Solvent-Free Functionalized Boron Nitride Nanotubes via Open-Air Cold Plasma for Highly Stable Dispersion in Water

For the dispersion of boron nitride nanotubes (BNNTs), noncovalent or covalent functionalization methods in a solvent with complex procedures, including acidic treatments, are widely used. Herein, we propose a solvent-free functionalization of BNNTs using a facile atmospheric-pressure cold-plasma treatment method. The plasma-treated BNNTs exhibited nearly threefold enhanced dispersibility and fourfold improved long-term dispersion stability compared with pristine BNNTs. These remarkable enhancements were attributed to the presence of the O atoms and OH molecules generated in the plasma, which reacted with the BNNT surface to form B-N-O and OH bonds. Consequently, the wettability of the plasma-treated BNNTs was transformed to superhydrophilicity, resulting in the exfoliation of the BNNT bundles in water. Small-angle X-ray scattering measurements confirmed the successful exfoliation of plasma-treated BNNTs from bundled structures in water. From an application perspective, the atmospheric-pressure cold plasma method offers a solvent-free, straightforward, and robust approach for BNNT functionalization, eliminating the need for additional post-procedures to remove residual surfactants from BNNTs.