Binary All-Nanoporous Composite Membrane Constructed via VaporPhase Transformation for High-Permeance Gas Separation

The metal-organic framework (MOF) membranes with ultra-small pore size (< 4 A) have shown a great perspective for the highly selective separation of small gas molecules such as hydrogen, while the narrow channels may result in the low gas permeance. To improve the gas permeance of ultra-microporous MOF membranes, the stable covalent organic framework (COF) with large and uniform pore is doped to construct a binary COF/MOF all-nanoporous composite (ANC) membrane, equivalent to reducing the effective membrane thickness but avoiding the challenging ultra-thin membrane preparation. The COF synthesized by ball milling is combined with the metal gel to form the precursor membrane, which then transformed to COF/MOF ANC membrane by the treatment of the MOF ligand vapor. A very small amount of solvent has been applied, offering an environmental-friendly preparation process. Compared with the pristine MOF membrane, the COF/MOF ANC membranes possess the highly improved gas permeance from 22 GPU to 551 GPU with a slight sacrifice of selectivity, which introduces a new strategy to optimize the separation performance of MOF membranes.