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 (Qst) 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.