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

Abstract

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 μm), medium (0.51 ± 0.21), and short (0.31 ± 0.19 μm) 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.

Scalable, Highly Pure, and Diameter‐Sorted Boron Nitride Nanotube by Aqueous Polymer Two‐Phase Extraction

“…It consists of nanotubular BN (i.e., pure BNNT) mixed with varying sizes and amounts of impurities, including (stacked) hexagonal BN (hBN) and boron oxide (B 2 O 3 ). [ 10a ] No additional treatment was applied, to properly assess the effect of the purification process that ensues.…”

“…While solution purification protocols developed for BNNT so far generally feature a few distinct advantages compared to those in a bulk (e.g., compatibility to the industrial processes, non‐destructiveness, and less energy‐intensiveness), [ 9b ] conventional solution processes have suffered severely from low yields of purified BNNT. [ 10 ] Specifically, being associated with poor dispersity of BNNT in common solvents, the necessity for high‐speed centrifugation has resulted in an indiscriminative loss of BNNT that may otherwise be secured. [ 11 ] As the majority of reported solution methods are adopting centrifugation as a necessary pre‐treatment, it is highly desirable that one develops a method that could possibly bypass it.…”

“…Our key finding was that a small difference in the surface energy originating from the size effect can be utilized in differentiating between the impurities and the pure form of BNNT. [ 10a ] Although the method was of very high resolution and of fast processing time, its scalability, need for high‐speed centrifugation, and a relatively high cost of the sorting material have been notable disadvantages. To address this, here we demonstrate a scalable, high‐throughput sorting of BNNT from its synthetic impurities, via a solution process of aqueous polymer two‐phase extraction (ATPE).…”

Influence of Impurities from Manufacturing Process on the Toxicity Profile of Boron Nitride Nanotubes

“…[ 14,15 ] Morphologically, apart from the tubular structures of BNNT, the impurities appear as a combination of fibrous, sheet‐ and powder‐like structures. Based on the synthesis route and the impurity/residual targeted for removal, several purification strategies have been proposed including gas phase purification by chlorine etching, [ 16 ] acid washing, [ 17 ] hydrocarbon solvent processing, [ 18 ] wet thermal etching, [ 19 ] hot‐water washing, [ 17 ] surfactant wrapping and centrifugation, [ 10,20 ] gel column chromatography, [ 21 ] and sonication assisted filtration. [ 10 ]…”

“…[14,15] Morphologically, apart from the tubular structures of BNNT, the impurities appear as a combination of fibrous, sheet-and powder-like structures. Based on the synthesis route and the impurity/residual targeted for removal, several purification strategies have been proposed including gas phase purification by chlorine etching, [16] acid washing, [17] hydrocarbon solvent processing, [18] wet thermal etching, [19] hot-water washing, [17] surfactant wrapping and centrifugation, [10,20] gel column chromatography, [21] and sonication assisted filtration. [10] With a wide range of applications and progress in development of efficient large-scale production processes, [22][23][24][25] the next step in successful large-scale commercialization is to determine if these tubes cause any adverse pulmonary toxicity, as inhalation is a prominent route of exposure in occupational settings.…”