Key Features of Polyimide-Derived Carbon Molecular Sieves

Carbon molecular sieve (CMS) membranes have impressive separation properties; however, both chemical and morphology structures need to be understood better. Here we characterize CMS with the simplest polyimide (PI) PMDA/pPDA (PMDA=pyromellitic dianhydride, pPDA=p-phenylenediamine), using FTIR, solid-state N-15-NMR and C-13-NMR, XPS, XRD, and Raman spectra to study chemical structure. We also compare gas separation properties for this CMS to a CMS derived from a more conventional PI precursor. The detailed characterization shows the presence of aromatic pyridinic, pyrrolic rings as well as graphitic, pyridonic components and a few other groups in both CMS types derived from the very different precursors. The CMS morphologies, while related to precursor and pyrolysis temperature details, show similarities consistent with a physical picture comprising distributed molecular sieving plate-like structures. These results assist in understanding diverse CMS membrane separation performance.

Automated summary

Carbon molecular sieve (CMS) membranes have impressive separation properties, and this study characterizes CMS with the simplest polyimide (PI) PMDA/pPDA to better understand the chemical and morphology structures. Comparisons were made with a CMS derived from a more conventional PI precursor, revealing the presence of various components in both types of CMS. The morphologies of CMS show similarities consistent with distributed molecular sieving plate-like structures, aiding in understanding the diverse CMS membrane separation performance.