Synthesis And Properties Of Boron Nitride Materials

In the recent years, boron nitride nanomaterials have attracted considerable attention for their enhanced properties and potential application such as polymeric composite, gas adsorption, electrical nano-insulators, field-emitting devices, ultraviolet lasers. Until now, there have been various methods, such as arc-discharge, laser ablation, chemical vapor deposition, for synthesizing boron nitride nanomaterials. But the main problem is how to obtain large scale materials with high purity, well-defined structure, and good crystallinity. The research about this problem not only helps to develop nanomaterials growth mechanism, but also will be a guarantee for the further application. What's more, after getting high quality boron nitride nanomaterials, it is still a great challenge to improve their prosperities via functionalization or doping, which leads to extend the application fields of these materials. In this dissertation, our research is focused on boron nitride nanosheets, surface modification of boron nitride nanosheets and boron nitride nanotubes. The major results are as follows:(1) 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℃. 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℃for BN nanosheets compared with only about 400℃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. (2) Platinum nanoparticles have been successfully decorated at the surface of boron nitride nanosheets (BNNSs) by a facile chemical method. The content of the Pt loading can be easily controlled by adjusting the concentration of H2PtCl6. Then a highly sensitive, selective, and fast responding amperometric glucose biosensor based on nanohybrids of Pt subnanoparticle decorated BN nanosheets was fabricated. The Pt-BNNSs/GC electrode displays a good linear relationship with a sensitivity of 207μAmM-1 cm-2 towards H2O2. The highly electrocatalytic activity towards H2O2 makes the Pt-BNNS/GC electrode attractive for amperometric measurement of glucose in connection with glucose oxidase as H2O2 is a product of the enzymatic reaction. It is shown that the biosensor presents a linear response to glucose concentration with a sensitivity of 9.64μAmM-1cm-2. It is envisaged that the unique Pt-BNNs nanohybrids provide a good biosensing platform for other redox proteins and enzymes and find more potential applications.(3) Boron nitride (BN) nanotubes have been prepared by chemical vapor deposition using two different precursors. The XRD and FTIR results demonstrate that the products we obtained were hexagonal boron nitride. SEM and TEM images show that the products were nanotube structure. When boron oxide and NH4Cl were used as precursor, the structure and morphology of BN nanotubes were controlled by the growth temperature. At low temperature, BN nanotubes with uniform size distribution and high crystalline were obtained, along with the increase of reaction temperature, the diameter of BN nantubes became larger while the layer numbers were first increased and then decreased with a maximum at about 1000℃. When amorous boron, magnesium oxide, and ferric oxide were used as precursor, the products were very sensitive to the reaction gas. In the N2 atmosphere, the main products were uniform bamboo-like BN nanotubes. However in the NH3 atmosphere, the products became complex. Both bamboo-like and cylindrical BN nanotubes existed, and the diameter distribution spanned a wide range from tens of nanometers to several microns.