Highly porous metal-organic framework liquids and glasses via a solvent-assisted linker exchange strategy of ZIF-8

By combining the porosity of crystalline metal-organic frameworks (MOFs) with the unique processability of the liquid state, melt-quenched MOF glasses offer exciting opportunities for molecular separation. However, progress in this field is limited by two factors. Firstly, only very few MOFs melt at elevated temperature and transform into stable glasses upon cooling of the corresponding MOF liquid. Secondly, the MOF glasses obtained thus far feature only very small porosities and extremely small pore sizes. Here we demonstrate solvent-assisted linker exchange (SALE) as a versatile method to prepare highly porous melt-quenched MOF glasses from the canonical ZIF-8. Two additional organic linkers are incorporated into the non-meltable ZIF-8, yielding high-entropy, linker-exchanged ZIF-8 derivatives undergoing crystal-to-liquid-to-glass phase transitions by thermal treatment. The ZIF-8 glasses demonstrate unprecedented porosities of about 25%, adsorb large amounts of technologically relevant C3 and C4 hydrocarbons, and feature high kinetic sorption selectivities for the separation of propylene from propane.