Thermodynamic–Kinetic Synergistic Separation for O₂/N₂ and CO₂/CH₄ on Nanoporous Carbon Molecular Sieves

Carbon molecular sieves (CMSs) are the key adsorbents for gas separation through pressure swing adsorption (PSA), a promising technique that has found many applications in air separation and natural gas purification. However, the current process of preparing CMSs with finely tuned nanopores based on the repeated CVD process is technically challenging and energy-consuming. In this work, we report a facial method of preparing CMSs through the one-step carbonization of a metal–organic framework. The direct carbonization of an rht-type metal–organic framework (MOF) affords a type of CMSs with an ultramicro–nanoporous structure that is comparable with the kinetic diameter of small gases (N2, O2, CO2, and CH4). As a result, this type of CMSs shows significant differences in both equilibrium adsorption properties and diffusion rates for O2/N2 and CO2/CH4. The kinetic separation coefficient for O2/N2 and CO2/CH4 is high up to 47 and 105, respectively. In addition to excellent equilibrium and kinetic selectivity, this MOF-CMS shows compatibility between equilibrium and kinetic adsorption properties, giving rise to a thermodynamic–kinetic synergistic effect for O2/N2 and CO2/CH4 separation. These outstanding separation performances can be attributed to the ultramicro–nanopores of CMSs, which are modulated by the uniform pore structure of the MOF precursor. The high selectivity combined with the facial preparation process for this CMS may open an avenue of preparing nanoporous CMSs with desired functionalities.