Microscopic insights on CO2/N2 separation in functionalized MOFs from molecular dynamics simulations and density functional theory calculation

SY Cai and JS Song and ER Huo and L Zhang and XD Liu and YP Chen, CHEMICAL ENGINEERING SCIENCE, 310, 121539 (2025).

DOI: 10.1016/j.ces.2025.121539

Developing efficient CO2/N2 separation technologies is crucial for mitigating carbon emissions from flue gas. Metal-organic frameworks (MOFs) have emerged as promising porous materials with significant potential for CO2 adsorption and separation. Among them, functionalized linkers play a critical role in enhancing CO2/N2 separation performance. However, the dynamic separation mechanisms of the functionalized links in MOFs remain unclear. In this study, we model five functionalized isoreticular MOFs (IRMOF-1 to-5) and evaluate their performance in flue gas (CO2/N2 mixture) purification using molecular dynamics simulations and density functional theory calculations. The results show that while additional functionalized linkers reduce flux (J) within the MOFs, they significantly increase the separation factor (alpha). Notably, in IRMOF-4, CO2 flux is nearly zero, whereas N2 flux reaches 12.68 kg/(m2 & sdot;s). Radial distribution functions reveal that CO2 exhibits stronger interactions with the IRMOFs than N2. Further analysis confirms that functionalized linkers enhance these interactions, particularly in IRMOF-4, where they are stronger than those between CO2/N2 and the aromatic rings or Zn atoms in the frameworks. The corrected diffusivities (D0) for CO2 and N2 in IRMOF-4 are 0.026 m2/s and 23.806 m2/s, respectively, while total transport resistance (Rt) values are 10.680 ps and 0.005 ps. Additionally, IRMOF-4 demonstrates the highest separation factor (alpha = 33.5), indicating highly selective N2 permeation over CO2. Potential of mean force and electron overlap area analyses further suggest that IRMOF-4 exhibits strong interactions with CO2 and relatively weak interactions with N2, leading to low CO2 permeability and relatively higher N2 permeability. These findings provide quantitative insights into CO2/N2 separation mechanisms in MOFs and offer guidance for designing new functionalized MOFs for high- performance CO2/N2 purification.

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