【作者】 孙常慧；

【导师】 钱逸泰；

【作者基本信息】 山东大学 ， 无机化学， 2012， 博士

【摘要】 氮化硼作为一种重要的Ⅲ-Ⅴ族无机非金属材料,具有一系列优异的物理化学性质,在很多方面具有潜在的应用前景。其主要结构有层状氮化硼(包括六方相和三方相)和立方相氮化硼。其中六方相和三方相氮化硼具有与石墨相似的层状晶体结构,它们具有相似的物理化学性质,如良好的润滑性、耐化学腐蚀性、高热导率等。与石墨不同的是,层状氮化硼是一种宽带隙半导体或者绝缘材料,还能实现n型和p型掺杂,具有中子吸收能力,是很好的耐高温电子器件材料和很有前途的声光电材料。具有不同微观形貌结构的氮化硼材料可能会导致更加优良的性能,因此最近二十几年来,氮化硼的合成技术得到大力发展,诸多新颖的氮化硼纳米材料被制备出来。而目前的研究大多集中于一维氮化硼纳米材料的合成和表征,如氮化硼纳米管、纳米纤维等,对于其它形貌和结构的氮化硼纳米材料的研究尚不够深入在本论文我们在低温低压条件下制备了几种新颖形貌的氮化硼纳米材料,并初步探索了它们的热学性质、发光性质等性能。(1)近年来,通过化学方法以零维、一维、二维等纳米结构基元构筑更复杂的多维、多级纳米结构材料是有序物质科学的重要进展,由于具有此类结构的材料常常表现出与常规低维度纳米材料不同的电学、热学、光学、磁学、力学及化学方面的性质,这为构筑和集成高级纳米器件提供了崭新的策略。目前,有关氮化硼多级纳米结构的研究尚存空白。在本文中,通过硼粉和氨基钠在500℃下反应,我们成功制备了由纳米薄片组装而成的多级花状氮化硼结构。X-射线衍射和红外分析表明所制备的样品为高结晶性的三方相氮化硼(r-BN)结构。通过电镜观察得知这些氮化硼纳米花直径有几百纳米,而这些纳米薄片的厚度约为15-25nm,并且具有尖锐的边缘的结构。热重测试表明这些氮化硼纳米花可以在空气中抵抗600℃以下的氧化侵蚀。对比试验发现,缩短反应时间只能得到一些小碎片和颗粒,因此可以推断反应初期首先形成氮化硼纳米晶颗粒,然后这些颗粒发生聚集,并在此基础上生长出氮化硼薄片,最后组装而成多级花状氮化硼纳米结构。具有尖端薄片的氮化硼纳米片有望用于场发射电子器件,在微电子学领域发挥应用。(2)空心纳米结构材料往往具有较大的比表面积和相对轻质的特点,在催化、药物释放、化学传感器、生物技术、分离以及光电子等诸多领域都有着潜在的应用前景。制备此类结构材料的一般策略是利用各种硬模板或软模板剂对目标结构进行复制。氮化硼作为一种重要的Ⅲ-Ⅴ族材料,具有优异的热传导性能和化学稳定性,其空心结构受到了极大的关注。但传统制备方法存在合成温度过高、合成步骤较繁琐等弊端。在本文中,我们探索了一条制备氮化硼空心颗粒的温和制备路线。通过选择NaNF4和NaN3为反应物,采取反应釜内的一步合成法在较低温度下(450℃)成功制备出氮化硼空心结构材料,所制备的产物由空心球和纳米管组成,空心球直径约为400-700nm,纳米管的直径在150-300nm之间,比表面积达到89.8m2/g,热重测试显示其抗氧化温度达到800℃。对比试验表明在300℃C时也能制备出氮化硼空心球和纳米管,但产量稍低,显示出氮化硼纳米管低温宏量制备的可能性。如此制备的氮化硼空心结构材料有望用于储氢及催化等领域。(3)三维有序大孔材料是多孔材料研究的新领域,其孔洞排列规整,分布均匀,可用作理想的光子晶体材料、催化剂或其载体、过滤以及分离材料、热阻材料、电池材料等。制备三维有序大孔材料一般采取胶晶模板法。目前有关氮化硼大孔材料的研究相对较少,有待进一步探索。在本文中,我们通过NH4BF4与铁粉在500℃反应制备了疏松的氮化硼大孔材料,孔隙率达到73.7%,比表面积为122m2/g,不过孔洞直径较大,达到亚微米级,而且孔洞结构也不均一。经过在条件不变的情况下加入适量的硫粉参与反应,同样得到了三维氮化侧大孔材料,但各项织构特征得到明显改善,孔隙率达到85.6%,比表面增大到230m2/g,并且呈现出一定的短程有序特征。对比试验显示在反应温度下硫粉变为硫蒸气,可能促进了氮化硼片层发生卷曲,形成更为丰富的孔洞结构,并且加入硫粉可能使反应物的接触机会增多,从而使反应更加完全,提高了产率。这种不需添加模板、制备过程简便的合成大孔氮化硼材料的路线将为制备其它氮化物或碳化物大孔材料提供参考。另外,这些新颖的具有丰富孔洞特征的三维氮化硼大孔材料有望在催化剂载体、气体吸附、光电子及其它领域发挥巨大的应用。更多还原

【Abstract】 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.更多还原