Ionic liquid-assisted COF materials enable fabrication of mixed matrix membranes with high CO2 permeability

Abstract

Mixed matrix membranes (MMMs) have become one of the optimal solutions for the development of high-performance gas separation membranes. Covalent organic frameworks (COFs) with highly ordered porous structures and tunable nanochannel microenvironments show great potential as porous filler materials. However, the large pore size and poor dispersion of COFs limit their enhancement of gas separation performance for mixed matrix membranes. In this work, imidazolium-based ionic liquid (IL) was used to post-modify COF to prepare liquid-like IL@COF materials to compensate for the above drawbacks. IL@COF was introduced into polymer of intrinsic microporosity (PIM-1) to prepare a series of mixed matrix membranes. The size of COF was reduced from the micrometer to the nanometer benefited from the stripping effect of IL. And the excess of IL filled the large pore size of COF narrowed its pore size and increased the affinity of COF for CO₂. COF@IL had better dispersion effects owing to its liquid-like behavior to realize the preparation of highly doped hybrid matrix membranes. In addition, nonequilibrium molecular dynamics simulations and gas transport studies showed that IL@COF provided an ultrafast transport pathway mainly controlled by diffusivity selectivity. At the optimal content, IL@COF/PIM-80 wt% MMM exhibited the best CO₂/N₂ permeability is 25380.40 Barrer and the selectivity of CO₂/N₂ is 17.3. Overall, the combination of IL and COF may provide new inspirations for the design of highly efficient CO₂ separation MMMs.