Multifunctional covalent organic framework (COF)-Based mixed matrix membranes for enhanced CO2 separation

Covalent organic frameworks (COFs) have stimulated an immense interest for membrane separation owing to their defined nanoscale channels, tailorable chemical functionality, and total organic backbone. However, the development of COF-based membranes for gas separation remains a great challenge due to the limited functional groups and relatively large pore size of the existing COFs. The rational design and appropriate modification of COFs are urgently demanded for more efficient CO2 separation. In this study, we propose a multi-function integration strategy for the design of COF fillers considering entire morphological structure, aperture adjustment and channel decoration, as well as interface optimization. The COF hollow microsphere with polyethylene glycol monomethyl ether (PEG) modification on both outer surface and inner channel wall was synthesized and filled into commercial Pebax polymer to fabricate mixed matrix membranes (MMMs). The hollow structure of COF fillers reduces the mass transport resistance. PEG functionalization provides channel wall with ethylene oxide groups and decreases the COF pore size for simultaneous enhancement of solubility selectivity and diffusion selectivity. Moreover, PEG chains on the outer surface improve the interface compatibility between COF fillers and Pebax matrix. The resulting MMMs exhibit superior CO2/CH4 separation performances, surpassing the 2008 Robeson's upper bound.