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

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 cm 2 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 C 3 H 6 , with good mixed gas selectivity (43.88 for C 3 H 6 /C 3 H 8 ). To illustrate its scale-up practicality, MOF membranes were prepared and incorporated into spiral-wound membrane modules with an active area of 4,800 cm 2 . The ZIF-8 membrane module presents high gas permeance (3,930 GPU for C 3 H 6 ) with acceptable ideal gas selectivity (37.45 for C 3 H 6 /C 3 H 8 ).