Tunable Alkylation of White Graphene (Hexagonal Boron Nitride) Using Reductive Conditions

Abstract

Hexagonal boron nitride (h-BN), also known as white graphene, presents an unparalleled combination of properties, including superior mechanical strength, good thermal conductivity, a wide band gap, and chemical and thermal inertness. However, because of its aversion to chemical modification, its applications have not progressed as much as those of carbon nanomaterials. In this manuscript, we show the functionalization of hexagonal boron nitride using alkyl halides in strongly reducing conditions (Billups–Birch conditions). The tunability of the Billups–Birch reaction is demonstrated by alkylating hexagonal boron nitride with 1-bromododecane and varying equivalents of Li to BN. We found that using a 1:20 BN/Li ratio yields the highest chemical modification, as demonstrated using thermogravimetric analysis and Fourier transform infrared spectroscopy, and supported by X-ray photoelectron spectroscopy. Imaging of the functionalized h-BN (fh-BN) revealed that its sheets exfoliate better in isopropanol than pristine h-BN, which displays highly stacked nanostructures. Moreover, bearing alkyl chains confers the nanosheets with improved dispersibility in nonpolar solvents, such as dodecane, and allows the formation of hydrophobic films.

The Synthesis and Characterization of h-BN Nanosheets with High Yield and Crystallinity

“…Hexagonal boron nitride (h-BN) is known by the name white graphite. − As an isoelectronic body of graphite, h-BN that possesses a graphene-like two-dimensional layered structure exhibits excellent insulation, thermal conductivity, and thermal stability. , High-temperature resistance, pressure resistance, chemical corrosion resistance, anti-oxidation property, and good neutron radiation shielding performance make h-BN a new material with excellent performances and great development potential . The h-BN in-plane B and N atoms are associated by σ covalent bonds, forming a honeycomb-like structure with an interlayer thermal conductivity that can reach 300 W/(m·K) and still maintain its properties at 900 °C .…”

Hexagonal boron nitride exfoliation and dispersion

“…43,82 Other methods utilize reactions with amine groups in edge or defect sites 83 or reductive conditions. 84 This section will analyze each type of covalent functionalization and how different techniques have progressed over time. A summary of the different techniques can be found in Table 3.…”

“…The Martí group demonstrated this in 2019 by using the Billups-Birch reaction between hBN and bromododecane to attach dodecyl groups to the hBN surface. 84 This reaction uses lithium in liquid ammonia to produce solvated electrons that exfoliate the hBN sheets and produce alkyl radicals. 101 After the reaction, the average f-hBN thickness decreased nearly ten-fold while the lateral dimensions remain roughly the same.…”

“…101 After the reaction, the average f-hBN thickness decreased nearly ten-fold while the lateral dimensions remain roughly the same. 84 Moreover, alkylated hBN sheets were more dispersible in dodecane and THF and less dispersible in water and IPA than pristine hBN, showing that they have become more hydrophobic. Finally, f-hBN was filtered to produce a transparent film whose hydrophobicity was demonstrated by contact angle measurements as shown in Fig.…”

Understanding the Exfoliation and Dispersion of Hexagonal Boron Nitride Nanosheets by Surfactants: Implications for Antibacterial and Thermally Resistant Coatings

“…The production of these dispersions on a large scale requires the exfoliation of the two-dimensional (2D) nanosheets from the three-dimensional (3D) bulk material. Some studies have explored exfoliation methods that can be applied to a variety of 2D materials, including graphene and transition-metal dichalcogenides. − Several groups have attempted to achieve hBN exfoliation in various ways, including the use of solvents, ,,− acids and bases, ,− covalent functionalization, ,,− biomolecules, ,, polymers, ,,− and surfactants, ,− among others. − Amid these many options, surfactants are advantageous for many industrial applications, as they have low toxicity, are inexpensive, and do not disrupt the sp 2 hybridization, and therefore the thermal and mechanical properties of hBN. Despite these advantages, very few surfactants have been tested for the dispersion of hBN.…”