【作者】 孙海燕；

【导师】 高超；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2014， 博士

【摘要】 单片石墨烯是具有光、电、热、机械等一系列优异性能的新型纳米材料,在复合材料、能量存储、电子器件等领域有着巨大的应用潜力。为了使单片石墨烯在纳米尺度上的性能真正为人们所用,必须将其组装成宏观材料,例如一维石墨烯纤维,二维薄膜,三维气凝胶等。其中三维气凝胶以其密度低、孔隙率高、比表面积大等优势倍受关注。尽管石墨烯气凝胶方面研究成果颇丰,然而还存在一系列重要的问题大大制约了其大量制备、性能提升以及在众多领域的应用,例如：如何通过简便的非模板制备方法实现宏量制备?如何通过结构设计同时实现超轻和高弹性能?原子级厚度的构筑单元所能达到的极限最低表观密度?针对这些重要的问题,本文展开相应的研究,实现了超轻弹性石墨烯气凝胶的宏量制备并探索其在诸如吸附、能量存储、相变材料等方面的应用潜力。借助大型建筑中常用的大跨度结构概念,本文提出“无模板溶液冷干法”,以超大片氧化石墨烯和碳纳米管为原料,通过协同组装制备出超轻弹性气凝胶。其基本的结构特征为：相互缠结的弹性纳米碳管网络吸附于柔软的石墨烯表面,形成一个具有弹性的微观尺度上的大跨度结构；再以这种杂化结构单元相互交叠、扭曲,搭接组装得到宏观尺度上的弹性气凝胶。氧化石墨烯与碳纳米管前驱体溶液具有良好的分散性能,如同真溶液一般可以进行稀释、浓缩等操作,从而实现对气凝胶密度的有效调节,且可以大量制备(如1000 cm3)。不添加碳纳米管时,气凝胶最低可达到0.16mg/cm3,是目前世界上表观密度最低的固体材料。石墨烯与碳纳米管协同组装超轻气凝胶具有无温度依赖的超弹性,在80%的大应变范围内能够实现上千次的可恢复性压缩,并且其超弹性在极宽的温度区间(-190-900℃)内保持稳定,可以适应极端温度环境下的应用。该材料的弹性来源于石墨烯与碳纳米管之间的协同效应,单一组分气凝胶并不具有弹性,只有两者以合适的比例相互作用才能实现弹性最大化。采用扫描电子显微镜原位观察了单片杂化结构单元在应力作用下的压缩和回弹,证明了气凝胶的宏观弹性来源于杂化结构单元的弯曲变形,而非片层之间的滑移。石墨烯弹性超轻气凝胶对有机溶剂具有超快、超高的吸附能力,依据溶剂密度不同可达到自身重量的215-913倍,是目前报道的最高值,且可以反复利用。吸附有机物之后形成的复合材料具有较高的导电性,克服了传统复合材料高填充低导电率的缺点,为制备低填充高导电复合物提供了新路径。除此之外,还将气凝胶吸油应用扩展至相变热储能领域,可吸收自身重量409倍的石蜡,无需另外封装而不发生泄漏,且熔融相变焓和凝固相变焓分别高于纯石蜡7.8%和28.7%,这种提高相变焓的现象并不多见。以超轻弹性气凝胶作为电极,组装成超级电容器,10 mV/s扫描速率下电容值为86.1 F/g,远高于纯碳纳米管气凝胶电容器相同速率下的48 F/g,且而其倍率性能优于纯石墨烯气凝胶电容器,表现出一定的协同效应。本文提出溶液冻干法,实现石墨烯气凝胶的宏量制备；超大片氧化石墨烯为构建单元,刷新气凝胶最低密度纪录,制备出世界上表观密度最低的固体材料；并借用大跨度建筑结构的概念,引入“钢筋”碳纳米管,对石墨烯“墙壁”进行增强,两者协同组装赋予超轻气凝胶以弹性。所制备气凝胶具有孔隙率大、比表面积大、高弹性、疏水等特点,在吸油、能量存储、相变材料等方面有着非常诱人的应用前景。更多还原

【Abstract】 Graphene, a two-dimensional (2D) mesh of carbon atoms, has received widespread attention due to its exceptional mechanical, electrical, and thermal properties. Integration of individual graphene sheets into macroscopic structures is essential for the application of graphene. And 3D aerogel has drawn great attention due to its low density, high porosity, large specific surface area and other advantages. Although many achievements of graphene aerogel have been made recently, there are still a number of important issues greatly restricting its large scale preparation, performance improvements and applications. For example, How to realize the large scale preparation of graphene aerogel with a facile non-template method? How to simultaneously achieve ultra-flyweight and high elastic aerogel through structural design? What is the ultimate apparent density of the aerogel with graphene as building blocks? Accordingly, this dissertation presented systemic studies on the fabrication of ultra-flyweight aerogel with graphene and carbon nanotubes as building blocks, and the explorations of its potential applications in areas such as adsorption, energy storage, phase change materials and others.The philosophy of’long span structures’in building architecture amazedly works in the micro world. We designed ultralight all-carbon aerogel from atomically thin graphenes as "walls", and extended the ultralight solids to their limit in density by utilizing the newly discovered graphene. Their ultralight graphene aerogel has extremely low density, down to 0.16 mg/cm3, obviously lower than that of plastic foams in our daily life, even only 15%that of air at room temperature, setting a new Guinness World Record as "the least dense solid". Also by the analogy of "enforcing ribs" in buildings, they implanted another carbon nanomaterial, one-dimensional carbon nanotube, onto the graphene "walls". The cooperative effect between graphene and carbon nanotube provides super elasticity to the graphene ultralight aerogel. After compression to the extent of 20%, this all-carbon aerogel is able to recover its shape, even for thousands times. More favorably, it can maintain the super elasticity in extreme temperature surroundings, even at high 900℃ and low -190℃ in liquid nitrogen.The aerogels possess super-high absorption capacities for organic solvents and oils, and can handle 900 times its weight in oil. In addition, paraffin can also be absorbed into the UFAs by melting infiltration to prepare phase-change energy storage materials. We found that the melting latent heat and freezing latent heatfor the paraffinn-filled UFAs are 7.8% and 28.7% higher than those of neat paraffin, rarely found in previous reports where the latent heat of composite is generally lower than that of neat phase-change materials. Additionally, the porous aerogel exhibited higher capacitance (86.1 F/g) than carbon nanotubes aerogel and better stability than graphene aerogle. The remarkable properties, such as outstanding temperature-invariant elasticity, ultralow density, excellent thermal stability, extremely high absorption capacities make the new stuff receive tremendous attention from both academia and mass media.In summary, a template-free, synergistic assembly strategy have been developed for the scalable fabrication of ultra-flyweight elastic aerogel with cell walls of giant graphene sheets and CNTs ribs. The ideal combination of giant size of constituent graphene sheets and their cooperative effect between graphene and CNTs offers the as-prepared aerogels integrated properties of outstanding temperature-invariant elasticity, ultralow density, excellent thermal stability, extremely high absorption capacities for organic liquids and PCMs, and good electrical conductivity. These charming multifunctional attributes would enable the UFAs many applications including elastic and flexible conductors, high-performance conductive polymer composites, organic absorbents, environmental remediation materials, phase-change energy storage, sensors, supercapacitors and catalyst beds.更多还原