Breaking the trade-off between selectivity and adsorption capacity for gas separation

The trade-off between selectivity and adsorption capacity with porous materials is a major roadblock to reducing the energy footprint of gas separation technologies. To address this matter, we report herein a systematic crystal engineering study of C(2)H(2) removal from CO(2) in a family of hybrid ultramicroporous materials (HUMs). The HUMs are composed of the same organic linker ligand, 4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, pypz, three inorganic pillar ligands, and two metal cations, thereby affording six isostructural pcu topology HUMs. All six HUMs exhibited strong binding sites for C(2)H(2) and weaker affinity for CO(2). The tuning of pore size and chemistry enabled by crystal engineering resulted in benchmark C(2)H(2)/CO(2) separation performance. Fixed-bed dynamic column breakthrough experiments for an equimolar (v/v = 1:1) C(2)H(2)/CO(2) binary gas mixture revealed that one sorbent, SIFSIX-21-Ni, was the first C(2)H(2) selective sorbent that combines exceptional separation selectivity (27.7) with high adsorption capacity (4 mmol·g(−1)).