An Anion Pillared Metal-Organic Framework for Thermodynamic-Kinetic Synergistic Sieving of Benzene from Benzene/Cyclohexane Mixture.

Adsorption of benzene (Bz) is important to reduce environmental pollution and provide high-purity cyclohexane (Cy). However, the efficient separation of Bz and Cy still faces significant challenges because of their very similar molecular sizes and boiling points. In this work, a fluorine functionalized Metal-Organic Framework (Cu-TiF-TPA, TiF = TiF6 2-, TPA = tri(pyridin-4-yl)amine) is synthesized with a large Brunauer-Emmett-Teller (BET) surface area (1372.1 m2 g-1) and suitable pore size (8.04 Å), and it can achieve molecular sieving of Bz. Cu-TiF-TPA shows higher adsorption capacity of Bz (76.36 cm3 g-1) at 298 K and 1.0 kPa, but the adsorption of Cy is negligible (0.90 cm3 g-1). Correspondingly, the adsorption selectivity value is as high as 456.9 (Bz/Cy, v/v = 1:1). When the temperature rises to 318 K, the adsorption capacity slightly decreases in the low-pressure zone (59.91 cm3 g-1 for Bz, 0.58 cm3 g-1 for Cy), but sieving behavior can still be achieved. Mechanism studies have shown that utilizing anion coordination to regulate pore environment and host-guest interactions is the key to achieving molecular sieving. Meanwhile, the breakthrough experiment further confirms the practical application value of Cu-TiF-TPA even under high flow conditions (200 mL min-1). The research results contribute to the design of efficient benzene adsorbents.