Primary Adsorption Sites of Light Alkanes in Multivariate UiO-66 at Room Temperature as Revealed by Solid-State NMR

The host-guest interaction between light alkanes and metal- organic frameworks (MOFs) plays essential roles in gas storage and chemical separation. A one-dimensional H-1{C-13} J-HMQC-SD nuclear magnetic resonance (NMR) experiment was introduced to explore the primary adsorption sites of light alkanes (methane, ethane, and propane) confined inside multivariate (MTV) UiO-66-(CH3)(0.24)-(NH2)(0.44)-(2OH)(0)(.3)(2). The preferential loading site of the light alkanes in MTV-UiO-66 could be deduced from the spin-diffusion buildup curves. It is found that the BDC-2OH site instead of BDC-NH2 and BDC-CH3 sites is the primary adsorption site of methane, ethane, and propane on MTV-UiO-66. The experimental observations are in good consistency with the computational results of adsorption energy of the light alkanes in UiO-66-X (X = -H, -CH3, -20H, and -NH2). The results presented herein would be helpful for understanding the host-guest interaction of light alkanes confined inside MOFs.