Molecular Simulation of Benzene Adsorption in Graphitic and Amorphous Carbon Slit Pores

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