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A summary of common methods used to characterize chemically functionalized single-walled carbon nanotubes (SWNTs).

Introduction

Characterization of nanoparticles in general, and carbon nanotubes in particular, remains a technical challenge even though the chemistry of covalent functionalization has been studied for more than a decade. It has been noted by several researchers that the characterization of products represents a constant problem in nanotube chemistry. A systematic tool or suites of tools are needed for adequate characterization of chemically functionalized single-walled carbon nanotubes (SWNTs), and is necessary for declaration of success or failure in functionalization trials.

So far, a wide range of techniques have been applied to characterize functionalized SWNTs: infra red (IR), Raman, and UV/visible spectroscopies, thermogravimetric analysis (TGA), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. A summary of the attribute of each of the characterization method is given in [link] .

Common characterization methodology for functionalized SWNTs.
Method Sample Information Limitations
TGA solid functionalization ratio no evidence for covalent functionalization, not specific
XPS solid elements, functionalization ratio no evidence of covalent functionalization, not specific, quantification complicated
Raman solid sp 3 indicated by D mode not specific, quantification not reliable
Infra red (IR) solid for (ATR-IR) or solution substituent groups no direct evidence for covalent functionalization, quantification not possible
UV/visible solution sidewall functionalization not specific or quantitative, need highly dispersed sample
Solution NMR solution substituents no evidence of covalent functionalization, high solubility of sample
Solid state NMR solid substituents, sp 3 molecular motions, quantification at high level of funcitionalization high functionalization needed, long time for signal acquisition, quantification not available for samples with protons on side chains
AFM solid on substrate topography only a small portion of sample characterized, no evidence of covalent functionalization, no chemical identity
TEM solid on substrate image of sample distribution dispersion only a small portion of sample characterized, no evidence of covalent functionalization, no chemical identity dispersion information complicated
STM solid on substrate distribution no chemical identity of functional groups small portion of sample conductive sample only

Elemental and physical analysis

Thermogravimetric analysis (tga)

Thermogravimetric analysis (TGA) is the mostly widely used method to determine the level of sidewall functionalization. Since most functional groups are labile or decompose upon heating, while the SWNTs are stable up to 1200 °C under Ar atmosphere. The weight loss at 800 °C under Ar is often used to determine functionalization ratio using this indirect method. Unfortunately, quantification can be complicated with presence of multiple functional groups. Also, TGA does not provide direct evidence for covalent functionalization since it cannot differentiate between covalent attachment and physical adsorption.

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Source:  OpenStax, Carbon nanotubes. OpenStax CNX. Sep 30, 2013 Download for free at http://cnx.org/content/col11576/1.1
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