Porous ionic liquids: beyond the bounds of free volume in a fluid phase

Abstract

After reviewing the synthesis, characterisation and applications of more than 150 porous suspensions reported so far in the literature, we conclude that type III porous liquids are either suspensions of pristine MOFs in ionic liquids and liquid polymers or of decorated MOFs in molecular solvents. The first are always stable suspensions, keep the ionic liquids structure and properties and are commonly designated as porous ionic liquids. Original calorimetry measurements reveal a drastic change on the heat effect measured when different MOFs are dispersed in the same ionic liquid or when ZIF-8 is dispersed in different ionic liquids pointing towards distinct solid-ionic liquid interactions. By associating these findings with molecular simulations we highlight the molecular reasons that explain the stability of the porous suspensions which depends not only on the solid-ionic liquid affinity but also on the structure of the ionic liquids near the solid particles. The unique properties of porous ionic liquids thus go beyond those of type III porous liquids in general. They are a new family of porous materials with great potential for all applications where solvents capable of dissolving large quantities of gases or small molecules are required.