Low-Temperature Triazine Functionalization of Boron Nitride Nanotubes for Applications from Drug Delivery to Advanced Composites

Boron nitride nanotubes (BNNTs) are emerging nanomaterials with impressive mechanical properties and unique multifunctional properties including high thermal stability, electrical insulation, optical transparency, neutron absorption capability, and piezoelectricity. To harness the true potential of BNNTs for applications from drug delivery to advanced coatings and composites, functionalization is necessary to enhance their solubility and processability. Current functionalization approaches require aggressive reaction conditions such as long reaction times, high temperatures, high pressures, aggressive reagents, and an inert atmosphere. Herein, we present the development of a low temperature covalent functionalization method for enhanced solution processing of BNNTs utilizing a nitrene based (2 + 1) cycloaddition reaction that results in enhanced BNNT processability and solubility in N-methyl-2-pyrrolidone and N,N-dimethylformamide. Confirmation and degree of covalent functionalization are established using infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA). Poly-(3-hexylthiophene) (P3HT) is used to assess the quality of the BNNTs postfunctionalization to again confirm covalent functionalization. Finally, secondary functionalization of the functionalized BNNTs with propargyl chloride is achieved to demonstrate that this functionalization not only enhances the processability of the BNNTs but also results in a BNNT surface platform in which a plethora of molecules and nanomaterials can be grafted based on the application case. This nondestructive method preserves the extraordinary properties of BNNTs while opening their widespread use in many new and exciting opportunities in materials development.