Molecular modeling of carbon aerogels

Abstract

Carbon aerogels are prepared via pyrolysis of resorcinol-formaldehyde gels. The structure consists of a highly porous three-dimensional network made up of interconnected, roughly spherical carbon particles. The aerogel studied in this work was mesoporous and had carbon particles having a diameter of ≈6 nm, connected in an open-cell structure with a porosity of ≈0.55. In addition to the mesopores between the carbon particles, the carbon particles themselves possess slit-shaped micropores with a width of ≈0.7 nm. We present a molecular model of this material, consisting of carbon spheres of diameter 6 nm in a connected network. This matrix is prepared by first generating a random close-packed structure of slightly overlapping spheres, followed by random removal of spheres to match the targeted porosity. Structural characteristics of the model have been studied using different MC techniques and compare well with those for the laboratory material. Nitrogen adsorption in this model aerogel was studied using a parallelized Grand Canonical Monte Carlo algorithm based on a domain-decomposition scheme. Large systems are needed for this simulation in order to represent the pore network in a realistic fashion. Adsorption occurs in the micropores at very low pressure, followed by adsorption in the mesopores, with capillary condensation occurring at the higher pressures.