Spectroscopic study on the centrifugal fractionation of soluble single-walled carbon nanotubes |
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Authors: | Yongfu Lian Takatsugu Wakahara Takeshi Akasaka Said Kazaoui Tetsuo Shimizu |
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Affiliation: | a Center for Tsukuba Advanced Research Alliance (TARA Center), University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan b National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan c Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan |
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Abstract: | Optical absorption and resonant Raman spectra are proven to be convenient and effective to monitor the centrifugal fractionation and to evaluate the quality of soluble single-walled carbon nanotubes (SWNTs) achieved by inorganic oxidation and organic functionalization. Through a systemic study of a series of centrifuged solutions, we confirmed that heavily functionalized amorphous carbon was fractionated into the early centrifuged solutions, whereas lightly functionalized graphite fragments as well as polyhedral carbon and metal catalysts particles were fractionated into the late centrifuged solutions and centrifuged residue, and then highly pure and well dispersed SWNTs were collected from the middle centrifuged solutions. It is proposed that the purity, dispersibility, and aggregation state of SWNTs can be qualitatively estimated by the relative intensity of their absorption features, the fine structure and slope of their absorption curves. The Raman features of centrifuged SWNTs are found systematically up-shifted except the disorder-induced D band in comparison with those of as-prepared material, indicating that the SWNTs in centrifuged solutions are individual or in thin bundles. Two new features were identified at 1428 and 941 cm−1 in the Raman spectrum of thermally annealed centrifuged SWNTs, which were assigned to achiral nanotubes and combined mode, respectively. |
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Keywords: | Carbon nanotubes Oxidation Raman spectroscopy Aggregation |
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