How structural parameters affect the reactivity of saturated and non-saturated nitrogen-doped single-walled carbon nanotubes of different chiralities: a density functional theory approach

Nitrogen-containing carbon nanotubes, or N-CNTs, are a class of materials with interesting catalytic properties and with less toxic properties than bare carbon nanotubes. Herein, the relative stability, the oxidation potential, conductivity, and structural characteristics of finite, open H-terminated single-walled N-CNTs and their saturated structures are investigated by density functional theory methods at the B3LYP/6-31G(d) level of theory. The principal aim is to understand the way different structural features can determine or modify N-CNTs properties and reactivity. Frequency calculations indicate that all of the final optimized nanostructures correspond to a minimum on the potential energy surface. The formation energies, band gaps, atomic charges, and reactivity descriptors such as chemical potential, hardness, electrophilicity index, and softness are compared. The results indicate that changes in hybridization, chirality, and diameter strongly modify the properties of N-CNTs. The nitrogen content and the length of the nanotubes also contribute to changes in their properties, albeit to a lesser degree. For instance, a (8,0) zigzag N-CNT with 4 nitrogen atoms exhibits a band gap of 0 eV. Moreover, the configuration or relative positions of the nitrogen atoms in the central part of the nanotube do not significantly affect the nanotube properties. Compared with zigzag and chiral nanotubes, armchair N-CNTs exhibit a favorable electrical charge distribution and are revealed as potentially good catalysts for oxygen reduction reactions.