Synthesis, structure and properties of homogeneous BC<SUB>4</SUB>N nanotubes

BCN nanotube brushes have been obtained by the high temperature reaction of amorphous carbon nanotube (a-CNT) brushes with a mixture of boric acid and urea. The a-CNT brushes themselves were obtained by the pyrolysis of glucose in a polycarbonate membrane. The BCN nanotubes have been characterized by EELS, XPS, electron microscopy, Raman spectroscopy and other techniques. The composition of these nanotubes is found to be BC<SUB>4</SUB>N. The nanotubes, which are stable up to 900&#176;C, are insulating and nonmagnetic. They exhibit a selective uptake of CO<SUB>2</SUB> up to 23.5 wt%. In order to understand the structure and properties, we have carried out first-principles density functional theory based calculations on (6,0), (6,6) and (8,0) nanotubes with the composition BC<SUB>4</SUB>N. While (8,0) BC<SUB>4</SUB>N nanotubes exhibit a semiconducting gap, the (6,0) BC<SUB>4</SUB>N nanotube remains metallic if ordered BN bonds are present in all the six-membered rings. The (6,6) BC<SUB>4</SUB>N nanotubes, however, exhibit a small semiconducting gap unlike the carbon nanotubes. The most stable structure is predicted to be the one where BN<SUB>3</SUB> and NB<SUB>3</SUB> units connected by a B-N bond are present in the graphite matrix, the structure with ordered B-N bonds in the six-membered rings of graphite being less stable. In the former structure, (6,0) nanotubes also exhibit a gap. The calculations predict BC<SUB>4</SUB>N nanotubes to be overall nonmagnetic, as is indeed observed