Spatial disposition of square-planar mononuclear nodes in metal-organic frameworks for C2H2/CO2 separation.

The efficient separation of acetylene (C2H2) from its mixture with carbon dioxide (CO2) remains a challenging industrial process due to their close molecular sizes/shapes and similar physical properties. Herein, we report a microporous metal-organic framework (JNU-4) with square-planar mononuclear copper(ii) centers as nodes and tetrahedral organic linkers as spacers, allowing for two accessible binding sites per metal center for C2H2 molecules. Consequently, JNU-4 exhibits excellent C2H2 adsorption capacity, particularly at 298 K and 0.5 bar (200 cm3 g-1). Detailed computational studies confirm that C2H2 molecules are indeed predominantly located in close proximity to the square-planar copper centers on both sides. Breakthrough experiments demonstrate that JNU-4 is capable of efficiently separating C2H2 from a 50 : 50 C2H2/CO2 mixture over a broad range of flow rates, affording by far the largest C2H2 capture capacity (160 cm3 g-1) and fuel-grade C2H2 production (105 cm3 g-1, ≥98% purity) upon desorption. Simply by maximizing accessible open metal sites on mononuclear metal centers, this work presents a promising strategy to improve the C2H2 adsorption capacity and address the challenging C2H2/CO2 separation.