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Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy.

Agustina E, Goak J, Lee S, Seo Y, Park JY, Lee N - ChemistryOpen (2015)

Bottom Line: Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration.A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration.Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction.

View Article: PubMed Central - PubMed

Affiliation: Hybrid Materials Center, HMC), Department of Nanotechnology and Advanced Materials Engineering, Sejong University 209 Neungdong-ro, Gwangjin-gu, Seoul, 143-747, Republic of Korea.

ABSTRACT
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.

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Related in: MedlinePlus

a) SEM and b) TEM images of CNTs. TEM images show their multilayered structure and an average diameter of 15.5 nm, calculated from 90 nanotubes. c) TEM image of a metal particle encapsulated in multiple graphitic layers. d) Red-colored ash formed by oxidizing CNTs at 900 °C, 3.51 % by weight, taken by a digital camera.
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fig01: a) SEM and b) TEM images of CNTs. TEM images show their multilayered structure and an average diameter of 15.5 nm, calculated from 90 nanotubes. c) TEM image of a metal particle encapsulated in multiple graphitic layers. d) Red-colored ash formed by oxidizing CNTs at 900 °C, 3.51 % by weight, taken by a digital camera.

Mentions: Figure 1 shows the CNT-A used to develop the Fe content determination method. Scanning electron microscopy (SEM) shows non-bundled and individually separated tubes, but some degree of entanglement appeared between the structures (Figure 1 a). Transmission electron microscopy (TEM) reveals multi-layered tubes with an average diameter of 15.5±4.79 nm, which was calculated from 90 nanotubes (Figure 1 b). Metal catalyst particles were usually enclosed by thick graphitic layers (Figure 1 c); the graphitic layer should be removed or at least cracked so that etchants may access and eliminate these metallic impurities. Raman spectra (not shown) of the CNTs had an average intensity ratio of the G and D bands (IG/ID) of 0.76±0.04, indicating that they possess quite low crystallinity. In a derivative of the TGA curve (not shown), the oxidation peak temperature of the CNTs was ∼650 °C. A 3-g sample of AP-CNTs was burned at 900 °C in air to completely remove all carbonaceous material, and the ashes obtained were 3.51 wt. % of the CNTs. As shown in Figure 1 d, the ashes were red in color, indicating that iron oxide was formed while burning the CNTs in air.


Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy.

Agustina E, Goak J, Lee S, Seo Y, Park JY, Lee N - ChemistryOpen (2015)

a) SEM and b) TEM images of CNTs. TEM images show their multilayered structure and an average diameter of 15.5 nm, calculated from 90 nanotubes. c) TEM image of a metal particle encapsulated in multiple graphitic layers. d) Red-colored ash formed by oxidizing CNTs at 900 °C, 3.51 % by weight, taken by a digital camera.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608529&req=5

fig01: a) SEM and b) TEM images of CNTs. TEM images show their multilayered structure and an average diameter of 15.5 nm, calculated from 90 nanotubes. c) TEM image of a metal particle encapsulated in multiple graphitic layers. d) Red-colored ash formed by oxidizing CNTs at 900 °C, 3.51 % by weight, taken by a digital camera.
Mentions: Figure 1 shows the CNT-A used to develop the Fe content determination method. Scanning electron microscopy (SEM) shows non-bundled and individually separated tubes, but some degree of entanglement appeared between the structures (Figure 1 a). Transmission electron microscopy (TEM) reveals multi-layered tubes with an average diameter of 15.5±4.79 nm, which was calculated from 90 nanotubes (Figure 1 b). Metal catalyst particles were usually enclosed by thick graphitic layers (Figure 1 c); the graphitic layer should be removed or at least cracked so that etchants may access and eliminate these metallic impurities. Raman spectra (not shown) of the CNTs had an average intensity ratio of the G and D bands (IG/ID) of 0.76±0.04, indicating that they possess quite low crystallinity. In a derivative of the TGA curve (not shown), the oxidation peak temperature of the CNTs was ∼650 °C. A 3-g sample of AP-CNTs was burned at 900 °C in air to completely remove all carbonaceous material, and the ashes obtained were 3.51 wt. % of the CNTs. As shown in Figure 1 d, the ashes were red in color, indicating that iron oxide was formed while burning the CNTs in air.

Bottom Line: Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration.A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration.Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction.

View Article: PubMed Central - PubMed

Affiliation: Hybrid Materials Center, HMC), Department of Nanotechnology and Advanced Materials Engineering, Sejong University 209 Neungdong-ro, Gwangjin-gu, Seoul, 143-747, Republic of Korea.

ABSTRACT
Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.

No MeSH data available.


Related in: MedlinePlus