First principles study of C3N4 carbon nitride nanotubes

We investigate the structural and optical properties of carbon nitride (C3N4) nanotubes (CNNts) built from condensed heptazine cores (C6N7) with different chirality and connection patterns. In particular, heterocycles in a hexagonal ordering exhibit the lowest energy configuration for the CNNts studied. Overall, heptazine-based CNNts are energetically preferred over triazine motifs. Correspondingly, recent experimental data show the prevalence of heptazine units in synthesized CNNts. Nitrogen-nitrogen lone pair repulsions prevent CNNts from presenting smooth tubular surfaces. Corrugation in general stabilizes C3N4 nano-structures with respect to extended conformations in comparison with pure carbon compositions. In connection to experiment, hexagonal nanotubes show optical properties that are almost independent of the chirality and tube diameter. CNNts show potential for similar applications as carbon nanotubes, and may even improve on the performance in some specific areas, as they have stable semiconducting parameters, and have polarized C-N bonds together with surface holes, which suggest them as better hosts as storage devices.