CO₂ adsorption thermodynamics over N-substituted/grafted graphanes: A DFT study

This work examines CO₂ adsorption over various N-substituted/grafted graphanes to identify the promotional effects of various N-functionalities have on the adsorption characteristics using DFT. CO ₂ adsorbs weakly on a graphane surface functionalized with a single, isolated substituted N- or grafted NH₂-sites. The presence of coadsorbed H₂O on the surface promotes CO₂ adsorption on both N- and NH₂-sites, with highly exothermic adsorption energies (∼-50 kJ mol^-1). Directly grafted -NH₂ or -OH functional groups on C atoms adjacent to C atoms which have a -NH₂ group grafted suffer from geometrical restrictions preventing dual stabilization of formed carbamate upon adsorption of CO₂. CO₂ adsorption can be greatly enhanced with the presence of a -OH group or second -NH₂ group in the proximity of a -NH₂ site on graphane, and only if a n(-CH₂-) (n ≥ 1) linker is introduced between the -NH₂ or -OH and graphane surface (adsorption energies of -58.8 or -43.1 kJ mol^-1 at n = 2). The adsorption mechanistics provided by DFT can be used to guide the atomic-level rational design of N-based graphane and carbon adsorbents for CO₂ capture.