A highly sensitive flexible metal–organic framework sets a new benchmark for separating propyne from propylene

Abstract

The stepwise adsorption behavior endows flexible metal–organic frameworks (MOFs) with theoretically high separation selectivity; however, their practical separation performance for gas mixtures is frequently far inferior to the theoretical value from pure-component sorption isotherms due to their retarded and unpredictable response to gas molecules under the mixed gas environment, especially for trace gas removal. Here we reported a novel and highly sensitive flexible MOF (TIFSIX-14-Cu-i, also termed as ZU-13) featuring ultra-low propyne (C₃H₄) threshold pressure for efficient separation of trace C₃H₄ from propylene (C₃H₆), a critical step to produce polymer-grade C₃H₆. We revealed how exerting threshold pressure control in anion-pillared flexible materials enabled ultra-high sensitivity to targeted C₃H₄ molecules as well as obvious exclusion of C₃H₆ molecules through precise control of the hydrogen-bonding interaction between organic linkers and anion pillars. The designed TIFSIX-14-Cu-i with ultra-low C₃H₄ threshold pressure (500 ppm) not only exhibited exceptionally high C₃H₄/C₃H₆ selectivity (355) but also set a new benchmark for the separation of 1/99 C₃H₄/C₃H₆ mixtures (1280 mL g⁻¹ with C₃H₆ purity over 99.9999%) in breakthrough experiments without disturbing the “leakage” phenomenon. The underlying mechanism of sensitive flexible MOFs for C₃H₄/C₃H₆ separation was revealed by density functional theory calculations.