Theoretical study on the functionalization of BC₂N nanotube with amino groups.

Using density functional theory calculations, we investigated properties of a functionalized BC₂N nanotube with NH₃ and five other NH₂-X molecules in which one of the hydrogen atoms of NH₃ is substituted by X = -CH₃, -CH₂CH₃, -COOH, -CH₂COOH and -CH₂CN functional groups. It was found that NH₃ can be preferentially adsorbed on top of the boron atom, with adsorption energy of -12.0 kcal mol(-1). The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the functional groups. The adsorption energies are calculated to be in the range of -1.8 to -14.2 kcal mol(-1), and their relative magnitude order is found as follows: H₂N(CH₂CH₃) > H₂N(CH₃) > NH₃ > H2N(CH₂COOH) > H2N(CH₂CN) > H₂N(COOH). Overall, the functionalization of BC₂N nanotube with the amino groups results in little change in its electronic properties. The preservation of electronic properties of BC₂N coupled with the enhancement of solubility renders their chemical modification with either NH₃ or amino functional groups to be a way for the purification of BC₂N nanotubes.