Liquid Exfoliation of Hexagonal Boron Nitride

Large-scale synthesis of hexagonal boron nitride (hBN) by a liquid exfoliation technique has been demonstrated in the present study. It is a low-cost and efficient method for exfoliating 2D materials like hBN. Here, a two-step approach was acquired to exfoliate the bulk hBN. In the first step, the bulk hBN was dispersed using a probe sonicator in a solution of gelatin, potassium chloride (KCl) and zinc chloride (ZnCl2), and in the second step, further exfoliation was achieved by centrifugation process. Exfoliation was achieved by both centrifugation and intercalation of Zn2+ and K+ ions within the layers of hBN. The supernatant obtained after centrifugation was heated to 600 °C for a duration of 1 h in an air atmosphere to eliminate the gelatin which was again heat treated for the same duration at 800 °C in an Ar atmosphere to improve its crystallinity. The hBN nanoplatelets obtained from the bulk hBN were characterized using various analytical techniques such as x-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and atomic force microscopy (AFM) to determine their properties. The hBN nanoplatelets showed a thickness range of ~ 50-270 nm and a lateral dimension range of ~ 1-3 μm. FTIR analysis confirmed the presence of hydroxyl (OH) functional group attached to the hBN nanoplatelets due to the absorption of surface moisture. The hBN nanoplatelets showed excellent thermal stability up to a temperature of ~ 726.16 °C. The liquid exfoliation approach used in the present work was found to be a highly effective method and shows potential for producing hBN nanoplatelets with a few layers.