氮化硼纳米片的制备、修饰及其聚合物基复合材料性能的调控

Hexagonal boron nitride (h-BN) sheet is a two-dimensional honeycomb comprising alternate boron and nitrogen atoms. h-BN sheet is an electrical insulator with many excellent properties such as good thermal conductivity and high mechanical strength. Furthermore, it is transparent, thermally stable, oxidation resistant, acid and alkali tolerate. While the extreme chemical stability makes h-BN sheets promising fillers in polymeric nanocomposites, it poses significant challenges to chemical exfoliation and subsequent functionalization of h-BN sheets. The lack of scalable production technique and effective functionalization approach greatly restricts the potential applications of h-BN sheets in polymeric nanocomposites. As a result, a reliable technique to produce and functionalize h-BN sheets at a relative large scale is pursued in this proposal, targeting high-performance polymeric nanocomposites with functionalized sheets as fillers. Specifically, the bulk h-BN powders are pretreated with alkali metals or ammonia plasma irradiation to increase the interlayer distance and introduce functional groups on the h-BN layer surface. Upon chemical exfoliation, the resulting h-BN sheets are functionalized with polymers via covalent and/or non-covalent linkage to improve the compatibility of h-BN sheets with polymer matrix and to tune the interfacial structures and interactions. Mechanistic studies are also carried out to illustrate the relationship between thermal/mechanical properties of polymeric h-BN nanocomposites and the morphology of functionalized h-BN sheets (such as thickness, lateral size, pretreatment condition, density of functional groups, and chemical linkage). These studies allow the preparation of h-BN sheets and their polymeric nanocomposites in a tunable fashion. Scientific issues involving the control of surface structures, interfacial interactions and properties of final nanocomposites are clarified as well.

六方氮化硼纳米片是由硼和氮原子组成的蜂窝状二维晶体。它是一种热稳定、抗氧化、耐酸碱的透明性绝缘材料，具有高热导系数、高机械强度等优良性能。氮化硼纳米片的化学惰性使之在聚合物基复合材料的应用中独具优势，但是也为其插层剥离和化学修饰造成了诸多困难。批量制备技术和高效修饰方法的缺乏极大地制约了氮化硼纳米片在聚合物基复合材料中的应用。本课题拟开展氮化硼纳米片的批量制备、化学修饰及其高性能聚合物基复合材料的研究。采用碱金属插层、氨等离子辐照等方法对氮化硼粉体进行处理，提高化学剥离法制备氮化硼纳米片的效率并使其表面功能化，经过聚合物的化学修饰增强氮化硼纳米片与基体材料的相容性，调控二者界面的微观结构与相互作用。研究氮化硼的形貌、层数、尺寸、表面处理、功能团浓度及修饰方式等对复合材料热学与机械性能的影响机制。通过上述研究深刻理解这些材料的可控制备、表面、界面以及性质调节等重要科学问题。

六方氮化硼纳米片是二维晶体，是石墨烯的等电子体并具有类似的结构。氮化硼纳米片层与层之间具有很强的啮合力，并且有很好的热和化学稳定性，因此造成氮化硼的插层剥离和化学修饰相对困难。本项目首先利用液相插层剥离法和球磨法制备氮化硼纳米片，产率可达到20%以上。探讨了溶剂、辅助剥离试剂和球磨参数等因素对氮化硼纳米片溶解性和表面活性基团的影响，实现了氮化硼纳米片的化学修饰。另外，利用CVD和高温热解法合成了碳或磷掺杂的纳米氮化硼，通过电子显微镜、X射线衍射、X射线光电子能谱和各种光谱表征了它们的形貌、组成和结构等性质。上述研究初步解决了宏观量的氮化硼纳米片的制备问题，为氮化硼纳米片在复合材料领域的应用打下基础。. 利用修饰后的氮化硼纳米片，制备了基于氮化硼的复合水凝胶和气凝胶。考察了氮化硼纳米片的表面官能团、尺寸、用量对凝胶机械性能和保水性的调控，建立和发展了基于氮化硼纳米片的高性能复合凝胶的制备方法，探索凝胶在缓释和吸附方面的应用。另外，本项目还探讨了氮化硼纳米片在催化剂载体领域的应用。首先对氮化硼纳米片进行化学修饰或者合成掺杂的氮化硼纳米材料，调节氮化硼的表面活性基团及其电子结构，进而在其上均匀负载了Pd、Pd-Ni、Pd-Fe等金属纳米粒子，考察金属粒子的催化活性。特别是利用不同金属与氮化硼纳米片之间作用的不同，得到合金或核壳结构的双金属纳米粒子，所得催化剂在选择性加氢和催化偶联等有机反应中呈现优良的催化性能，优于碳纳米材料和氧化铝等传统催化剂载体。