Tailored design of mixed-linker MOF membranes for enhanced gas separation

Abstract

Metal-organic framework (MOF) with narrow molecular-sized channels are attractive membrane materials for molecular-sieving gas separation. One of the greatest challenges currently facing MOF membranes is the development of appropriate membranes for specific mixture separation considering the matching of pore sizes. Postsynthetic linker exchange modification for precise control of the pore size could resolve this difficulty and endow MOF membranes with enhanced gas separation property. Herein, an economical and environment-friendly vapor phase linker exchange method is reported to introduce benzimidazole (ZIF-7 linker) and 2-imidazolecarboxaldehyde (ZIF-90 linker) to narrow and enlarge the effective aperture diameter of ZIF-8 framework, respectively. The as-prepared ZIF-8-7 membrane shows extraordinary molecular sieving effect with CO₂/CH₄ separation factor of 62, which soars around thirtyfold compared with the parent ZIF-8 membranes. Intriguingly, the mixed-linker ZIF-8-7 membrane suggests extraordinary long-term stability of more than 300 days. The C₃H₆ permeance of the hybrid ZIF-8-90 membrane has been enhanced by more than 10 times, while maintaining C₃H₆/C₃H₈ selectivity of over 30 which exceeds the requirements for commercial applications. The microstructural engineering and performance manipulation in this work has significantly broadened the separation efficiency of MOF membranes in different application scenarios.