On the physical adsorption of gases on carbon materials from molecular simulation

Abstract

In this paper we present a series of work covering a range of aspects relating molecular simulation to experiment. The importance of surface mediation type effects to the adsorption of simple and complex gases is demonstrated. Coupled with the adsorption of simple gases is their projection area when used for surface area determination. The pressure dependence of a projection area is demonstrated for argon at 77 and 87.3 K. A simple model is used to account for the degree of graphitisation of a surface is demonstrated and used to account for the isosteric heat behaviour of nongraphitised carbon blacks. Turning from surfaces to porous solids, an alternative treatment of experiment data (either sub or super critical) is presented that avoids the ambiguity of excess amounts adsorbed. Using this method one is able to obtain pore size distributions and amounts adsorbed without relying on such things as helium expansion volumes. Since this type of method is usually applied to composite solids we also demonstrate the correct method for calculating the heat of adsorption using independent sets of simulations. The final topic covered in this paper is an example of the information that can be gained from the heat capacity of an adsorbed phase. Abbreviations a m Molecular projection area nm 2 C V Heat capacity J/mol·K Surface mediation factorg(r) Radial distributionk B Boltzmann's constant J/K k sf Binary interaction parameter -L Length of simulation box nm m p Mass of adsorbent particles in cell kg N A Avogadro's number mol −1 N cell Total amount in adsorption cell mol P Pressure Pa q Partial charge on Coulombs site e Q Heat released J q st Isosteric heat kJ/mol r Separation of interaction sites nm S Particle surface area m 2 /kg V Volume m 3 z 0Distance from surface at zero potential nm ε LJ well depth J σ LJ collision diameter nm ε 0 Permittivity of a vacuum C 2 /J·m ρ s Surface density of carbon atoms nm −2 ρ b Bulk density kmol/m 3 ρ Average pore density kmol/m 3 Δ Carbon layer separation nm χ Surface mediation damping constant -Γ Surface adsorption μmol/m 2 α Volume of specific pore m 3 /kg ϕ Interaction energy J

Simple model of adsorption on external surface of carbon nanotubes—a new analytical approach basing on molecular simulation data

“…As we mentioned above packing effect changes the value of monolayer capacity in the whole isotherm range. A similar effect was observed for other systems (Birkett and Do 2007;Cascarini de Torre et al 1996;Do et al 2007;Furmaniak et al 2009a;Gauden 2010;Wongkoblap et al 2009). …”

The role of accessibility in the characterization of porous solids and their adsorption properties

“…The importance of gas phase adsorption in the characterization has been considered in a number of review papers (Kaneko et al 2002;Birkett and Do 2007). For simplicity nitrogen and argon are among the commonly used molecular probes for this purpose, and are recommended as a suitable probe for the determination of structural parameters of porous solids (Sing et al 1985;Rouquerol et al 1994).…”

Adsorption potential distributions for carbons having defined pore structure—GCMC simulations of the effect of heterogeneity

“…This idea was also applied by Do et al who, to introduce the defects, proposed the simple numerical procedure (Brikett and Do 2007;Do and Do 2006) used also in this study. We considered the spheres having the center located inside the six-member carbon ring.…”