Highly Pure, Length-Sorted Boron Nitride Nanotubes by Gel Column Chromatography

Boron nitride nanotubes (BNNTs) have attracted enormous attention owing to their exceptional physical, chemical, and thermal properties. However, the implementation of such properties into practical applications has been hindered severely by limitations on the synthesis that results in a BNNT mixture containing significant amounts of impurities with varying size dispersity. Here, we present simultaneous purification and length sorting of such a mixture via gel column chromatography, where the components are effectively separated based on their affinity difference to the matrix. We report near-complete removal of the major impurities including >99% of the boron allotropes and 99.9% of the hexagonal boron nitrides while showing a series of length fractions containing long (1.00 +/- 0.36 mu m), medium (0.51 +/- 0.21), and short (0.31 +/- 0.19 mu m) BNNTs in a one-step process that takes less than an hour. We expect the protocol established here to serve as a simple, fast, and scalable processing method amenable to the low-cost industrial processes, targeting various future BNNT applications that require high-purity BNNTs with tailored nanotube length.