Local and Global Electronic Effects in Single and Double Boron-Doped Carbon Nanotubes

Abstract

The foreign atom doping influences the properties of carbon materials, and it is a possible way of designing materials of desired characteristics. Density functional calculations have been carried out on various isomers of boron-doped (4,0) and (9,0) carbon nanotubes as templates to investigate the doping effect on the structure and electronic properties on such systems. The results indicate that these boron-doped carbon nanotubes show local structural changes, mostly due to the elongation of bonds. The insertion of heteroatoms perturbs the π-conjugation system, which, in effect, destabilizes the material through higher energy cost of formation. The position of the foreign atom controls the new organization of electron density and leads to one of two possible distributions, viz., global (where electron density is distributed over the molecular surface) or local (localized distribution of electron density). This feature, in turn, can influence the bonding of the reactants while interacting with the surface. The charge distribution at a particular boron-doped site always possesses the local characteristics with a positively charged boron atom surrounded by negatively charged carbons. Such a character is also a measure of the driving force for influencing the substitution reaction in the vicinity of boron through an ionic mechanism.

DFT calculation of structures and NMR chemical shifts of simple models of small diameter zigzag single wall carbon nanotubes (SWCNTs)

“…Recent studies also probe the local and global electronic environment of CNT doped by other elements, for example, boron. [7] The diameter of experimentally observed SWCNT varies from ultra-thin [6] to larger, over one and more nanometers. [6] Commercial HiPco samples of SWCNT are available as raw material containing metal impurities and amorphous carbon, as well as well-defined nanotubes of 0.8-1.2 nm diameter and length of about 100 nm, and of high uniformity and purity.…”

DFT studies on armchair (5, 5) SWCNT functionalization. Modification of selected structural and spectroscopic parameters upon two-atom molecule attachment

“…The latter one is used It is possible to assume a theoretical formation of (5, 5) armchair and (9, 0) zigzag SWCNTs by cutting a popular C 60 fullerene in the middle and adding subsequent belts formed by cyclacenes (see [35]) These metallic nanotubes are of roughly identical diameter (6.9 and 7.1 Å, as calculated at the B3LYP/3-21G level of theory [36,37]. Interestingly, the energy of one hydrogen atom replacement at the rim of open end (9, 0) zigzag or (5,5) armchair SWCNTs (with dangling bonds saturated with H atoms) by -OH or -COOH groups differed consistently (about -40 and -38 for hydroxylation and -21 and -16 kcal/mol for carboxylation of zigzag and armchair SWCNTs, see ref. [36,37].…”

A review of boron enhanced nanoporous carbons for hydrogen adsorption: numerical perspective

“…The loss of electron, due to the B presence, allows for different π -bonding conjugation as the function of B/C exchange site. Such a conjugation in case of boron nanotubes leads to two possible organizations (local or global) of electron spin density (Saloni et al 2010) and in an effect to different reactivity regarding the H 2 physisorption.…”

“…The binding energy of hydrogen to the surface is also affected by the presence of boron (Saloni et al 2010). In graphene, the binding energy of hydrogen adatoms forming dimer-like configurations is by nearly 100 kJ/mol atom higher than the binding energy of two isolated H monomers (E bH = 94.8 kJ/mol).…”