A new SIFSIX anion pillared cage MOF with crs topological structure for efficient C2H2/CO2 separation

Abstract

Due to the similar physicochemical properties of acetylene (C₂H₂) and carbon dioxide (CO₂), separating C₂H₂ from a CO₂/C₂H₂ mixture poses a significant challenge in the petrochemical industry. Herein, we successfully synthesized a novel SiF₆²⁻ anion pillared cage metal-organic framework ZNU-15 possessing a new crs topological structure for the selective capture of C₂H₂. As a linear bidentate linker, the fluorinated SiF₆²⁻ anion partitions the pores into various sized cages. ZNU-15 displays moderate adsorption for C₂H₂ with a capacity of 36.0 cm³ g⁻¹ at 298 K and 1 bar, which is 2.7 times higher than the CO₂ uptake. The IAST selectivity of C₂H₂/CO₂ for ZNU-15 at 298 K and 100 kPa is 10.5, surpassing that of most reported materials. The Q_st values for C₂H₂ and CO₂ at zero coverage are 54.0 and 42.8 kJ mol⁻¹, respectively. Moreover, breakthrough experimental tests show that ZNU-15 is capable of effectively separating C₂H₂ from a C₂H₂/CO₂ mixture. Theoretical calculations further indicate that C₂H₂ is preferentially trapped by the small cage with four cooperative hydrogen bonds.