Investigating the adsorption behavior of cyano radical on zigzag aluminum nitride and aluminum phosphide nanotubes: A DFT study

Density functional theory (DFT) calculations were utilized to evaluate the adsorption of cyano radical (^.C≡N) on H-capped (5, 0), (6, 0), and (8, 0) zigzag aluminum nitride nanotubes (AlNNTs) and the results were compared to the adsorption on a (6, 0) zigzag aluminum phosphide nanotube (AlPNT). The most stable configuration (C-side) involves the attachment of CN to the outer surfaces of pure AlPNT and AlNNT via a covalent bond. The adsorption energy of^.CN on the (5, 0) AlNNT surface, with a tube diameter of 4.82 Å and length of 16.4 Å, was found to be -253.17 kJ mol⁻¹ through N-side (IV) and -259.12 kJ mol⁻¹ through C-side (V), indicating a chemisorption process. The adsorption of^.CN through the C-side on (5, 0) AlNNT is more stable than through the C-side on (6, 0) and (8, 0) AlNNTs. Natural bond orbital (NBO) revealed that in these configurations, there was a charge about 0.254 (C-side) and 0.357 (N-side) |e| transferred from the (5, 0) AlNNT to the^.CN as an electron acceptor, demonstrated by a strong orbital hybridization during the adsorption process. The decrease in softness, energy gap, and electrophilicity of^.CN-adsorbed AlNNT can indicate a shift toward enhanced stability and reduced reactivity. Increasing the diameter and length of AlNNTs leads to significant alterations in the structural and electronic features of the nanotubes, as suggested by our findings. The analysis of the total density of states (DOS) illustrated the interaction between^.CN and the nanotube surfaces resulted in alterations in the electronic structure of the nanotubes.