Molecular Simulations and Experimental Studies of CO2, CH4, and N2 Adsorption in the UNT-14 Metal-Organic Framework.

Selective adsorption of CO2 over CH4 and N2 using porous materials is a promising approach for the capture of CO2 and upgrading of natural gas. Herein, we present a combined simulation and experimental study of the adsorption uptakes of CO2, CH4, and N2 in UNT-14, a copper-based metal-organic framework. Grand Canonical Monte Carlo (GCMC) simulations were employed to predict the pure component adsorption isotherms at 273 and 298 K using atomic charges calculated via three different charge methods. Among those, the Mulliken charge set agrees best with the experimental adsorption data. UNT-14 exhibits greater affinity for CO2 as compared to CH4 and N2, revealed by higher Henry's constant (KH) and isosteric heats of adsorption at infinite dilution (Qst0). Density functional theory (DFT) calculation displays a larger binding energy (BE) value for CO2 than for CH4 and N2. Radial distribution function (RDF) analysis reveals that CO2 molecules tend to adsorb preferentially on the peripheral benzene rings, whereas CH4 and N2 molecules tend to adsorb more preferentially on the central benzene ring of the linker. The ideal adsorbed solution theory (IAST) suggests a favorable adsorption selectivity of UNT-14 for equimolar CO2/CH4 and CO2/N2 gas mixtures (for both the experimental and simulated data), demonstrating efficient CO2 capture and natural gas upgrading ability.