Quantification of hexagonal boron nitride impurities in boron nitride nanotubes via FTIR spectroscopy

Abstract

Preparation of high-quality boron nitride nanotubes (BNNTs) from commercially available stock is critical for eventual industry adoption and to perform comprehensive experimental studies of BNNTs. Separation of hexagonal boron nitride (h-BN) and BNNTs is a significant challenge, and equally so, quantification of h-BN content in mixed samples is a major challenge due to their nearly identical properties. This work introduces a simple method of quantifying h-BN content in BNNTs based on FTIR analysis. Quantification is achieved by "spiking" a BNNT sample with pure nanoscale h-BN as an internal standard. To demonstrate the efficacy of the quantification technique two BNNT enrichment methods, surfactant wrapping and centrifugation, and a novel sonication-assisted isovolumetric filtration are introduced. FTIR spectra of enriched samples show clear trends throughout the processes. We propose and demonstrate that FTIR peak ratios of the transverse and buckling modes of mixed h-BN/ BNNT samples can be used to calibrate and quantify h-BN content in any BNNT sample. Hopefully, this method enables as-received BNNTs to be quantifiably enriched from low purity commercial feedstocks, enabling future development and study of BNNTs and related technology.

Purification of Boron Nitride Nanotubes Enhances Biological Application Properties

“…BNNT purification processes that we conducted are shown in Figure 1. Since amorphous boron is oxidized to B2O3 and boric acid during this process, the sample color changed from gray to white, as shown in Figure 2B [18]. These impurities could be removed by washing the sample with hot water or methanol.…”

“…The remained impurities are mainly h-BN particles with various sizes, which are difficult to separate from BNNTs because of their similar chemical properties. Recently, it was reported that h-BN impurities could be selectively removed by ultrasonically assisted diffusion separation [18,30]. The BNNTs and h-BN particles were dispersed in water by ultrasonication for 10 min, and the solution was vigorously stirred for 1 hr at 1400 rpm and filtered using a porous membrane (Stainless Steel Woven Wire Mesh) with 35 micrometer pore size.…”

“…The separation of h-BN and BNNTs was conducted by repeating filtration process using porous membrane. During the filtration, BNNT-rich samples were collected on the membrane where h-BN impurities were diffused Since amorphous boron is oxidized to B 2 O 3 and boric acid during this process, the sample color changed from gray to white, as shown in Figure 2B [18]. These impurities could be removed by washing the sample with hot water or methanol.…”

“…Current commercially available BNNTs have low (~50%) purity and contain significant amounts of hexagonal boron nitride (h-BN) and BNH compounds such as ammonia borane [18][19][20]. The low level of purity and the impurities contained in BNNTs can contribute to BNNT-induced cytotoxicity as well as hinder their dispersion in aqueous solution [21][22][23].…”

A mini-review on dispersion and functionalization of boron nitride nanotubes

“…Therefore, it was recognized that there was a layer of water molecules in the presence of surfactant located adjacent to BNNTs, while surfactant's hydrophobic and hydrophilic segments were placed, distantly. In addition to MD simulation, it has been proven that Triton X-100 could produce slightly higher BNNT enrichment than cause the dispersion of BNNTs in experimental analysis [69]. The encapsulation of the dopamine and caffeine within (14,0) BNNTs was investigated by García-Toral et al applying MD simulation and DFT calculations.…”