Unveiling the Flexible-Robust Feature of a Porous Organic Cage Crystal for Acetylene Separation

Porous organic cages (POCs) are promising materials for industrial gas separation applications, although substantial improvements in adsorption selectivity are still being sought. Herein, we report porous organic cage crystals (NKPOC-1-a) of a flexible-robust nature for the efficient separation of C2H2/C2H4 mixtures. The intrinsic porosity of the organic cage and extrinsic porosity of stacking for C2H2 account for its high uptake capacity and selectivity, as evidenced by the large-amplitude continuous-breathing behavior for C2H2 adsorption experiments. But for C2H4, the breathing behavior comes only from the extrinsic porosity and not from the intrinsic porosity of the organic cage, which has been proved by adsorption experiments and molecular dynamics simulations. Furthermore, NKPOC-1-a adsorbs a large amount of C2H2 through a gate opening and only a negligible amount of C2H4 at 253 and 273 K. Breakthrough experiments demonstrate that this flexible, robust material can efficiently separate C(2)H(2 )from C2H2/C2H4 mixtures. Furthermore, NKPOC-1-a is the first POC crystal to exhibit selective adsorption of C2H2 over C2H4, which provides a new direction for the rational design of POCs for industrial gas separations.