Adsorption energies for a nanoporous carbon from gas–solid chromatography and molecular mechanics

Determining molecule–carbon surface adsorption energies using molecular mechanics and graphene nanostructures

“…In prior work the 127 ring graphene structure and 3 layers were found to be of adequate size to represent the carbon surface. The MM2 parameters were found to be superior to MM3 in representing the gas-carbon interactions [5]. Using the default 0.9 nm cut off for van der Waals (VDW) forces, more rings and more layers did not further enhance the interaction energy [5].…”

“…Larger E * values indicate that the gas molecule is more strongly attracted to the surface. As shown elsewhere [5], E * can implicitly incorporate information about more complex gas-solid adsorption energy potentials and surface structures.…”

“…As illustrated in prior work [5], available molecular mechanics software can be used to calculate the adsorption energy, E * cal . A comparison of the experimental E * and calculated E * cal based on a linear regression gives…”

“…Dispersion or van der Waals forces dominate the adsorption of neutral molecules on a carbon surface. Although more sophisticated density functional theory (DFT) [4] and quantum mechanical/molecular mechanical (QM/MM) methods have been used to calculate gas-solid interactions, it has been shown in prior work [5] that standard molecular mechanics software could be used to calculate gas-solid adsorption energies, E * cal , for a series of nine alkanes and haloalkanes on Carbosieve S-III (Supelco, N 2 BET surface area of 995 m 2 /g).…”

“…Murata, Kaneko, et al used high-resolution adsorption analysis to determine the N 2 interaction of 2.29 kcal/mol on flat graphite and 3.36 kcal/mol in carbon nanopores of the single wall carbon nanohorn particles [10]. The general purpose of this work is to extend the approach used previously [5] to new gas-solid systems involving a set of 16 molecules (alkanes, haloalkanes, and ethers) on Carbopack B carbon powder. The specific objectives of the current investigation are: (first) to create five simple surface models where the positions of nanostructures on a graphene layer create a surface "roughness" that can be adjusted, (second) to use MM2 molecular mechanics parameters to calculate adsorption energies E * cal for 16 different molecules with each model, and (third) to compare the resulting calculated E * cal with experimental E * values to select the optimal surface model.…”