Purification procedure of carbon nanotubes

doi:10.1016/S0379-6779(98)01087-X

Synthetic Metals

Volume 103, Issues 1–3, June 1999, Pages 2492-2493

https://doi.org/10.1016/S0379-6779(98)01087-X Get rights and content

Abstract

We report results on purification and characterization of single wall carbon nanotubes prepared by the electric arc method. The process consists of a chemical treatment based on a reflux with nitric acid followed by successive filtration steps (tangential flow and frontal filtration) of a suspension of the raw material. The effects of each step are analysed by SEM and TEM.

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Iijima
Nature
(1991)

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An aqueous route based on electrostatics for preparing heterostructures from carbon nanotubes (CNT) and Zinc Sulfide doped with manganese (ZnS:Mn) is demonstrated. This was achieved by one-pot synthesis of negatively charged multiwalled carbon nanotubes and positively charged ZnS quantum dots, in a reaction driven by the electrostatic interaction between the binary components. The structural and optical properties of the heterostructures were characterized by particle size, zeta potential, x-ray diffraction, transmission and scanning electron microscopy, and photoluminescence measurements. A size-restriction effect of the CNTs on the growth of the ZnS nanoparticles during synthesis was observed, particle sizes of the prepared composites were smaller with higher amounts of CNT. Remarkably, all ZnS:Mn/CNT composites showed a blue shift of in the excitation spectra compared to ZnS:Mn only. Further experiments attributed the blue shift to an increased band gap of the ZnS:Mn, originating from an effective electrostatic interaction between the CNT and the attached ZnS:Mn. This effect was indicative of an intimate contact between the CNTs and the ZnS:Mn which was affirmed by images obtained from Transmission Electron Microscopy as well. Composites with such controlled morphology between the binary components are relevant in the fabrication of inorganic nanomaterial-carbon nanotube heterostructures, directed towards applications in optoelectronics.
Reducing structural defects and improving homogeneity of nitric acid treated multi-walled carbon nanotubes
2015, Carbon
Citation Excerpt :
Another aspect is that oxidation debris (or carboxylated carbonaceous fragments) generated in acid treatment could also contribute to the intensities of D-band and G-band in Raman spectrum of CNTs [20], which had not been taken into account in those aforementioned work. To the best of our knowledge, oxidation debris were first observed to coat the surface of CNTs after nitric acid reflux by Vaccarini and coworkers using SEM [21]. Those debris were found to be oxidized more easily and able to dampen a sufficient functionalization of CNTs [22].
Scanning Raman spectroscopy was employed to statistically examine the effects of nitric acid treatments on the defects and their distribution on the surface of multi-walled carbon nanotubes (MWCNTs). After acid treatments, the amount of structural defects significantly increased and the homogeneity became worse. However, after a 384-h base wash the amount of structural defects remarkably decreased and the homogeneity was significantly improved. By comparison of these values we can conclude that the observed increase of structural defects of MWCNTs caused by acid treatment mainly originates from oxidation debris covering the surface of MWCNTs after acid treatment. These oxidation debris can protect MWCNTs from further destruction in acidic condition leaving MWCNTs with little defects after base wash. Simultaneously, base wash is capable of largely improving the homogeneity of MWCNTs.
Polyaniline and polyaniline-carbon black nanostructures as electrochemical capacitor electrode materials
2014, International Journal of Hydrogen Energy
Citation Excerpt :
After stirring the preparation with an ultrasonic bath, it was kept at room temperature for 20 h, then filtered and washed to achieve neutral pH in the filtrate solution. Finally, the residue consisting in CBf particles was dried at 37 °C for 2 h [20]. The synthetized nanostructures were characterized through various physicochemical techniques.
Polyaniline (PANI) and polyaniline-carbon black (PANI-CB) nanostructures were developed and their behavior in relation to supercapacitors properties was tested. Different nanostructures were prepared by a simple chemical method of self-organization. SEM and TEM images revealed PANI nanotubes of ca. 95 nm in diameter; nanoparticles, nanobelts, nanosheets and/or nanotubes could be recognized in PANI-CB nanocomposites as a result of the use of CB particles with and without chemical pretreatment, CBf and CBnf, respectively. From EDS, XRD, UV–Vis and FTIR characterization techniques, the development of the various nanostructures was attributed to the chemical polymerization process that provoked a doped PANI state and hydrogen links that stabilized the changes in the structures. The resulted morphologies influenced the capacitance, specific power and specific energy values. PANI-CBf nanocomposites displayed improved capacitive properties in H₂SO₄ solutions, namely 1486 F g⁻¹ at 2 A g⁻¹. The charge–discharge tests indicated that the loss of capacitance during the charge/discharge cycles was lower than 18% for the checked materials.
Synthesis and characterization of polyaniline and polyaniline - Carbon nanotubes nanostructures for electrochemical supercapacitors
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Nanostructures of polyaniline (PANI) and PANI with embedded carbon nanotubes (CNT) were synthesized through a chemical method of self-organization. An oxidative polymerization process was performed in the monomer acid solution with the presence of a surfactant and the addition of multi-walled CNT. The CNT were added with and without pretreatment, CNTf and CNTnf, respectively. Furthermore, ammonium persulfate and sodium dodecyl sulfate were incorporated to the reaction solution as dispersant and oxidizing agents, respectively. Different nanostructures such as nanoparticles or nanotubes were obtained depending on the CNT added, and characterized by scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy, infrared spectroscopy and electrochemical techniques. Spectroscopy results showed variations in the observed bands of the synthetized nanostructures attributed to changes in the molecular structures, to the state of doped PANI reached during polymerization and to the stabilization of these links by hydrogen bridge interactions. PANI and PANI–CNT composites were evaluated by electrochemical techniques to test their behavior in relation to supercapacitors properties. PANI–CNTf nanocomposites displayed improved capacitive properties in H₂SO₄ solutions, namely 1744 F g⁻¹at 2 A g⁻¹. Also, the specific capacitance was strongly influenced by the developed morphologies. These characteristics point to their feasible application as supercapacitors materials.
Pt-Ru polymeric electrocatalysts used for the determination of carbon monoxide
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Different PtRu polyaniline composite catalysts were studied for the electro-oxidation of carbon monoxide (CO) in order to ascertain their response to the changes in CO bulk concentration in acid solutions. The catalyst substrate consisted of polyaniline films with incorporated carbon nanotubes grown over a Ni wire. To build the electrode, PtRu particles were added to the polymeric film by immersion at open circuit from a solution containing Pt(IV) and Ru(III). The concentration relationship R = [Pt(IV)]/[Ru(III)] was established fixing the Pt(IV) concentration and varying Ru(III) concentration in order to have 0.5 < R < 5.
CO electro-oxidation in acid media was studied applying cyclic voltammetry and chronoamperometry, carefully controlling the amount of CO that flowed into the cell. A linear relationship was established between the CO oxidation current density and its concentration in solution for the catalyst prepared with lower R.
X-ray fluorescence as a method of monitoring metal catalyst content during the purification of carbon nanotubes
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There have been several studies that suggest that catalyst metals in carbon nanotubes (CNTs) may pose a health threat. As there are many potential applications of CNTs in medicine, it is important to be able to quantitatively determine the amount of metal catalyst contained in a CNT sample. The relative catalyst content of carbon nanotube samples synthesized via arc-discharge has been determined at various stages of the purification process using X-ray fluorescence (XRF) analysis. Purification was achieved by immersing samples in heated nitric acid. The intensities of the nickel K_α X-rays were studied to determine the relative catalyst content in the samples. Scanning electron microscopy (SEM) images of purified nanotubes have been compared to the images of a sample that has been irradiated by 0–15 keV bremsstrahlung in order to determine if the XRF analysis of the nanotubes is in any way destructive. No obvious structural defects were observed as the result of irradiation.

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Purification procedure of carbon nanotubes

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