Simultaneously Enhanced Permeability and Selectivity of Pebax-1074-Based Mixed-Matrix Membrane for CO₂ Separation

Membrane technology is a promising methodology for carbon dioxide separation due to its benefit of a small carbon footprint. However, the trade-off relationship between gas permeability and selectivity is one obstacle to limiting its application. Herein, branched polyethyleneimine (BPEI) containing a rich amino group was successfully grafted on the surface of the metal-organic framework (MOF) of AIFFIVE-1-Ni (KAUST-8) through coordination between N in BPEI and open metal sites in the MOF and with the resultant maintained BET surface area and pore volume. Both the strengthened CO₂ solubility coefficients coming from the additional CO₂ adsorption sites of amino groups in BPEI and the reinforced CO₂ diffusivity coefficients originating from the fast transport channels created by KAUST-8 led to the promising CO₂ separation performance for KAUST-8@BPEI/Pebax-1074 MMM. With 5 wt.% KAUST-8@BPEI loading, the MMM showed the CO₂ permeability of 156.5 Barrer and CO₂/N₂ selectivity of 16.1, while the KAUST-8-incorporated MMM (5 wt.% loading) only exhibited the CO₂ permeability of 86.9 Barrer and CO₂/N₂ selectivity of 13.0. Such enhancement is superior to most of the reported Pebax-1074-based MMMs for CO₂ separation indicating a wide application for the coordination method for MOF fillers with open metal sites.