Growth of boron nitride nanotubes from magnesium diboride catalysts

Abstract

The difficulty in synthesizing boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace by chemical vapor deposition (CVD) may be ascribed to the failure to identify suitable catalysts and nucleation particles. This report demonstrates that magnesium diboride (MgB₂) can effectively catalyze the growth of BNNTs in such a tube furnace from various boron sources, including boron oxide (B₂O₃), boric acid (H₃BO₃), and a mixture of boron (B) and calcium oxide (CaO). This catalyst is more efficient than the possible magnesium oxide (MgO) or magnesium nitride (Mg₃N₂) catalysts. MgB₂ efficiently catalyzes the formation of BNNTs by maintaining a liquid state and showing a dissolving capacity for B₂O₃ at the growth temperature, thus satisfying the criteria for the vapor–liquid–solid (VLS) mechanisms of one-dimensional nanomaterials. First-principles simulations demonstrate that B₂O₃ can be dissolved into the MgB₂ nanoparticle. We believe that the strong catalytic behavior of MgB₂ can be attributed to its robust nucleation for BNNTs and dissolubility for B₂O₃.