DFT Studies on the Interaction of an Open-Ended Single-Walled Aluminum Nitride Nanotube (AINNT) with Gas Molecules

The interaction of various gas molecules including H-2, N-2, O-2 (in triplet and singlet), and H2O on the geometrical structures, energies, and electronic structures with open edges of zigzag (10, 0) and armchair (6, 6) aluminum nitride nanotubes (AlNNTs) has been systematically studied using density functional theory. It is shown that the sigma-type species including H-2 and H2O will dissociate when chemisorbed on open AlNNTs, whereas the 'r-type species including N-2 and O-2 prefer to form cyclic structures on open AlNNTs; for example, a [2 + 2] cycloaddition configuration c is formed when singlet O-2 is adsorbed on the Al-N at the armchair edge. The edge of the open N-rich-ended (10, 0) AlNNT generally shows higher reactivity toward gas molecules than that of the open Al-rich-ended (10, 0), open-ended (6, 6) except for O-2 (in triplet and singlet) on the Al-rich-ended (10, 0) AlNNT. However, unlike the largest adsorption energy from 02 on B-rich-ended (8, 0) BNNT, that of AlNNT comes from the H-2 on the N-rich-ended (10, 0) AlNNT with the E-ad of -12.17 eV. Moreover, we note that the adsorbates at the edges of the open AlNNT can modify their electronic properties in various ways. A considerable amount of charge transferred through the adsorption of gas molecules on the open-ended AlNNTs may account for the changes of the electronic properties. Interestingly, the adsorption of open-ended (10, 0) AlNNT will narrow band-gaps, for example, N-2 and triplet O-2 adsorbed on the Al-rich-ended (10, 0) AlNNT decrease gaps from 1.58 to 0.62 and 0.83 eV, respectively, whereas both triplet and singlet O-2 adsorbed on the N-rich-ended (10, 0) AlNNT decrease gaps from 2.71 to 0.30 and 0.31 eV, respectively, which should result from the influence of introduced energy-levels of N-2 and O-2 on the energy bands of the AlNNT. Accompanied by the change of HOMO-LUMO gaps, the adsorption of H-2, N-2, and H2O on the N-rich-ended (10, 0) AlNNT lift the Fermi level toward conduction band largely at 15.9, 14.7, and 15.9%, respectively, thus significantly decreasing the work function. The present results may be useful for the design of AlNNT-based nanomaterials devices such as chemical sensor and field emitter.