Grand canonical Monte Carlo simulation of argon adsorption at the surface of silica nanopores: Effect of pore size, pore morphology, and surface roughness J. Chem. Phys. 120, 2913 (2004) In this paper we consider the adsorption of argon on the surface of graphitized thermal carbon black and in slit pores at temperatures ranging from subcritical to supercritical conditions by the method of grand canonical Monte Carlo simulation. Attention is paid to the variation of the adsorbed density when the temperature crosses the critical point. The behavior of the adsorbed density versus pressure ͑bulk density͒ shows interesting behavior at temperatures in the vicinity of and those above the critical point and also at extremely high pressures. Isotherms at temperatures greater than the critical temperature exhibit a clear maximum, and near the critical temperature this maximum is a very sharp spike. Under the supercritical conditions and very high pressure the excess of adsorbed density decreases towards zero value for a graphite surface, while for slit pores negative excess density is possible at extremely high pressures. For imperfect pores ͑defined as pores that cannot accommodate an integral number of parallel layers under moderate conditions͒ the pressure at which the excess pore density becomes negative is less than that for perfect pores, and this is due to the packing effect in those imperfect pores. However, at extremely high pressure molecules can be packed in parallel layers once chemical potential is great enough to overcome the repulsions among adsorbed molecules.
This paper presents a detailed analysis of adsorption of supercritical fluids on nonporous graphitized
thermal carbon black. Two methods are employed in the analysis. One is the molecular layer structure
theory (MLST), proposed recently by our group, and the other is the grand canonical Monte Carlo (GCMC)
simulation. They were applied to describe the adsorption of argon, krypton, methane, ethylene, and sulfur
hexafluoride on graphitized thermal carbon black. It was found that the MLST describes all the experimental
data at various temperatures well. Results from GCMC simulations describe well the data at low pressure
but show some deviations at higher pressures for all the adsorbates tested. The question of negative
surface excess is also discussed in this paper.
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