A Polymorphic Azobenzene Cage for Energy‐Efficient and Highly Selective p‐Xylene Separation

Abstract

Developing the competence of molecular sorbents for energy‐saving applications, such as C8 separations, requires efficient, stable, scalable, and easily recyclable materials that can readily transition to commercial implementation. Herein, we report an azobenzene‐based cage for the selective separation of p‐xylene isomer across a range of C8 isomers in both vapor and liquid states with selectivity that is higher than the reported all‐organic sorbents. The crystal structure shows non‐porous cages that are separated by p‐xylene molecules through selective CH–π interactions between the azo bonds and the methyl hydrogen atoms of the xylene molecules. This cage is stable in solution and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest‐induced crystal‐to‐crystal phase transition in non‐porous organic solids for energy‐intensive separations.

Adsorptive Molecular Sieving of Styrene over Ethylbenzene by Trianglimine Crystals

“… 18 Lately, nonporous adaptive crystals (NACs) and organic cages have been proven to be extremely stable and versatile for a wide range of molecular sieving applications, including the selective adsorption of ST over EB employing pillar[6]arene. 19 − 26 Nonetheless, pillar[6]arene crystals can only work via vapor-based adsorption as they are soluble in both EB and ST.…”

Creating porosity in a trianglimine macrocycle by heterochiral pairing

“…The separation of xylene isomers is challenging because they have similar molecular structures and physical properties. Recently, molecular materials such as cucurbit [7]uril 38 and the polymorphic azobenzene cage 39 have been studied as adsorbents for the separation of xylene isomers. The largest included sphere along the free sphere path (D if ) calculated by Zeo++ 31,40 in activated 1-rac is 4.26 Å, which is close to the molecular size of para-xylene (pX) (4.2 Â 6.8 Å) (Table S1, ESI †).…”

Selective adsorptive separation of cyclohexane over benzene using thienothiophene cages

“…Most recently, the easily scalable and processable organic cages with guest-adaptive porosity were successfully used in a wide range of adsorptive separations such xylene isomers separation. [28][29][30][31][32][33][34][35][36][37][38][39] Herein, we report an efficient method to successfully separate Cy from an equimolar Bz/Cy mixture by a thienothiophene organic cage (ThT-cage) with a selectivity of 94% and high recyclability (Scheme 1…”