Can carbon surface oxidation shift the pore size distribution curve calculated from Ar,N2 andCO2 adsorption isotherms? Simulation results for a realistic carbon model

Abstract

Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbonsurface oxidation on the pore size distribution (PSD) curve determined from simulated Ar,N2 andCO2 isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton,and that all pores are accessible for studied molecules (i.e., only the effect of the change ofsurface chemical composition is studied). The results obtained show two important things,i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculatedfrom the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curvescalculated from simulated isotherms are to a greater or lesser extent affected by thepresence of surface oxides. The most reliable results are obtained from Ar adsorption data.Not only is adsorption of this adsorbate practically independent from the presenceof surface oxides, but, more importantly, for this molecule one can apply theslit-like model of pores as the first approach to recover the average pore diameterof a real carbon structure. For nitrogen, the effect of carbon surface chemicalcomposition is observed due to the quadrupole moment of this molecule, and thiseffect shifts the PSD curves compared to Ar. The largest differences are seen forCO2, and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms ofthis molecule contain artificial peaks and the average pore diameter is strongly influencedby the presence of electrostatic adsorbate–adsorbate as well as adsorbate–adsorbentinteractions.