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Figure 25. Temperature programmed oxidation profiles of the carbonaceous species present in (a) raw HipCO material and (b) purified HipCO material. The profiles were obtained using a mixture of 5% of O2 in He at a heating rate of 12 0 C/min.

(low D/G ratio) indicate that SWNTs are the predominant carbon species present on both purified and raw samples. That is, all of the TPO peaks in the purified material are associated with SWNTs. Consequently, the different TPO peaks in the purified sample are only due to parts of the sample that contain different amounts of residual Fe.

A second example of the combined application of TPO and Raman is a study of two different raw SWNT materials synthesized by CO disproportionation: one obtained over a highly selective Co-Mo metallic catalyst (low Co:Mo ratio) in which SWNTs are the dominant species, and the other obtained over an unselective catalysts (high Co:Mo ratio) in which SWNTs, MWNTs, graphite, and amorphous carbon are present [29]. Figure 27a and b shows the TPO profiles of each material. As expected, the sample obtained over the highly selective catalyst, which contains mostly SWNTs shows a single peak centered at 570 0 C. It has been previously shown that under the TPO conditions and while still immersed in this particular catalyst, the SWNTs get oxidized in a relatively narrow temperature range, which lies

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