Large-Area Ultrathin Metal–Organic Framework Membranes Fabricated on Flexible Polymer Supports for Gas Separations

Abstract

Ultrathin continuous metal–organic framework (MOF) membranes have the potential to achieve high gas permeance and selectivity simultaneously for otherwise difficult gas separations, but with few exceptions for zeolitic-imidazolate frameworks (ZIF) membranes, current methods cannot conveniently realize practical large-area fabrication. Here, we propose a ligand back diffusion-assisted bipolymer-directed metal ion distribution strategy for preparing large-area ultrathin MOF membranes on flexible polymeric support layers. The bipolymer directs metal ions to form a cross-linked two-dimensional (2D) network with a uniform distribution of metal ions on support layers. Ligand back diffusion controls the feed of ligand molecules available for nuclei formation, resulting in the continuous growth of large-area ultrathin MOF membranes. We report the practical fabrication of three representative defect-free MOF membranes with areas larger than 2,400 cm² and ultrathin selective layers (50–130 nm), including ZIFs and carboxylate-linker MOFs. Among these, the ZIF-8 membrane displays high gas permeance of 3,979 GPU for C₃H₆, with good mixed gas selectivity (43.88 for C₃H₆/C₃H₈). To illustrate its scale-up practicality, MOF membranes were prepared and incorporated into spiral-wound membrane modules with an active area of 4,800 cm². The ZIF-8 membrane module presents high gas permeance (3,930 GPU for C₃H₆) with acceptable ideal gas selectivity (37.45 for C₃H₆/C₃H₈).