Synthesis, characterisation and applications of core-shell carbon-hexagonal boron nitride nanotubes

Heteroatomic nanotubes consisting of graphitic carbon (g-C) and hexagonal boron nitride (h-BN) were first synthesised over two decades ago, representing the earliest example of a carbon nanotube (CNT) covalently doped with h-BN. This opened up a exiting new field of study into BxCyNz heteronanotubes that exhibit tunable electronic properties based on stoichiometry. Increased research focus on such heteronanotubes has also led to the development of novel configurations of g-C and h-BN in van der Waals type hybrids. In particular, heteronanotubes consisting of a core CNT sheathed with h-BN, coaxial shell layers (CNT@BN), have recently witnessed advances in their synthesis and exploitation. CNT@BNs exhibit superior thermal stability, chemical inertness and mechanical robustness in comparison to CNTs, whilst the h-BN also adds the rare duo of thermal conduction pathways and electrical insulation. The various synthesis methods yield a range of different structure, crystallinity and composition profiles in CNT@BN. Here, we review the current methods of CNT@BN production and characterisation and highlight the prospect for application of these heteronanotubes in high temperature composites, nano-mechanical components, nano-electronics, field emitters and thermal management materials, and propose future avenues of research