Green synthesis of high-purity hexagonal boron nitride nanoparticles

Traditional methods, such as chemical vapor deposition (CVD), often require toxic and flammable organic reagents or result in a high carbon footprint, raising both health and environmental concerns. In this paper, we present an improved method for synthesizing hexagonal boron nitride (h-BN) nanoparticles using affordable and widely available precursors, boric acid, and urea. Our approach modifies the conventional techniques by introducing a two-step thermal treatment process, with nitrogen serving as an inert atmosphere and hydrogen as a diffusing agent. The resulting h-BN nanoparticles exhibit remarkable uniformity and high crystallinity. Characterization through scanning and transmission electron microscopy (SEM, TEM), high-resolution TEM (HR-TEM), selected-area electron diffraction (SAED), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed the formation of amorphous nanoparticles with an average size of 10 nm during the initial heat treatment at 600 °C under a nitrogen atmosphere. Further heat treatment at 1000 °C in a nitrogen-hydrogen gas mixture led to the crystallization of highly uniform h-BN nanoparticles, reducing their size to approximately 6 nm. This method ensures high morphological homogeneity and product purity, making it effective for the large-scale production of h-BN nanoparticles.