Feasibility of Single-Walled Carbon Nanotubes as Materials for CO2 Adsorption: A DFT Study

The adsorption of CO 2 by zigzag and armchair single-walled carbon nanotubes (SWNTs) of different diameters (4.70–10.85 Å) has been studied using DFT with empirical dispersion correction (B97-D/SVP). Different binding sites have been considered, namely, in the interior (side-on and end-on binding modes) and on the surface (parallel or perpendicular) of the nanotube. Our calculations predict larger interaction energies for interior than exterior adsorption, with the strongest interactions observed for the (9,0) and (5,5) SWNTs (−12.8 and −12.5 kcal·mol –1, respectively). Therefore, these SWNTs can be considered to be very good potential candidates for carbon capture and storage in reducing CO 2 emissions, as corroborated by the computed Δ H and Δ G adsorption energies. Moreover, we predict that interior adsorption would be more favorable than interstitial adsorption in bundles for (9,0), (10,0), (11,0), and (5,5) nanotubes. Furthemore, the diffusion of CO 2 from the outside to the interior of the (5,5) SWNT is an energetically barrierless and favorable process. We have also analyzed the interplay between CO 2 ·SWNT and CO 2 ·CO 2 interactions when more than one CO 2 molecule is inside the tube, showing interesting cooperativity effects for SWNTs with large diameters. Finally, the symmetry-adapted perturbation theory partition scheme was used to investigate the physical nature of the interactions and to analyze the different energy contributions to the binding energy.