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Sorption and Transport of Vapors in ZIF-11: Adsorption, Diffusion, and Linker Flexibility
journal contribution
posted on 2019-04-30, 00:00 authored by Brian
R. Pimentel, Melinda L. Jue, Er-Kang Zhou, Ross J. Verploegh, Johannes Leisen, David S. Sholl, Ryan P. LivelyThe adsorption and
diffusion of alcohol and hydrocarbon vapors
in zeolitic imidazolate frameworks (ZIF)-11 are reported as a function
of loading at 308 K. The hydrophobicity of the benzimidazole linkers
provides moderate ideal adsorbed solution theory selectivities for
adsorptive alcohol/water separations until high relative humidity
conditions. Sorbates well beyond the crystallographic pore aperture
are admitted into the framework at decreasing diffusivities with increasing
molecular size. The diffusion of methane is also probed as a function
of temperature, revealing a nonconstant activation energy of diffusion,
which is linked to the temperature-dependent flexibility of the ligands
comprising the six- and eight-membered aperture rings, as revealed
through solid-state NMR. Compared to ZIF-8, ZIF-11 surprisingly demonstrates
higher diffusivities and lower activation energies despite the smaller
crystallographic aperture size. This phenomenon is explained via molecular
dynamics simulations that highlight the greater flexibility of the
benzimidazole linker in ZIF-11 relative to the 2-methylimidazolate
linker in ZIF-8 and emphasizes the importance of structural flexibility
in identifying diffusionally-selective materials.
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pore apertureaperture sizesolution theory selectivitiesactivation energieseight-membered aperture ringsbenzimidazole linkerZIF -11hydrocarbon vaporsdynamics simulationszeolitic imidazolate frameworksbenzimidazole linkersdiffusionally-selective materials2- methylimidazolate linkernonconstant activation energyZIF -8NMRhumidity conditionsLinker Flexibility308 Ktemperature-dependent flexibility
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