Highly selective separation of benzene/cyclohexane by 3D covalent organic framework with 8,8-connected bcu net topology

Covalent assembly of organic linkers with higher denticity toward three-dimensional (3D) covalent organic framework (COF) nets of increasing connectivity can not only elevate the architectural intricacy of the framework but also impart it with unprecedented functionalities. The synthesis of highly-connected 3D COFs is in its incipient stage and the 3D COFs built from octadentate linkers are limited to (8,2), (8,3) and (8,4)-connected nets. Here we report the discovery of the first (8,8)-connected 3D COF, TUS-88, having bcu topology by linking an 8-connected D4h-symmetric quadrangular prism node to an 8-connected D2h-symmetric tetragonal prism node. Derived from the π-aromatic conjugated system of pyrene and the abundant aromatic phenyl rings composing the COF scaffold which promotes to stronger π···π interactions with aromatic benzene (Bz) molecules, a superlative Bz uptake of 1618 mg g-1 was achieved for TUS-88, coupled with exemplary cyclohexane (Cy) uptake of 842 mg g-1 and ideal Bz/Cy selectivity of 1.92 which are the current benchmark. Breakthrough experiments accomplished using Bz/Cy (1:1, v/v) mixture corroborated the preferential adsorption of Bz by the COF from the mixture to generate high purity Cy with a significant time interval of 75.4 min g-1 and record-setting Bz/Cy breakthrough selectivity of 2.46.