Tuning the physicochemical properties of the single-walled boron nitride nanotube by covalent grafting of triazolium-based [MTZ][X1–3] (X1–3 = NTf2−, TfO− and BF4−) ionic liquids in the gas phase and solvent media: A quantum chemical approach

Abstract

Covalent grafting of boron nitride nanotubes (BNNTs) using ionic liquids can effectively adjust their electronic structures, magnetic properties and solubility, and leads to the development of applications of the boron nitride nanotubes. Because of the localization features of the BNNT π electron system, the empty p orbitals of boron sites can be filled by excess electrons, which encourage covalent bonding with an unpaired electron. In the present work, physicochemical characteristics of the (8,0) zigzag boron nitride nanotubes (BNNTs) functionalized by methyl 1,2,4 triazolium [MTZ] [X1–3] (X1–3=NTf2−, TfO−, and BF4−) based ionic liquids (ILs) were explored at the M06-2X/6–31+G(d,p) level of theory. Three different functionalized-NTs (NTMTZ-X1–3) were found on the potential energy surface. Comparison of the corrected binding energies showed that the stability of the complexes decreases in the order of NTMTZ-X2≈NTMTZ-X1>NTMTZ-X3. From the solvation Gibbs free energies, it was predicted that the solubility in water increases upon surface functionalization of the BNNT. A remarkable reduction in the HOMO-LUMO gap was predicted from 7.30eV in BNNT to 2.91eV in [NTMTZ]+, and 3.18, 3.26 and 4.46eV in NTMTZ−X1–3 complexes, respectively. The density of states (DOS) analysis revealed that the covalent functionalization of BNNT with ILs results in the spin polarization and induces spontaneous magnetization. In addition, the charge transfer values, electron density properties, dipole moment, electrochemical windows (ECW), non-covalent interactions (NCI) index, anodic and cathodic stability were also evaluated. The results also showed that complexes formed from the [BF4]− anion have a wider ECW.