Adsorption and surface reactivity on single-walled boron nitride nanotubes containing stone-wales defects

Adsorption of chemical species H, O, CO, H-2, O-2, H2O, and NH3 on the sidewall of zigzag (8,0) and armchair (5, 5) boron nitride nanotubes (BNNTs) is studied using density-functional theory. Particular attention is paid to searching for the most-stable configuration of the adsorbates at a perfect site (PS) and near a Stone-Wales (SW) defect, and the surface reactivity at the PS and near the SW defect. Reactivity near the SW defect is generally higher than that at the PS because of the formation of frustrated B-B and N-N bonds and the local strain caused by pentagonal and heptagonal pairs. O-2 is prone to dissociative chemisorption near SW defects, but is more likely physisorbed at the PS. The adsorption of H2O and NH3 on the sidewall of BNNT can be described as molecular chemisorption due to modest interaction between HOMO of H2O or NH3 with LUMO of BNNT. Adsorption of NH3 can affect electronic properties of BNNT through lifting the Fermi level. As such, NH3 can be viewed as an n-type impurity. CO and H, can only be physisorbed on the sidewall of BNNT through van der Waals interactions.