Low-Temperature Synthesis And Properties Of Porous Boron Nitride Nanomaterials

Porous boron nitride attracts more and more attention because of its excellent properties and potential applications. Until now, there have been various methods to prepare porous boron nitride nanomaterials, such as templates methods, self-assistance, chemical vapor deposition and so on. However, the high reaction temperature and intricate processes are the main shortcomings that embarrass the mass production of porous BN with low cost. So it is of great significance to explore a simple route to prepare porous nitride boron at a low temperature.Mesoporous BN film was prepared at a low temperature of 550℃for 10 h via a simple reaction between CO(NH2)2 and NaBH4 without using additional templates. The yield of the resulting product was about 65 wt.% based on the starting material of NaBH4. The byproduct of NaCN and the gases produced during the reaction acted as the templates for the formation of the mesoporous BN. X-ray diffraction demonstrates the formation of t-BN with lattice constants a=2.46 and c=6.67 A, the reaction temperature influences the crystallinity of BN and the crystallinity improves at high temperature. High-resolution transmission electron microscopy displays a lot of porous films in the product, which possesses a high surface area of 219 m2·g-1 and a pore size primarily around 3.8 nm tested by nitrogen adsorption-desorption method. The mesoporous BN exhibits a strong luminescence emission around 3.41 eV in the cathodoluminescence spectra, a high stability in both morphology and structure, and good oxidation resistance up to 800℃.Meshy BN was prepared via a reaction between CS(NH2)2 and NaBH4, the sulfur-containing compound CS(NH2)2 replaced CO(NH2)2 as the nitride source and it can promote the cross-linking among borazine molecules during the formation of meshy BN. X-ray diffraction indicates the formation of hexagonal boron nitride (h-BN) with lattice constants a=2.501 and c=6.724 A. Observations by TEM show that the BN obtained has a meshy structure with a quantity of pores distributing on each mesh. The nitrogen adsorption-desorption test gives a high surface area of 220 m2·g-1 for the meshy BN. The cathode-luminescence spectrum exhibits a strong peak at 354 nm in the ultraviolet range. Thermogravimetric analysis proves that the meshy BN has good thermal stability and oxidation resistance up to 800℃.In order to increase the yield of the products, we tried to use thiosemicarbazideand(CH5N3S) and NaBH4 as the raw materials to synthesis porous BN. The yield of the resulting product was about 92 wt.% based on the starting material of NaBH4.X-ray diffraction and Fourier transform infrared spectra confirm the formation of hexagonal BN. Examination by High-resolution transmission electron microscope reveals that the product is comprised of nanoporous films, which exhibit a high surface area of 214 m2·g-1 characterized by nitrogen adsorption-desorption isotherms. The nanoporous BN films have good thermal stability and oxidation resistance up to 800℃measured by thermogravimetric analysis. So using CH5N3S as nitride source, which can greatly improve the yield of the hexagonal BN, also can effectively control the pore size of the nanoporous films.