Boosting Adsorption and Selectivity of Acetylene by Nitro Functionalisation in Copper(II)-Based Metal-Organic Frameworks

Abstract

Purification and storage of acetylene (C₂H₂) are important to many industrial processes. The exploitation of metal-organic framework (MOF) materials to address the balance between selectivity for C₂H₂ vs carbon dioxide (CO₂) against maximising uptake of C₂H₂ has attracted much interest. Herein, we report that the synergy between unsaturated Cu(II) sites and functional groups, fluoro (-F), methyl (-CH₃), nitro (-NO₂) in a series of isostructural MOF materials MFM-190(R) that show exceptional adsorption and selectivity of C₂H₂. At 298 K, MFM-190(NO₂) exhibits an C₂H₂ uptake of 216 cm³ g^-1 (320 cm³ g^-1 at 273 K) at 1.0 bar and a high selectivity for C₂H₂/CO₂ (up to ~150 for v/v = 2/1) relevant to that in the industrial cracking stream. Dynamic breakthrough studies validate and confirm the excellent separation of C₂H₂/CO₂ by MFM-190(NO₂) under ambient conditions. In situ neutron powder diffraction reveals the cooperative binding, packing and selectivity of C₂H₂ by unsaturated Cu(II) sites and free -NO₂ groups.