Electron Paramagnetic Resonance Investigation of Purified Catalyst-free Single-Walled Carbon Nanotubes

Abstract

Electron paramagnetic resonance of single-walled carbon nanotubes (SWCNTs) has been bedevilled by the presence of paramagnetic impurities. To address this, SWCNTs produced by laser ablation with a nonmagnetic PtRhRe catalyst were purified through a multiple step centrifugation process in order to remove amorphous carbon and catalyst impurities. Centrifugation of a SWCNT solution resulted in sedimentation of carbon nanotube bundles containing clusters of catalyst particles, while isolated nanotubes with reduced catalyst particle content remained in the supernatant. Further ultracentrifugation resulted in highly purified SWCNT samples with a narrow diameter distribution and almost no detectable catalyst particles. Electron paramagnetic resonance (EPR) signals were detected only for samples which contained catalyst particles, with the ultracentrifuged SWCNTs showing no EPR signal at X-band (9.4 GHz) and fields < 0.4 T.

Electron spin resonance study of single‐walled carbon nanotubes

“…Contrary to the results reported by Zaka et al 17 and to the theoretical work by Dóra et al 19, we always obtain an ESR signal. In our opinion, the conditions assumed in Ref.…”

“…This is in agreement with the assumption that line I 2 of selected metallic samples is due to magnetic catalyst particles. Since in the process used to select the metallic nanotubes (from Nanointegris) a reduced amount of these particles remain in the supernatant part 17, they are included in the selected metallic samples rather than in the selected semiconducting nanotubes.…”

Nitroxide Radicals@US‐Tubes: New Spin Labels for Biomedical Applications

“…Wide (4000‐G) scans of the EPR spectra of the US‐tubes with or without nitroxides (Figure 6a–c) exhibit a strong broad signal with peak‐to‐peak linewidth of 650 G at about 3200 G (g ∼ 2.2). This broad signal is attributed to magnetic metal catalyst impurities from the carbon arc‐discharge SWNT production method 47–49. To more clearly see signals in the vicinity of g ∼ 2.00 that are characteristic of organic radicals, including nitroxides,50 200 G scans centered at 3519 G were recorded (see insets in Figure 6).…”

Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

“…18 All those carbon-inherited EPR-active defect centers are probably affecting the electronic and optical properties of a material. Zaka et al 17 indicated that high-quality pure carbon nanotubes (CNTs) are indeed EPR inactive, however, they observed an EPR signal of Lorentzian line shape at g ¼ 2.001, which was attributed to catalyst impurities in the CNTs. When the size of graphite is reduced to nanodimensions, the localized edge states couple with itinerant electrons, thus leading to a narrow EPR signal, while antiferromagnetism develops when the experiment temperature decreases below 23 Although the magnetic properties of graphene have recently been attracting high attention, due to the graphene's potential application in spintronics devices, there have been only few EPR studies performed on graphene and graphenelike structures.…”