Nitric Acid Purification of Single-Walled Carbon Nanotubes

Hu, Hui; Zhao, Bin; Itkis, and Mikhail E.; Haddon, Robert C.

doi:10.1021/jp035719i

Cited by 498 publications

(428 citation statements)

References 34 publications

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“…27 Removal of the catalyst is usually accomplished with a nitric acid reflux, which also eradicates any remaining superfluous carbon. 41,[46][47][48] Although dry and wet purification methods remove the majority of residual carbon and metal catalysts, it is important to note that some residual impurities remain in all current SWNT samples.…”

Section: Purification Of Swntsmentioning

confidence: 99%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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Single-walled carbon nanotubes (SWNTs) are cylindrical graphitic molecules that have remained at the forefront of nanomaterials research since 1991, largely due to their exceptional and unusual mechanical, electrical, and optical properties. The motivation for understanding how nanotubes interact with light (i.e., SWNT photophysics) is both fundamental and applied. Individual nanotubes may someday be used as superior near-infrared fluorophores, biological tags and sensors, and components for ultrahigh-speed optical communications systems. Establishing an understanding of basic nanotube photophysics is intrinsically significant and should enable the rapid development of such innovations. Unlike conventional molecules, carbon nanotubes are synthesized as heterogeneous samples, composed of molecules with different diameters, chiralities, and lengths. Because a nanotube can be either metallic or semiconducting depending on its particular molecular structure, SWNT samples are also mixtures of conductors and semiconductors. Early progress in understanding the optical characteristics of SWNTs was limited because nanotubes aggregate when synthesized, causing a mixing of the energy states of different nanotube structures. Recently, significant improvements in sample preparation have made it possible to isolate individual nanotubes, enabling many advances in characterizing their optical properties. In this Account, single-molecule confocal microscopy and spectroscopy were implemented to study the fluorescence from individual nanotubes. Single-molecule measurements naturally circumvent the difficulties associated with SWNT sample inhomogeneities. Intrinsic SWNT photoluminescence has a simple narrow Lorentzian line shape and a polarization dependence, as expected for a one-dimensional system. Although the local environment heavily influences the optical transition wavelength and intensity, single nanotubes are exceptionally photostable. In fact, they have the unique characteristic that their single molecule fluorescence intensity remains constant over time; SWNTs do not “blink” or photobleach under ambient conditions. In addition, transient absorption spectroscopy was used to examine the relaxation dynamics of photoexcited nanotubes and to elucidate the nature of the SWNT excited state. For metallic SWNTs, very fast initial recovery times (300–500 fs) corresponded to excited-state relaxation. For semiconducting SWNTs, an additional slower decay component was observed (50–100 ps) that corresponded to electron–hole recombination. As the excitation intensity was increased, multiple electron–hole pairs were generated in the SWNT; however, these e−h pairs annihilated each other completely in under 3 ps. Studying the dynamics of this annihilation process revealed the lifetimes for one, two, and three e−h pairs, which further confirmed that the photoexcitation of SWNTs produces not free electrons but rather one-dimensional bound electron–hole pairs (i.e., excitons). In summary, nanotube photophysics is a rapidly developing area o...

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Section: Purification Of Swntsmentioning

confidence: 99%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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“…But low purity of the MWNTs and hydrophobic and inert nature of the surface of MWNTs reduce their applications. The oxidation of MWNTs by using wet chemical [1][2][3][4][5][6][7][8][9], photo oxidation [10][11][12][13], gas phase treatment [13], and oxygen plasma [10] method is a basic technique for purification and also improvement of the chemical reactivity of the MWNTs.…”

Section: Introductionmentioning

confidence: 99%

“…At both methods, the nitric acid opens the end caps of MWNTs, creates the carboxylic groups at the open ends and the side wall of MWNTs, also introduces the damage on the walls of MWNTs, and even can cut the MWNTs into short of pieces [5,20]. So the oxidation condition of MWNTs should be chosen carefully to avoid losing the valuable materials, and introducing further functional groups on the surface of MWNTs.…”

Section: Introductionmentioning

confidence: 99%

A study on the dependence of structure of multi-walled carbon nanotubes on acid treatment

et al. 2015

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In the current research, the role of both concentrated nitric acid and ultrasound waves on oxidation of multi-walled carbon nanotubes (MWNTs) was studied. The functionalized MWCNTs were characterized by transmission electron microscopy (TEM), thermogravimetric analyzer, and Fourier transform infrared spectroscopy (FTIR) techniques. It was found that desirable modifications to MWNTs occurred after acid treatment. Carboxylic acid groups were appeared on the side surfaces of MWNTs. FTIR presented the formation of oxygen-containing groups such as C=O and COOH after modification by concentrated nitric acid. The TEM images showed that the aspect ratio of opened MWCNTs was controlled by both ultrasonic waves and acid treatment time. It was also found that the exposure of about 4 h in nitric acid led to the highest removal of the impurities with the least destructive effect.

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“…Many commercial carbon nanotube samples have been post-processed to reduce metal and/or amorphous carbon, and to increase the nanotube fraction, but even these "purified" samples typically contain significant quantities (1.2-14.3%) of residual metal [1,2]. Nanotube purification technologies continue to improve [3][4][5][6][7][8][9], but deep purification can damage tube structure [10][11][12] and for the foreseeable future, most CNT samples will contain metals.…”

Section: Introductionmentioning

confidence: 99%

Targeted removal of bioavailable metal as a detoxification strategy for carbon nanotubes

Liu

Guo

Morris

et al. 2008

Carbon

124

110

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There is substantial evidence for toxicity and/or carcinogenicity upon inhalation of pure transition metals in fine particulate form. Carbon nanotube catalyst residues may trigger similar metal-mediated toxicity, but only if the metal is bioavailable and not fully encapsulated within fluid-protective carbon shells. Recent studies have documented the presence of bioavailable iron and nickel in a variety of commercial as-produced and vendor "purified" nanotubes, and the present article examines techniques to avoid or remove this bioavailable metal. First, data are presented on the mechanisms potentially responsible for free metal in "purified" samples, including kinetic limitations during metal dissolution, the re-deposition or adsorption of metal on nanotube outer surfaces, and carbon shell damage during last-step oxidation or one-pot purification. Optimized acid treatment protocols are presented for targeting the free metal, considering the effects of acid strength, composition, time, and conditions for post-treatment water washing. Finally, after optimized acid treatment, it is shown that the remaining, non-bioavailable (encapsulated) metal persists in a stable and biologically unavailable form up to two months in an in vitro biopersistence assay, suggesting that simple removal of bioavailable (free) metal is a promising strategy for reducing nanotube health risks.

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Nitric Acid Purification of Single-Walled Carbon Nanotubes

Cited by 498 publications

References 34 publications

Photophysics of Individual Single-Walled Carbon Nanotubes

Photophysics of Individual Single-Walled Carbon Nanotubes

A study on the dependence of structure of multi-walled carbon nanotubes on acid treatment

Targeted removal of bioavailable metal as a detoxification strategy for carbon nanotubes

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