van der Waals forces and confinement in carbon nanopores: Interaction between CH4, COOH, NH3, OH, SH and single-walled carbon nanotubes

Highlights: • Interactions between CH₄, COOH, NH₃, OH, SH and SWCNTs are studied with DFT-D2. • Endohedrally-confined CH₄ can weakly physisorb to the walls of the largest SWCNTs. • CH₄ and COOH are the only species that can physisorb exohedrally to SWCNT wall. • SWCNT chemical reactivity is studied with Fukui functions and Pearson's principle. Interactions between CH₄, COOH, NH₃, OH, SH and armchair $\left(n\text{,}n\right)$ $(n=4\text{,}7\text{,}14)$ and zigzag $\left(n\text{,}0\right)$ $(n=7\text{,}12\text{,}25)$ single-walled carbon nanotubes (SWCNTs) have been systematically investigated within the framework of dispersion-corrected density functional theory (DFT-D2). Endohedral and exohedral molecular adsorption on SWCNT walls is energetically unfavorable or weak, despite the use of $C_6/r^6$ pairwise London-dispersion corrections. The effects of pore size and chirality on the molecule/SWCNTs interaction were also assessed. Chemisorption of COOH, NH₃, OH and SH at SWCNT edge sites was examined using a H-capped $\left(7\text{,}0\right)$ SWCNT fragment and its impact on electrophilic, nucleophilic and radical attacks was predicted by means of Fukui functions.