Molecular simulation study on gas adsorption and separation performance of alkyl-functionalized HKUST materials

Abstract

The atomic partial charges of three metal–organic frameworks (MOFs), including Cu-BTC (HKUST-1), Cu-MBTC (methyl-modified Cu-BTC) and Cu-EBTC (ethyl-modified Cu-BTC), are calculated by first-principle density functional method. According to the Grand Canonical Monte Carlo (GCMC) method and the Ideal Adsorbed Solution Theory (IAST), their gas adsorption and separation ability are studied, and the effects of alkyl functionalization on the performance are analyzed and discussed. Studies have shown that temperature and pressure have significant effects on the gas adsorption ability of Cu-BTC, Cu-MBTC and Cu-EBTC. Under 298 K, the order of adsorption amount of CH4, CO2, N2 is CO2 > CH4 > N2, which is consistent with the calculated results of adsorption heat. The molecular density distribution charts indicate that the alkyl functional groups may provide the new sites for the material to adsorb gas molecules. The results show that the addition of alkyl groups can change the pore volume, surface area and charge distribution of MOFs, which, in turn, modulates the gas adsorption and separation performance of the materials. The IAST simulation shows that compared with Cu-BTC and Cu-MBTC, Cu-EBTC shows higher selectivity for gas separation and can be potentially applied to absorption of CO2 greenhouse gases from air mixture.