Porous Liquid: A Stable ZIF-8 Colloid in Ionic Liquid with Permanent Porosity

We reported an example of metal-organic framework (MOF)-based porous liquid by dispersing ZIF-8 ({Zn(mim)2}, mim = 2-methylimidazole) nanocrystallites in ionic liquid (IL) of [Bpy][NTf2] ( N-butyl pyridinium bis(trifluoromethyl sulfonyl)imide). Two essential challenges, stable colloid formation and porosity retention, have been overcome to prepare MOF-based porous liquid. Preventing ZIF-8 nanocrystals from aggregation before dispersing is vital to form a stable ZIF-8 colloid in IL via enhancing the interaction between ZIF-8 and IL. The resultant ZIF-8-[Bpy][NTf2] colloid is able to be stable over months without precipitating. [Bpy][NTf2] with larger ion sizes cannot occupy pores in ZIF-8, leaving the ZIF-8 cage empty for enabling access by guest molecules. The porosity of this porous liquid system was verified by positron (e+) annihilation lifetime spectroscopy and I2 adsorption in ZIF-8 in the colloid. MOF-based porous liquids could provide a new material platform for liquid-bed-based gas separations.