Nitrogen Adsorption in Carbon Aerogels:  A Molecular Simulation Study

We present a molecular model for carbon aerogel in which the mesopore space is represented by carbon spheres in a connected network. This matrix was prepared by first generating a random close-packed structure of slightly overlapping spheres, followed by removal of spheres to match the targeted porosity, while maintaining connectivity. The spheres were then replaced by a model microporous carbon generated by applying the Reverse Monte Carlo method to fit the experimental carbon radial distribution function, g(r), obtained by X-ray diffraction. The resulting model aerogel had a surface area, porosity, and pore size distribution that closely matches that of the experimental material. We used a parallelized Grand Canonical Monte Carlo algorithm to study nitrogen adsorption in this model aerogel. The resulting adsorption isotherm shows satisfactory agreement with the experimental results. Adsorption occurred in the micropores at very low pressure, followed by adsorption in the mesopores, with capillary condensation occurring at the higher pressures.