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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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Comparison of Fe concentrations measured by UV/Vis spectroscopy and ICP-OES for the solutions prepared by treating a) CNTs and ash in the HCl/HNO3 (3:1) mixture as a function of reflux time and b) CNTs in various single and mixed acid solvents for 6 h. Solvent numbers are denoted as follows (mixture ratios as v/v): 1. H2SO4, 2. HCl, 3. HNO3, 4. f-HNO3, 5. HClO4, 6. HCl/HNO3 (3:1), 7. H2SO4/HNO3 (3:1), 8. HClO4/HNO3 (1:3), 9. HClO4/HNO3 (1:1), 10. HClO4/HNO3 (3:1), 11. HClO4/f-HNO3 (3:1). Data are the average ±SD of three independent measurements. c)–f) Images of solutions taken by digital camera after holding CNTs at reflux for 6 h in acid mixtures of c) HCl/HNO3 (3:1), d) H2SO4/HNO3 (3:1), e) HClO4/HNO3 (3:1), and f) HClO4/ f-HNO3 (3:1).
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fig03: Comparison of Fe concentrations measured by UV/Vis spectroscopy and ICP-OES for the solutions prepared by treating a) CNTs and ash in the HCl/HNO3 (3:1) mixture as a function of reflux time and b) CNTs in various single and mixed acid solvents for 6 h. Solvent numbers are denoted as follows (mixture ratios as v/v): 1. H2SO4, 2. HCl, 3. HNO3, 4. f-HNO3, 5. HClO4, 6. HCl/HNO3 (3:1), 7. H2SO4/HNO3 (3:1), 8. HClO4/HNO3 (1:3), 9. HClO4/HNO3 (1:1), 10. HClO4/HNO3 (3:1), 11. HClO4/f-HNO3 (3:1). Data are the average ±SD of three independent measurements. c)–f) Images of solutions taken by digital camera after holding CNTs at reflux for 6 h in acid mixtures of c) HCl/HNO3 (3:1), d) H2SO4/HNO3 (3:1), e) HClO4/HNO3 (3:1), and f) HClO4/ f-HNO3 (3:1).

Mentions: For ICP-OES measurement, CNTs are usually held at reflux in a strong acid. The Fe concentration in the acid solution may vary depending on how completely the metal impurities are dissolved. The dissolution of metal impurities can also be affected by various factors such as the morphology and volume of CNTs dissolved, acid type, reflux temperature, and time, so the acid reflux conditions should be optimized for accurate Fe analysis. Aqua regia, HCl/HNO3=3:1, was used in this study to dissolve metal catalysts in the CNTs because it is a strong oxidant that is frequently used to purify CNTs through liquid oxidation.41 Figure 3 a shows Fe concentrations extracted by aqua regia from the CNTs and ashes as a function of reflux time. For these same solutions, the Fe concentrations were measured by UV/Vis spectroscopy (solid lines in Figure 3 a) and ICP-OES (dashed lines in Figure 3 a), which are in good agreement with each other (Figure 3 a). The colorimetric method using UV/Vis spectroscopy is reliable and applicable for assessing Fe content in CNTs and ashes, as confirmed by ICP-OES.


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)

Comparison of Fe concentrations measured by UV/Vis spectroscopy and ICP-OES for the solutions prepared by treating a) CNTs and ash in the HCl/HNO3 (3:1) mixture as a function of reflux time and b) CNTs in various single and mixed acid solvents for 6 h. Solvent numbers are denoted as follows (mixture ratios as v/v): 1. H2SO4, 2. HCl, 3. HNO3, 4. f-HNO3, 5. HClO4, 6. HCl/HNO3 (3:1), 7. H2SO4/HNO3 (3:1), 8. HClO4/HNO3 (1:3), 9. HClO4/HNO3 (1:1), 10. HClO4/HNO3 (3:1), 11. HClO4/f-HNO3 (3:1). Data are the average ±SD of three independent measurements. c)–f) Images of solutions taken by digital camera after holding CNTs at reflux for 6 h in acid mixtures of c) HCl/HNO3 (3:1), d) H2SO4/HNO3 (3:1), e) HClO4/HNO3 (3:1), and f) HClO4/ f-HNO3 (3:1).
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fig03: Comparison of Fe concentrations measured by UV/Vis spectroscopy and ICP-OES for the solutions prepared by treating a) CNTs and ash in the HCl/HNO3 (3:1) mixture as a function of reflux time and b) CNTs in various single and mixed acid solvents for 6 h. Solvent numbers are denoted as follows (mixture ratios as v/v): 1. H2SO4, 2. HCl, 3. HNO3, 4. f-HNO3, 5. HClO4, 6. HCl/HNO3 (3:1), 7. H2SO4/HNO3 (3:1), 8. HClO4/HNO3 (1:3), 9. HClO4/HNO3 (1:1), 10. HClO4/HNO3 (3:1), 11. HClO4/f-HNO3 (3:1). Data are the average ±SD of three independent measurements. c)–f) Images of solutions taken by digital camera after holding CNTs at reflux for 6 h in acid mixtures of c) HCl/HNO3 (3:1), d) H2SO4/HNO3 (3:1), e) HClO4/HNO3 (3:1), and f) HClO4/ f-HNO3 (3:1).
Mentions: For ICP-OES measurement, CNTs are usually held at reflux in a strong acid. The Fe concentration in the acid solution may vary depending on how completely the metal impurities are dissolved. The dissolution of metal impurities can also be affected by various factors such as the morphology and volume of CNTs dissolved, acid type, reflux temperature, and time, so the acid reflux conditions should be optimized for accurate Fe analysis. Aqua regia, HCl/HNO3=3:1, was used in this study to dissolve metal catalysts in the CNTs because it is a strong oxidant that is frequently used to purify CNTs through liquid oxidation.41 Figure 3 a shows Fe concentrations extracted by aqua regia from the CNTs and ashes as a function of reflux time. For these same solutions, the Fe concentrations were measured by UV/Vis spectroscopy (solid lines in Figure 3 a) and ICP-OES (dashed lines in Figure 3 a), which are in good agreement with each other (Figure 3 a). The colorimetric method using UV/Vis spectroscopy is reliable and applicable for assessing Fe content in CNTs and ashes, as confirmed by ICP-OES.

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