Advances in boron nitride-based nanomaterials for environmental remediation and water splitting: a review

Boron nitride has gained wide-spread attention globally owing to its outstanding characteristics, such as a large surface area, high thermal resistivity, great mechanical strength, low density, and corrosion resistance. This review compiles state-of-the-art synthesis techniques, including mechanical exfoliation, chemical exfoliation, chemical vapour deposition (CVD), and green synthesis for the fabrication of hexagonal boron nitride and its composites, their structural and chemical properties, and their applications in hydrogen production and environmental remediation. Additionally, the adsorptive and photocatalytic properties of boron nitride-based nanocomposites for the removal of heavy metals, dyes, and pharmaceuticals from contaminated waters are discussed. Lastly, the scope of future research, including the facile synthesis and large-scale applicability of boron nitride-based nanomaterials for wastewater treatment, is presented. This review is expected to deliver preliminary knowledge of the present state and properties of boron nitride-based nanomaterials, encouraging the future study and development of these materials for their applications in various fields.

Four-dimensional vibrational spectroscopy for nanoscale mapping of phonon dispersion in BN nanotubes

Directly mapping local phonon dispersion in individual nanostructures can advance our understanding of their thermal, optical, and mechanical properties. However, this requires high detection sensitivity and combined spatial, energy and momentum resolutions, thus has been elusive. Here, we demonstrate a four-dimensional electron energy loss spectroscopy technique, and present position-dependent phonon dispersion measurements in individual boron nitride nanotubes. By scanning the electron beam in real space while monitoring both the energy loss and the momentum transfer, we are able to reveal position- and momentum-dependent lattice vibrations at nanometer scale. Our measurements show that the phonon dispersion of multi-walled nanotubes is locally close to hexagonal-boron nitride crystals. Interestingly, acoustic phonons are sensitive to defect scattering, while optical modes are insensitive to small voids. This work not only provides insights into vibrational properties of boron nitride nanotubes, but also demonstrates potential of the developed technique in nanoscale phonon dispersion measurements.