Supramolecular Metal-Organic Framework for CO2/CH4 and CO2/N-2 Separation

Supramolecular metal-organic frameworks (SMOFs) are emerging as a new family of porous materials. In this work, a SMOF, [Cu-2(ade)(4)(H2O)(2)](SiF6)(2) (SMOF-SIFSIX- 1, ade = adenine) was successfully synthesized from the cationic complex of copper and adenine and hexafluorosilicate anions by a slow diffusion method and was demonstrated for trapping carbon dioxide in preference to methane and nitrogen. With one-dimensional pores of about 3.6 x 3.6 angstrom to induce their distinguishing interactions with the three components, SMOF-SIFSIX-1 exhibited excellent selective gas sorption behaviors for CO2/CH4 (50:50) and CO2/N-2 (15:85) gas mixtures with ideal adsorbed solution theory selectivities of 21.1 and 131.7 at 273 K and 100 kPa pressure, respectively, outperforming most of reported hydrogen-bonded organic frameworks so far. Neutron powder diffraction and DFT-D calculations were also carried out to investigate the CO2 adsorption configuration on SMOF-SIFSIX-1a, which suggested that this framework catch CO2 due to "C-F" and "O-H" supramolecular interactions between CO2 molecules and SMOF-SIFSIX-1a. This study demonstrates that the rarely studied SMOF material shows promising potential in gas adsorption separation.