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Title: Transport Mechanism of Guest Methane in Water-Filled Nanopores

We computed the transport of methane through 1 nm wide slit-shaped pores carved out of selected solid substrates using classical molecular dynamics simulations. The transport mechanism was elucidated via the implementation of the well-tempered metadynamics algorithm, which allowed for the quantification and visualization of the free energy landscape sampled by the guest molecule. Models for silica, magnesium oxide, alumina, muscovite, and calcite were used as solid substrates. Slit-shaped pores of width 1 nm were carved out of these materials and filled with liquid water. Methane was then inserted at low concentration. The results show that the diffusion of methane through the hydrated pores is strongly dependent on the solid substrate. While methane molecules diffuse isotropically along the directions parallel to the pore surfaces in most of the pores considered, anisotropic diffusion was observed in the hydrated calcite pore. The differences observed in the various pores are due to local molecular properties of confined water, including molecular structure and solvation free energy. The transport mechanism and the diffusion coefficients are dependent on the free energy barriers encountered by one methane molecule as it migrates from one preferential adsorption site to a neighboring one. It was found that the heterogeneous water distributionmore » in different hydration layers and the low free energy pathways in the plane parallel to the pore surfaces yield the anisotropic diffusion of methane molecules in the hydrated calcite pore. Our observations contribute to an ongoing debate on the relation between local free energy profiles and diffusion coefficients and could have important practical consequences in various applications, ranging from the design of selective membranes for gas separations to the sustainable deployment of shale gas.« less
Authors:
 [1] ;  [1] ;  [2] ; ORCiD logo [1]
  1. Univ. College London, London (United Kingdom). Dept. of Chemical Engineering
  2. The Ohio State Univ., Columbus, OH (United States). School of Earth Sciences
Publication Date:
Grant/Contract Number:
SC0006878; AC02-05CH11231; 640979
Type:
Published Article
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 29; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Univ. College London, London (United Kingdom)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); European Union (EU)
Contributing Orgs:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1358639
Alternate Identifier(s):
OSTI ID: 1373294