By Josh Perry, Editor
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Researchers at the University of Illinois at Chicago (UIC) are the first to alter boron nitride so that it will bond with other materials, such as those in electronics, to dramatically improve performance, according to a report from the university.

Treatment with a superacid causes boron nitride layers to separate and become positively charged, allowing for it to interface with other nanoparticles, like gold. (Berry, et al/UIC)

Boron nitride has been in the news a lot lately, as different research groups have increased its thermal conductivity, while others have demonstrated how to create the material in bulk. Its properties, including being ultrathin, strong, thermally-conductive, and lightweight, have made it an in-demand materials for a variety of applications.

“However, boron nitride’s natural resistance to chemicals and lack of surface-level molecular binding sites have made it difficult for the material to interface with other materials used in these applications,” the article explained.

UIC researchers treated the boron nitride with a superacid, chlorosulfonic acid, which caused it to separate into atomically thin sheets. These sheets had binding sites that interacted with nanoparticles and other 2-D materials like graphene. The acid caused protonation (addition of positive charges to atoms) on the internal and edge nitrogen atoms, which created sites on which other materials could bind.

Researchers believe that this will make boron nitride viable in applications such as electronics, solar cells, and diagnostic devices.

The research was recently published in ACS Nano. The abstract stated:

“Hexagonal boron nitride (h-BN) sheets possess an exclusive set of properties, including wide energy band gap, high optical transparency, high dielectric breakdown strength, high thermal conductivity, UV cathodoluminescence, and pronounced thermochemical stability. However, functionalization of large h-BN layers has remained a challenge due to their chemical resistance and unavailable molecular-binding sites.

“Here we report on the protonation of h-BN via treatment with chlorosulfonic acid that not only exfoliates “large” h-BNs (up to 10?000 μm²) at high yields (∼23%) but also results in their covalent functionalization by introducing four forms of aminated nitrogen (N) sites within the h-BN lattice: sp²-delocalized and sp³-quaternary protonation on internal N sites (>N⁺? and >NH⁺−) and pyridinic-like protonation on the edge N sites (?NH⁺– and −NH−).

“The presence of these groups transforms the chemically passive h-BN sheets to their chemically active form, which as demonstrated here can be used as scaffolds for forming composites with plasmonic gold nanoparticles and organic dye molecules. The dispersion of h-BNs exhibits an optical energy band gap of 5.74 eV and a zeta potential of ζ = +36.25 mV at pH = 6.1 (ζ_max = +150 mV), confirming high dispersion stability.

“We envision that these two-dimensional nanomaterials with an atomically packed honeycomb lattice and high-energy band gap will evolve next-generation applications in controlled-UV emission, atomic-tunneling-barrier devices, ultrathin controlled-permeability membranes, and thermochemically resistive transparent coatings.”