Reinforcing CO₂ Permeable Performance of Polyimide Based on Functionalized Multiwall Carbon Nanotubes

Abstract

This study incorporated multiwalled carbon nanotubes (MWCNTs) containing different functional groups (MWCNT-NH 2 , MWCNT-OH, and MWCNT-COOH) into a 6FDA-based copolyimide with a crown ether structure (6FDA-HFBAPP/DAB18C6). The incorporation of functionalized MWCNTs improved the gas permeability of polyimide. MMMs with MWCNT-OH and MWCNT-NH 2 showed significant increases in gas permeability with higher filler content while maintaining high gas selectivity. Gas permeability enhancement in MMMs occurred via two mechanisms:(1) intrinsic MWCNT tunnels acting as fast gas channels and (2) increased free volume between the polymer and MWCNTs, providing more diffusion pathways. Notably, PI/MWCNT-NH 2 with 1 wt % loading maintained comparable selectivity (65.25 for the CO 2 /N 2 gas mixture and 100.82 for the CO 2 /CH 4 gas mixture) while increasing CO 2 permeability by 36−40% (from 95.6 to 134.3 Barrer for the CO 2 /N 2 gas mixture and from 92.8 to 125.9 Barrer for the CO 2 /CH 4 gas mixture), highlighting its potential for CO 2 separation in PI-based MMMs.