Boron Nitride Nanotubes: Recent Advances in Their Synthesis, Functionalization, and Applications

Abstract

A comprehensive overview of current research progress on boron nitride nanotubes (BNNTs) is presented in this article. Particularly, recent advancements in controlled synthesis and large-scale production of BNNTs will first be summarized. While recent success in mass production of BNNTs has opened up new opportunities to implement the appealing properties in various applications, concerns about product purity and quality still remain. Secondly, we will summarize the progress in functionalization of BNNTs, which is the necessary step for their applications. Additionally, selected potential applications in structural composites and biomedicine will be highlighted.

Keywords: biomedical applications; boron nitride nanotubes; functionalization; mass production; polymer composites.

Figure 1

(a) Experimental setup for the growth of BNNTs in a horizontal tube furnace. Adapted with permission from [30]. Copyright 2008 IOP Publishing Ltd.; (b) TEM image showing tubular structure of BNNT with amorphous free side walls; (c) Well-defined patterned growth of BNNTs on a substrate. Adapted with permission from [4]. Copyright 2010 American Chemical Society; (d) Photograph of water droplet on the surface of BNNT film produced by CCVD showing superhydrophobicity; (e) Zoom-in cross sectional view of BNNTs on Silicon substrate showing that these BNNTs are grown vertically aligned on the substrate surface. Adapted with permission from [8]. Copyright 2012 American Chemical Society.

Figure 2

SEM images of (a) BNNT fibrils and (b) the entangled BNNT network produced by the pressurized vapour/condenser method (PVC). The white arrow in (a) indicates the growth direction, parallel to the BNNT fibrils. The short arrow in (b) marks a round, solidified boron droplet in the network. Adapted with permission from [43]. Copyright 2009 IOP Publishing Ltd.; (c) Entangled BNNTs within the BNNT fibrils grown from hydrogen catalysed inductively coupled plasma. Adapted with permission from [46]. Copyright Published 2014 by American Chemical Society; (d) Image of entangled BNNT fibril produced by the EPIC system. Adapted with permission from [47]. Copyright 2014 American Chemical Society

Figure 3

Macroscopic photographs of BNNTs produced by different techniques: (a) modified laser vaporization PVC/HTP method; (b) EPIC method; (c) Inductive thermal plasma. (a) The results of a 200 mg BNNT by PVC production. The unprocessed material has the appearance of cotton balls, though the texture is somewhat softer and the material finer-grained. Adapted with permission from [43]. Copyright IOP Publishing Ltd.; (b) Production via the EPIC method. BNNT felt-like sheet peeled intact from the walls of the reaction chamber. Adapted with permission from [47]. Copyright 2014 American Chemical Society; (c) BNNT materials grown by an induction plasma process. The as-grown BNNT materials exhibit three distinct morphologies: (c-1) entangled fibril materials consist of many fibrils formed naturally, and BNNT yarns can be drawn directly from them; (c-2) Cloth-like sheets have a multi-layered structure, and thin diaphanous membranes can be easily peeled off; (c-3) Fluffy cotton-like deposits have a low density and cover the entire wall of the filtration chamber. Inset is a close-up image. Adapted with permission from [46]. Copyright Published 2014 by American Chemical Society.

Figure 4

(a) Schematic of BNNTs functionalized with m-PEG-DSPE molecules in water. (b) Appearance of well-dispersed BNNTs functionalized with mPEG-DSPE molecules in water. These suspension is very stable versus unfunctionalized BNNTs suspended in ethanol (c); (d) The lengths of the functionalized BNNTs as a function of sonication/cutting duration. TEM images of cut BNNTs are shown in the inset. Adapted with permission from [52]. Copyright 2010 American Chemical Society; (e) Overlay of fluorescence images of HeLa cells (nuclei stained in blue) incubated with functionalized BNNTs (in red).

Figure 5

Schematic representation of potential applications of BNNTs in biomedicine. Adapted with permission from [81]. Copyright 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.