Insights into the mechanism of the gas-phase purification of HiPco SWNTs through a comprehensive multi-technique study

Abstract

While the purification of carbon nanotubes may be considered as an already sorted matter, their use in some highly demanding fields such as electrochemistry, biological studies or magnetism may be precluded by the remaining catalyst and carbonaceous impurities. For these purposes, the widely-used purification methods need to be improved. In this paper, a comprehensive study of the well-known gas-phase purification procedure of single wall nanotubes (SWNTs) is performed, which aims at depicting the nature and the amount of the remaining impurities, of both the catalyst and carbon types, and at getting insights into its mechanism. This has been achieved by cross-referencing data emerging from transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), electron diffraction, magnetization measurements, X-ray diffraction (XRD) and Raman spectroscopy. We demonstrate that this method can lead to the elimination of the largest part of the impurities while maintaining fairly good yields. According to the mechanistic picture we have drawn, we suggest some possible improvement to the procedure that should lead to fully purified SWNTs with limited subsequent losses.

Intracellular fate of carbon nanotubes inside murine macrophages: pH-dependent detachment of iron catalyst nanoparticles

“…The diameter of the pristine SWCNT used in the present study has been previously evaluated by some of us [14] and estimated to be in the 0.8-1.2 nm range, while their individual length was in the 100–1000 nm range, according to supplier information. Thermogravimetric analysis measured an iron content of about 25-wt%, confirming the unpurified nature of the sample.…”

Regulatory Peptides Are Susceptible to Oxidation by Metallic Impurities within Carbon Nanotubes

“…[4][5][6] CNTs are strongly heterogeneous materials containing carbon nanotubes, other forms of carbon (nanographite, amorphous carbon), [7] and residual metal-catalyst impurities. [8,9] The discrepancies in the toxicological data are likely due to the heterogeneous nature of CNTs. The differences have been attributed to the varying amounts of metallic impurities in the CNT samples.…”

“…However, cases in which the amount of metallic impurities is close to 30 wt % of the CNT material are not unusual. [9,21] A wide range of purification methods is available, but these techniques are not very effective. That is, if the purification procedure is successful in reducing the metallic content to 0.5-1 wt %, the resulting CNTs are dubbed "high quality".…”

Magnetic Bistability of Individual Single‐Molecule Magnets Grafted on Single‐Wall Carbon Nanotubes

“…For the design of information storage devices based on single magnetic molecules (albeit at very low temperatures), one major challenge is to confirm the presence of magnetic bistability at the level of individual molecules. The first studies focused on archetypal Mn 12 SMMs. Unfortunately, because of the relatively weak stability of this family of compounds and the very high sensitivity of the orientation of the easy axis of magnetization towards the environment, no magnetic hysteresis was observed when the molecules were anchored on surfaces.…”

“…We demonstrate that the individual molecules maintain their chemical integrity and still present magnetic bistability when assembled on the surface of the nanotubes. The pristine SWNTs were purified using a procedure derived from that reported by Chiang et al, [11,12] and the grafting of POM molecules was simply achieved by sonication of a suspension of the nanotubes in a dichloroacetic acid buffer containing the Fe 6 -POM (see the Supporting Information). To ensure the efficiency of the grafting process and to check the integrity of the complex, we used complementary and independent characterization techniques.…”