Recent Developments in Purification of Single Wall Carbon Nanotubes

Abstract

The status of SWNT purification sciences within the last two decades are reviewed. Over the years, the aggressive search for effective and efficient post-synthetic purification technique has given rise to the development of numerous methods. Unfortunately, most of these methods do not possess the potentials of being selective, scalable, nor effective. On the other hand, the mechanisms behind the promising separation methods are yet to be fully understood. For such techniques, it is recommended that interest should now lie more on investigating the underpinning mass transfer kinetics and equilibrium thermodynamics with a view to making them more efficient.

On thermodynamic equilibrium of carbon deposition from gaseous C-H-O mixtures: updating for nanotubes

“…Proportions of those carbon forms depend mainly on temperature and the catalyst type and its granularity. Similar conclusions about coexistence of different forms of solid carbon were drawn by Snoeck and Froment (2002) and Makama et al (2014). Thermodynamic data for singlewalled CNTs in bundles were also obtained using an indirect solid galvanic cell method .…”

“…Carbon can deposit in variety of crystallographic forms on different catalysts, including singlewalled and multi-walled nanotubes (Jankhah et al 2008, Gozzi et al 2008, Makama et al 2014. Although thermodynamic criteria indicate either graphite or fibrous carbon as stable solid forms at T < 1500 K, the kinetics of their mutual direct transformation can be extremely slow and difficult to detect.…”

Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups–Birch Reduction

“…We postulate that to improve functionalization it is necessary to remove as much of the catalyst residue as possible. Chemical purification methods commonly use gas-phase − and wet-chemistry methods. − While liquid-phase oxidation is effective in removing both amorphous carbon and metallic catalyst particles, it generally requires the use of strong oxidants. − These oxidation routes result in the sidewall of the SWCNT becoming functionalized with oxygen-containing groups in addition to cutting the SWCNTs . Given that an advantage of the Billups–Birch reduction process is that it does not cut the SWCNTs, it is important to employ a purification process that also limits damage.…”

Dramatic enhancement of double-walled carbon nanotube quality through a one-pot tunable purification method

“…Damaging of CNTs can be minimized by combining several chemical treatments [9e13]. They are based on the use of i) strong oxidants in liquid medium (HNO 3 , H 2 SO 4 or KMnO 4 ) and/or gas-phase oxidation even in the more recent works [8,14,15], see also review papers [7,12]; ii) halogens [16e18]; iii) microwave assisted methods that enhance the efficiency by reducing the exposure time [19,20], and see for a review paper [21]. For such approach, the operating conditions used for each treatment have to be optimized depending on the CNT type and source.…”