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Title: Translational and Rotational Motion of C8 Aromatics Adsorbed in Isotropic Porous Media (MOF-5): NMR Studies and MD Simulations

For this, we combined nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulation to study xylene behavior in MOF-5, probing the effects of adsorbate geometry in a weakly interacting model isotropic metal organic framework (MOF) system. We employed NMR diffusometry and relaxometry techniques at low field (13 MHz) to quantify the self-diffusion coefficients (D s) and the longitudinal relaxation times (T 1) of xylenes in MOF-5 as a function of temperature at the saturated loading for each xylene. These experiments reveal the translational motion activation energies to be 15.3, 19.7, and 21.2 kj mol -1 and the rotational activation energies to be 47.26, 12.88, and 11.55 for the (p-, m-, o-) xylene isomers, respectively. Paraxylene exhibits faster translational motion, yet shows four times the activation energy barrier for rotational motion vis-à-vis the other isomers. MD simulations performed on these model systems corroborate the findings for paraxylene and suggest that paraxylene has the lower free energy barrier for hopping away from its binding sites, yet has the slowest rotational motion in the plane of the xylene molecule.
Authors:
ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [3] ; ORCiD logo [4] ;  [5]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering
  2. Federal Inst. of Technology, Lausanne (Switzerland). Inst. of Chemical Sciences and Engineering
  3. Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Materials Science and Engineering
  4. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Federal Inst. of Technology, Lausanne (Switzerland). Inst. of Chemical Sciences and Engineering
  5. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; SC0001015; 1106400; 68024013; SPP 1570; NN9414K
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 28; Related Information: © 2017 American Chemical Society.; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division; National Science Foundation (NSF); Enersense International OYJ, Pori (Finland); German Research Foundation (DFG); UNINETT Sigma2 AS, Trondheim (Norway)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 74 ATOMIC AND MOLECULAR PHYSICS
OSTI Identifier:
1464150