Thermal-induced shape evolution from uniform triangular to hexagonal r-BN nanoplates

The shape evolution from uniform triangular boron nitride nanoplates of rhombohedral phase (r-BN) to hexagonal r-BN nanoplates was achieved through a simple calcination process in flowing N-2 at 1000 degrees C for 8 h. The average thickness of the triangular and hexagonal r-BN nanoplates is similar (similar to 50 nm), while their average edge sizes are 360 and 320 nm, and their intense emission bands are centered at 316 and 297 nm (lambda(ex) = 200 nm), respectively. TGA analysis results reveal that hexagonal r-BN nanoplates have superior thermal stability compared with the triangular nanoplates especially above 800 degrees C under ambient atmosphere. The possible mechanism of the thermally induced conversion from triangular to hexagonal r-BN nanoplates is discussed.