Solid-State NMR Analysis of Fluorinated Single-Walled Carbon Nanotubes: Assessing the Extent of Fluorination
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- 作者：Lawrence B. Alemany ; Lei Zhang ; Liling Zeng ; Christopher L. Edwards ; Andrew R. Barron
- 刊名：Chemistry of Materials
- 出版年：2007
- 出版时间：February 20, 2007
- 年：2007
- 卷：19
- 期：4
- 页码：735 - 744
- 全文大小：213K
- 年卷期：v.19,no.4(February 20, 2007)
- ISSN：1520-5002
文摘
Fluorinated single-walled carbon nanotubes (F-SWNTs) have been characterized by magic angle spinning13C NMR spectroscopy and the results correlated with Raman, IR, and X-ray photoelectron spectroscopymeasurements. The 13C NMR shift for the sp3 fluorine-substituted (CF) carbon atoms of the SWNTsidewall is observed at 
= 83.5 ppm. This apparently unusual shift compared to those of most othertertiary alkyl fluorides is confirmed to be due to the CF moieties from ab initio calculations on an 80-carbon fragment of the 5,5 (armchair) SWNT and is in good agreement with the predominance of 1,2-addition rather than 1,4-addition of fluorine. The lack of observable scalar 13C-19F coupling for the CFcarbon signal over a wide range of spinning speeds and at two different field strengths apparently resultsfrom interaction between 19F-19F and 13C-19F dipolar couplings and from magnetization exchange betweenthe 13C doublet components caused by fluorine spin diffusion. The assignment of the 83.5 ppm peak isfurther confirmed by the correlation of its diminished intensity upon thermolysis of the F-SWNT (400,450, and 550 
C) with the relative intensity of the D (disorder) band in Raman and the C:F ratio fromX-ray photoelectron spectroscopy (XPS). On the basis of the XPS signal, it appears that the CF2 defectunits decompose at a lower temperature than the CF sidewall moieties, suggesting that cutting chemistryprecedes sidewall functional group removal. We propose that, where a comparison of samples with ahigh degree of functionalization is required, NMR provides a much better quantification than Raman.However, where a comparison between samples with low levels of functionalization or large differencesin degree of functionalization is required, Raman provides a much better quantification than NMR.
= 83.5 ppm. This apparently unusual shift compared to those of most othertertiary alkyl fluorides is confirmed to be due to the CF moieties from ab initio calculations on an 80-carbon fragment of the 5,5 (armchair) SWNT and is in good agreement with the predominance of 1,2-addition rather than 1,4-addition of fluorine. The lack of observable scalar 13C-19F coupling for the CFcarbon signal over a wide range of spinning speeds and at two different field strengths apparently resultsfrom interaction between 19F-19F and 13C-19F dipolar couplings and from magnetization exchange betweenthe 13C doublet components caused by fluorine spin diffusion. The assignment of the 83.5 ppm peak isfurther confirmed by the correlation of its diminished intensity upon thermolysis of the F-SWNT (400,450, and 550 C) with the relative intensity of the D (disorder) band in Raman and the C:F ratio fromX-ray photoelectron spectroscopy (XPS). On the basis of the XPS signal, it appears that the CF2 defectunits decompose at a lower temperature than the CF sidewall moieties, suggesting that cutting chemistryprecedes sidewall functional group removal. We propose that, where a comparison of samples with ahigh degree of functionalization is required, NMR provides a much better quantification than Raman.However, where a comparison between samples with low levels of functionalization or large differencesin degree of functionalization is required, Raman provides a much better quantification than NMR.