Statistical Raman Spectroscopy: An Method for the Characterization of Covalently Functionalized Single-Walled Carbon Nanotubes
Statistical Raman Spectroscopy: An Method for the Characterization of Covalently Functionalized Single-Walled Carbon Nanotubes
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DOI：
10.1002/anie.201204791
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Hirsch, Andreas
中科院分区：
文献类型：
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作者：
Hof, Ferdinand;Bosch, Sebastian;Hirsch, Andreas
单壁碳纳米管的共价化学功能化是碳同素异形体研究领域的一个重要课题。[1]它允许克服许多固有的障碍，例如聚集、低溶解度和难加工性，这些障碍阻碍了单壁碳纳米管作为高性能材料中的结构单元的直接开发。化学功能化提供了将其前所未有的性质与其他化合物类别相结合的机会，并且它是通过电子性质进行分离的有前途的方法。已经报道了许多反应，这些反应显示出附着物对金属或半导体管的优先攻击。[2]我们最近已经证明了一个选择性的羧化的半导体管，剥离和减少修改后的桦树条件下。[3]然而，从半导体管中有效地大规模分离金属管仍然是碳纳米管化学中的主要挑战。因此，提供可靠和直接洞察共价官能化程度、本体样品的均匀性和通过电子性质的总体选择性的分析方法是特别期望的。虽然传统的拉曼光谱提供了关于单壁碳纳米管的共价修饰的重要信息，但它缺乏关于本体材料中的性质分布的定量描述。事实证明，在不同点记录的拉曼光谱可能会有很大差异（支持信息，图S1）。这导致对反应的具体结果的严重误解。因此，未提供不同反应产物之间的可比性。在此，我们提出了使用扫描拉曼显微镜（SRM）和相应的统计数据分析的明确表征共价官能化的单壁碳纳米管。随着拉曼缺陷（RDI）、拉曼均匀性（RHI）和拉曼选择性指数（RSI）的引入，我们现在能够提供对官能化程度以及反应序列的产物均匀性和选择性的直接和明确的洞察。我们在分析许多不同官能化的反应产物（方案1）后提出了这种定量。我们最初关注新官能化序列的反应产物的数据分析，即用四氟硼酸重氮苯（BDT;方案1a，图1a）对带负电荷的管进行湿化学处理。后来，这些结果与其他共价衍生序列获得的结果进行了比较。相应的SWCNT还原已经在我们先前报道的改进的Birch条件下[4]用液氨中的锂金属和作为共溶剂的THF进行。在氨蒸发后，将重氮盐小心地加入到带负电荷的纳米管中，然后对反应产物进行水性后处理。与最初由Tour埃塔尔介绍的中性SWCNT与重氮盐的反应相反，[5]我们预期带负电的管和带正电的重氮物质之间的库仑吸引力将进一步提高加成反应的效率。通过TG/MS分析（支持信息，图S2）和统计拉曼分析表征反应产物A。为此，进行了10 000 μm2的映射，每个映射对应于2500个光谱（图1b）。一般来说，D波段强度是衡量
Covalent chemical functionalization of single-walled carbon nanotubes (SWCNTs) has become a very important subject within the field of carbon allotrope research.[1] It allows a number of intrinsic hurdles to be overcome, such as aggregation, low solubility, and difficult processability, which impede a straightforward development of SWCNTs as building blocks in high-performance materials. Chemical functionalization offers the opportunity to combine their unprecedented properties with those of other compound classes and it is a promising approach for separation by electronic properties. A number of reactions have been reported that show preferential attack of addends to either metallic or semiconducting tubes.[2] We have recently demonstrated a selective carboxylation of semiconducting tubes that were exfoliated and reduced under modified Birch conditions.[3] Nevertheless, an efficient large-scale separation of metallic tubes from semiconducting tubes is still a major challenge in carbon nanotube chemistry. Therefore, analytical methods that provide reliable and direct insights into the degree of covalent functionalization, homogeneity of the bulk sample, and overall selectivity by electronic properties are particularly desirable. Although conventional Raman spectroscopy provides important information with respect to covalent modifications of SWCNTs, it lacks a quantitative description about the distribution of properties in the bulk material. It has turned out that Raman spectra recorded at different spots may vary considerably (Supporting Information, Figure S1). This leads to severe misinterpretations on the specific outcome of a reaction. As a consequence, comparability between different reaction products is not provided. Herein, we present the use of scanning Raman microscopy (SRM) and the corresponding statistical data analysis for the unequivocal characterization of covalently functionalized SWCNTs. With the introduction of the Raman defect (RDI), Raman homogeneity (RHI), and Raman selectivity indices (RSI), we are now able to provide a straightforward and unambiguous direct insight into the degree of functionalization as well as into the product homogeneity and the selectivity of a reaction sequence. We present this quantification upon analyzing a number of differently functionalized reaction products (Scheme 1).We initially focus on the data analysis of the reaction product of a new functionalization sequence, namely the wet chemical treatment of negatively charged tubes with benzenediazonium tetrafluoroborate (BDT; Scheme 1 a, Figure1a). Later on these results are compared with those obtained for other covalent derivatization sequences. The corresponding SWCNT reduction has been carried out under our previously reported modified Birch conditions [4] with lithium metal in liquid ammonia and THF as a co-solvent. After evaporation of the ammonia, the diazonium salt was carefully added to the negatively charged nanotubes, followed by an aqueous work-up of the reaction product. In contrast to the reaction of neutral SWCNTs with diazonium salts, originally introduced by Tour etal.,[5] we expect that the Coulomb attraction between the negatively charged tubes and the positively charged diazonium species will further increase the efficiency of the addition reaction. The reaction product A was characterized by TG/MS analysis (Supporting Information, Figure S2) and by statistical Raman analysis. For this purpose, mappings of 10 000 μm2, which corresponds to 2500 spectra in each, were carried out (Figure 1b). In general the D-band intensity is a measure for