CNRS, Centre de Recherche Paul Pascal, UPR, Pessac, France.
Acc Chem Res. 2013 Jan 15;46(1):129-37. doi: 10.1021/ar300141s. Epub 2012 Oct 25.
Growing interest in graphene over past few years has prompted researchers to find new routes for producing this material other than mechanical exfoliation or growth from silicon carbide. Chemical vapor deposition on metallic substrates now allows researchers to produce continuous graphene films over large areas. In parallel, researchers will need liquid, large scale, formulations of graphene to produce functional graphene materials that take advantage of graphene's mechanical, electrical, and barrier properties. In this Account, we describe methods for creating graphene solutions from graphite. Graphite provides a cheap source of carbon, but graphite is insoluble. With extensive sonication, it can be dispersed in organic solvents or water with adequate additives. Nevertheless, this process usually creates cracks and defects in the graphite. On the other hand, graphite intercalation compounds (GICs) provide a means to dissolve rather than disperse graphite. GICS can be obtained through the reaction of alkali metals with graphite. These compounds are a source of graphenide salts and also serve as an excellent electronic model of graphene due to the decoupling between graphene layers. The graphenide macroions, negatively charged graphene sheets, form supple two-dimensional polyelectrolytes that spontaneously dissolve in some organic solvents. The entropic gain from the dissolution of counterions and the increased degrees of freedom of graphene in solution drives this process. Notably, we can obtain graphenide solutions in easily processable solvents with low boiling points such as tetrahydrofuran or cyclopentylmethylether. We performed a statistical analysis of high resolution transmission electronic micrographs of graphene sheets deposited on grids from GICs solution to show that the dissolved material has been fully exfoliated. The thickness distribution peaks with single layers and includes a few double- or triple-layer objects. Light scattering analysis of the solutions shows the presence of two-dimensional objects. The typical size of the dissolved flakes can be determined by either static or dynamic light scattering (DLS) using models available in the literature for disk-shape objects. A mean lateral size of ca. 1 μm is typically observed. We also used DLS to monitor the reaggregation that occurs as these sensitive solutions are exposed to air. The graphenide solutions reported in this Account can be used to deposit random arrays of graphene flakes and large single flakes of a lateral size of tens of micrometers onto different substrates. Using the graphenide solutions described in this Account, we foresee the large-scale production of graphene-based printings, coatings, and composites.
在过去的几年中，人们对石墨烯的兴趣日益浓厚，这促使研究人员寻找除机械剥离或从碳化硅生长以外的生产这种材料的新途径。现在，化学气相沉积在金属衬底上可以使研究人员在大面积上生产连续的石墨烯薄膜。与此同时，研究人员将需要液态、大规模的石墨烯配方，以生产利用石墨烯的机械、电气和阻隔性能的功能性石墨烯材料。在本报告中，我们描述了从石墨中制备石墨烯溶液的方法。石墨为碳提供了廉价的来源，但石墨不溶。经过广泛的超声处理，可以将其分散在有机溶剂或水中，并加入适当的添加剂。然而，这个过程通常会在石墨中产生裂纹和缺陷。另一方面，石墨插层化合物（GICs）提供了一种溶解而不是分散石墨的方法。GICS 可以通过碱金属与石墨的反应获得。这些化合物是石墨烯盐的来源，并且由于石墨烯层之间的解耦，它们也是石墨烯的极好的电子模型。带负电荷的石墨烯片组成柔韧的二维聚电解质，可在一些有机溶剂中自发溶解。溶解抗衡离子的熵增益和石墨烯在溶液中增加的自由度推动了这一过程。值得注意的是，我们可以在四氢呋喃或环戊基甲醚等易于加工且沸点较低的溶剂中获得易于加工的 graphenide 溶液。我们对从 GICS 溶液沉积在网格上的石墨烯片的高分辨率透射电子显微镜进行了统计分析，以证明溶解的材料已完全剥离。厚度分布的峰值为单层，并包括几个双层或三层物体。溶液的光散射分析表明存在二维物体。可以通过使用文献中提供的用于盘形物体的模型，通过静态或动态光散射（DLS）来确定溶解薄片的典型尺寸。通常观察到约 1 μm 的平均横向尺寸。我们还使用 DLS 来监测这些敏感溶液暴露在空气中时发生的再聚集。本报告中报道的 graphenide 溶液可用于将随机排列的石墨烯薄片和数十微米的大单个薄片沉积到不同的基底上。使用本报告中描述的 graphenide 溶液，我们预计将大规模生产基于石墨烯的印刷品、涂料和复合材料。
