Synthesis And Characterization Novel Boron Nitride Nanomaterials

Boron nitride (BN) is an important III-V inorganic non-metallic material with excellent physical and chemical properties indicating promising applications in many fields. The main phases include layered (hexagonal and rhombohedral boron nitride) and cubic boron nitride. The former has similar layered crystal structure to graphite, so they have similar physical and chemical properties, such as good lubrication, chemical resistance and high thermal conductivity. Unlike graphite, layered boron nitride is a semiconductor with wide band gap or insulator and can be doped for both n-and p-type conductivity. Moreover, layered boron nitride can absorb neutron, thus can be used as excellent high-temperature electronic device materials and promising optoelectronic materials.Different microstructure and morphology may induce different properties. During the last two decades, the synthetic techniques of boron nitride have been developed largely and many novel boron nitride nanomaterials have been prepared. Most of the current studies are focused on the synthesis and characterization of one dimensional (ID) boron nitride nanomaterials, such as boron nitride nanotubes, nanofibres, etc. However, investigations on other morphology and structure of boron nitride nanomaterials are limited and need further efforts. In the dissertation, we have successfully prepared several kinds of boron nitride nanomaterials with novel morphology at low temperature and low pressure and have exploited preliminarily their thermal and luminescent properties.(1) In the recent years, making more complex multi-dimensional and hierarchical structural materials via chemical methods using zero dimensional (OD), ID, two dimensional (2D) nanostructures as building blocks is the important progress in ordered matter science. The materials with such structures usually exhibit different electronic, thermal, optical, magnetic, mechanical, chemical properties from routine low-dimensional nanomaterials, which provide new strategies for constructing and integrating advanced nanodevices. So far, there are no related reports about hierarchical boron nitride nanostructure as far as we know. Here, we have successfully prepared hierarchical boron nitride nanoflowers (BNNF) constructed by nanosheets using B powders and NaNH4as reactants at500℃. The XRD and FT-IR analysis confirmed the highly crystalline rhombohedral feature of the product. Electron microscopy images showed that the BNNFs have diameters up to hundreds of nanometers and the nanosheets were about15-25nm in thickness with sharp edges. Thermogravimetric analysis (TGA) results showed that the as-obtained BNNFs have high thermal stability below600℃. Contrast experiments showed that shortening reaction time caused the production of little flakes and particles. So we deduced that boron nitride nanocrystalline particles were formed first; then the nanocrystallite congregated together and boron nitride nanosheets began to grow on the congeries leading to formation of hierarchical BNNFs. Such BNNFs particles with novel nanostructures have been envisioned to be used as field emission nanodevice.(2) Hollow nanoscale structural materials have large surface area and light-weight feature, which can be used in catalysis, drug release, chemical sensors, biotechnology, separation and optoelectronic fields. Generally the hollow nanomaterials are prepared by using various hard or soft templates. As an important Ⅲ-Ⅴ material, boron nitride nanomaterials with hollow interiors have attracted numerous interests. However, the conventional methods are complicated and high temperature. Here, we develop a mild route to prepare boron nitride hollow particles. By using NaNF4and NaN3as reactants, boron nitride hollow nanomaterials were prepared via a one-pot route in an autoclave at450℃. The product was composed by hollow spheres and nanotubes. The diameters of them were400-700nm and150-300nm, respectively. The surface area of the product was up to89.8m2/g. TGA results showed that the anti-oxidation temperature can reach to800℃. Moreover, boron nitride hollow spheres and nanotubes can be produced even at300℃in this route, indicating the probability of large-scale synthesis of boron nitride nanotubes at low temperature. The as-prepared boron nitride hollow nanomaterials can be applied in hydrogen storage and catalysis.(3) Three-dimensional ordered macroporous (3DOM) materials are the research field of porous materials. They possess ordered and uniform pores and can be used as excellent photonic crystal materials, catalyst or its carriers, filtration or separation materials, anti-thermal materials, battery materials, and so on. Generally such3DOM materials are prepared by colloid templating method. However, there are few reports about boron nitride macroporous materials which need further exploits. Here, we prepared floppy boron nitride macroporous materials via the reaction of NH4BF4and Fe powders at500℃. The porosity and surface area are73.7%and122m2/g, respectively. However, the diameters of the pores were relatively large and up to sub-micrometer scale. Moreover, the structures of the pores were not uniform. When S powders were added into the reaction system while keeping other conditions constant, similar boron nitride macroporous materials were obtained with improved textural properties. The porosity and surface area of the new product rised to85.6%and230m2/g, respectively. Moreover, the new product presented short-range order. Contrast experiments showed that the S vapor produced at high temperature provided a transient driving force for rolling of the h-BN layers to form cavities of porous boron nitride materials. Moreover, the addition of sulfur may make the reactants mixed homogeneously and reduce the diffusion barriers, which led to more complete reaction and higher yield. Such template-free and facile route to3D macroporous boron nitride materials can be extended to prepare other macroporous nitride or carbide materials. Besides, the as-prepared macroporous boron nitride materials with rich pore characters will find competitive applications in catalysts support, gas adsorption, optoelectronic materials and other fields.