Synthesis of boron nitride nanotubes and their applications

Abstract

Boron nitride nanotubes (BNNTs) have been increasingly investigated for use in a wide range of applications due to their unique physicochemical properties including high hydrophobicity, heat and electrical insulation, resistance to oxidation, and hydrogen storage capacity. They are also valued for their possible medical and biomedical applications including drug delivery, use in biomaterials, and neutron capture therapy. In this review, BNNT synthesis methods and the surface modification strategies are first discussed, and then their toxicity and application studies are summarized. Finally, a perspective for the future use of these novel materials is discussed.

Keywords: boron nitride nanotubes; chemical modifications; medical applications; synthesis methods; toxicity.

Figure 1

SEM images of BNNTs grown based on a CVD method. (a) Experimental setup, (b) stretching of dense BNNTs from the sample surface, (c) high magnification SEM image of BNNTs, (d) SEM images of slightly compressed BNNTs on a Si substrate, and (e) cross-sectional view of vertically aligned BNNTs. Figure adapted with permission from [56], copyright 2010 American Chemical Society.

Figure 2

SEM images of the BNNTs products at the different reaction time and colemanite/catalyst ratios (w/w) after CVD application. The respective reaction time and colemanite/catalyst ratio (w/w) were (a) 30 min and 12:1, (b) 60 min and 12:1, (c) 120 min and 12:1, (d) 120 min and 32:1, and (e) 120 min and 8:1. (f) Boat surface after removal of the BNNTs, at 120 min and with a ratio of 12:1.

Figure 3

Summary of chemical modification routes of BNNTs.

Figure 4

Low (a) and high (b) magnification confocal images of fluorescently labeled, functionalized BNNTs, where red, green, and blue are the cytoskeletal actin, functionalized BNNT, and nuclei, respectively. Figure adapted with permission from [15], copyright 2012 Elsevier.

Figure 5

TEM images of ferritin molecules immobilized onto BNNT surfaces (a), EDS spectrum of BNNTs with immobilized ferritin molecules (b), ferritin molecules on the surface and inside of a BNNT (c). Figure adapted with permission from [13], copyright 2005 American Chemical Society.

Figure 6

Scintigraphic image of radiolabeled, glycol chitosan BNNTs after (a) 30 min, (b) 1 h, and (c) 4 h after injection. Figure adapted with permission from [86], copyright 2012 Elsevier.

Figure 7

Preparation process of PLC (left) and PLC–BNNTs (right) and (a,b) SEM images of a PLC–BNNT composite exhibiting improved mechanical properties due to BNNTs bridges (red). Figure adapted with permission from [75], copyright 2010 Acta Biomaterialia.

Figure 8

Schematic representation of a humidity sensor test system with a single BNNT and a single BNNT–AgNPs. (a) SEM image (left) and EDS spectrum (right) and (b) TEM and HRTEM image of the BNNTs, (c) and (e) the SEM images with a single BNNT and single AgNP–BNNT, (d) and (f) the higher magnification SEM images in (c) and (e) marked with red square (f) AFM (upper) and TEM (lower) images. Figure adapted with permission from [90], copyright 2013 Elsevier.

Figure 9

Schematic representation of a poly-L-lysine-, fluorescent probe- and folate-modified BNNT. Figure adapted with permission from the authors [97].