An investigation was made of the influence of structural heterogeneity upon the transport properties of simple gases in a hybrid reverse Monte Carlo constructed model of SiC-derived C. The energy landscape of the system was based upon a free energy analysis of the atomistic model. The overall energy barriers of the system for different gases were computed together with properties such as Henry’s constant, the differential enthalpy of adsorption at infinite dilution and the hydrophobicity of the SiC-derived carbon structure and its affinity for CO2 and CH4 adsorption. Also studied were the effects of molecular geometry, pore structure and energy heterogeneity. Various scenarios were considered, for the diffusion of CO2 and CH4 through ultra-micropores, using the nudged elastic band method. It was shown that the energy barrier to a hopping molecule was very sensitive to the shape of the pore entry. Evidence was provided for the influence of structural heterogeneity upon the self-diffusivity of methane and carbon dioxide using molecular dynamics simulations based upon a maximum in the variation of self-diffusivity with loading. A comparison of the molecular dynamics simulation results with self-diffusivities from quasi-elastic neutron scattering measurements and with macroscopic uptake-based low-density transport coefficients, revealed the existence of internal barriers that were not seen by molecular dynamics simulations and quasi-elastic neutron scattering experiments. The simulation and macroscopic uptake-based diffusion coefficients nevertheless agreed within a factor of 2 to 3; indicating that the present hybrid reverse Monte Carlo model structure captured most of the important energy barriers affecting the transport of CH4 in the present nanostructure.

Influence of Structural Heterogeneity on Diffusion of CH4 and CO2 in Silicon Carbide-Derived Nanoporous Carbon. A.H.Farmahini, A.Shahtalebi, H.Jobic, S.K.Bhatia: Journal of Physical Chemistry C, 2014, 118[22], 11784-98