Insights into the structural evolution of the MOFs-doped mixed matrix carbon molecular sieve membranes

Carbon molecular sieve (CMS) membranes derived from metal-organic frameworks (MOFs)-doped mixed matrix membranes (MMMs) are highly appealing for gas separation applications. However, there remains a significant lack of in-depth understanding of their nanoporous structures. Herein, ZIF-8-doped MMMs-derived CMS membranes were systematically investigated via in-situ scanning electron microscope (SEM) and in-situ X-ray diffraction (XRD) to monitor the real-time evolution of their microstructures during the pyrolysis process. Meanwhile, gas molecules were employed as molecular probes to elucidate the nanoporous architectures of the resultant mixed matrix CMS membranes. We found that ZIF-8 nanoparticles underwent structural collapse (with particle size shrinkage) and achieved in-situ amorphization and carbonization within the MMMs matrix. Furthermore, the Zn species underwent a sequential phase transformation from ZnF 2 , ZnO to metallic Zn embedded in the carbon matrix, which may be conducive to the gas separation. The 6FDA-DAM polyimide precursor was converted into amorphous carbon molecular sieves after pyrolysis. Notably, the formation process of interfacial defects between the polyimide matrix and ZIF-8 particles was directly visualized via in-situ SEM, which was not conductive to enhance gas selectivity of the MMMs-derived CMS membranes. These novel findings provide valuable insights for the rational design and fabrication of high-performance mixed matrix CMS membranes.