Pore accessibility of N-2 and Ar in disordered nanoporous solids: theory and experiment

Nguyen, T.X. and Bhatia, S. (2007) Pore accessibility of N-2 and Ar in disordered nanoporous solids: theory and experiment. Adsorption, 13 3-4: 307-314. doi:10.1007/s10450-007-9061-1

Author Nguyen, T.X.
Bhatia, S.
Title Pore accessibility of N-2 and Ar in disordered nanoporous solids: theory and experiment
Journal name Adsorption   Check publisher's open access policy
ISSN 0929-5607
Publication date 2007-08-01
Year available 2007
Sub-type Article (original research)
DOI 10.1007/s10450-007-9061-1
Open Access Status DOI
Volume 13
Issue 3-4
Start page 307
End page 314
Total pages 8
Editor Knaebel, K.S.
Place of publication United States
Publisher Springer
Language eng
Subject 290603 Membrane and Separation Technologies
780102 Physical sciences
Abstract Recently (Nguyen and Bhatia, J. Phys. Chem. C 111:2212-2222, 2007) we have proposed a new algorithm utilising cluster analysis principles to determine pore network accessibility of a disordered material. The algorithm was applied to determine pore accessibility of the reconstructed molecular structure of a saccharose char, obtained in our recent work using hybrid reverse Monte Carlo simulation (Nguyen et al., Mol. Simul. 32:567-577, 2006). The method also identifies kinetically closed pores not accessed by adsorbate molecules at low temperature, when their low kinetic energy cannot overcome the potential barrier at the mouths of pores that can otherwise accommodate them. In the current work, the results are validated by transition state theory calculations for N-2 and Ar adsorption, showing that N-2 can equilibrate in narrow micropores at practical time scales at 300 K, but not at 77 K. Large differences between time scales for micropore entry and exit are predicted at low temperature for N-2, the latter being smaller by over three orders of magnitude. For N-2 at 77 K the time constant for pore entry exceeds 3 hr., while for exit it is 134 days. At 300 K these values are smaller than 1 mu s, indicating good accessibility at this temperature. These results are verified by molecular dynamics simulations, which reveal that while N-2 molecules enter and leave all pores frequently at 300 K, entry and exit events for apparently inaccessible pores are absent at 77 K. For Ar at 87 K better accessibility is evident for the saccharose char compared to N-2 at 77 K. This finding is now experimentally shown in this work by comparison of pore size distributions obtained from experimental nitrogen adsorption isotherms of nitrogen and argon at 77 K and 87 K.
Keyword Chemistry, Physical
Engineering, Chemical
Gas phase adsorption
Molecular modeling
Pore accessibility
Transition state theory
Reverse Monte-carlo
Density-functional Theory
Microporous Carbons
Q-Index Code C1
Institutional Status UQ

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Created: Tue, 19 Feb 2008, 01:47:45 EST