purification of yard-glass shaped boron nitride nanotubes

an efficient method for purification of yard-glass shaped boron nitride nanotubes (yg-bnnts) fabricated via a chemical vapour reaction (cvr) route has been developed. impurities including carbon, boron nitride (bn), and fe species in the pristine yg-bnnt sample are removed by a combined physical and chemical procedure which involves ultrasonication, high temperature oxidation, hot-water washing and acid washing. the samples at different stages of the purification process are monitored using x-ray powder diffraction (xrd), x-ray photoelectron spectroscopy (xps) and transmission electron microscopy (tem). the results reveal that the carbon and bn impurities could be easily eliminated.however, the catalyst nanoparticles (fe3c) encaged in the tubes prove to be effectively shielded from oxidation and acid corrosion. although the content of catalyst nanoparticles could be satisfactorily reduced to about 1.0 wt% by prolonged ultrasonication and acid washing, a small number of such magnetic nanoparticles are still left in the final purified yg-bnnts. the yg-bnnts exhibit a typical ferromagnetic behaviour even after a longtime oxidizing and acid washing treatment, indicating thatthey could be potentially used for harsh-environment magnetic devices.