【作者】 张顺杰；

【导师】 王琪珑； 崔得良；

【作者基本信息】 山东大学 ， 无机化学， 2013， 硕士

【摘要】 近几年,由于单壁碳纳米管和石墨烯研究的快速发展,具有超薄结构特性的六方氮化硼纳米材料也得到了科学家们的广泛关注。本文在中热固相反应方法的基础上,通过调控实验参数和利用自主设计的可控体积热压反应釜合成了由超薄氮化硼纳米片(BNNSs)自组装而成的具有三维多级结构的纳米材料,并考察了这种材料的性质及应用。首先,我们在普通反应釜中合成了由BNNSs自组装而成的三维多级结构,分析了这种材料的物相和形貌及基本的性质,并探索了反应机理。其次,我们向反应体系中加入了催化剂硫和通过调控反应体系的压力的方法将BN纳米片的厚度降低到超薄的尺度,并且通过HRTEM照片分析了这种材料的特殊边缘结构。再次,我们利用超薄BNNSs自组装三维多级结构吸附性良好的性质将其用在废水处理中,通过接触角测试考察了超薄BNNSs自组装三维多级结构自身的超疏水性。最后将超薄BNNSs自组装具有三维多级结构的材料与高分子材料复合考察了复合材料的热学性质。具体结果如下：首先利用中热固相反应,在50mL反应釜中大产率的合成了三维BN纳米材料。这种材料为纳米BN薄片呈放射状排列方式自组装而成的三维纳米多级结构,大小在200～300nm左右,并且BN薄片的厚度在8～10nm左右。通过改变反应恒温时间,我们发现了这种三维材料从纳米碎片到表面突起状结构再到放射状纳米片的演变过程,并提出了一种气-固和气-气结合的缓释反应机理。其次为了减薄BN纳米片的厚度,我们加入了催化剂硫。加入硫后我们减少了反应时间和降低了纳米片的厚度。硫主要有两个作用：一个是在反应初期与叠氮钠反应释放大量的热量,为后续反应提供能量；另一个作用是催化反应中间产物叠氮氨的分解,促使产物BN的生成及减小纳米片的厚度。接着通过调控反应釜的体积达到调控反应体系的压力,从而使组成三维BN纳米材料的薄片由厚度8nm左右减小到3nm左右,实现了超薄BN纳米片的可控合成。分析了不同体系压力对实验结果的影响,并且通过TEM和HRTEM照片详细研究了超薄BN纳米片的形状和边缘结构,发现BN纳米片的形状基本为正三角形,其边缘为zigzag结构。最后,在可控合成的基础上,我们考察了超薄BNNSs自组装具有三维多级结构材料的一些性质。通过测试其在不同pH值水溶液中的zeta电势值,并以亚甲基蓝(MB)为例考察了其在不同pH下对MB的吸附量大小,发现了吸附量随负电势增大而增大的规律且在pH=11时吸附量达到最大。接着在pH=11的条件下,测试了这种三维材料对MB的吸附速率曲线,发现超薄BNNSs自组装具有三维多级结构材料对MB的吸附为快速吸附过程。测试了不同样品的比表面积和对MB的吸附平衡曲线,我们发现样品对MB的吸附能力随着比表面积的提高而增大。在超薄BNNSs自组装三维材料的纳米粗糙结构的基础上,我们研究了超薄BNNSs自组装三维多级结构涂层的超疏水性。首先重复测试了超薄BNNSs自组装三维多级结构涂层的同一点的接触角,并记录了水滴在其表面的移动过程,说明了超薄BNNSs自组装三维多级结构的疏水性能很稳定。然后测试了样品在不同pH值下的接触角大小,发现了样品的疏水性能不随水的酸碱度变化而变化。最后通过测试超薄BNNSs自组装三维多级结构的不同样品,发现了当BN薄片厚度为3nm时接触角大于150°,说明了我们制备的BN样品自身就具有超疏水性。利用BN的导热率高的性质,我们将所制备的超薄BNNSs自组装三维多级结构材料与高分子材料进行了复合：将超薄BNNSs自组装三维多级结构材料添加进结构性电子封装材料PA66中,得到了高导热率的和低热膨胀系数的BNNSs/PA66复合材料；我们也把超薄BNNSs自组装三维多级结构材料与PVA进行了复合得到了导热率高的复合薄膜材料,当添加量为3wt.%时其导热率为纯PVA薄膜的3.44倍。更多还原

【Abstract】 Recently, hexagonal boron nitride (hBN) with ultrathin layer structure has attracted extensive interest in the past few years owing the development of graphene and single-walled carbon nanotube. Herein, with the foundation of middle temperature solid phase reaction method, we have seccessfully fabricated3D hierarchical structure self-assembled by ultrathin BN nanosheets (BNNSs) using middle temperature solid state reaction method. These3D hierarchical structures are composed of radialy aligned ultrathin nanosheets. First, we synthesized3D hierarchical structure self-assembled by BNNSs and analyzed the phase and morphology of the material. Second, we reduced the thickness of nanosheet to ultrathin through adding initiater sulfur and regulating the pressure of reaction system. We also discussed the shape and special edge structures of BNNSs. Then we used3D hierarchical structure self-assembled by ultrathin BNNSs in wastewater treatment for its good adsorption property, and investigated the superhydrophobicity of themselves by contact angle tests. Finally, we synthesized BNNSs/polymer composite materials, which have good thermal properties. The results are as follows.Using midle-temperature solid reaction, we successfully synsethsized3D hierarchical structure self-assembled by BNNSs in50mL reaction kettle with a big yield. These structures are self-assembled by radialy aligned nanosheets and about200-300nm. The thicknesses of these nanosheets are about8nm. By changing the time of constant temperature, we found the evolution process of3D hierarchical structure from nanodebris to bump structure and then to radial nanosheets. Then we put forward a gas-solid and gas-gas combined reaction mechanism with slow-release process.For reducing the thickness of BN nanosheet, we added the sulfur into the reaction as an initiater, which reduced the reaction time and the thickness of BN nanosheets. One main function of sulfur is generating a lot of heat by reacting with NaN3at initial stage. The other main function is catalyzing the decomposition of azide ammonia, prompting the production of BN and reducing the thickness of nanosheet. Then we regulated the volume of the autoclave for getting different pressures of the reaction system. And through the regulating of pressure, we successfully achieved the controllable synthesis of ultrathin BNNSs with the thickness of nanosheet reducing from8nm to3nm. Finally, through investigating the TEM and HRTEM images, we found that the nanosheets were regular triangle and the edges of BN nanosheets were zigzag structure.On the basis of controllable synthesis, we investigated the properties of3D hierarchical structure self-assembled by BNNSs. First, by testing the zeta potential value and the adsorbing capacity of3D hierarchical structure self-assembled by ultrathin BNNSs for MB in aqueous solution with different pH value, we found the adsorption quantity increased with the adding of absolute value of the negative potential and reached the maximum at pH=11. Then under the condition of pH=11, we tested the rate curves of adsorption of3D hierarchical structure self-assembled by ultrathin BNNSs for MB and found the process of the the adsorption on BNNSs was a rapid adsorption process. Finally, we investigated the specific surface area of3D hierarchical structure self-assembled by ultrathin BNNSs and the adsorption equilibrium curves for MB. we found the adsorption capacity of3D hierarchical structure self-assembled by ultrathin BNNSs for MB increased with the increase of specific surface area.Knowing the special rough structure, we investigated the super hydrophobicity of3D hierarchical structure ultrathin BNNSs coatings. We first retested the the contact angle of water on3D hierarchical structure ultrathin BNNSs coatings at the same point and recorded the moving process of water droplet on the surface of the coating, which prove that the hydrophobic performance of3D hierarchical structure ultrathin BNNSs coating is very stable. Then we tested the size of the contact angle of sample under different pH value, and we found the hydrophobic performance had nothing to do with the pH value of water. At last, we investigated the contact angles of different samples and found the contact angle was more than150°when the thickness of BN nanosheet was3nm, which illustrates that3D hierarchical structure BNNSs have the super hydrophobic performance itself.Using the high thermal conductivity of BN, we prepared BNNSs/polymer composite by3D hierarchical structure self-assembled by ultrathin BNNSs. We first added3D hierarchical structure self-assembled by ultrathin BNNSs into PA66, which is the structural and electronic packaging material. And we achieved the BNNSs/PA66composite with high thermal conductivity and low thermal expansion coefficient. We also got the BNNSs/PVA film composite by putting3D hierarchical structure self-assembled by ultrathin BNNSs into PVA. When the the quantity of BNNSs is3wt.%, the thermal conductivity of composite is3.44times of pure PVA membrane.更多还原