Exploration of porous metal-organic frameworks for gas separation and purification

As a new generation of porous materials, metal-organic frameworks (MOFs, also known as porous coordination polymers) have shown great promise for gas separation and purification because of their unique pore structures and surfaces for their differential recognition of small gas molecules. In this review article, we summarize our ongoing research endeavors to explore and discover microporous MOFs for gas separation and purification. We have developed several approaches to systematically tune the pores and to immobilize functional sites, including (1) the primitive cubic net of interpenetrated microporous MOFs from the self-assembly of the paddle-wheel clusters, ${\text{M}}_2{\left(\text{C}{\text{O}}_2\right)}_4\left(\text{M}=\text{C}{\text{u}}^{2+},\text{Z}{\text{u}}^{2+}\dots \right)$ ), with two types of organic dicarboxylic acid and pillar bidentate linkers; (2) microporous mixed-metal-organic frameworks (M0 MOFs) through the metallo-ligands, and (3) microporous MOFs with dual functionalities. Such efforts have enabled us to make some breakthroughs on microporous MOFs for gas separation and purification, as demonstrated in the gas chromatographic separation of hexane isomers, kinetic D₂/H₂ separation, acetylene/ethylene separation, carbon dioxide capture, C₂H₂/CO₂ and C₃H₄/C₃H₆ separation. Our group is one of the first groups who have envisioned the practical promise of microporous MOFs for the industrial gas separation and examined their separation capacities and efficiency using the fixed-bed adsorption and/or breakthrough experiments. Some of the very important and representative examples of these microporous MOFs for diverse gas separation and purification are highlighted in this review.