Highly efficient separation of C2H2 from CO2 and C2H4 enabled by an anion-pillared metalloporphyrin MOF with sandwich-like binding sites

Abstract

Development of multipurpose adsorbents for highly efficient separation of acetylene (C₂H₂) from carbon dioxide (CO₂) and ethylene (C₂H₄) is of great importance but highly challenging due to their very similar sizes and physical properties. While many adsorbents have been developed to show efficient separation of either C₂H₂/CO₂ or C₂H₂/C₂H₄, multipurpose materials with high selectivities for both gas mixtures are elusive. Herein, we developed an anion-pillared metalloporphyrin SIFSIX material (termed ZJUT-6) as a multipurpose adsorbent for highly efficient separation of C₂H₂ from CO₂ and C₂H₄. Unlike routine SIFSIX materials with strong fluorine binding sites for gas separations, the use of metalloporphyrin as a building block enables ZJUT-6a to create unique sandwich-like binding sites with dual open metal sites, which can more optimally interact with the C₂H₂ molecule over CO₂ and C₂H₄. ZJUT-6a thus exhibits large C₂H₂ capture capacities and simultaneous high C₂H₂/CO₂ (8.9) and C₂H₂/C₂H₄ (12.2) selectivities under ambient conditions. Theoretical simulations reveal that the oppositely adjacent copper(II) centers and porphyrin groups from metalloporphyrin ligands in ZJUT-6a can construct a sandwich-type adsorption site to offer dually stronger interactions with C₂H₂ over CO₂ and C₂H₄. Dynamic breakthrough experiments on ZJUT-6a demonstrate its highly efficient separation of C₂H₂ from actual C₂H₂/CO₂ (50/50) and C₂H₂/C₂H₄ (1/99) gas mixtures.