Comprehensive Study on the Dissociative Chemisorption of NH3 on the Sidewalls of Stone-Wales Defective Armchair (5,5) Single-Walled Carbon Nanotubes

Dissociative chemisorption of NH3 into H and NH2 on the sidewalls of (5,5) armchair Stone-Wales defective single-walled carbon nanotubes (SWCNTs) has been investigated using B3LYP/6-31G(d) and M06-2X/6-31G(d) levels of theory. In particular, H-center dot and NH2 center dot have been attached to the adjacent carbon atom sites on and around the Stone-Wales defect (SWD). Here, we consider SWD with two different orientations in finite H-terminated (5,5) SWCNTs. The reaction energy data suggest that the dissociative chemisorption of NH3 on the surface of the Stone-Wales defective SWCNTs is mostly endothermic except the adsorption at very few defect sites, wherein the chemisorption process is exothermic at the M06-2X/6-31G(d) level. Our systematic study reveals that the SWD generated by 90 degrees rotation of nearly axial C-C bond in (5,5) SWCNT is more favorable for the chemisorption of ammonia than the nanotube containing SWD with another orientation. The HOMO-LUMO energy gap values of defect-free and Stone-Wales defective SWCNTs are slightly altered by the chemisorption of ammonia. We have reported characteristic vibrational frequencies associated with H and NH2 chemisorbed in the lowest energy products. Expectedly, the more preferred carbon atom sites for chemisorption of NH3 are located in the SW defect region. We identified low-energy adsorption sites in the Stone-Wales defective (5,5) SWCNTs.