Confining Water Nanotubes in a Cu₁₀O₁₃-Based Metal-Organic Framework for Propylene/Propane Separation with Record-High Selectivity

Energy-efficient separation of propylene (C₃H₆)/propane (C₃H₈) is in high demand for the chemical industry. However, this process is challenging due to the imperceptible difference in molecular sizes of these gases. Here, we report a continuous water nanotube dedicatedly confined in a Cu₁₀O₁₃-based metal-organic framework (MOF) that can exclusively adsorb C₃H₆ over C₃H₈ with a record-high selectivity of 1570 (at 1 bar and 298 K) among all the porous materials. Such a high selectivity originates from a new mechanism of initial expansion and subsequent contraction of confined water nanotubes (∼4.5 Å) caused by C₃H₆ adsorption rather than C₃H₈. Such unique response was further confirmed by breakthrough measurements, in which one adsorption/desorption cycle yields each component of the binary mixture high purity (C₃H₆: 98.8%; C₃H₈: >99.5%) and good C₃H₆ productivity (1.6 mL mL^-1). Additionally, benefiting from the high robustness of the framework, the water nanotubes can be facilely recovered by soaking the MOF in water, ensuring long-term use. The molecular insight here demonstrates that the confining strategy opens a new route for expanding the function of MOFs, particularly for the sole recognition from challenging mixtures.