A gating ultramicroporous metal-organic framework showing high adsorption selectivity, capacity and rate for xylene separation

Adsorptive separation of p -xylene ( p X) from xylene isomers is a key process in chemical industry, but known adsorbents cannot simultaneously achieve high adsorption selectivity, capacity, and rate. Here, we demonstrate gating ultramicropore as a solution for this challenge. Slight modification of the synthetic condition gives rise to isomeric metal-organic frameworks α-[Zn(pba)] (MAF-88, H 2 pba = 4-(1 H -pyrazol-4-yl)benzoic acid) and β-[Zn(pba)] (MAF-89) possessing similar pillared-column structures, porosities, and high p X capacities of 2.0 mmol g −1 , but very different framework/pore topologies, pore sizes, and p X selectivities. For binary and ternary mixtures of liquid xylene isomers, MAF-88 with narrow one-dimensional (1D) channels shows p X selectivity of 11 and 1.6, while MAF-89 with 3D-connected quasi-discrete pores shows p X selectivity up to 221 and 46, respectively. Thermogravimetry, differential scanning calorimetry, and time-dependent separation experiments reveal that the kinetic effects of the gating pores play more important roles than the thermodynamic effects, which is further confirmed by single-crystal X-ray diffraction and computational simulations.