School of Physics and CRANN, Trinity College Dublin, Ireland.
Acc Chem Res. 2013 Jan 15;46(1):14-22. doi: 10.1021/ar300009f. Epub 2012 Mar 20.
Due to its unprecedented physical properties, graphene has generated huge interest over the last 7 years. Graphene is generally fabricated in one of two ways: as very high quality sheets produced in limited quantities by micromechanical cleavage or vapor growth or as a rather defective, graphene-like material, graphene oxide, produced in large quantities. However, a growing number of applications would profit from the availability of a method to produce high-quality graphene in large quantities. This Account describes recent work to develop such a processing route inspired by previous theoretical and experimental studies on the solvent dispersion of carbon nanotubes. That work had shown that nanotubes could be effectively dispersed in solvents whose surface energy matched that of the nanotubes. We describe the application of the same approach to the exfoliation of graphite to give graphene in a range of solvents. When graphite powder is exposed to ultrasonication in the presence of a suitable solvent, the powder fragments into nanosheets, which are stabilized against aggregation by the solvent. The enthalpy of mixing is minimized for solvents with surface energies close to that of graphene (∼68 mJ/m(2)). The exfoliated nanosheets are free of defects and oxides and can be produced in large quantities. Once solvent exfoliation is possible, the process can be optimized and the nanosheets can be separated by size. The use of surfactants can also stabilize exfoliated graphene in water, where the ζ potential of the surfactant-coated graphene nanosheets controls the dispersed concentration. Liquid exfoliated graphene can be used for a range of applications: graphene dispersions as optical limiters, films of graphene flakes as transparent conductors or sensors, and exfoliated graphene as a mechanical reinforcement for polymer-based composites. Finally, we have extended this process to exfoliate other layered compounds such as BN and MoS(2). Such materials will be important in a range of applications from thermoelectrics to battery electrodes. This liquid exfoliation technique can be applied to a wide range of materials and has the potential to be scaled up into an industrial process. We believe the coming decade will see an explosion in the applications involving liquid exfoliated two-dimensional materials.
由于其前所未有的物理性质,石墨烯在过去 7 年中引起了极大的兴趣。石墨烯通常通过两种方法之一制备:一种是通过微机械劈裂或气相生长制备的非常高质量的薄片,数量有限;另一种是大量制备的、相当有缺陷的类石墨烯材料氧化石墨烯。然而,越来越多的应用将受益于能够大量生产高质量石墨烯的方法。本综述描述了最近的工作,这些工作受到以前关于碳纳米管溶剂分散的理论和实验研究的启发,旨在开发这样一种处理路线。该工作表明,纳米管可以有效地分散在与纳米管表面能匹配的溶剂中。我们描述了将相同的方法应用于石墨的剥离,以在各种溶剂中得到石墨烯。当石墨粉末在合适的溶剂存在下进行超声处理时,粉末会碎裂成纳米片,这些纳米片被溶剂稳定,防止聚集。对于表面能接近石墨烯(约 68 mJ/m(2))的溶剂,混合焓最小化。剥离的纳米片无缺陷和氧化物,可以大量生产。一旦溶剂剥离是可能的,该过程可以被优化,并且纳米片可以按尺寸分离。表面活性剂的使用也可以稳定水中剥离的石墨烯,其中表面活性剂涂覆的石墨烯纳米片的 ζ 电位控制分散的浓度。液体剥离的石墨烯可用于一系列应用:石墨烯分散体作为光限幅器、石墨烯薄片膜作为透明导体或传感器,以及剥离的石墨烯作为聚合物基复合材料的机械增强剂。最后,我们将该过程扩展到剥离其他层状化合物,如 BN 和 MoS(2)。这些材料将在从热电学到电池电极的一系列应用中很重要。这种液体剥离技术可以应用于广泛的材料,并有可能被扩大到工业规模。我们相信,在未来十年,涉及液体剥离二维材料的应用将呈爆炸式增长。
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