Thermal degradation of ragged single-wall carbon nanotubes produced by polymer-assisted ultrasonication

doi:10.1016/S0009-2614(01)00507-3

Chemical Physics Letters

Volume 341, Issues 5–6, 29 June 2001, Pages 461-466

https://doi.org/10.1016/S0009-2614(01)00507-3 Get rights and content

Abstract

As-grown single-wall carbon nanotubes (SWNTs) and a monochlorobenzene (MCB) solution of polymethylmethacrylate (PMMA) were sonicated using an ultrasonic processor. The SWNTs obtained were short and contained many holes and defects; therefore, they were called `ragged single-wall carbon nanotubes (r-SWNTs)'. The r-SWNTs were degraded at and above 800°C in a vacuum (10⁻⁷ Torr). All the r-SWNTs disappeared after heat-treatment at 1200°C for 1 h. Since thermal degradation was not observed for as-grown SWNTs or for acid-purified SWNTs, we suggest that the holes and defects in the r-SWNTs were formed by oxidation of chemically damaged sites formed during the polymer-assisted ultrasonication.

Introduction

Since the discovery of single-wall carbon nanotubes (SWNTs) [1] their nature, including their structure, and electronic and mechanical properties, has been revealed as a result of many investigations. However, many impurities, such as amorphous carbon, fullerenes, and metal catalysts, are produced together with SWNTs. High-quality SWNTs need to be produced to study the detailed bulk properties of SWNTs and to develop applications for their use. Some methods for purifying SWNTs have been reported. Carbonaceous impurities can be removed by gas-phase oxidation [2], and metal impurities can be eliminated using a strong acid, followed by filtration and centrifugation [3].

The separation of SWNTs and impurities is more difficult than general separation techniques, largely because SWNTs of various lengths form bundles, to which impurities adhere. Ultrasonic irradiation is one effective method for dispersing, disentangling, and thinning bundles of SWNTs when SWNTs are purified. Smalley and co-workers [4] reported purifying and cutting SWNTs by ultrasonically assisted filtration. Recently, our group has reported that ultrasonication and filtration of a mixture of SWNTs and polymethylmethacrylate (PMMA) was a more effective method for removing carbonaceous impurities, and we also found a number of short SWNTs (about 1 μm) and thin bundles containing one to three SWNTs [5].

In this study, we found that SWNTs purified by polymer-assisted ultrasonication had worm-eaten-like holes and they rapidly sublimed at temperatures over 800°C. These were named `ragged SWNTs (r-SWNTs)'. Here we report the first successful observation of the degradation of SWNTs and the characterization of r-SWNTs.

Section snippets

Experimental

SWNTs were produced by a conventional laser ablation method. A pellet (diameter $10 mm ×5 mm$ ) was prepared as the laser target by compressing powdered graphite containing metal catalysts, Co and Ni, with atomic concentrations of 0.6% each. The second harmonic output of an Nd:YAG laser (532 nm, 10 Hz, 6–7 ns, 0.7 J/pulse, Spectra Physics GCR-350) was used to ablate the Ni/Co/graphite target at a temperature of 1200°C in an Ar flow (750 Torr, 300 ml/min).

Approximately 5 mg of the as-grown SWNTs and

Results and discussion

As-grown SWNTs contained impurities, such as metal particles, carbonaceous particles, and amorphous carbons (Fig. 1a); the impurities adhered to the surface of bundles of SWNTs. Most of the as-grown SWNTs formed arch-like bundles. The inset in Fig. 1a indicates that most of the bundles contained about 50 SWNTs with diameters of ca. 1.3 nm.

Fig. 1b shows a TEM image of SWNTs (US) obtained by ultrasonication followed by filtration through 5 μm pores. SWNTs (US) were not clearly observed by TEM, as

Conclusions

In this study, we found that r-SWNTs were produced by polymer (PMMA)-assisted ultrasonication and oxidation. We have also observed their unusual property of thermal degradation by heat treatment in a vacuum. The degradation occurs at temperatures exceeding 800°C. We suggest that the holes and defects in the r-SWNTs are formed by oxidation at sites damaged by the polymer-assisted ultrasonication, and that these sites are the starting point for the degradation. The instability and reactivity of

References (9)

K.B. Shelimov et al.
Chem. Phys. Lett.
(1998)
R. Katoh et al.
Ultason. Sonochem.
(1998)
A. Kuznetsova et al.
Chem. Phys. Lett.
(2000)
S. Iijima et al.
Nature
(1993)

There are more references available in the full text version of this article.

Cited by (47)

Surface modification and Pt functionalisation of multi-walled carbon nanotubes in methanol expanded with supercritical CO<inf>2</inf>
2010, Chemical Engineering Journal
Citation Excerpt :
It can be observed that the ID/IG ratio increases from 1.10 in the purified MWNTs to 1.28 in the ultrasonicated MWNTs, due to the wall structure damage caused by ultrasonication in acid. This is consistent with the results of Koshio et al. [35] and Chu et al. [36]. However, the ID/IG ratio decreases to 1.03 in the Pt functionalised MWNTs treated in supercritical CO2.
Microwave acid purification with H₂SO₄ was performed on multi-walled carbon nanotubes (MWNTs) synthesised by fluidised-bed chemical vapour deposition (CVD) to remove Fe catalysts and Al₂O₃ substrates. The surface of these purified MWNTs was then modified with HNO₃ under the influence of an ultrasonic field followed by functionalised with Pt nanoparticles in methanol expanded with supercritical CO₂. The weight loss profile of the purified sample treated at 200 °C under microwave irradiation shows the MWNT purity to be 96.5 wt%. TEM images of Pt functionalised MWNTs show that Pt nanoparticles of approximately 4 nm were deposited on the outer tube walls. SEM/EDX results confirm that the Pt nanoparticles were mono-sized and evenly distributed. Raman spectroscopy suggested that supercritical processing conditions can repair wall defects in MWNTs. XRD analysis confirmed the presence of crystalline Pt particles.
Functionalization and applications of carbon nanotubes
2006, Carbon Nanotechnology: Recent Developments in Chemistry, Physics, Materials Science and Device Applications
This chapter summarizes the recent progress in the research on functionalization of carbon nanotubes (CNTs) for multifunctional materials, and device applications. CNTs can be viewed as graphite sheet(s) that have been rolled up into a tiny tube form. These elongated nanotubes usually have a diameter in the range from a few angstroms to tens of nanometers, and a length upto centimeters. The ends of CNTs are normally capped by fullerene-like structures containing pentagons. It has been demonstrated that the tips of CNTs are more reactive than sidewalls with the seamless arrangement of hexagon rings. A judicious application of site-selective reactions to non-aligned, and aligned CNTs, has opened up a rich field of carbon nanotube chemistry for chemical functionalization of the nanotube tips, inner-, and/or outer-walls.
Functionalization and applications of carbon nanotubes
2006, Carbon Nanotechnology
This chapter summarizes the recent progress in the research on functionalization of carbon nanotubes (CNTs) for multifunctional materials, and device applications. CNTs can be viewed as graphite sheet(s) that have been rolled up into a tiny tube form. These elongated nanotubes usually have a diameter in the range from a few angstroms to tens of nanometers, and a length upto centimeters. The ends of CNTs are normally capped by fullerene-like structures containing pentagons. It has been demonstrated that the tips of CNTs are more reactive than sidewalls with the seamless arrangement of hexagon rings. A judicious application of site-selective reactions to non-aligned, and aligned CNTs, has opened up a rich field of carbon nanotube chemistry for chemical functionalization of the nanotube tips, inner-, and/or outer-walls.
Coating MWNTs with Cu<inf>2</inf>O of different morphology by a polyol process
2005, Journal of Solid State Chemistry
Homogeneous cuprous oxide (Cu₂O) nanoparticles with size of 8–10 nm are deposited on multiwall carbon nanotubes (MWNTs) by a polyol process using Cu(CH₃COO)₂·H₂O as a precursor and diethylene glycol as both solvent and reducing agent. The composition of the resulting Cu₂O/MWNTs composites is confirmed by XRD pattern, XPS spectrum and HRTEM images. With the change of the reaction conditions, it is found that Cu₂O nanoparticles on the surface of MWNTs can be leafage-like or big spherical particle coated on the surface of MWNTs. HRTEM images indicate that all the leafage-like and big spherical particles are assembled by small Cu₂O particles with size of about 2–5 nm. With the assistance of FTIR spectrum, a tentative mechanism is proposed for the formation of Cu₂O nanoparticles with different morphologies on the surface of MWNTs.
Field emission from the film of the finely dispersed arc discharge black core material
2005, Carbon
Citation Excerpt :
We derived needle-like materials from a black core material by simply pounding it and then dispersed them using a high-intensity ultrasonic processor. High-intensity ultra-sonic processors have been employed as tools for various sample preparations of a wide range of organic and inorganic materials, i.e., cell lysing, disaggregation and particle size reduction [15,16]. Fig. 2 shows the needle-like materials treated with different duration.
We have studied, for the first time, the field emission from the film, prepared by a spray method, of the finely dispersed black core material, including multi-walled carbon nanotubes (MWNTs), fabricated by arc discharge. We dispersed the black core material by using an ultrasonic processor and found that the dispersed ones were much finer than those observed when treated with a ball mill and normal ultra-sonic bath. By SEM, HRTEM and Raman analyses, the MWNTs were almost not deformed and damaged during ultra-sonication. The field emission current density measured from the film of the dispersed black core material was about 15 mA/cm² at an applied field of 8 V/μm, which was about 23 times higher than that found by a ball mill. A current density of 1 mA/cm², which is required basically for flat panel display, has been obtained at 5.3 V/μm. The lifetime test of the dispersed black core material showed that the current density was almost unchanged while the field was applied. Therefore, it is concluded that a black core material fabricated by arc discharge could be used to flat panel displays as field emitters by dispersing with an ultrasonic processor, without further treatment like extraction or purification.
Photoelectrochemical properties of donor-acceptor nanocomposite films composed of porphyrin-functionalized cup-shaped nanocarbon materials
2010, Journal of Porphyrins and Phthalocyanines

View all citing articles on Scopus

View full text