Adsorption of Ar and SO2 on graphitized carbon black: The importance of functional groups

Grand Canonical Monte Carlo (GCMC) simulation was used to determine the isotherms and isosteric heats of argon and the strongly polar molecule, sulphur dioxide (SO2), adsorbed at 78 and 273 K on a graphitized thermal carbon black (GTCB) surface with functional groups. The functional group, was modelled as oxygen atoms bonded to a C-atom in the graphene surface, since these have been shown to be retained after thermal treatment of GTCB. The simulated adsorption isotherms and isosteric heats of argon and SO2 were compared with the experimental data. It is shown that, while functional groups do not affect the adsorption of argon, adsorption of SO2 is very sensitive to their concentration, especially at low loadings, where the adsorption is dominated by the electrostatic interaction between SO2 and the functional group. This is confirmed by analysis of the various contributions to the isosteric heat: (1) fluid-functional group interactions, (2) fluid-basal plane interactions, and (3) fluid–fluid interactions. Finally, we investigated the orientation of SO2 in the first and second layers depends on loading as well as on the distance of the molecule from the surface.