A Combined NMR and Molecular Dynamics Study of Methane Adsorption in M2(dobdc) Metal–Organic Frameworks

V. J. Witherspoon, R. Mercado, E. Braun, A. K. Mace, J. E. Bachman, J. R. Long, B. Blümich, B. Smit, and J. A. Reimer, A Combined NMR and Molecular Dynamics Study of Methane Adsorption in M2(dobdc) Metal–Organic Frameworks J Phys Chem C (2019) http://dx.doi.org/10.1021/acs.jpcc.9b01733


Abstract: We examine the diffusion of methane in the metal–organic frameworks M2(dobdc) (M = Mg, Ni, Zn; dobdc4− = 2,5-dioxido-1,4-benzenedicarboxylate) as a function of methane loading through a combination of nuclear magnetic resonance (NMR) and molecular dynamics simulations. At low gas densities, our results suggest that favorable CH4–CH4 interactions lower the free energy barrier for methane hopping between coordinatively unsaturated metal sites and thus enhance the translational motion of methane down the c-axis. At higher gas densities, CH4–CH4 interactions become more significant, CH4–CH4 collisions become more frequent, and the gas self-diffusion begins to decrease. Finally, we observe that the self-diffusion coefficient of methane is inversely related to the binding energy at the coordinatively unsaturated metal sites, such that diffusion is most rapid in the Zn2(dobdc) framework.


© Berend Smit 2019