Two novel 4,6-connected anion-pillared metal-organic frameworks for simultaneous separation of C3 and C4 olefins

The adsorptive separation of C3 (propane/propylene) and C4 olefins (1,3-butadiene/C4 alkenes) by a single material are of great commercial significance to make full use of these raw chemicals and adsorbents; however, the precise fabrication of porous materials with fine-tuning pores and multiple binding sites to discriminate these guest molecules remain challenging. Herein, we report two new 4,6-connected fsc-net anion-pillared copper MOFs (TIFSIX-Cu-TPB and SIFSIX-Cu-TPB) for which the cavity and functional sites can be tuned by altering the anion pillars. The unique pore structure and abundant electronegative anions, as well as aromatic rings of MFSIX-Cu-TPB (M = Ti, Si), enabled the selective discrimination of both propylene/propane (C3H6/C3H8) and 1,3-butadiene/C4 olefins, displaying high propylene (2.85 mmol g−1) and 1,3-butadiene (3.35 mmol g−1) uptake at 1 bar and 298 K. Their separation performances are confirmed by breakthrough experiments, and the adsorption sites are identified by DFT-D calculations. To the best of our knowledge, the MFSIX-Cu-TPB (M = Ti, Si) represent the first example of anion-pillared MOFs that demonstrate the high separation efficiency in C3 and C4 olefin separations.