cavities, good thermal stability and long-term durability have captured high CO₂ compared to neat ionic liquids. Besides, they are found separating CO₂ from N₂ and CH₄ molecules not only as an entity but also as supported porous liquid membranes. We expect that the present strategy can be used to construct other porous liquids with specific functionality for additional applications.