Combination of Low-Polar and Polar Binding Sites in Aliphatic MOFs for the Efficient C₂H₆/C₂H₄ Separation

The selective capture of C2H6 from C2H6/C2H4 mixtures is of critical importance to realize the efficient one-step purification of C2H4 but remains challenging due to their similar properties and smaller quadrupole moment of C2H6 that usually result in C2H4-preferring adsorption. Herein, we reported two isostructural pillared-layer metal-organic frameworks, ZUL-C3 and ZUL-C4, which were constructed by mixed polycycloalkane-type ligands. Their low-polar pore environment along with more accessible low-polar C-H binding sites on the pore surface are conducive to generate more van der Waals interactions with C2H6 while the carboxylic groups distributed at four corners of pores form stronger and more dipolar interactions with C2H6, cooperatively resulting in a good C2H6/C2H4 uptake ratio of 1.50 for ZUL-C3 and 1.72 for ZUL-C4 in static adsorption experiments and a high C2H4 (>99.99% purity) productivity of 10.1 L/kg for ZUL-C3 and 14.6 L/kg for ZUL-C4 from an equimolar C2H6/C2H4 mixture in breakthrough experiments.