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(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.

Post-Functionalization of Bromo-Substituted Ether-Linked Polymers via Ullman Coupling Reaction: Synthesis, Characterization and Their Role toward Carbon Dioxide Capture

A new open-chain ether-linked polymer has been prepared via nucleophilic aromatic substitution reaction on a C-F bond of 1,4-dibromo-2,5-difluorobenzene by using 2,2-bis(4-hydroxyphenyl) hexafluoropropane (bisphenol AF or BAF). The new polymer (PE-AF) has shown a good solubility in non-polar solvents, good thermal stability (up to 300 °C) and random surface morphology. Tailoring these properties has been achieved by utilizing the post-modification synthetic methodology on the bromo-sites of the polymer backbone via the application of an Ullmann coupling reaction with aniline to form the polymer (PE-Sec-NHPh). The successful synthesis of the polymers has been confirmed by elemental analysis, infrared spectroscopy (IR), 1H- and 13C-NMR and 13C CP-MAS solid state. Upon incorporation of the aniline linker, the nitrogen content increased when compared with the parent polymer chain, and thus PE-Sec-NHPh revealed a higher thermal stability up to 350 °C and a more uniformly aggregated morphology (spherical particles ca. 0.3–0.1 µm). A further evaluation has been conducted on the polymers by measuring their surface tendency toward carbon dioxide capture. Interestingly, despite their non-porous nature, the polymers demonstrated a reasonable amount of gas capture that reached 90.0 and 41.0 mg/g for PE-Sec-NHPh and PE-AF, respectively. Furthermore, the calculated CO2 binding affinities of the polymers are consistent with data reported previously in the literature.