Temperature-responsive crystal dynamic accelerates sieving of propane/propylene mixtures

Abstract

Soft nanoporous crystals with structural dynamics are among the most exciting of recently discovered materials. However, designing or controlling this system, which can recognize very similar gases, remains a challenge. Here we report a soft crystal (NTU-68) in which one-dimensional channel opening delicately expands and contracts ~4 Å at elevated temperature. A completely different adsorption model for propane (C3H8: kinetic dominance) and propylene (C3H6: thermodynamic preference) allows sieving of C3H8/C3H6 mixtures at 273 K (10 min·g-1), as well as boosted performance at 298 K (22 min·g-1). This 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 model calculations reveal that slight pore enlargement in the temperature response provides plausible traffic for C3H6 but remains constriction on C3H8. The finely controlled dynamic systems and efficient molecular recognition provide a new route for design of next-generation sieve materials.