High yield exfoliation of sub-micron hexagonal boron nitride using a solvent free method

Abstract

Sodium fluoride (NaF) has been found to be an activation agent in exfoliating a hexagonal boron nitride (hBN) platelet, using a solvent free method. The procedure was carried out by enhancing the intercalation of ferric chloride (FeCl₃) in an intermediate step, up to 330 °C, followed by removal of the by-product at room temperature. In this research, five additional common salts, including lithium fluoride, potassium fluoride, lithium chloride, sodium chloride, and potassium chloride, were examined and compared to NaF for their effectiveness in achieving maximum exfoliation of commercially available sub-micron-sized hBN. It was found that all fluoride and chloride salts significantly activated the intercalation of FeCl₃ into this hBN. Analyses and characterization by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy revealed NaCl to be one of the most effective agents without further heat treatment and the least expensive salt for the intercalation reaction and exfoliation process. The synthetic route of this solvent free method is straightforward, achieving yields of 89% or higher, making it suitable for large scale production.