A High-Capacity Molecular Sieve With Ultrafast Adsorption Kinetics for Separating C₃F₆/C₃F₈

The efficient separation of fluorocarbon mixtures, such as perfluoropropene (C₃F₆) and perfluoropropane (C₃F₈), is critical for producing high-purity electronic gases, but remains a formidable challenge due to their similarity in physicochemical characteristics. Herein, we report the size-sieving separation of C₃F₆ and C₃F₈ by a robust zinc-based metal-organic framework, NCU-542, which features a "dual-channel bottleneck-cavity" pore architecture. We show that its specific pore geometry and optimal pore dimensions are beneficial to overcome the intrinsic trade-off between size-sieving precision and diffusion efficiency. The framework contains narrow sieving necks (∼5.2 Å) that fully exclude bulky C₃F₈, interconnected by larger cavities that serve as diffusion highways for C₃F₆. Consequently, NCU-542 exhibits a high C₃F₆/C₃F₈ uptake ratio of 65.6 and a high C₃F₆ capacity of 52.5 cm³ g^-1 at 298 K and 1 bar, while achieving ultrafast adsorption kinetics. In situ IR spectroscopy and DFT calculations elucidate that the specific recognition of C₃F₆ is driven by multiple cooperative C-H···F interactions at the imidazolate-zinc junctions. Furthermore, the shaped pellets of NCU-542 retain excellent structural integrity and separation performance, validating its industrial potential for C₃F₆ and C₃F₈ separation.