Nitrogen-doped (6, 0) carbon nanotubes: A comparative DFT study based on surface reactivity descriptors

A density functional theory study was carried out to investigate the electronic structure properties of pristine and nitrogen-doped (6, 0) carbon nanotubes (CNTs). We examine the usefulness of local reactivity descriptors to predict the reactivity of carbon/nitrogen atom sites on the external surface of the tubes. The properties determined include the electrostatic potential VS(r) and average local ionization energy I ¯ S ( r ) on the surfaces of the investigated tubes. Our results reveal that the characteristic surface patterns and evaluated surface reactivity descriptors are considerably influenced by N-doping. Comparison with the I ¯ S ,min of the pristine CNT indicates correctly that in the N-doped models, the nitrogen atom tends to activate the surface toward electrophilic/radical attack. On the other hand, there is a good correlation between the minima of the local ionization energies and chemical shielding isotropy values at the sites of nitrogen atoms, indicating that I ¯ S ,min provides an effective means for rapidly and inexpensively assessing the chemical environments of the nitrogen sites of N-doped CNTs. These results should be useful for designing and developing metal-free catalyst based on N-doped CNTs.