Bulk quantities of hexagonal boron nitride (h-BN) nanosheets have been synthesized via a simple template- and catalyst-free chemical vapor deposition process at 1100−1300 °C. Adjusting the synthesis and chemical reaction parameters, the thickness of the BN nanosheets can be tuned in a range of 25−50 nm. Fourier transform infrared spectra and electron energy loss spectra reveal the typical nature of sp2-hybridization for the BN nanosheets. It shows an onset oxidation temperature of 850 °C for BN nanosheets compared with only about 400 °C for that of carbon nanotubes under the same conditions. It reveals a strong and narrow cathodoluminescence emission in the ultraviolet range from the h-BN nanosheets, displaying strong ultraviolet lasing behavior. The fact that this luminescence response would be rather insensitive to size makes the BN nanosheets ideal candidates for lasing optical devices in the UV regime. The h-BN nanosheets are also better candidates for composite materials in high-temperature and hazardous environments.

The discovery of the carbon nanotube has opened a challenging new field in materials, solid-state physics, and chemistry, offering a wide perspective for many possible applications.[1] The successful synthesis of functional ceramic micro-or nanostructures such as BN, [2,3] WS 2 , [4] MoS 2 , [5] In 2 O 3 , [6] TiO 2 , [7] and so forth has been reported. The theoretical prediction of a super-hard carbon nitride solid of composition C 3 N 4 (space group P6 3 /m) by Liu and Cohen [8] has directed the efforts of many experimental groups to synthesize this compound.[9±14] It has been extensively claimed that the carbon nitride compound could be formed in thin amorphous films by several methods such as shock-wave compression technology, pyrolysis of high nitrogen content precursors, diode sputtering, solvothermal preparation, pulsed laser ablation, and ion implantation. The hypothetical b-C 3 N 4 has the same crystal structure as b-Si 3 N 4 , with a hexagonal network of tetrahedrally (sp 3 ) bonded carbon and trigonal planar nitrogen (sp 2 ). Besides its predicted hardness, carbon nitride is also considered to be very promising in the fields of tribological and wear-resistance coating and optical and electronic engineering. [15±19] Although extensive studies on the synthesis and the characterization of carbon nitride materials have been reported, so far the nitrogen concentration of the formed carbon nitrogen compound is usually below the ideal composition for C 3 N 4 . Furthermore, the bonding between C and N tends to be of sp 2 -type character. An appropriate synthetic route to obtain the C 3 N 4 solid is still unknown. The difficulties in the synthesis of hard carbon nitrides are very likely related to their low thermodynamic stability with respect to the elements (C and N), indicated by a positive value of the enthalpies of formation. [20] Therefore, it will be particularly important to find effective and low-cost methods for synthesizing carbon nitride single crystals with a chemical composition of 3:4 for C/N. With this aim in view, we have recently succeeded for the first time in synthesizing single crystal b-C 3 N 4 nanorods in gram quantities via a simple route. As is known, the mechanochemical reaction may offer a possible method for materials synthesis under non-equilibrium condition with several advantages over conventional methods such as the production of non-aggregate and uniform particles in the nanometer scale range. [21,22] It may be used to drive a wide range of chemical reactions and can be performed under a controlled atmosphere to initiate solid±solid and solid±gas reactions to obtain special phases that could only be synthesized under extreme conditions such as high pressure and high temperature (HPHT), thus providing a low-cost method for synthesizing carbon nitride crystal. In this communication, nanostructured porous amorphous carbon powders with a high surface area and structural defects were firstly obtained by a high-energy mechanical process, then they were continually high-en...

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