Density Functional Theory Studies of the Influence of Pore Diameter and Nitrogen-Containing Functional Groups on CO₂ Capture in Nanoporous Graphene

The CO₂ adsorption performance of nanoporous graphene depends on the pore size and type of nitrogen-containing functional groups (N-groups) introduced into the graphene structure. In this study, N-groups, such as amine, cyanide, and pyridine, were introduced into graphene with three different pore sizes to assess their CO₂ adsorption performance. In particular, N-containing graphene with a pore size of 8.26 Å exhibited a high adsorption performance, which was attributed to the formation of additional hydrogen bonds between CO₂ molecules and hydrogen atoms on the inner edges of the pore. Additionally, Lewis acid-base interactions between the nitrogen atom of the N-groups and carbon atoms of CO₂ also contributed to the enhanced adsorption. The CO₂ adsorption performance decreased in the order cyanide > amine > pyridine in this structure. The adsorption performances of the N-groups were different because the cyanide group lacked steric hindrance, while the amine and pyridine groups were affected by steric hindrance owing to the hydrogen atoms on the inner edge. CO₂ adsorption performance decreased with increasing pore size. Additionally, adsorption approached that of the N-groups introduced on the outer edge because of the decreased effect of pores on CO₂ adsorption and the morphological similarities of hydrogen atoms between the inner and outer edges. The findings of this study underscore the importance of introducing N-groups into the inner edges of nanoporous graphene with appropriately sized pores for effective CO₂ adsorption and offer valuable insights into the development of efficient systems for capturing and storing CO₂ using nanoporous graphene.