Hydrogenated double wall carbon nanotubes

Abstract

Herein, we investigate the chemisorption of hydrogen on double wall carbon nanotubes (DWCNT) employing density functional theory and periodic boundary conditions. In agreement with recent investigations based on Lennard-Jones potentials, we found that the (n,m)@(n+9,m) combination is favored for tubes with small diameters. The C-H binding energies determined for the (16,0) single wall carbon nanotubes (SWCNT) are nearly identical to those computed for the (7,0)@(16,0) and (8,0)@(16,0) DWCNTs. For both of the latter we found that interlayer interaction modifies the band structure of the inner tube. In the case of hydrogenated DWCNTs, the electronic structure of the inner tube experiences very small changes at high coverages (50%). However, at lower hydrogen coverages (3%-25%) changes are observed in the electronic structure of the inner tube. In agreement with recent experimental results we conclude that, for heavily functionalized DWCNTs, the electronic properties of the inner tube remain unchanged. For zigzag SWCNTs, the band gap becomes larger upon increase in hydrogen coverage; at 50% of coverage the hydrogenated (16,0) SWCNT has a band gap of 3.38 eV. Finally, based on the fact that high coverages significantly elongate C-H bond distances, we propose that the hydrogenation coverage may be determined measuring the C-H vibrational modes.

On the applicability of cluster models to study the chemical reactivity of carbon nanotubes

“…Indeed, energy changes in excess of 30 kcal/mol were detected for different clusters. On the other hand, for the addition of methylene, the oscillations were significantly damped, although convergence was not observed for models as large as C 210 H 20 . In the same context, Baldoni et al 6 used finite length Clar sextet models to study the addition of fluorine and methylene to the (6,4) and (6,5) SWCNTs.…”

“…The methodology used herein is the same as the one we applied to successfully study phosphorous 17 and sulfur 18 doped graphene, thiolated graphene, 14 nitrene functionalized graphene, 16 hydrogenated graphene, 15 thioepoxidated SWCNTs, 19 thiolated SWCNTs, 8,9 hydrogenated DWCNTs, 20 the addition of sulfur centered radicals to fullerenes, 21 the addition of azomethine ylides to carbon nanostructures, 22 the adsorption of CH 4 on SWCNTs, 23 and thiophene onto graphene and nanotubes. 24 Briefly, we performed density functional calculations using the UPBE functional 25 for all carbon nanostructures.…”

“…To simulate infinite SWCNTs, we have undertaken periodic boundary calculations for the (5,5), (6,6), (8,8), (12,12), (15,15), (10,0), (14,0), (20,0), and (25,0) SWCNTs. Three unit cells were used to model the metallic tubes and two for the semiconducting ones.…”

“…As evidenced by UB3LYP/6-31G*/UPBE/3-12G calculations performed by Bettinger, 5 the use of cluster models introduces some problems. In effect, for the addition of fluorine to (5,5) SWCNT segments ranging from C 30 H 20 to C 210 H 20 , it was observed that the addition energy has an oscillatory behavior. Indeed, energy changes in excess of 30 kcal/mol were detected for different clusters.…”

“…Regardless of the metallic properties that we observed for the hydroxylated nanotubes, we expect that when higher levels of functionalization are attained the tubes will become insulators as previously found for hydrogenated nanotubes. 20 As for the 1,3 dipolar cycloaddition reaction, the (5,5) SWCNT remains metallic after functionalization, even though the DOS is significantly depleted near the Fermi level with respect to the pristine nanotube. For the (8,8) and (12,12) species a band gap equal to 0.07 eV was observed.…”