Synthesis, structure, and magnetic properties of Ni and Co nanoparticles encapsulated by few-layer h-BN

Metal nanoparticles with high magnetization values and good stability in acid and base environments have potential applications in industry, biological, and environmental fields. In this paper, we demonstrated a novel approach to synthesize Ni and Co nanoparticles encapsulated by few-layer h-BN (i.e., Ni@h-BN and Co@h-BN) via annealing of freshly prepared metal ammine complexes ([Ni(NH3)6]Cl2 or [Co(NH3)6]Cl3) and KBH4 with flowing nitrogen gas at 900 °C for 2 h. Formation of Ni@h-BN and Co@h-BN was observed from X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy. Bonding nature and elemental composition were also characterized by Fourier-transform infrared spectroscopy and Energy-dispersive X-ray spectroscope. Bonding formation process was illustrated by DSC/TGA analysis. Ni and Co NPs were found encapsulated into h-BN shells (c.a. 15 layers) with a high yield amounting to 42.6%. Additionally, the obtained saturation magnetization and coercivity of Ni@h-BN and Co@h-BN were 10.9 emu/g and 116 Oe, 83.3 emu/g and 62 Oe, respectively. Hence, the excellent performance of Co@h-BN and Ni@h-BN, especially the latter of which was prepared for the first time, could pave the way for application of h-BN encapsulation.