Restricting Linker Rotation in Nanocages of ZIF‐8 Membranes using Crown Ether “Molecular Locks” for Enhanced Propylene/Propane Separation
Zinan Zhang, Han Zhu, Hua Jin, Yi Cao, Wei Fang, Zhenxin Zhang, Qiang Ma, Jungkyu Choi, Yanshuo Li
Abstract
Abstract ZIF‐8 membranes have long been prized for their exceptional C 3 H 6 /C 3 H 8 separation performance. On the other hand, ZIF‐8 has structural flexibility, where the external pressure triggers channel expansion, potentially deteriorating the molecular sieving ability. Here, we demonstrate a reliable strategy to fine‐tune the flexible pore structure of ZIF‐8 by embedding crown ether within a ZIF‐8 membrane. Benzo‐15‐crown‐5 (15C5) was selected as the cavity occupant and perfectly confined in the sodalite (SOD) cage of ZIF‐8. The 15C5 molecules, which have a size comparable to the nanocage, impose a spatial constraint on linker rotation, enabling the phase transition to a rigid structure in the flexible ZIF‐8. The corresponding 15C5@ZIF‐8 membranes achieve an ultrahigh C 3 H 6 /C 3 H 8 selectivity of 220, outperforming that of most membranes. Unlike their flexible counterparts, the resulting membranes manifest a positive increase in the C 3 H 6 /C 3 H 8 separation factor with elevated pressure, securing a record‐high C 3 H 6 /C 3 H 8 separation factor of 331 under 7 bar. More importantly, extraordinary separation stability was demonstrated with continuous measurement, which is highly desirable for practical applications.