Effective Nondestructive Purification of Single-Walled Carbon

Feb 14, 2014 - high-speed centrifugation of water-dispersed SWCNTs using the photo- reactive dispersant we previously investigated. SWCNTs wrapped wit...
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Effective Nondestructive Purification of Single-Walled Carbon Nanotubes Based on High-Speed Centrifugation with a Photochemically Removable Dispersant Yoko Matsuzawa,* Yuko Takada, Tetsuya Kodaira, Hideyuki Kihara, Hiromichi Kataura, and Masaru Yoshida* Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5-2, 1-1-1 Higashi, Tsukuba 305-8565, Japan S Supporting Information *

ABSTRACT: A purification method for raw single-walled carbon nanotubes (SWCNTs) without damage to their intrinsic structures has been desired in many applications. We investigated the purification of SWCNTs based on high-speed centrifugation of water-dispersed SWCNTs using the photoreactive dispersant we previously investigated. SWCNTs wrapped with the dispersant were separated from impurities, such as an amorphous carbon and metal particles by centrifugation, similarly to conventional physical purification using surfactants. In contrast to general surfactants that form micelles to disperse SWCNTs in aqueous solutions, the photoreactive dispersant did not form micelles. Therefore, an excess amount of the dispersant, which did not adsorb onto the SWCNT surfaces, was removable by dialysis of the supernatant. Since the amount of the dispersant was minimized by dialysis, we tuned the UV-irradiation time to eliminate the dispersibility of SWCNTs in water to as low a value as ∼2 h. The SWCNT precipitates were collected, and their chemical and structural purity were evaluated using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and resonance Raman spectroscopy. It was found that present methods combining high-speed centrifugation and photoreactive dispersant provided an effective procedure to purify SWCNTs without any apparent changes to their intrinsic properties.

1. INTRODUCTION Single-walled carbon nanotubes (SWCNTs) have attracted a great deal of attention as a result of their various applications, including nanoscale transistors, supercapacitors, and gas sensors.1 However, raw SWCNTs, for example, prepared by the HiPco method contain a substantial amount of impurities such as metal catalysts and carbonaceous impurities, which adversely affect practical applications of SWCNTs.2 Therefore, intensive studies have focused on the purification of SWCNTs, and a number of purification methods have actually been developed.3,4 Purification procedures can be mainly classified into two categories of methods: one involves directly destroying impurities using a strong acid treatment,5 while the other involves the separation of SWCNTs from impurities by a combination of CNT dispersants and traditional purification methods such as centrifugation,6−12 filtration,13−15 and chromatography.16−19 Although acid treatment can effectively purify close to 98%, the surface structures of SWCNTs are unavoidably damaged during the highly active chemical processes. In contrast, physical separation methods using dispersants can maintain the intrinsic structure of SWCNTs and thus are superior to acid treatments on this point. The separation methods are mostly performed in solution. Therefore, the suitable selection of dispersants is © 2014 American Chemical Society

significantly important to improve the purification efficiency.20,21 However, dispersants are likely to remain on the SWCNT surfaces even after separation from the impurities, and the attached dispersants have a harmful influence on SWCNT performance as a form of incidental impurities. Since it has been known that useful dispersants tend to adsorb tightly onto the SWCNT surface, repetitive washing using various solvents,22 overnight soaking in suitable solvents, and annealing in an oven at 350 °C have been used to remove dispersants.23 Recently, a number of stimuli-responsive dispersants have been reported to possess the ability to tune the dispersibility of the SWCNTs. For example, pH-induced structural changes of a metal complex used as a dispersant are used to control adhesion and desorption of the dispersant molecules on the SWCNT surfaces.24 Conformational changes of polymers and oligomers induced by temperature25 and polarity26 of the solvent have been developed to tune the affinity of the polymers for the SWCNTs, resulting in controlled dispersibility. Decomposition of biopolymers based on RNA using an enzyme treatment27 and hydrolysis of natural polymers28 have also been used to Received: December 6, 2013 Revised: February 13, 2014 Published: February 14, 2014 5013

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Figure 1. Chemical structures of the photoresponsive dispersant and schematic diagram of dispersibility change of SWCNTs by photoirradiation.

of the dispersion. Second, in order to reduce the photoreaction time to induce precipitation, we attempted dialysis of the supernatant before photoirradiation to remove any excess amount of free dispersants, which are likely to act as a molecular filter blocking penetration of light. Finally, the physical characteristics of the SWCNTs obtained by photoinduced precipitation are described with respect to the analysis results of scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Raman spectroscopy.

precipitate SWCNTs by causing the loss of their solubility. Photoinduced dispersibility tuning of SWCNTs has also been studied using the photoisomerization of azo-dendrimer surfactant29 and photocleaving of a malachite-green-substituted polymeric surfactant,30 through the use of which the affinity for interaction between the dispersants and the SWCNT surfaces is changed by photoreactions. However, to the best of our knowledge, a detailed analysis of precipitated SWCNTs to evaluate the possible application of such stimuli-responsive dispersants as a practical purification method for SWCNTs has not been well investigated. We have also focused on stimuli-responsive affinity changes toward SWCNT based on photoreactive dispersants to obtain dispersant-free SWCNTs by the photochemical detachment of dispersant after the separation procedure from impurities. Herein, we describe a novel purification procedure that is a combination of high-speed centrifugation (28500g) and the photoreaction of the photofunctional dispersant we have previously reported.31 As shown in Figure 1, the rigid and nearly planar structure of molecule 1 enables the dispersant to interact with the SWCNTs via π−π interactions, resulting in the stable dispersion of the SWCNTs without the occurrence of bundling. In contrast, the photocyclized product 2, which possesses a bent structure, is not favorable for π−π interactions with the SWCNTs. Such a drastic change in the molecular structure of the dispersant triggered by photoreaction has a strong effect on the affinity between the dispersant and the SWCNT surfaces, and thus we achieved photochemical on−off switching of the dispersibility of the SWCNTs. However, we only observed the precipitation of SWCNTs after photoirradiation, and the degree of dispersant detachment from the SWCNTs has not been analyzed. In other words, the chemical composition of the precipitated SWCNTs has been unclear so far. Furthermore, photoirradiation took a very long time (10 h) to attain complete precipitation. We thus focused on three topics in this study as mentioned below. First, the dispersibility of the photoresponsive dispersant was evaluated using resonance Raman spectroscopy to compare it with the dispersibilities of deoxycholate sodium salts (DOC). Although DOC has been well-known as one of the most excellent dispersants for SWCNTs,21,32 it takes a lot of effort to remove them from the SWCNT surfaces after the preparation

2. EXPERIMENTAL SECTION 2.1. Materials. The purification procedure for SWCNTs is shown in Figure 2. Crude SWCNTs (Nano Integris) synthesized by high-pressure CO conversion (HiPco) were used as the starting material. Deoxycholate sodium salt (DOC) was purchased from Sigma and used without further purification. The photofunctional dispersant (1) was synthesized by a previously described procedure.31 2.2. Sample Preparation. 3 mg of 1 was dissolved in 3 mL of pure deionized water (ELGA Purelab Ultra) in a glass vial. The solution was then sonicated (SHARP UT-105, 80 W, 35 kHz) at room temperature for 1 h. Next, 1 mg of the HiPco SWCNTs was added to the aqueous solution of 1. The mixture was then sonicated again at room temperature for 3 h, followed by centrifugation using a centrifuge (Eppendorf 5417R) equipped with an angle-rotor (Eppendorf FA-45-24-11) at 16 400 rpm (28500g) for 3 h. The supernatant was decanted and transferred to a dialysis tube (SPECTRUM, Spectra/Por(R)7, cutoff MW of 1000) to remove the excess amount of 1 from the dispersion. The tube filled with the supernatant of the 1/ SWCNT system was put into a glass beaker with 3 L of pure water. After stirring overnight, we obtained the 1/SWCNT system without an excess amount of dispersant 1. For comparison of the dispersibility of the 1/SWCNT system to that of the DOC/SWCNT system, the dispersions were prepared using a horn-type ultrasonic homogenizer (Branson, Sonifire 250D, 20 W, 4 h) and a centrifuge (Hitachi, Himac CS100GXL) equipped with an angle-rotor (Hitachi, S58A) at 50 000 rpm (215000g) for 30 min. Approximately 2 mg of SWCNTs was collected from 8 mg of raw-SWCNTs. The aqueous dispersions of 1/SWCNTs were added to quartz cells and irradiated by an LED light source (365 nm, 100 5014

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membrane filter by vacuum filtration (Advantec 0.1 μm PTFE). The filtered materials were washed several times with water and dried in vacuo. 2.3. Characterization. Raman spectra were measured in backscattering geometry using a single monochromator (Horiba HR 640) equipped with a charge coupled device (CCD, ANDOR DU401-DV-120). The sample was excited by a He−Ne laser with excitation at 633 nm (6 mW). To avoid laser heating, the laser beam was focused onto the sample with a cylindrical lends to produce a linear beam spot. TGA was carried out with a RIGAKU EVO II, series TG8120, under the following conditions: 5 °C/min ramp rates from room temperature to 800 °C, with a dried air flow rate of 50 mL/ min. Scanning electron microscopy (SEM) measurements were carried out with a Hitachi S-4300 operating at approximately 3−5 kV. The morphology and elemental analysis of the residues after TGA measurements was performed using Hitachi S800 SEM equipped with an energy-dispersed spectroscope (EDS, Kevex 3600-0398). Samples for the SEM analysis were sputter-coated with an approximately 1 nm thick layer of platinum. UV−vis−NIR spectra of SWCNT solutions were recorded with a JASCO V-670 spectrometer using a handmade sandwich quartz cell with a 0.5 mm silicon spacer.

3. RESULTS AND DISCUSSION First, the isolation and solubilization degrees of the SWCNT using the photofunctional dispersant 1 were evaluated by comparison with DOC, which has been known to be one of the most efficient dispersants. Various methods, such as absorption, fluorescence, and Raman spectroscopy, have been used to characterize the solubilization and debundling of SWCNTs. Among these techniques, we applied resonance Raman spectroscopy because the G-band Raman intensity, which is associated with the tangential stretching mode of SWCNTs at 1593 cm−1, corresponds to the concentration of freely isolated SWCNTs.33 Raman spectra of the 1/SWCNT dispersion and the DOC/SWCNT dispersion are shown in Figure 3. Radial breathing mode (RBM) Raman spectra of these two systems before and after centrifugation are also shown in the insets. The RBM spectra indicate clearly that the diameter distribution of SWCNTs was not changed through centrifugation because the RBM spectra correlated with the diameter of SWCNTs.34 These results suggest that the resonance condition did not change, and thus the G-band Raman intensity can be used to evaluate the concentration of isolated SWCNTs in a solvent.33 As shown in Figure 3a, the G-band Raman intensity of the 1/ SWCNT supernatant was 1.9 times larger than that of the

Figure 2. Schematic flowchart of SWCNT purification.

mW/cm2) for 2 h. The fluids were magnetically stirred (2000 rpm, Variomag Magnetic Stirrers, Thermo Electron Corporation) during the irradiation process. After the completion of the photochemical reaction, the SWCNTs were precipitated from the aqueous solution. The sediments were collected on a membrane filter (Millipore, pore size 0.2 μm PTFE) by vacuum filtration, and the filtered materials were washed several times with deionized water and dried in vacuo. The precipitated SWCNTs were redispersed in an aqueous solution of 1 (0.1 wt %). The mixture was then sonicated at room temperature for 1 h, followed by centrifugation (KUBOTA 2410) using a centrifuge equipped with an anglerotor (KUBOTA RS-240) at 2000 rpm (635g) for 5 min. For comparison, the 1/SWCNT complex dissolved in the supernatant was also collected, without photoirradiation, on a

Figure 3. G- and D-band Raman spectra of SWCNTs in dispersions before (dotted-black) and after (solid-red) ultracentrifugation. Insets show RBM Raman spectra. (a) 1/SWCNTs system and (b) DOC/SWCNT system. 5015

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Figure 4. UV−vis−NIR absorption spectra of the 1/SWCNT dispersion before (dashed line) and after (solid line) dialysis in the UV−vis (a) and the vis−NIR regions (b). The inset shows the UV−vis transmittance spectra.

precipitation in our previous study.31 In the present study, with dialysis the photoinduced precipitation of SWCNTs finished within 2 h because light is able to penetrate the 1/SWCNT dispersion more effectively than in the previous study. Figure 5 displays typical SEM images of the raw SWCNTs as a starting material and the photochemically purified sample as a final adduct. Electron microscopic measurements can directly evaluate the amount of amorphous carbon, metal particles, and defects in the SWCNT samples.2 Not only the SWCNT

dispersion not subjected to ultracentrifugation. For the DOC/ SWCNT system, G-band Raman intensity increased 1.8 times after ultracentrifugation (Figure 3b). It can be thus considered that the photoresponsive dispersant 1 acted effectively to isolate the bundles of SWCNTs, causing them to disperse in water as well as DOC. On the basis of these results, we subsequently investigated the detachment of dispersant upon photoirradiation, required to obtain pure and dispersant freeSWCNTs. In our previous study, we reported that dispersant 1 did not form micelles in SWCNT dispersions, judging from a concentration-dependent nuclear magnetic resonance (NMR) study.31 In this study, we actually found that in this purification procedure based on the photodetachment of the dispersant, the dialysis of the 1/SWCNT dispersion to remove an excess amount of dispersant prior to irradiation was workable and quite important. Figure 4 shows the ultraviolet−visible−nearinfrared (UV−vis−NIR) spectra before and after the dialysis. It has been observed that the absorption band attributed to the π−π* transition of 1 significantly decreased after the dialysis procedure. It is quite interesting that the absorption peaks of the SWCNTs were mostly unchanged even after dialysis (Figure 4b), showing no formation of SWCNT aggregates by the dialysis. The results showed that the dispersibility of the SWCNTs was maintained through the removal of an excess amount of 1. These results suggest that the free dispersant molecules 1 that do not adsorb onto the SWCNTs were removable from the 1/SWCNT dispersion by dialysis. In the case of sodium dodecyl sulfate (SDS) and DOC, 2 wt % of aqueous solution (50 mL) is necessary to disperse 50 mg of raw SWCNTs.12 Because the formation of micelles is crucial to disperse SWCNTs, the concentration of the surfactants must be maintained above critical micelle concentration. However, in this case, it is noteworthy that 50 mL of aqueous solution with 20 times lower concentration of 1 (∼0.1 wt %) than that of DOC can disperse 50 mg of raw SWCNTs. Since dispersant 1 adsorbed directly onto the surfaces of debundled SWCNTs without micelle formation, the excess amount of dispersant 1 can be removed from the dispersion by dialysis. It is a useful feature that the amount of dispersants can be reduced for dispersant 1 compared to general surfactants. As shown in the inset of Figure 4a, the transmittance near 365 nm increased after dialysis, and the photoreaction of 1 effectively progressed as a result of suppression of the filter effect of the free dispersants 1. Because the incident light was blocked by the filter effect of the free dispersant having large ε365 (∼7 × 104 L mol−1 cm−1), it took over 10 h to complete photoinduced

Figure 5. SEM images of (a) raw SWCNTs and (b) purified SWCNTs. 5016

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TGA measurements carried out at least 3 times for each samples to evaluate reproducibility. Dispersant 1 itself decomposed in two stages. Compound 1 has a benzyl quaternary ammonium component, and it has been reported that the pyrolysis of such benzyl quaternary ammonium salts usually take place at approximately 250−300 °C.35−37 The origin of the first decomposition would be, therefore, the presence of tertiary amine and alkyl halide formed from the reactions between the chloride anion and the quaternary ammonium cation, as reported elsewhere.35−37 From the TGA results, 30% of the weight loss was observed at 250 °C. Since the molecular weight of N,N-dimethylbutylamine is 101 amu, the weight percentage of the amines (101 amu × 2) to that of 1 (MW = 716) was estimated to be 30%. This result was in line with our consideration of the first thermal decomposition, producing tertiary amines and the corresponding alkyl halides (Scheme 1). The residue was then completely burned at approximately 550 °C. The data from the crude SWCNTs (HiPco) indicate a slight increase in weight at approximately 300 °C, probably as a result of the oxidation of metal catalysts (Figure 7c) existing as an impurity, similar to the results in the literature.3 After that, weight loss begins at 300 °C. The SWCNTs and carbonaceous fractions were mostly gone by oxidation below 400 °C. The remaining materials above 400 °C were the oxidized metals (approximately 45%), as already pointed out in the literature.3 The TGA results for 1/SWCNTs obtained by the filtration of the supernatant after high-speed centrifugation showed that the thermal decomposition occurred via three continuous stages (Figure 7b). Since the endothermic peak at the first weight loss was observed in the differential thermal analysis (DTA) curves, the weight loss below 100 °C would be attributed to the detachment of water molecules, i.e., thermal dehydration.38 The second and small (14 wt %) weight loss at 250 °C is likely to originate from the initial pyrolysis of dispersant 1, similar to the result for pure dispersant 1 shown in Figure 7a. The third weight loss at 400 °C is likely attributable to the burning of the SWCNTs and the residual dispersant. The metal content calculated from the TGA results indicates a decrease from ∼45% in the crude SWCNTs to ∼10% in the 1/ SWCNT system. Since the weight loss at 250 °C was attributed to thermal decomposition into the volatile amine derivative cleaved from 1 (30 wt % of 1), the weight ratio of 1 to SWCNTs was estimated to be 1/SWCNTs = 0.56/0.44. On the assumption that all of the free dispersant 1 would be removed by dialysis, one can roughly calculate, using the weight ratio and a MW of 1, that the molar ratio for molecule 1 and elemental carbon of SWCNT in the 1/SWCNT system is 1/C = 1/47.

bundles but also a number of particles that could be derived from amorphous carbon or metal particles were observed in Figure 5a. Alternatively, SWCNTs without any particles of amorphous carbon and metals after the centrifugation and the phototreatment are shown in Figure 5b. The purity of the SWCNTs was enhanced by the photochemical purification process insofar as we could confirm in the SEM images. Raman spectroscopy was again used to determine whether any structural damage to the SWCNTs was induced during the entire purification process (Figure 6). The precipitate from

Figure 6. Raman spectra of purified SWCNTs. The inset shows Raman spectra of the 1/SWCNT dispersion prior to UV irradiation.

photochemical purification was easily redispersed within 1 h of sonication in an aqueous solution of 1 (0.1 wt %), and the dispersion was also subjected to UV−vis−NIR spectroscopy (see Supporting Information). We observed that the UV−vis− NIR spectrum was identical to that of the dispersion before photoirradiation, showing the photoreaction did not induce any spectroscopic changes in the SWCNTs. The inset spectrum displays the Raman spectra of the 1/SWCNT dispersion prior to UV irradiation. It is well-known that the intensity ratio of the G band (1590 cm−1) and D band (1310 cm−1) is substantially related to the structural quality of SWCNTs. As shown in Figure 6, the G/D intensity ratio of the purified SWCNTs (approximately 32) was nearly unchanged compared to the 1/ SWCNT dispersion (approximately 30) prior to UV irradiation. An unchanged G/D intensity ratio clearly confirmed that the photoinduced peeling off process of 1 did not cause structural damage to the SWCNTs. Next, we analyzed the thermal properties of dispersant 1, crude SWCNTs, 1/SWCNT hybrid, and purified SWCNT obtained by the photochemical method in order to discuss the purity of the materials from the chemical viewpoint. The TGA curve of 1 under an air flow condition is shown in Figure 7a.

Figure 7. TGA results for (a) the dispersant 1, (b) the 1/SWCNT system, and (c) raw SWCNTs (dashed line) and purified-SWCNTs (solid line). Scheme 1 shows the possible pyrolysis of compound 1. 5017

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Scheme 1

Conventionally, the physical purification of SWCNTs using a dispersant has been only the removal of impurities, where the dispersants still remains on the sidewalls of SWCNTs. The present purification procedure based on the combination of precentrifugation and postphotoreaction of the photoreactive dispersant provide us purified SWCNTs which contain less than 1 wt % of dispersants and retain their intrinsic physical properties. We believe this study shows, for the first time, the promising possibility of stimuli-responsive dispersants for the practical purification of raw SWCNTs. Although the purified SWCNTs in this study still contained almost 10% metal impurities based on the TGA and EDS data, we consider that a relatively weak acid treatment would be applicable for SWCNTs purified by our present nondestructive method, due to the significant reduction of the amount of impurities. Therefore, optimization of the photochemical purification procedure should be an essential protocol in research on the application of CNTs in a variety of electronic devices.

For the TGA curve of the purified SWCNTs obtained by the photochemical procedure (Figure 7c), the weight decline temperature shift to a higher number was observed as a result of removing the metal catalyst and amorphous carbons in a similar manner to that in the former report.39 It is noteworthy that the weight decline occurs through only one stepwise weight loss for the purified SWCNTs. The results indicated that molecules of 1 could be peeled off from the SWCNT surfaces as a result of the photoreaction induced by the exposure to UV light, as conceptually suggested in our previous study.31 The SWCNTs were completely burned at 500 °C. The remaining materials were oxidized metal, which was ∼10% of the starting material. Actually, judging from the energy dispersive spectroscopy (EDS), the remaining materials were determined to be metallic impurities (see Supporting Information). The iron residue can be considered to be the main contents of the nanoparticles, which are encased in thin carbon shells and tightly adhere to the terminal and the sidewall of SWCNTs.40,41 Unfortunately, the stuck metal particles hardly remove from the SWCNT surfaces by applying ultrahigh centrifugation.12 According to the TG-DTA results, rawSWCNTs used in this study contain 45 wt % of metals. The present purification procedure provide us 2 mg of nondestructive and relatively pure-SWCNT with 10% metal impurities from 8 mg of raw-SWCNTs. Therefore, the formal yield of the SWCNTs by the photochemical purification in this study is approximately 23% (1.8 mg/8 mg). From the perspective of the purification yield, the present efficiency to remove impurities is comparable to that of refluxing in acids, air oxidation, and annealing methods, which are likely to destroy the structure of SWCNTs.42 The advantage of the present method compared to the acidic methods, therefore, is obviously the nondestructive nature for the SWCNTs confirmed by the spectroscopic analyses.

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ASSOCIATED CONTENT

S Supporting Information *

UV−vis−NIR spectra of 1/SWCNT dispersion in D2O before (a) and after (b) purification, SEM images of the residual materials and corresponding EDS spectrum; Figures S1 and S2. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.M.). *E-mail [email protected] (M.Y.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Adaptable and Seamless Technology Transfer Program through Target-driven R&D AS242Z03940J (A-STEP), Japan Science and Technology Agency (JST).

4. CONCLUSION By applying the combination procedure, high-speed centrifugation using the dispersant with not only an efficient debundling behavior but also photoresponsiveness, we have demonstrated a new purification procedure for SWCNTs to rid them of common impurities such as amorphous carbon and metal particles without destroying the intrinsic SWCNT structures. The photofunctional dispersant 1 was highly effective for dispersing SWCNTs into water as well as DOC. Upon UV irradiation of the supernatant of 1/SWCNT, purified SWCNTs were collected as a precipitate. Furthermore, we reduced the reaction time to induce precipitation from 10 to 2 h in comparison with our previous result by the dialysis treatment before the photoreaction to remove an excess amount of dispersant 1 resulting in a filter effect. We also confirmed that the present method did not induce any apparent defects in the SWCNT structures by analyses with SEM as well as UV−vis−NIR and Raman spectroscopy. The possible chemical composition of the 1/SWCNT hybrid was also calculated for the first time using a comparison of TGA results between the 1/SWCNT hybrid and the purified SWCNTs.

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REFERENCES

(1) Jariwala, D.; Sangwan, V. K.; Lauhon, L. J.; Marks, T. J.; Hersam, M. C. Carbon Nanomaterials for Electronics, Optoelectronics, Photovoltaics, and Sensing. Chem. Soc. Rev. 2013, 42, 2824−2860. (2) Nikolaev, P.; Bronikowski, M. J.; Bradley, R. K.; Rohmund, F.; Colbert, D. T.; Smith, K. A.; Smalley, R. E. Gas-Phase Catalytic Growth of Single-Walled Carbon Nanotubes from Carbon Monoxide. Chem. Phys. Lett. 1999, 313, 91−97. (3) Hou, P. X.; Liu, C.; Cheng, H. M. Purification of Carbon Nanotubes. Carbon 2008, 46, 2003−2025. (4) Pillai, S. K.; Ray, S. S.; Moodley, M. Purification of Single-Walled Carbon Nanotubes. J. Nanosci. Nanotechnol. 2007, 7, 3011−3047. (5) Hu, H.; Zhao, B.; Itkis, M. E.; Haddon, R. C. Nitric Acid Purification of Single-Walled Carbon Nanotubes. J. Phys. Chem. B 2003, 107, 13838−13842. (6) O’Connell, M. J.; Bachilo, S. M.; Huffman, C. B.; Moore, V. C.; Strano, M. S.; Haroz, E. H.; Rialon, K. L.; Boul, P. J.; Noon, W. H.;

5018

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Kittrell, C.; et al. Band Gap Fluorescence from Individual SingleWalled Carbon Nanotubes. Science 2002, 297, 593−596. (7) Yu, A. P.; Bekyarova, E.; Itkis, M. E.; Fakhrutdinov, D.; Webster, R.; Haddon, R. C. Application of Centrifugation to the Large-Scale Purification of Electric Arc-Produced Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2006, 128, 9902−9908. (8) Hu, H.; Yu, A. P.; Kim, E.; Zhao, B.; Itkis, M. E.; Bekyarova, E.; Haddon, R. C. Influence of the Zeta Potential on the Dispersability and Purification of Single-Walled Carbon Nanotubes. J. Phys. Chem. B 2005, 109, 11520−11524. (9) Lian, Y.; Maeda, Y.; Wakahara, T.; Akasaka, T.; Kazaoui, S.; Minami, N.; Shimizu, T.; Choi, N.; Tokumoto, H. Nondestructive and High-Recovery-Yield Purification of Single-Walled Carbon Nanotubes by Chemical Functionalization. J. Phys. Chem. B 2004, 108, 8848− 8854. (10) Takahashi, T.; Tsunoda, K.; Yajima, H.; Ishii, T. Purification of Single Wall Carbon Nanotubes Using Gelatin. Jpn. J. Appl. Phys. 2004, 43, 1227−1230. (11) Bandow, S.; Asaka, S.; Zhao, X.; Ando, Y. Purification and Magnetic Properties of Carbon Nanotubes. Appl. Phys. A: Mater. Sci. Process. 1998, 67, 23−27. (12) Nishide, D.; Miyata, Y.; Yanagi, K.; Tanaka, T.; Kataura, H. Effective Separation of Carbon Nanotubes and Metal Particles from Pristine Raw Soot by Ultracentrifugation. Jpn. J. Appl. Phys. 2009, 48, 015004. (13) Bandow, S.; Rao, A. M.; Williams, K. A.; Thess, A.; Smalley, R. E.; Eklund, P. C. Purification of Single-Wall Carbon Nanotubes by Microfiltration. J. Phys. Chem. B 1997, 101, 8839−8842. (14) Bonard, J. M.; Stora, T.; Salvetat, J. P.; Maier, F.; Stockli, T.; Duschl, C.; Forro, L.; deHeer, W. A.; Chatelain, A. Purification and Size-Selection of Carbon Nanotubes. Adv. Mater. 1997, 9, 827−831. (15) Shelimov, K. B.; Esenaliev, R. O.; Rinzler, A. G.; Huffman, C. B.; Smalley, R. E. Purification of Single-Wall Carbon Nanotubes by Ultrasonically Assisted Filtration. Chem. Phys. Lett. 1998, 282, 429− 434. (16) Duesberg, G. S.; Muster, J.; Krstic, V.; Burghard, M.; Roth, S. Chromatographic Size Separation of Single-Wall Carbon Nanotubes. Appl. Phys. A: Mater. Sci. Process. 1998, 67, 117−119. (17) Holzinger, M.; Hirsch, A.; Bernier, P.; Duesberg, G. S.; Burghard, M. A New Purification Method for Single-Wall Carbon Nanotubes (SWNTs). Appl. Phys. A: Mater. Sci. Process. 2000, 70, 599−602. (18) Niyogi, S.; Hu, H.; Hamon, M. A.; Bhowmik, P.; Zhao, B.; Rozenzhak, S. M.; Chen, J.; Itkis, M. E.; Meier, M. S.; Haddon, R. C. Chromatographic Purification of Soluble Single-Walled Carbon Nanotubes (s-SWNTs). J. Am. Chem. Soc. 2001, 123, 733−734. (19) Zhao, B.; Hu, H.; Niyogi, S.; Itkis, M. E.; Hamon, M. A.; Bhowmik, P.; Meier, M. S.; Haddon, R. C. Chromatographic Purification and Properties of Soluble Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2001, 123, 11673−11677. (20) Moore, V. C.; Strano, M. S.; Haroz, E. H.; Hauge, R. H.; Smalley, R. E.; Schmidt, J.; Talmon, Y. Individually Suspended SingleWalled Carbon Nanotubes in Various Surfactants. Nano Lett. 2003, 3, 1379−1382. (21) Wenseleers, W.; Vlasov, I. I.; Goovaerts, E.; Obraztsova, E. D.; Lobach, A. S.; Bouwen, A. Efficient Isolation and Solubilization of Pristine Single-Walled Nanotubes in Bile Salt Micelles. Adv. Funct. Mater. 2004, 14, 1105−1112. (22) Liu, G.; Wang, F.; Chaunchaiyakul, S.; Saito, Y.; Bauri, A. K.; Kimura, T.; Kuwahara, Y.; Komatsu, N. Simultaneous Discrimination of Diameter, Handedness, and Metallicity of Single-Walled Carbon Nanotubes with Chiral Diporphyrin Nanocalipers. J. Am. Chem. Soc. 2013, 135, 4805−4814. (23) Peng, N.; Zhang, Q.; Yuan, S. N.; Li, H.; Tian, J. Z.; Chan, L. Current Instability of Carbon Nanotube Field Effect Transistors. Nanotechnology 2007, 18, 424035. (24) Nobusawa, K.; Ikeda, A.; Kikuchi, J. I.; Kawano, S. I.; Fujita, N.; Shinkai, S. Reversible Solubilization and Precipitation of Carbon

Nanotubes through Oxidation-Reduction Reactions of a Solubilizing Agent. Angew. Chem., Int. Ed. 2008, 47, 4577−4580. (25) Wang, D.; Chen, L. W. Temperature and pH-Responsive SingleWalled Carbon Nanotube Dispersions. Nano Lett. 2007, 7, 1480− 1484. (26) Zhang, Z. X.; Che, Y. K.; Smaldone, R. A.; Xu, M. A.; Bunes, B. R.; Moore, J. S.; Zang, L. Reversible Dispersion and Release of Carbon Nanotubes Using Foldable Oligomers. J. Am. Chem. Soc. 2010, 132, 14113−14117. (27) Jeynes, J. C. G.; Mendoza, E.; Chow, D. C. S.; Watts, P. C. R.; McFadden, J.; Silva, S. R. P. Generation of Chemically Unmodified Pure Single-Walled Carbon Nanotubes by Solubilizing with RNA and Treatment with Ribonuclease A. Adv. Mater. 2006, 18, 1598−1602. (28) Takahashi, T.; Tsunoda, K.; Yajima, H.; Ishii, T. Isolation of Single-Wall Carbon Nanotube Bundles through Gelatin Wrapping and Unwrapping Processes. Chem. Lett. 2002, 31, 690−691. (29) Kordel, C.; Setaro, A.; Bluemmel, P.; Popeney, C. S.; Reich, S.; Haag, R. Controlled Reversible Debundling of Single-Walled Carbon Nanotubes by Photo-Switchable Dendritic Surfactants. Nanoscale 2012, 4, 3029−3031. (30) Chen, S.; Borrmann, H.; Huang, Y. X.; Zhang, Z. J.; Chen, H. H.; Zhao, J. T. Templated Synthesis of Mesolamellar n-Alkylamine Borophosphates. Langmuir 2008, 24, 9323−9327. (31) Matsuzawa, Y.; Kato, H.; Ohyama, H.; Nishide, D.; Kataura, H.; Yoshida, M. Photoinduced Dispersibility Tuning of Carbon Nanotubes by a Water-Soluble Stilbene as a Dispersant. Adv. Mater. 2011, 23, 3922−3925. (32) Yanagi, K.; Miyata, Y.; Kataura, H. Optical and Conductive Characteristics of Metallic Single-Wall Carbon Nanotubes with Three Basic Colors; Cyan, Magenta, and Yellow. Appl. Phys. Express 2008, 1, 034003. (33) Nishide, D.; Miyata, Y.; Yanagi, K.; Tanaka, T.; Kataura, H. PERIPUTOS: Purity Evaluated by Raman Intensity of Pristine and Ultracentrifuged Topping of Single-Wall Carbon Nanotubes. Phys. Status Solidi B 2009, 246, 2728−2731. (34) Saito, R.; Takeya, T.; Kimura, T.; Dresselhaus, G.; Dresselhaus, M. S. Raman Intensity of Single-Wall Carbon Nanotubes. Phys. Rev. B 1998, 57, 4145−4153. (35) Ono, Y.; Hayama, Y.; Tanaka, S. Analysis of Quaternary Ammonium-Salts by Gas-Chromatography and GC-MS Method Using Pyrolysis Technique. Bunseki Kagaku 1976, 25, 736−742. (36) Haskins, N. J.; Mitchell, R. Thermal-Degradation of Some Benzyltrialkylammonium Salts Using Pyrolysis-Gas Chromatography Mass-Spectrometry. Analyst 1991, 116, 901−903. (37) Karna, M.; Lahtinen, M.; Valkonen, J. Preparation and Characterization of New Low Melting Ammonium-Based Ionic Liquids with Ether Functionality. J. Mol. Struct. 2009, 922, 64−76. (38) Kodaira, T.; Ikeda, T. Characters of the Tetramethylammonium Ion in ZK-4 Zeolites Depending on Their Si/Al Ratios. J. Phys. Chem. C 2010, 114, 12885−12895. (39) Chiang, I. W.; Brinson, B. E.; Smalley, R. E.; Margrave, J. L.; Hauge, R. H. Purification and Characterization of Single-Wall Carbon Nanotubes. J. Phys. Chem. B 2001, 105, 1157−1161. (40) Chiang, I. W.; Brinson, B. E.; Huang, A. Y.; Willis, P. A.; Bronikowski, M. J.; Margrave, J. L.; Smalley, R. E.; Hauge, R. H. Purification and Characterization of Single-Wall Carbon Nanotubes (SWNTs) Obtained from the Gas-Phase Decomposition of CO (HiPco process). J. Phys. Chem. B 2001, 105, 8297−8301. (41) Park, T. J.; Banerjee, S.; Hemraj-Benny, T.; Wong, S. S. Purification Strategies and Purity Visualization Techniques for SingleWalled Carbon Nanotubes. J. Mater. Chem. 2006, 16, 141−154. (42) Martinez, M. T.; Callejas, M. A.; Benito, A. M.; Cochet, M.; Seeger, T.; Anson, A.; Schreiber, J.; Gordon, C.; Marhic, C.; Chauvet, O.; et al. Modifications of Single-Wall Carbon Nanotubes upon Oxidative Purification Treatments. Nanotechnology 2003, 14, 691−695.

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