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NanoPower Research Labs

Carbon Nanotubes

Material Characterization

In addition to novel synthesis capabilities, the NPRL is well positioned for extensive characterization of carbon nanotubes involving microscopic (SEM, AFM), spectroscopic (optical absorption, Raman, fluorescence), surface area, and thermal (TGA, DSC) analysis. Recently, the NPRL has advanced the understanding of SWCNT purity assessment using optical absorption spectroscopy (B.J. Landi et al. J. Phys. Chem. B 2004, 108, 17089; and B.J. Landi et al. J. Phys. Chem. B 2005, 109, 9952). This work analyzed stable dispersions of laser-synthesized SWCNTs in N,N-dimethylacetamide (DMA) to determine the mass fraction of SWCNTs in the carbonaceous portion of a sample. This was strongly aided by the development of constructed sample sets which varied the SWCNT mass fraction of purified SWCNTs with respect to a representative carbonaceous by-product. Such SWCNT calibration samples allowed numerous mathematical approaches to be applied in reference to a known metric of comparison. The publication’s review of the linear subtraction method for the second interband electronic transition of the semiconducting SWCNTs (SE22) peak showed how this linear approach overestimates the actual SWCNT content, supported by both experimental data and a mathematical derivation. Instead, the NPRL developed alternative approaches which showed a better correlation to the constructed sample sets. These included a nonlinear regression model and multiple rapid assessment protocols using peak maxima values (absolute absorbance intensity, peak maxima ratio, tie line slope, and a Beer’s law analysis derived from calculated extinction coefficients). This framework allows the NPRL to work with standardized purity SWCNT materials, and assess the purty of materials purchased from commercial vendors.

(a) Image of a Beer’s Law dilution series for SWCNT-DMA dispersions. (b) Optical absorption data for a SWCNT constructed sample set for purity assessment.

There is considerable ongoing effort to develop control over individual single wall carbon nanotube (SWCNT) properties (chirality, length, purity, electronic type ratio, etc.) for a variety of applications. This control can either be accomplished during synthesis or in conjunction with subsequent processing steps aimed at purification and separation of the desired products. Although substantial work has been done in the last decade involving synthesis techniques and conditions for varying SWCNT diameter, the ability to manipulate production of specific SWCNT chiralities is still a sought-after research goal. The synthetic tunability of SWCNT chiralities has been a research challenge, in large part, due to the absence of a characterization technique which can rapidly discriminate the (n, m) SWCNT types in a sample. The discovery of SWCNT fluorescence has provided a straightforward approach with the capability to “map” the semiconducting distribution in a sample. This is a major improvement over absorption spectroscopy where multiple SWCNT features can be convolved within a series of peaks that fluorescence mapping can highlight due to selective excitation. The figure illustrates this advantage of fluorescence mapping given that multiple chiralites absorb (emit) over a very close wavelength range. Therefore, such spectroscopy can assist in understanding effects of experimental parameters on SWCNT distributions during synthesis, as well as offering insight during electronic type separations.

The NPRL has developed a carbonaceous purity assessment technique, using Raman spectroscopy, to assess the purity of the CVD grown MWCNTs. Raman spectroscopy has been performed on a reference sample set containing predetermined ratios of MWCNTs and representative synthesis by-products. Changes in the characteristic Raman peak ratios (i.e., ID/ IG, IG’ / IG, and IG’ / ID) as a function of MWCNT content were measured. Calibration curves were generated from the reference samples and used to evaluate MWCNTs synthesized under different conditions with varying purity. The efficacy of using Raman spectroscopy in conjunction with thermogravimetric analysis for quantitative MWCNT purity assessment is discussed.

(a) Digital image of a 488 nm laser exciting a MWCNT sample, the Raman single from which is measured to determine the carbonaceous purity using the NPRL purity assessment technique for CVD MWCNTs. (b) The calibration curve for purity assessment
Recent Publications:
Landi, Brian J.; Raffaelle, Ryne P., J. Nanosci. Nanotech., 7(3), 2007, pp. 883-890(8).
Landi Brian J; Ruf Herbert J; Evans Chris M; Cress Cory D; Raffaelle Ryne P., J. Phys. Chem. B. (2005), 109(20), 9952-65.
Landi, Brian J.; Ruf, Herbert J.; Worman, James J.; Raffaelle, Ryne P. J. Phys. Chem. B. (2004), 108(44), 17089-17095.
Fagan, J. A.; Simpson, J. R.; Landi, B. J.; Richter, L. J.; Mandelbaum, I.; Bajpai, V.; Ho, D. L.; Raffaelle, R.; Hight Walker, A. R.; Bauer, B. J.; Hobbie, E. K. ” Dielectric Response of Aligned Semiconducting Single-wall Nanotubes.” Phys. Rev. Lett. 2007, 98, 147402.
Krysak, M.; Parekh, B.; Debies, T.; DiLeo, R.A.; Landi, B.J.; Raffaelle, R.P.; Takacs, G.A. “Gas-phase surface functionalization of multi-walled carbon nanotubes with vacuum UV photo-oxidation.” J. Adhesion Sci. Technol., 2007, 21, 999–1007.
Landi, B.J.; Cress, C.D.; Evans, C.M.; Raffaelle, R.P. “Thermal Oxidation Profiling of Single-Walled Carbon Nanotubes.” Chem. Mater. 2005, 17, 6819-6834.
Landi, B.J.; Ruf, H.J.; Evans, C.M.; Cress, C.D.; Raffaelle, R.P. “Purity Assessment of Single Wall Carbon Nanotubes, Using Optical Absorption Spectroscopy.” J. Phys. Chem. B. 2005, 109, 9952-9965.
Fagan, J.A.; Landi, B.J.; Mandelbaum, I.; Simpson, J.R.; Bajpai, V.; Bauer, B.J.; Migler, K.; Hight Walker, A.R.; Raffaelle, R.; Hobbie, E.K.; "Comparative Measures of Single-Wall Carbon Nanotube Dispersion." J Phys. Chem. B 2006, 110, 23801.
Landi, B.J.; Ruf, H.J.; Worman, J.J.; Raffaelle, R.P. “Effects of Alkyl Amide Solvents on the Dispersion of Single Wall Carbon Nanotubes.” J. Phys. Chem. B. 2004, 108, 17089-17095.

» Carbon Nanotubes

» SWCNT Synthesis

» MWCNT Synthesis

» Carbon Nanotube Electrodes for batteries and fuel cells

» Single Wall Carbon Nanotube Wire Harness