Flexible and highly-loaded mixed-matrix membrane with bi-continuous metal–organic frameworks transfer pathway for gas separation

Abstract

Highly-loaded metal–organic frameworks (MOFs) based mixed matrix membranes (MMMs) are essential for high-efficiency gas separation. However, the continuous distribution of MOFs across the membrane with intensified interface remains challenging. Herein, a flexible and defects-free MMM with a bi-continuous MOFs pathway is constructed by dopamine (DA)-assisted MOFs growth along nanofibers. Nanofibers are used to upload and distribute ZIF-8, which continues to grow via an epitaxial growth strategy to obtain ZIF-8 fibers, achieving ZIF-8 continuous both in long and short range. DA promotes heterogeneous nucleation and growth of ZIF-8 on fiber surface by chelating with Zn2+ through –OH and –NH2 groups. DA also ensures excellent interfacial compatibility by hydrogen bonding interaction between amino groups of DA and ether-oxygen groups of PEO. Finally, the highly-loaded MMM is constructed by in-situ photopolymerization of Poly (ethylene glycol) diacrylate) to embrace ZIF-8 fibers tightly. The resultant MMM presents ZIF-8 loading as high as 72.41 vol% with Young’s modulus of 33.42 MPa, and unchanged morphology and separation performances after bending for 180° over 50 times, revealing outstanding mechanical properties. The CO2 permeability and CO2/N2 selectivity are 280.3 % and 73.0 % higher than the PEO membrane, surpassing the 2019 McKeown upper bound.