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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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a) Scheme of Fe–phen complex formation; coordination of an Fe2+ ion with three phen molecules via lone-pair electrons on the N atoms of phen. b) Standard solutions of Fe–phen complex used for calibration, containing Fe concentrations from 0–9 ppm, taken by a digital camera. The red–orange color of the solutions becomes stronger as the Fe concentration increases. c) Absorption spectra of the standard solutions in the visible spectral range, measured by UV/Vis spectroscopy. d) Linear relationship between optical absorbance and Fe concentration for the standard solutions. The absorbance was measured at the maximum peak position of 510 nm for the absorption spectra shown in panel c. Linear fitting: A=0.20423 C+0.00716, R2=0.99994. The coefficient of determination to designate linearity is calculated using R2=. Here, yi is the observed absorbance value, ȳ is the mean absorbance, and ŷ1 is the fitted absorbance value. e) Fe concentrations measured from the constructed solutions containing both Al and Fe ions, using UV/Vis spectroscopy. The constructed solutions were prepared by mixing pure Fe and Al solutions. Linear fitting: y=0.99114 x+0.00701, R2=0.99998.
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fig02: a) Scheme of Fe–phen complex formation; coordination of an Fe2+ ion with three phen molecules via lone-pair electrons on the N atoms of phen. b) Standard solutions of Fe–phen complex used for calibration, containing Fe concentrations from 0–9 ppm, taken by a digital camera. The red–orange color of the solutions becomes stronger as the Fe concentration increases. c) Absorption spectra of the standard solutions in the visible spectral range, measured by UV/Vis spectroscopy. d) Linear relationship between optical absorbance and Fe concentration for the standard solutions. The absorbance was measured at the maximum peak position of 510 nm for the absorption spectra shown in panel c. Linear fitting: A=0.20423 C+0.00716, R2=0.99994. The coefficient of determination to designate linearity is calculated using R2=. Here, yi is the observed absorbance value, ȳ is the mean absorbance, and ŷ1 is the fitted absorbance value. e) Fe concentrations measured from the constructed solutions containing both Al and Fe ions, using UV/Vis spectroscopy. The constructed solutions were prepared by mixing pure Fe and Al solutions. Linear fitting: y=0.99114 x+0.00701, R2=0.99998.

Mentions: Phen then reacts with Fe2+ to form the red–orange colored Fe–phen complex, by the reaction shown in Figure 2 a.


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) Scheme of Fe–phen complex formation; coordination of an Fe2+ ion with three phen molecules via lone-pair electrons on the N atoms of phen. b) Standard solutions of Fe–phen complex used for calibration, containing Fe concentrations from 0–9 ppm, taken by a digital camera. The red–orange color of the solutions becomes stronger as the Fe concentration increases. c) Absorption spectra of the standard solutions in the visible spectral range, measured by UV/Vis spectroscopy. d) Linear relationship between optical absorbance and Fe concentration for the standard solutions. The absorbance was measured at the maximum peak position of 510 nm for the absorption spectra shown in panel c. Linear fitting: A=0.20423 C+0.00716, R2=0.99994. The coefficient of determination to designate linearity is calculated using R2=. Here, yi is the observed absorbance value, ȳ is the mean absorbance, and ŷ1 is the fitted absorbance value. e) Fe concentrations measured from the constructed solutions containing both Al and Fe ions, using UV/Vis spectroscopy. The constructed solutions were prepared by mixing pure Fe and Al solutions. Linear fitting: y=0.99114 x+0.00701, R2=0.99998.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig02: a) Scheme of Fe–phen complex formation; coordination of an Fe2+ ion with three phen molecules via lone-pair electrons on the N atoms of phen. b) Standard solutions of Fe–phen complex used for calibration, containing Fe concentrations from 0–9 ppm, taken by a digital camera. The red–orange color of the solutions becomes stronger as the Fe concentration increases. c) Absorption spectra of the standard solutions in the visible spectral range, measured by UV/Vis spectroscopy. d) Linear relationship between optical absorbance and Fe concentration for the standard solutions. The absorbance was measured at the maximum peak position of 510 nm for the absorption spectra shown in panel c. Linear fitting: A=0.20423 C+0.00716, R2=0.99994. The coefficient of determination to designate linearity is calculated using R2=. Here, yi is the observed absorbance value, ȳ is the mean absorbance, and ŷ1 is the fitted absorbance value. e) Fe concentrations measured from the constructed solutions containing both Al and Fe ions, using UV/Vis spectroscopy. The constructed solutions were prepared by mixing pure Fe and Al solutions. Linear fitting: y=0.99114 x+0.00701, R2=0.99998.
Mentions: Phen then reacts with Fe2+ to form the red–orange colored Fe–phen complex, by the reaction shown in Figure 2 a.

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