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

Abstract

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(CO2) and nitrogen ∆E(N2). 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(CO2) to ∆E(N2) ratios of 1.7, 1.8, and 1.9, respectively. To enhance the CO2 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 CO2. Both the single-layer and double-layer versions of this pore gave significant enhancement in the ability to trap CO2 preferentially to N2. The two-layer version of this pore gave ∆E(CO2) = 73 and ∆E(N2) = 6.8 kJ/mol. The one- and two-layer versions of this novel pore averaged a ∆E(CO2) to ∆E(N2) ratio of 12.