Recent Advances in the Production, Applications and Characterization of Single Wall Carbon Nanotubes (SWCNT)

By AZoM

Table of Contents

Introduction
Structure of Carbon Nanotubes
Unique Characteristics of SWCNT
Synthesis of SWNTs
Characterization of SWNTs and Quality Assurance Parameters
     Raman spectroscopy
     Optical absorption
     Thermogravimetric analysis (TGA)
Applications of SWNTs
Conclusion
About Southwest Nanotechnologies

Introduction

Carbon nanotubes have excellent properties that enable their use in a broad range of novel and improved applications in sensors, printed electronics, e-readers, flexible displays, energy storage, medical treatment and more.

In this article the physico-chemical nature and characterization of single-wall carbon nanotubes (SWNTs) and the status of their commercialization are discussed..

Structure of Carbon Nanotubes

SWNTs are an allotrope of sp2 hybridized carbon similar to fullerenes. The structure may be a cylindrical tube including six membered rings as in graphite. One or both ends of the cylindrical tubes may be capped with a fullerene or the buckyball structure.

Understanding the SWNT structure is possible by being familiar with nanotube chirality, and the chirality map shown in Figure 1, has been developed as a tool for understanding chirality and its implications.

Figure 1. A graphic displaying a chirality map which shows the various types of SWNTs that can be formed. The properties are governed by the way in which they are rolled as shown in the inset. The SWNT will be metallic in the armchair configuration, or when m-n is a multiple of 3.

Unique Characteristics of SWCNT

Unique properties of SWCNTs are listed below:

  • Mechanical: Individual SWNTs have a higher strength than steel.

  • Electrical: Individual SWNTs have current carrying capacities of 109 amp.cm-2, more than that of gold and copper and semiconductors show higher electron mobility than silicon.

  • Optical: SWNTs have a unique fluorescence response and distinct optical absorption, with each chirality showing its own fluorescence spectrum and its own characteristic absorption and fluorescence spectrum.

  • Thermal: Room temperature thermal conductivity of a single nanotube can be compared to that of in-plane graphite or diamond that shows the highest measured thermal conductivity of any known material at moderate temperatures.

Synthesis of SWNTs

The methods of synthesizing SWNTs are listed below:

  • Laser Ablation: This is mainly used for research materials.

  • Carbon arc process: This process produces long tubes in the diameter range of 1.4 to 2.0 nm however carbon arc material contains a lot of impurities and for most applications need extensive purification.

  • CVD Processes: These are probably the best for manufacturing large quantities of SWNTs, with probably the most scalable being the CoMoCAT® process that uses a fluidized bed reactor similar to that used in petroleum refining, presently on a very small scale. The unique capability to offer a considerable degree of chiraliity control during synthesis is offered by the supported catalyst approach.

Characterization of SWNTs and Quality Assurance Parameters

There are three commonly available techniques that are used to make sure consistent high quality SWCNTs are produced. These are discussed below:

Raman spectroscopy

In order to determine both the detailed combination of chiralities in the SWNTs material and to assess purity, Raman spectroscopy has been widely used.

There are three Raman spectrum areas of primary interest for SWNTs. The radial breath mode (RBM) from around 120 to 300 cm-1 is unique to SWNTs and can be used to determine tube diameter from the equation:

where, d is the SWNT’s diameter in nm and ν is the wave number in cm-1.

It is essential that several lasers of different excitation frequencies are used to obtain a comprehensive picture of the chiralities.

In the Raman spectrum of SWNTs, two additional bands, the D band at ~ 1350 cm-1 and the G band at 1500 to 1586 cm-1 are seen. The ratio of the height of the G band to that of the D band has been widely used as a measure of the purity of SWNTs.

Figure 2. Raman spectrum of SWeNT® SG65i SWNT (Aldrich Prod. No. 773735)

A typical Raman Spectrum for SWeNT® SG65i (Aldrich Prod. No. 773735) is shown in Figure 2.

Optical absorption

Optical absorption (OA) measurements in the UV-Vis-NIR region show characteristic peaks of individual (n,m) species superimposed on the π-plasmon background.

Figure 3 shows a typical OA spectrum for SWeNT® SG65i material. The inset shows the spectrum in the more conventional form with the absorption plotted as a function of wavelength. Primarily P2B is used as a control parameter for SWeNT® SG65i (Aldrich Prod. No. 773735) and SG76 (Aldrich Prod. No. 704121) nanotubes where one particular tube type is dominant.

P2B is defined as :

Figure 3. Optical absorbance spectrum in the region of UV-Vis-NIR of SWeNT® SG65i (Aldrich Prod. No. 773735)

Thermogravimetric analysis (TGA)

Figure 4 shows a typical TGA curve for SG65i SWNTs. TGA is used to evaluate a material’s purity. The key quality parameters determined from the TGA analysis is the residual mass at 625 °C. This shows how much residual residual catalyst metals (now oxidized) retained in the material.

The presence of other forms of graphitic carbon that oxidize at higher temperatures than SWNT is indicated by the second peak in the derivative curve. The residual mass is expressed as a percentage normalized for the weight loss at 200 °C.

Figure 4. Thermogravimetric analysis of SWeNT® SG65i (Aldrich Prod. No. 773735)

Applications of SWNTs

The applications of SWNTs are:

  • As SWNTs are highly conductive and have large surface areas they can be used prepare conductive polymer composites and films, improved lithium ion batteries, and supercapacitors.

  • Optical properties enable their use as solar cells, electrodes in displays, and emerging solid state lighting technologies.

  • The semiconducting nature of certain SWNTs enable their adaptation to logic devices, non-volatile memory elements, sensors and security tags.

  • SWNTs are also used in the medical sector mostly for cancer treatment. SWNTs when irradiated with light in the near-infrared (NIR) region fluoresce in the infrared, enabling the heating of internal tissue in the cancer area by irradiation of SWNT placed in the area of the malignant tissue.

  • For transparent conductive films (TCFs), SWNT are finding application as replacement for ITO and conductive polymers such as PEDOT:PSS (Aldrich Prod. Nos. 768642 and 739316).

  • SWeNT® has developed its most conductive grade CG300 (Aldrich Prod. No. 775533), made by CoMoCAT®, recognized for its scalability and the consistent product it produces, with optimized characteristics that make it suited for inclusion in the inks required for printing and coating.

Southwest Nanotechnologies (SWeNT®) has introduced the SG65i (Aldrich Prod. No. 773735). SG65i that is an enhancement over SG65 (Aldrich Prod. No. 704148), A comparison of the two materials is provided in Table 1:

Table 1. Comparison of SWeNT® SG65i and SG65

Parameter SG65 (Aldrich Prod. No. 704148) SG65i (Aldrich Prod. No.773735)
(6,5) content (% of SWNTs) <40 > 40
Semiconducting tube Content (%) 90 - 91 ≥ 95
Residual Mass (%) 7.6 <5
Average diameter (nm) 0.8 0.78
Raman Q = (1-D/G) > 0.95 ≥ 0.97
Relative Purity (T1%) 79 ≥93

Both the materials are fabricated using the patented CoMoCAT® synthesis process, well known to be more selective for diameter and chirality when compared to alternative methods. These improved properties are enabling accelerated development of printed semiconductor devices, notably thin film transistors (TFTs).

Conclusion

Even though SWNTs are highly promising, the commercial exploitation of the technology has been restricted. However, momentum is now building, driven by substantial recent progress in several fundamental areas. Table 2 below are CoMoCAT® high purity SWNTs manufactured by SouthWest NanoTechnologies (SWeNT®), Inc. and available in research quantities exclusively from Aldrich® Materials Science.

Table 2. High purity SWNTs manufactured by SWeNT

Aldrich Prod. No. SWeNT® Product Product Name Features
773735 SG 65i Carbon nanotube, single-walled (6,5) chirality carbon =95 % ≥93% (carbon as SWNT) 0.7-0.9 nm diameter
  • High purity single-walled carbon nanotubes
  • Small diameter
  • Precise chirality and diameter control
  • > 95% semiconducting character
704148 SG 65 Carbon nanotube, single-walled (6,5) chirality carbon >90% ≥77% (carbon as SWNT) 0.7-0.9 nm diameter
  • High purity single-walled carbon nanotubes
  • Small diameter
  • Precise chirality and diameter control
  • >90% semiconducting character
704121 SG 76 Carbon nanotube, single-walled (7,6) chirality ≥77% (carbon as SWNT) 0.7-1.1 nm diameter
  • High purity single-walled carbon nanotubes
  • Precise chirality and diameter control
  • Good conductivity
704113 CG 100 Carbon nanotube, single-walled ≥70% (carbon as SWNT) 0.7-1.3 nm diameter
  • High purity single-walled carbon nanotubes
  • Uniform chiral distribution
724777 CG 200 Carbon nanotube, single-walled ≥90% (carbon as SWNT), 0.7-1.4 nm diameter
  • High purity single-walled carbon nanotubes
  • Large diameter
  • High metallic tube content
  • High electrical conductivity
775533 CG 300 Carbon nanotube, single-walled >95% (carbon as SWNT) 0.6-1.1 nm diameter
  • High purity single-walled carbon nanotubes
  • Small diameter
  • Precise chirality and diameter control
  • lower metallic tube content
  • better for transparent conductive coatings

About Southwest Nanotechnologies

SouthWest NanoTechnologies Inc. (SWeNT) produces carbon nanotubes using the patented CoMoCAT® catalytic method in fluidized bed reactors. This results in selective synthesis of single-wall carbon nanotubes and remarkable control of diameter, chirality and purity.

Single-wall carbon nanotubes exhibit unique properties due to their unusual structure. They consist of a hollow cylinder of carbon ~ 1nm in diameter, up to 1,000 times as long as it is wide. This structure has remarkable optical and electronic properties, tremendous strength and flexibility, and high thermal and chemical stability. As a result, carbon nanotubes are expected to have dramatic impact on several industries, including displays, electronics, health care and composites.

SWeNT was founded in April 2001 to commercialize nanotube technology developed by Professor Daniel Resasco at the University of Oklahoma. The CoMoCAT® brand is widely recognized for quality and scalability.

This information has been sourced, reviewed and adapted from materials provided by SouthWest NanoTechnologies (SWeNT).

For more information on this source, please visit SouthWest NanoTechnologies (SWeNT).

Date Added: May 23, 2013 | Updated: Jun 11, 2013
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