Delicate Softness in a Temperature-Responsive Porous Crystal for Accelerated Sieving of Propylene/Propane.

Soft nanoporous crystals with structural dynamics are among the most exciting recently discovered materials. However, designing or controlling a porous system with delicate softness that can recognize similar gas pairs, particularly for the promoted ability at increased temperature, remains a challenge. Here, we report a soft crystal (NTU-68) with a one-dimensional (1D) channel that expands and contracts delicately around 4 Å at elevated temperature. The completely different adsorption processes of propane (C3H8: kinetic dominance) and propylene (C3H6: thermodynamic preference) allow the crystal to show a sieving separation of this mixtures (9.9 min·g-1) at 273 K, and the performance increases more than 2-fold (20.4 min·g-1) at 298 K. This phenomenon is contrary to the general observation for adsorption separation: the higher the temperature, the lower the efficiency. Gas-loaded in situ powder X-ray analysis and modeling calculations reveal that slight pore expansion caused by the increased temperature provides plausible nanochannel for adsorption of the relatively smaller C3H6 while maintaining constriction on the larger C3H8. In addition, the separation process remains unaffected by the general impurities, demonstrating its true potential as an alternative sorbent for practical applications. Moving forward, the delicate crystal dynamics and promoted capability for molecular recognition provide a new route for the design of next-generation sieve materials.