Modular Type III Porous Liquids based on Porous Organic Cage Microparticles

Abstract

The dispersion of particulate porous solids in size-excluded liquids has emerged as a method to create Type III porous liquids, mostly using insoluble microporous materials such as metal-organic frameworks (MOFs) and zeolites. Here, we present the first examples of Type III porous liquids based on porous organic cages (POCs). By exploiting the solution processability of the POCs, racemic and quasiracemic cage microparticles were formed by chiral recognition. Dispersion of these porous microparticles in a range of size-excluded liquids, including oils and ionic liquids, formed stable POC-based Type III porous liquids. The flexible pairing between the solid POC particles and a carrier liquid allows the formation of a range of compositions, pore sizes, and other physicochemical properties to suit different applications and operating conditions. For example, we show that it is possible to produce porous liquids with relatively low viscosities (7-14 mpa•s) or high thermal stability (325 °C). A 12.5 wt. % Type III porous liquid comprising racemic POC microparticles and an ionic liquid, [BPy][NTf2], shows a CO2 working capacity (104.30 μmol/gL) that is significantly higher than the neat ionic liquid (37.27 μmol/gL) between 25 °C and 100 °C. This liquid is colloidally stable and can be recycled at least 10 times without loss of CO2 capacity.