Sequential ethane filling induced structural transitions in a flexible-robust metal-organic framework for ethylene...

The preferential identification of inert ethane molecules and the corresponding pore-filling mechanism are fundamentally challenging. Although flexible metal-organic frameworks are considered promising candidates to enhance ethane selectivity, their gate-opening pressures for ethane and ethylene are usually similar, which limits further improvement in their separation performance. Here, we report a flexible-robust metal-organic framework, TYUT-18, whose binary pore system combined with the flexible deformation of the framework produces significantly different gate-opening pressures for ethane (0.18 bar) and ethylene (0.48 bar) at 298 K, effectively reducing competitive adsorption in the same pore and improving overall separation efficiency, and achieves the purification of ultra-high purity ethylene (99.995%) with a separation productivity of 15.7 L kg^-1. More importantly, we have systematically elucidated the dynamic filling behavior of ethane molecules in the flexible-robust framework system, a process of preferentially occupying the large pore cavities then filling into the small ones was uncovered using a combination of extensive single-crystal X-ray diffraction studies and density functional theory calculations. The evolution of this sequential guest-filling mechanism demonstrated the merit of binary pore networks for challenging gas separation tasks and thereby offers valuable insights for the design of highly selective separation materials.