Efficient catalytic conversion of ammonia borane to borazine and its use for hexagonal boron nitride (white graphene)

Nickel nanoparticles (NiNPs) prepared in tetraglyme (TG) efficiently catalyzed the conversion of ammonia borane (AB, NH₃BH₃) to borazine (B₃N₃H₆). Under the optimized conditions, 3 mol% of the NiNPs were introduced into a 1.5 M AB solution in TG and held at 80 °C for 6 h under a dynamic vacuum that was maintained at 30 torr. Borazine was isolated through a series of -45 °C, -78 °C, and -196 °C traps to give (-78 °C trap) pure borazine in 53% yield. The borazine produced was then utilized as a molecular precursor for high quality h-BN (white graphene) and large area h-BN sheets were prepared by applying low pressure chemical vapor deposition (LPCVD). Ultra-thin (single to few layers) h-BN was synthesized on Ni foil at the optimal ratio between borazine and NH₃, and the number of layers was tuned by varying the NH₃ partial pressure.