Micropore size distributions from CO2 using grand canonical Monte Carlo at ambient temperatures: cylindrical versus slit pore geometries

The Monte Carlo method was used in its grand ensemble variant (GCMC) in combination with CO2 experimental isotherm data at ambient temperatures (298 and 308 K), in order to characterize microporous carbons and obtain the corresponding slit and cylindrical pore size distributions (PSD). In particular, the CO2 densities at 298 and 308 K, inside single, slit-shaped as well as cylindrical, graphitic pores of given dimensions were found on the basis of GCMC for pressures ranging from 1 to 10 bar. Significant differences of the adsorption characteristics of slit-shaped and cylindrical pores were observed and were attributed to different molecular packing originating from the different confinement geometries. Consequently, the optimal PSDs for slits and cylinders for which the best match is obtained between computed and measured isotherms were determined. Comparisons were made between the PSDs found for the same carbon sample for different pore geometries, and conclusions concerning the applicability of the method and the reliability of the resulting micropore size distributions were drawn.