Department of Chemistry and Biochemistry and ‡Maryland NanoCenter, University of Maryland , College Park, Maryland 20742, United States.
ACS Nano. 2017 Sep 26;11(9):9231-9238. doi: 10.1021/acsnano.7b04429. Epub 2017 Aug 16.
Attaining aqueous solutions of individual, long single-walled carbon nanotubes is a critical first step for harnessing the extraordinary properties of these materials. However, the widely used ultrasonication-ultracentrifugation approach and its variants inadvertently cut the nanotubes into short pieces. The process is also time-consuming and difficult to scale. Here we present an unexpectedly simple solution to this decade-old challenge by directly neutralizing a nanotube-chlorosulfonic acid solution in the presence of sodium deoxycholate. This straightforward superacid-surfactant exchange eliminates the need for both ultrasonication and ultracentrifugation altogether, allowing aqueous solutions of individual nanotubes to be prepared within minutes and preserving the full length of the nanotubes. We found that the average length of the processed nanotubes is more than 350% longer than sonicated controls, with a significant fraction approaching ∼9 μm, a length that is limited by only the raw material. The nondestructive nature is manifested by an extremely low density of defects, bright and homogeneous photoluminescence in the near-infrared, and ultrahigh electrical conductivity in transparent thin films (130 Ω/sq at 83% transmittance), which well exceeds that of indium tin oxide. Furthermore, we demonstrate that our method is fully compatible with established techniques for sorting nanotubes by their electronic structures and can also be readily applied to graphene. This surprisingly simple method thus enables nondestructive aqueous solution processing of high-quality carbon nanomaterials at large-scale and low-cost with the potential for a wide range of fundamental studies and applications, including, for example, transparent conductors, near-infrared imaging, and high-performance electronics.
获得单个长单壁碳纳米管的水溶液是利用这些材料非凡性质的关键第一步。然而，广泛使用的超声-超速离心方法及其变体不可避免地将纳米管切成小段。该过程也耗时且难以规模化。在这里，我们通过在脱氧胆酸钠存在下直接中和纳米管-氯磺酸溶液，意外地提出了一种解决这个十年来挑战的简单方法。这种简单的超酸-表面活性剂交换完全不需要超声和超速离心，可以在几分钟内制备出单个纳米管的水溶液，并保留纳米管的全长。我们发现，处理后的纳米管的平均长度比超声处理的对照物长 350%以上，其中相当一部分接近~9μm，这一长度仅受原材料限制。这种非破坏性通过极低的缺陷密度、近红外区域明亮且均匀的光致发光以及透明薄膜中的超高电导率（83%透光率时为 130Ω/sq）来体现，这远远超过了氧化铟锡的电导率。此外，我们证明我们的方法与通过电子结构对纳米管进行分类的现有技术完全兼容，也可以很容易地应用于石墨烯。这种出人意料的简单方法因此可以在大规模和低成本的情况下对高质量的碳纳米材料进行无损水溶液处理，具有广泛的基础研究和应用潜力，例如透明导体、近红外成像和高性能电子学。
