Journal Article

PreJuSER-9359

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Diffusion and adsorption of methane confined in nano-porous carbon aerogel: A combined quasi-elastic and small-angle neutron scattering study

Chathoth, S. ; Mamontov, E. ; Melnichenko, Y. ; Zamponi, M.FZJ*

2010
Elsevier Amsterdam [u.a.]

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Please use a persistent id in citations: doi:10.1016/j.micromeso.2010.02.012

Abstract: The diffusion of methane confined in nano-porous carbon aerogel with the average pore size 48 angstrom and porosity similar to 60% was investigated as a function of pressure at T = 298 K using quasi-elastic neutron scattering (QENS). The diffusivity of methane shows a clear effect of confinement: it is about two orders of magnitude lower than in bulk at the same thermodynamic conditions and is close to the diffusivity of liquid methane at 100 K (i.e. similar to 90 K below the liquid-gas critical temperature T-c approximate to 191 K). The diffusion coefficient (D) of methane initially increases with pressure by a factor of similar to 2.5 from 3.47 +/- 0.41 x 10(-10) m(2) s(-1) at 0.482 MPa to D = 8.55 +/- 0.33 x 10(-10) m(2) s(-1) at 2.75 MPa and starts to decrease at higher pressures. An explanation of the observed non-monotonic behavior of the diffusivity in the confined fluid is based on the results of small-angle neutron scattering experiments of the phase behavior of methane in a similar carbon aerogel sample. The initial increase of the diffusion coefficient with pressure is explained as due to progressive filling of bigger pores in which molecular mobility in the internal pore volume is less affected by the sluggish liquid-like molecular mobility in the adsorbed phase. Subsequent decrease of D, is associated with the effect of intermolecular collisions, which result in a lower total molecular mobility with pressure, as in the bulk state. The results are compared with the available QENS data on the methane diffusivity in zeolites, metal organic frameworks, and porous silica as well as with the molecular dynamics simulations of methane in nano-porous carbons and silica zeolites. (C) 2010 Elsevier Inc. All rights reserved.

Keyword(s): J ; Aerogel (auto) ; Methane (auto) ; Diffusivity (auto) ; Neutron scattering (auto)

Note: The authors wish to thank G.D. Wignall for careful reading the manuscript and helpful suggestions. This Research at Oak Ridge National Laboratory's Spallation Neutron Source and High Flux Isotope Reactor was sponsored by the Laboratory Directed Research and Development Program and the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. This research was supported in part by the ORNL Postdoctoral Research Associates Program, administered jointly by the ORNL and the Oak Ridge Institute for Science and Education.

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Contributing Institute(s):

1. Neutronenstreuung (IFF-5)
2. Streumethoden (IFF-4)
3. JCNS (Jülich Centre for Neutron Science JCNS (JCNS) ; JCNS)

Research Program(s):

1. BioSoft: Makromolekulare Systeme und biologische Informationsverarbeitung (P45)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)

Appears in the scientific report 2010

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