Interpenetrated Three-Dimensional Covalent Organic Framework for Selective Adsorption of C₂H₂ Over CO₂ and C₂H₄

Selective separation of acetylene (C₂H₂) from carbon dioxide (CO₂) and ethylene (C₂H₄) mixtures is critical in the petrochemical industry due to their similar size and physicochemical properties. Developing three-dimensional porous covalent organic frameworks (3D COFs) remains challenging in this context. In this work, a non-symmetrical 2-phenyl pyridine based three-dimensional covalent organic framework (COF-PPy) has been synthesized, which features a rare dia-C9 fold interpenetrated structure as suggested by computational simulations. COF-PPy exhibits high acetylene (C₂H₂) adsorption capacity (4.5 mmol g^-1 at 298 K), as well as excellent separation and purification performance for C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures. The in situ-FTIR studies suggest that the multi-point interactions between nitrogen centers of COF-PPy and H-C≡CH (COF-Pyridine-N···H-C≡C-H and COF-imine-N··H-C≡CH) account for the higher affinities for C₂H₂ over other gases. Furthermore, dynamic breakthrough studies reveal that COF-PPy can be employed as an effective adsorbent for the efficient separation of C₂H₂ from CO₂ and C₂H₄. In addition, COF-PPy exhibits lower heat of adsorption (Q_st) values with high adsorption capacity for C₂H₂ as compared to previously reported C₂H₂-selective adsorbents, indicating less regeneration energy. Our work therefore provides some new avenues for the design and construction of 3D COFs for efficient C₂H₂ capture and separation.