Carbon Dioxide Capture by Adsorption in a Model Hydroxy-Modified Graphene Pore.

Concerns regarding the environmental impact of increasing levels of anthropogenic carbon dioxide have led to a variety of studies examining solid surfaces for their ability to trap this greenhouse gas (GHG). Atmospheric or post-combustion carbon capture requires an efficient separation of carbon dioxide and nitrogen gas. We used the molecular mechanics MM3 parameter set (previously shown to provide good estimates of molecule-surface binding energies) to calculate theoretical surface binding energies for carbon dioxide ∆E(CO) and nitrogen ∆E(N). For efficient separation, differentiation of these two gas-surface adsorption energies is required. Examined structures based on graphene, carbon slit width pore, and carbon nanotube gave ∆E(CO) to ∆E(N) ratios of 1.7, 1.8, and 1.9, respectively. To enhance the CO adsorption, we developed a model graphene surface pore lined with four hydroxy groups whose orientation allowed them to form hydrogen bonds with the oxygens in CO. Both the single-layer and double-layer versions of this pore gave significant enhancement in the ability to trap CO preferentially to N. The two-layer version of this pore gave ∆E(CO) = 73 and ∆E(N) = 6.8 kJ/mol. The one- and two-layer versions of this novel pore averaged a ∆E(CO) to ∆E(N) ratio of 12.