Side-wall opening of single-walled carbon nanotubes (SWCNTs) by chemical modification: A critical theoretical study
Side-wall opening of single-walled carbon nanotubes (SWCNTs) by chemical modification: A critical theoretical study
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DOI：
10.1002/anie.200353087
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
Schleyer, PV
中科院分区：
文献类型：
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作者：
Chen, ZF;Nagase, S;Schleyer, PV
单壁碳纳米管（SWCNTs）具有独特的电子、机械和结构特性；因此，从这些材料衍生的有前途的应用，如化学传感器或纳米级电子器件，[1]可以预期。结构改变的纳米管加上适当的加成物可以通过改善溶解度、可加工性和易于分散，以及为表面和聚合物基质提供化学附着位点来促进其使用如何确定纳米管衍生物制备后的详细结构是一个棘手的问题。表征功能化SWCNTs是困难的；所有试图确定新连接基团的精确位置和添加方式的实验都失败了。由氧、亚甲基和氢加成的可能带有三元环（3MRs）的swcnts加合物是简单但非常重要的侧壁功能化衍生物。氧化反应被广泛应用于纳米管的提纯，而碳纳米管的电学性质对氧暴露极为敏感亚甲基加合物和NH加合物是最近合成的共价键二氯碳[5]和亚硝基[6]加合物的原型。现有的关于纳米管氧化物[7]和二氯甲烷加合物[8]结构的理论研究，包括扶手椅[7a， 8]或之字形管[7b-f]模型，采用了相当不令人满意的方法（见下文）。由于纳米管的尺寸很大，因此需要仔细选择适合所研究问题的截断模型。一种方法使用小的纳米管片段来模拟完整的纳米管，但在相对较高的水平上进行计算。[7b， 9]另一种方法使用了ONIOM技术，[10]将系统的一部分置于较高的理论水平，而将系统的其余部分置于较低的水平。这种策略允许以实际的计算成本模拟更大的系统。[7a-c， 11]因此，最近的一项ONIOM （B3LYP/6-31G*: AM1）研究采用C16片段（图1a）进行高级计算，模拟扶手椅型SWCNTs的侧壁化学。[7a， 11a - 11f]但是，目前还没有系统地证实非统组织的方法适用于这种应用。本文报道了B3LYP/6-31G*对（5,5）和（8,0）SWCNTs的O、CH2和NH纳米管衍生物以及假设的SiH2加合物的计算。此外，还对两级ONIOM方法中的几种方法组合进行了评价。（5,5）扶手椅swcnts衍生物：以13层管模型的NH加合物的优化结构为例，如图2所示（其他请参见支持信息）。（5,5）扶手椅型swcnts模型上O、CH2、SiH2和NH加数附着位点的两个碳原子之间的距离均大于2（表1）。无论（5,5）模型的加数和长度如何，所有修饰的纳米管都具有开放结构，而不是3MRs结构。我们已经获得了
Single-walled carbon nanotubes (SWCNTs) have unique electronic, mechanical, and structural characteristics; consequently, promising applications derived from these materials, such as chemical sensors or nanometer-scale electronic devices,[1] can be expected. Structurally altered nanotubes with appropriate addends should facilitate their use by improving solubility, processability, and ease of dispersion, as well as by providing sites for chemical attachment to surfaces and polymer matrices.[2] A vexing problem is ascertaining the detailed structures of nanotube derivatives after their preparation. The characterization of functionalized SWCNTs is difficult; all experimental attempts to determine the precise location and mode of addition of newly attached groups have failed. SWCNT adducts with possible three-membered rings (3MRs) that result from oxygen, methylene, and NH additions are simple but very important side-wall functionalized derivatives. Oxidation reactions are used widely to purify nanotubes,[3] and the electrical properties of carbon nanotubes are extremely sensitive to oxygen exposure.[4] Methylene and NH adducts are the prototypes of the recently synthesized covalently bonded dichlorocarbene [5] and nitrene [6] adducts. The available theoretical studies on the structures of nanotube oxide [7] and dichlorocarbene adducts [8] that involve either armchair [7a, 8] or zigzag tube [7b–f] models, employed rather unsatisfactory methodology (see below). Owing to the large size of nanotubes, carefully chosen truncated models, appropriate for the problem being investigated, are required. One approach uses small nanotube fragments to simulate a full nanotube, but carries out computations at a relatively high level.[7b, 9] The other approach uses the ONIOM technique,[10] which treats part of the system at a high theoretical level but the rest of the system at a lower level. This strategy allows larger systems to be simulated at a practical computational cost.[7a–c, 11] Thus, a recent ONIOM (B3LYP/6-31G*: AM1) study employed a C16 fragment (Figure1a) for the high-level computation to simulate the side-wall chemistry of the armchair SWCNTs.[7a, 11a–11 f] However, no systematic validation of the ONIOM approach for such applications is available. Herein we report B3LYP/6-31G* computations [12] on the O, CH2, and NH nanotube derivatives, as well as the hypothetical SiH2 adduct, for both (5, 5) and (8, 0) SWCNTs. In addition, several combinations of methods in the two-level ONIOM approach are evaluated.(5, 5) Armchair SWCNT Derivatives: The optimized structure of the NH adduct of the 13-layered tube model is shown in Figure2 as an example (see the Supporting Information for others). The separations between the two Catoms at the site at which the O, CH2, SiH2, and NH addends are attached to the (5, 5) armchair SWCNT models are all over 2 (Table 1). Regardless of the addend and of the length of the the (5, 5) model, all the modified nanotubes have opened structures rather than 3MRs. We have obtained the