Molecular Simulation of Benzene Adsorption in Graphitic\nand Amorphous Carbon Slit Pores

Abstract

Atmospheric soot consists of fractal\naggregates of spherical particles,\nwhich are made of ordered (graphitic) and disordered (amorphous) carbon.\nCondensation of polycyclic aromatic hydrocarbons (PAHs) on the surface\nof spherical particles and in the junctions between these particles\ninduces morphological changes in soot aggregates. We studied the interactions\nof benzene molecules with graphitic and amorphous carbon slit pores,\nwhere benzene represented PAHs and slit pores represented the junctions\nbetween carbon spheres in a soot aggregate. We used Monte Carlo simulations\nin the grand canonical ensemble (GCMC) to calculate benzene adsorption\nisotherms and molecular dynamics simulations to analyze benzene fluid\nstructure inside the pores. As expected, confinement in graphitic\nand amorphous carbon pores resulted in significantly different adsorption\nisotherms and the local structure of benzene in the pores. We also\nfound that using two different force fields for benzene (all-atom\nOPLS and a nine-site united atom TraPPE, which takes into account\nthe quadrupole moment of benzene) produced similar adsorption isotherms,\nbut a different orientation of benzene molecules in the pores.