Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

Abstract

Separation of acetylene (C2H2) from carbon dioxide (CO2) or ethylene (C2H4) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C2H2 from CO2 and C2H4. Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C2H2 capacity (7.94 mmol/g) and a high C2H2/CO2 (10.3) or C2H2/C2H4 (11.6) selectivity. The calculated capacity of C2H2 per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF62− anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C2H2/CO2 mixtures and 1/99 C2H2/C2H4 mixtures under various conditions with excellent recyclability and benchmark productivity of pure C2H2 (5.13 mmol/g) or C2H4 (48.57 mmol/g).