Large‐area vacuum‐treated ZIF‐8 mixed‐matrix membrane for highly efficient methane/nitrogen separation

Abstract Development of materials with excellent separation performances remains an ongoing challenge in methane/nitrogen (CH4/N2) separation science. Herein, a facile and effective method for enhancing CH4 uptake, binding, and CH4/N2 selectivity using the surface‐carbonized and stiffened zeolitic imidazolate framework‐8 (CSZ) via high‐vacuum‐resistance calcination (HVRC) was demonstrated. Such vacuum‐treated CSZ nanoparticles, with carbonized structures that contain Zn‐rich sites, high stability, and satisfactory compatibility with polymers, were then uniformly mixed with the strong basic polymer polyvinylamine (PVAm) to obtain large‐area mixed‐matrix membranes (1120 cm2, which is ca. 2 pieces of A4‐size paper). Owing to the presence of Zn‐rich sites and amino groups, CH4 molecules were bound more readily to CSZ and PVAm than N2, as confirmed by gas adsorption isotherms and DFT calculations. The obtained MMM modules (ca. 2000 cm2) exhibited outstanding CH4 separation performances at 85 wt% CSZ loading, achieving a CH4 permeance of 7600 GPU and CH4/N2 selectivity of 4.35.