Non-oxidizing Purification Method for Large Volumes of Long, Undamaged Single-Walled Carbon Nanotubes

Abstract

A mild route to the purification of single-walled carbon nanotube (SWNT) soot has been investigated. The removal of all forms of impurities commonly found in bulk SWNT material (metal catalyst nanoparticles, amorphous carbon, and bundles of SWNTs) has been obtained. This technique, which involves purification based on centrifugation at low centrifugal force, results in deposits that are composed of individual SWNTs that do not have the defects that result from harsh oxidative treatments. While ultracentrifugation has been used to separate and purify raw SWNT soot, this method removes all but the shortest nanotubes. Therefore, it is not practical for many electronic applications. The method presented in this manuscript removes carbonaceous and metallic impurities, while leaving long undamaged SWNTs in suspension. A liquid deposition method under development in this group was used to form electrically continuous two-dimensional networks of SWNTs. Atomic force microscopy (AFM) then is used to verify the efficacy of centrifugation cycles for purification of SWNT suspensions. AFM images of the deposits indicate significant improvement of deposit morphology, with long individual SWNTs that are observed without the presence of impurities. SWNT networks formed from these purified deposits behaved as metallic conductors at high density and as semiconductive thin films at low density. This further indicates that bundles of SWNTs were removed, along with other undesirable materials.

Preparation and modification of carbon nanotubes: Review of recent advances and applications in catalysis and sensing

“…These impurities often interfere with the desired properties of SWNTs. Therefore, there have been extensive recent investigations into methods of removal of impurities and several highly effective purification techniques: flocculation [94], microfiltration [95,96], chromatographic procedures [97][98][99], and centrifugation [100,101].…”

“…Many potential applications have been proposed for carbon nanotubes, including conductive, high-strength composites and paint additives. Recent studies have involved the possible applications of SWNTs as nano test-tubes [27,28], H 2 storage media [29,30], batteries [31], field-emission materials [3,29,[32][33][34][35][36][37], tips for scanning probe microscopy [38][39][40][41][42][43][44], chromatographic stationary phases [45,46], transistors [47,48], diodes [49], and sensors [1,22,[50][51][52][53][54][55][56][57][58][59][60][61][62]. SWNTs have interesting physical, morphological and electronic properties and find applications in a variety of areas ranging from biosensors to transistors.…”

Optical absorption response of chemically modified single-walled carbon nanotubes upon ultracentrifugation in various dispersants

“…We have previously demonstrated the complete elimination of graphite particles and the reduction of the amorphous carbon levels by centrifugation in a surfactant [1,2]. Dispersions of increasing SWCNT relative purity can be obtained by repeated centrifugation cycles [3]. Researchers from Flinders University in Australia have systematically studied the enormous possibilities of high speed centrifugation for the preparation of dispersions of purified arc-discharge SWCNTs in aqueous solutions of sodium dodecylbenzene sulfonate (SDBS) [4].…”

Photochemical vapor generation for removing nickel impurities from carbon nanotubes and its real-time monitoring by atomic fluorescence spectrometry

“…They found that the SWCNTs retained their chemical and physical properties and were not functionalized. In addition, it has been reported that ultracentrifugation, with high centrifugal forces (typically in excess of 100 000 g), could be a nondestructive and non-oxidizing method for CNT purification [33,34]. Recently, Meyer-Plath et al have developed a very fast and entirely gas-phase based plasma-thermal purification technique for CNTs, neither acids nor other chemical reagents were used, and structural integrity of the purified CNTs was preserved [35].…”