Improved CO2/N2 separation performance by relatively continuous and defect-free distribution of IL-encapsulated ZIF-67 in ion gel membranes

Metal-organic frameworks (MOFs), as a typical type of porous materials, are widely used as fillers in mixed matrix membranes (MMMs) to enhance the gas separation performance. However, non-selective interface defects are prone to appear in MMMs under high MOF loading conditions, meanwhile, the discontinuous dispersion of MOF particles in polymeric matrices makes the gas molecules diffuse along the MOF-polymer-MOF intersection path and difficult to achieve efficient molecular transfer. These factors greatly compromise the ability of MOF to enhance membrane separation performance. Herein, the [C5min][BF4] encapsulated ZIF-67 (IL@ZIF) composites were embedded into the defect-free IL/Pebax ion gel matrix to form a mixed matrix ion gel membrane without interface defects. On the basis of good interfacial compatibility, the relatively continuous and highly selective CO2 transmission channels were constructed via increasing the filler loading up to 80 wt%. In this context, the typical IL@ZIF/IL/Pebax membrane with 80 wt% IL content and 70 wt% IL@ZIF doping amount exhibits a CO2 permeability of 408.2 Barrer and CO2/N2 selectivity of 97.2, surpassing the latest upper line. This work may have high reference value in the construction and preparation of MOF-based MMMs with high performance in gas separation.

Automated summary

Metal-organic frameworks (MOFs) are commonly used as fillers in mixed matrix membranes (MMMs) to enhance gas separation performance. However, non-selective interface defects and discontinuous dispersion of MOF particles in polymeric matrices affect the efficiency of molecular transfer. This study successfully constructs a defect-free mixed matrix ion gel membrane by embedding [C5min][BF4] encapsulated ZIF-67 (IL@ZIF) composites into an IL/Pebax ion gel matrix, resulting in a CO2 permeability of 408.2 Barrer and CO2/N2 selectivity of 97.2 with 80 wt% IL content and 70 wt% IL@ZIF doping amount. This work has significant reference value for the development of high-performance MOF-based MMMs for gas separation.