Enhancing the absorption of 1-chloro-1,2,2,2-tetrafluoroethane on carbon nanotubes: an ab initio study

We have investigated the possibility of utilizing various single-walled pristine and doped carbon nanotubes as adsorbents for the 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124) gaseous molecule. Three candidates, including pristine carbon nanotube (CNT), silicon carbide nanotube (SiCNT) and germanium-doped SiCNT (SiCGeNT) are identified and evaluated theoretically. The quantum simulations have been performed at the density functional theory (DFT) level with four different functionals (i.e., M06-2X, ωB97XD, CAM-B3LYP and B3LYP-D3) with a split-valence triple-zeta basis set (6-311G(d)). We found that adsorption on the SiCGeNT is most favourable, while that on the pristine CNT yields the lowest adsorption energy. Adsorption on these nanotubes is not accompanied by an active charge-transfer phenomenon; instead, it is driven by weak van der Waals forces. The HOMO–LUMO energy gaps drastically change when the dopant atom is added to the SiCNT, thereby improving their overall adsorption capability. Among all of the adsorbents investigated here, SiCGeNT shows the most favourable for designing effective HCFC-124 nanosensors.