Framework Materials As Porous Liquids

Abstract

Porous liquids have recently been introduced as a new class of material with great potential for gas storage and purification. The permanent porosity and fluid properties of porous liquids provide an avenue for gas storage and transportation that avoids the processing restrictions of solid porous materials. Despite the promise of porous liquids, only a handful of these materials have been realized to date, including functionalized hollow-silica particles, cage-like organic materials, and metal organic frameworks or zeolites suspended in bulky ionic liquids. This work describes an approach to make porous liquids out of covalent organic frameworks (COFs) by functionalizing the outer shell with ionic liquids or liquid polymer chains. COF particle size can be controlled down to 60 nm by varying the solvent and reaction parameters. The injection of a capping agent during synthesis can further control particle size and prevent future aggregation during processing. Click chemistry is one effective synthetic route to functionalize the outer shell with ionic liquids. The functionalized COFs are then suspended in a bulky ionic liquid solvent that is size-excluded from entering the COF pore. Another synthetic route involves directly attaching a liquid polymer chain to the outer framework, thereby introducing stable, unoccupied pores into a liquid. A series of imine-based COFs with different pore and particle sizes are functionalized with liquid polymers and different sizes of ionic liquids. The uptake of various gasses into these materials is then evaluated. This work presents a new type of tunable organic porous liquid that can be used for gas storage and separation.