Customizing Pore System in a Microporous Metal-Organic Framework for Efficient C₂H₂ Separation from CO₂ and C₂H₄

Selective-adsorption separation is an energy-efficient technology for the capture of acetylene (C₂H₂) from carbon dioxide (CO₂) and ethylene (C₂H₄). However, it remains a critical challenge to effectively recognize C₂H₂ among CO₂ and C₂H₄, owing to their analogous molecule sizes and physical properties. Herein, we report a new microporous metal-organic framework (NUM-14) possessing a carefully tailored pore system containing moderate pore size and nitro-functionalized channel surface for efficient separation of C₂H₂ from CO₂ and C₂H₄. The activated NUM-14 (namely NUM-14a) exhibits sufficient pore space to acquire excellent C₂H₂ loading capacity (4.44 mmol g^-1) under ambient conditions. In addition, it possesses dense nitro groups, acting as hydrogen bond acceptors, to selectively identify C₂H₂ molecules rather than CO₂ and C₂H₄. The breakthrough experiments demonstrate the good actual separation ability of NUM-14a for C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures. Furthermore, Grand Canonical Monte Carlo simulations indicate that the pore surface of the NUM-14a has a stronger affinity to preferentially bind C₂H₂ over CO₂ and C₂H₄ via stronger C-H···O hydrogen bond interactions. This article provides some insights into customizing pore systems with desirable pore sizes and modifying groups in terms of MOF materials toward the capture of C₂H₂ from CO₂ and C₂H₄ to promote the development of more MOF materials with excellent properties for gas adsorption and separation.