Theoretical study of chemisorption of hydrogen atoms on the sidewalls of armchair single-walled carbon nanotubes with Stone-Wales defect

The geometrical structures and electronic properties as well as thermal stabilities of hydrogenated armchair (n, n) (n = 4-8) SWCNTs with Stone-Wales (SW) defect were investigated using density functional theory (DFT-B3LYP) in combination with the 6-31G* basis set. It is found that the chemisorptions of two hydrogen atoms inside and outside the SW defective SWCNTs are exothermic processes. As the nanotube diameter increases, the reaction energy of exohedral addition decreases, whereas that of endohedral addition increases. Exohedral nanotube adsorption is energetically more favorable than endohedral adsorption for smaller diameter (4,4)-SW, (5,5)-SW SWCNTs, but not for larger diameter (7,7)-SW and (8,8)-SW SWCNTs. The result is different from hydrogen on perfect nanotubes. Significantly, compared with the adsorption on the exterior sidewalls of perfect SWCNTs, the reaction energies of the endo-hydrogenated (7,7)-SW and (8,8)-SW SWCNTs are more exothermic, meaning that the central C-C bond of SW defect inside the armchair (7,7)-SW and (8,8)-SW SWCNT sidewalls is more reactive than that in perfect sites. This is different from the result reported on the sidewall reactivity of SW defects outside the armchair SWCNTs. The calculated energy gaps indicate that the hydrogen-chemisorbed SW defective armchair tubes are always wide energy gap structures. The energy gaps of endohedral hydrogen-chemisorbed tubes are higher than those of the corresponding perfect tubes. (C) 2012 Elsevier B.V. All rights reserved.