Fluorine-functionalized 2D covalent organic frameworks with kgd topology for efficient C2H2/CO2 separation

The effective separation of C2H2/CO2 is important for the purification of acetylene. However, because of their highly similar physical properties, separating them efficiently is challenging. Due to the special physical and chemical properties of fluorine, fluorine-containing frameworks have potential applications in gas separation. Here, two isoreticular two-dimensional covalent organic frameworks with kgd topology, defined as TFT-COF and TMT-COF, were designed and constructed via the [6+3] imine condensation reaction. Experimental studies show that the IAST selectivity of a fluorine-functionalized TFT-COF for C2H2/CO2 separation is 4.18, which is higher than that of the fluorine-free counterpart of 2.72, at 298 K and 1 bar. GCMC simulation indicates that the improved selectivity of the TFT-COF for C2H2/CO2 separation arises from the strong electronegativity of fluorine groups and the resulting increased polarity of the pore surface, leading to enhanced C⋯H interactions between C2H2 and the skeleton.