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-α) of a flexible–robust nature for the efficient separation of C 2 H 2 /C 2 H 4 mixtures. The intrinsic porosity of the organic cage and extrinsic porosity of stacking for C 2 H 2 account for its high uptake capacity and selectivity, as evidenced by the large-amplitude continuous-breathing behavior for C 2 H 2 adsorption experiments. But for C 2 H 4, 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-α adsorbs a large amount of C 2 H 2 through a gate opening and only a negligible amount of C 2 H 4 at 253 and 273 K. Breakthrough experiments demonstrate that this flexible, robust material can efficiently separate C 2 H 2 from C 2 H 2 /C 2 H 4 mixtures. Furthermore, NKPOC-1-α is the first POC crystal to exhibit selective adsorption of C 2 H 2 over C 2 H 4, which provides a new direction for the rational design of POCs for industrial gas separations.