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Journal of Nanotechnology
Volume 2012 (2012), Article ID 376160, 5 pages
http://dx.doi.org/10.1155/2012/376160
Research Article

Synthesis of Nickel-Encapsulated Carbon Nanocapsules and Cup-Stacked-Type Carbon Nanotubes via Nickel-Doped Fullerene Nanowhiskers

1Institute of Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8753, Japan
2Fullerene Engineering Group, Materials Processing Unit, National Institute for Materials Science, Namiki, Tsukuba, Ibaraki 305-0044, Japan

Received 12 July 2011; Revised 25 September 2011; Accepted 26 September 2011

Academic Editor: Zheng Hu

Copyright © 2012 Tokushi Kizuka et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Nickel- (Ni) doped C60 nanowhiskers (NWs) were synthesized by a liquid-liquid interfacial precipitation method using a C60-saturated toluene solution and isopropanol with Ni nitrate hexahydrate Ni(NO3)2·6H2O. By varying the heating temperature of Ni-doped C60 NWs, two types of one-dimensional carbon nanostructures were produced. By heating the NWs at 973 and 1173 K, carbon nanocapsules (CNCs) that encapsulated Ni nanoparticles were produced. The Ni-encapsulated CNCs joined one dimensionally to form chain structures. Upon heating the NWs to 1373 K, cup-stacked-type carbon nanotubes were synthesized.

1. Introduction

Crystals of fullerene molecules have been synthesized by precipitation methods [113]. Such fullerene crystals show various morphologies, that is, plates, films, and rods, and the morphology can be controlled by varying the precipitation conditions. By using a liquid-liquid interfacial precipitation (LLIP) method, Miyazawa et al. have produced fullerene nanowhiskers (NWs) and nanotubes with high length-to-diameter aspect ratios [1417]. By heating fullerene NWs, carbon nanocapsules (CNCs) are produced [1822]. Using the LLIP method, Miyazawa et al. also found that fullerene NWs incorporate metal nanoparticles using C60 derivatives or metal nitrate hydrates in solutions [2326]. It is expected that the alloying of metals and CNCs can be performed using metal-doped fullerene NWs. In this study, metal-CNC structures were produced by the heating nickel- (Ni) doped C60 NWs which were synthesized by the LLIP method.

2. Method

C60 powders were dissolved in toluene to prepare a C60-saturated solution with a solubility of 2.8 g/L. Ni nitrate hexahydrate [Ni(NO3)2·6H2O] was dissolved in 2-propanol with concentrations of 0.01 M and 0.68 M (hereafter labeled as specimens A and B, resp.). The C60 toluene solution was poured into a glass vial, and the 2-propanol was then added to form a liquid-liquid interface. After the vial was maintained at 278 K for one week, the solution was filtered to extract precipitates. The precipitates were dried and heated in high vacuum at 973, 1173, and 1323 K for 1 h. Next, the specimens were dispersed on microgrids and observed by transmission electron microscopy (TEM). Thermogravimetric analyses (TGA) and differential thermal analyses (DTA) of the specimens were performed in a nitrogen flow.

3. Results and Discussion

Figure 1(a) shows a bright-field image of an as-precipitated Ni-doped C60 NW in specimen A. The diameter of this NW is 740 nm. The surfaces of the Ni-doped NWs were porous, as shown in Figure 1(b). Figure 2(a) shows a bright-field image of an as-precipitated Ni-doped C60 NW in specimen B. The diameter of this NW is 240 nm. The NWs showed undulating surfaces. Ni particles with a face-centered cubic structure were observed in the NWs, as shown in Figure 2(b).

fig1
Figure 1: (a) Bright-field image of Ni-doped C60 nanowhiskers synthesized using isopropyl alcohol with concentration of 0.01 M Ni(NO3)2·6H2O. (b) Enlarged image of (a).
fig2
Figure 2: (a) Bright-field images of Ni-doped C60 nanowhiskers synthesized using isopropyl alcohol with concentration of 0.68 M Ni(NO3)2·6H2O. The arrows indicate Ni particles in dents. (b) High-resolution image of Ni particles in the NW in (a).

The surfaces of the Ni-doped NWs in both specimens A and B were rough. The roughness increases with the Ni(NO3)2·6H2O concentration. Pure C60 NWs are surrounded by planar surfaces [1417]. Thus, we attribute the rough surfaces of the as-precipitated Ni-doped NWs to the addition of Ni(NO3)2·6H2O in 2-propanol. In particular, Ni particles were observed in the dents of Ni-doped NWs, implying that the crystal growth of the NWs was inhibited by the Ni particles. This is similar to the crystal growth of C60-derivative NWs [2325].

Figure 3 shows TGA and DTA curves of the Ni-doped NWs in specimen A and C60 bulk crystals. For C60 bulk crystals, the DTA curve starts to decrease around 773 K. On the other hand, no change is observed in the TGA curve around this temperature. This shows that the mass of the specimen remained unchanged, whereas the structure changed. The transformation from a crystalline to an amorphous configuration of C60 molecules starts at this temperature [27]. Around 1173 K, the TGA curve decreases, and a downward peak is observed in the DTA curve, which shows that an endothermic reaction occurred. Furthermore, it has been reported that sublimation of C60 molecules takes place at this temperature [27]. On the other hand, for the Ni-doped NWs, an upward peak was observed in the DTA curve around 773 K, which corresponds to an exothermic reaction. No change is observed in the TGA curve around this temperature. TEM observations showed that grain coarsening of Ni particles started near this temperature. This TEM result suggests that the upward peak around 773 K was caused by the grain coarsening of Ni particles.

fig3
Figure 3: (a) Thermogravimetric analysis curves and (b) differential thermal analysis curves of Ni-doped nanowhiskers (specimen A, solid lines) and pure C60 bulk (broken lines) in nitrogen flow.

Around 1123 K, the TGA curve decreases and the DTA curve shows a downward peak. This implies that the sublimation of C60 molecules occurred, as similarly observed in C60 bulk crystals. Note that the sublimation temperature of C60 molecules in the Ni-doped NWs is approximately 50 K lower than that in the C60 bulk crystals. From this result, we infer that Ni particles act as catalysts for the weakening of intermolecular C60 molecular bonds.

On the basis of the results of TGA and DTA, we heated the specimens to temperatures higher than 973 K and observed them by TEM. Figures 4(a) and 4(b) show bright-field and high-resolution images of specimen A after heating at 973 K, respectively. Ni-encapsulated CNCs are formed by this heat treatment. The diameter of the CNCs ranged from 12 to 51 nm. The diameter of the encapsulated Ni particles ranged from 8 to 33 nm. A portion of the CNCs aligned one dimensionally to form chain structures, as shown in Figure 4(c). Such chain structures have also been produced by arc discharge [28, 29]. As shown in Figure 4(b), Ni particles were attached on the tips of the chains, indicating that the chain structures were produced by the cycles of the precipitation of graphene shells around Ni particles and the movement of the Ni particles. Note that in Figure 4(b), the Ni particle protrudes from the center of the hollow region of the CNC. This state corresponds to the movement of the Ni particle from the precipitated graphene shell.

fig4
Figure 4: (a) Bright-field images of Ni-encapsulated carbon nanocapsules prepared by heating Ni-doped C60 nanowhiskers (specimen A) at 973 K. (b) High-resolution image of Ni-encapsulated carbon nanocapsule. (c) High-resolution image of chain of Ni-encapsulated carbon nanocapsules.

Figures 5(a) and 5(b) show bright-field and high-resolution images of specimen B after heating it at 1173 K. Ni-encapsulated CNCs and their chain structures were formed. The formation rate of CNC chains in this specimen was higher than that in specimen A owing to a higher concentration of Ni particles.

fig5
Figure 5: (a) Bright-field images of Ni-encapsulated carbon nanocapsules prepared by heating Ni-doped C60 nanowhiskers (specimen B) at 1173 K. The nanocapsules form chain structures. (b) High-resolution image of the chain of Ni-encapsulated carbon nanocapsules.

By heating Ni-doped C60 NWs in specimen B to 1323 K, cup-stacked-type carbon nanotubes (CNTs) were produced, as shown in Figure 6. Ni particles were attached to the tip of CNTs, and the graphene layers were aligned parallel to the surfaces of Ni particles. Thus, CNTs were produced by the continuous precipitation of graphene cones and the continuous movement of Ni particles. However, for CNC formation, the movement of Ni particles and the precipitation of graphene shells are intermittent.

fig6
Figure 6: (a) Cup-stacked-type carbon nanotube synthesized by heating Ni-doped C60 nanowhiskers (specimen B) at 1323 K. (b) High-resolution image of the cup-stacked-type carbon nanotube depicted in (a).

In this experiment, cup-stacked-type CNTs were produced at the highest temperature (1373 K). As observed in Figures 4(b) and 5(a), the Ni particles in the specimens heated at temperatures lower than 1173 K formed spherical shapes, whereas Ni particles in the specimens heated to 1373 K formed clear crystal habits. At higher temperatures, the metal particles show more stable shapes surrounded by crystal planes with lower surface energies. Cup-stacked-type CNTs are formed by one-directional continuous precipitation of graphitic cones from metal particles having such clear crystal habits [3039]. The solubility limit of carbon atoms in metals also increases at higher temperatures, and the precipitation speed increases. We infer that both the formation of crystal habits and the increase in precipitation speed promote the production of cup-stacked-type CNTs.

4. Conclusion

Ni-doped C60 NWs synthesized by the liquid-liquid interfacial precipitation method allow us to produce Ni-encapsulated CNCs and cup-stacked-type CNTs. In particular, the CNCs form chain structures. The two types of one-dimensional carbon nanostructures were produced using Ni-doped C60 NWs by varying heating temperature.

Other transition metals such as iron and cobalt can be doped into fullerene NWs using similar synthetic methods, and CNCs encapsulating nanoparticles of various metal elements can be produced using NWs.

Acknowledgment

This study was partly supported by Grants-in-Aid from the Ministry of Education, Culture, Sport, Science, and Technology, Japan (nos. 22310065 and 23651127).

References

  1. W. Krätschmer, L. D. Lamb, K. Fostiropoulos, and D. R. Huffman, “Solid C60: a new form of carbon,” Nature, vol. 347, no. 6291, pp. 354–358, 1990. View at Publisher · View at Google Scholar · View at Scopus
  2. W. I. F. David, R. M. Ibberson, J. C. Matthewman et al., “Crystal structure and bonding of ordered C60,” Nature, vol. 353, no. 6340, pp. 147–149, 1991. View at Scopus
  3. S. J. Duclos, K. Brister, R. C. Haddon, A. R. Kortan, and F. A. Thiel, “Effects of pressure and stress on C60 fullerite to 20 GPa,” Nature, vol. 351, no. 6325, pp. 380–382, 1991. View at Scopus
  4. P. A. Heiney, J. E. Fischer, A. R. McGhie et al., “Orientational ordering transition in solid C60,” Physical Review Letters, vol. 66, no. 22, pp. 2911–2914, 1991. View at Publisher · View at Google Scholar · View at Scopus
  5. R. L. Meng, D. Ramirez, X. Jiang et al., “Growth of large, defect-free pure C60 single crystals,” Applied Physics Letters, vol. 59, no. 26, pp. 3402–3403, 1991. View at Publisher · View at Google Scholar · View at Scopus
  6. W. Krakow, N. M. Rivera, R. A. Roy, R. S. Ruoff, and J. J. Cuomo, “Epitaxial growth of C60 thin films on mica,” Journal of Materials Research, vol. 7, no. 4, pp. 784–787, 1992. View at Scopus
  7. X. D. Shi, A. R. Kortan, J. M. Williams, A. M. Kini, B. M. Savall, and P. M. Chaikin, “Sound velocity and attenuation in single-crystal C60,” Physical Review Letters, vol. 68, no. 6, pp. 827–830, 1992. View at Scopus
  8. Y. Yosida, “Scanning electron microscope images of C60 whiskers,” Japanese Journal of Applied Physics, Part 2, vol. 31, no. 4, pp. L505–L507, 1992. View at Scopus
  9. M. Haluška, H. Kuzmany, M. Vybornov, P. Rogl, and P. Fejdi, “A double-temperature-gradient technique for the growth of single-crystal fullerites from the vapor phase,” Applied Physics A, vol. 56, no. 3, pp. 161–167, 1993. View at Publisher · View at Google Scholar
  10. J. Z. Liu, J. W. Dykes, M. D. Lan, P. Klavins, R. N. Shelton, and M. M. Olmstead, “Vapor transport growth of C60 crystals,” Applied Physics Letters, vol. 62, no. 5, pp. 531–532, 1993. View at Publisher · View at Google Scholar · View at Scopus
  11. J. L. de Boer, S. van Smaalen, V. Petricek, M. DusekP, M. A. Verheijen, and G. Meijer, “Hexagonal close-packed C60,” Chemical Physics Letters, vol. 219, no. 5-6, pp. 469–472, 1994. View at Scopus
  12. F. Michaud, M. Barrio, S. Toscani et al., “Solid-state studies on single and decagonal crystals of C60 grown from 1,2-dichloroethane,” Physical Review B, vol. 57, no. 17, pp. 10351–10358, 1998. View at Scopus
  13. S. Toscani, H. Allouchi, J. L. Tamarit et al., “Decagonal C60 crystals grown from n -hexane solutions: solid-state and aging studies,” Chemical Physics Letters, vol. 330, no. 5-6, pp. 491–496, 2000. View at Scopus
  14. K. Miyazawa, A. Obayashi, and M. Kuwabara, “C60 nanowhiskers in a mixture of lead zirconate titanate sol-C60 toluene solution,” Journal of the American Ceramic Society, vol. 84, no. 3–12, pp. 3037–3039, 2001. View at Scopus
  15. K. Miyazawa, “C70 nanowhiskers fabricated by forming liquid/liquid interfaces in the systems of toluene solution of C70 and isopropy/alcohol,” Journal of the American Ceramic Society, vol. 85, no. 5, pp. 1297–1299, 2002. View at Scopus
  16. K. Miyazawa, Y. Kuwasaki, A. Obayashi, and M. Kuwabara, “C60 nanowhiskers formed by the liquid-liquid interfacial precipitation method,” Journal of Materials Research, vol. 17, no. 1, pp. 83–88, 2002. View at Scopus
  17. K. Miyazawa, K. Hamamoto, S. Nagata, and T. Suga, “Structural investigation of the C60/C70whiskers fabricated by forming liquid-liquid interfaces of toluene with dissolved C60/C70 and isopropyl alcohol,” Journal of Materials Research, vol. 18, no. 5, pp. 1096–1103, 2003. View at Scopus
  18. K. Asaka, R. Kato, Y. Maezono, R. Yoshizaki, K. Miyazawa, and T. Kizuka, “Light-emitting filaments composed of nanometer-sized carbon hollow capsules,” Applied Physics Letters, vol. 88, no. 5, Article ID 051914, pp. 1–3, 2006. View at Publisher · View at Google Scholar · View at Scopus
  19. K. Asaka, R. Kato, K. Miyazawa, and T. Kizuka, “Deformation of multiwalled nanometer-sized carbon capsules,” Applied Physics Letters, vol. 89, no. 19, Article ID 191914, 2006. View at Publisher · View at Google Scholar · View at Scopus
  20. K. Asaka, R. Kato, R. Yoshizaki, K. Miyazawa, and T. Kizuka, “Conductance of carbon nanocapsule junctions,” Physical Review B, vol. 76, no. 11, Article ID 113404, 2007. View at Publisher · View at Google Scholar · View at Scopus
  21. T. Kizuka, R. Kato, and K. Miyazawa, “Structure of hollow carbon nanocapsules synthesized by resistive heating,” Carbon, vol. 47, no. 1, pp. 138–144, 2009. View at Publisher · View at Google Scholar · View at Scopus
  22. T. Kizuka, R. Kato, and K. Miyazawa, “Surface breakdown dynamics of carbon nanocapsules,” Nanotechnology, vol. 20, no. 10, Article ID 105205, 2009. View at Publisher · View at Google Scholar · View at Scopus
  23. K. Miyazawa, T. Mashino, and T. Suga, “Structural characterization of the C60[C(COOC2H5)2] whiskers prepared by the liquid-liquid interfacial precipitation method,” Journal of Materials Research, vol. 18, no. 11, pp. 2730–2735, 2003. View at Scopus
  24. K. Miyazawa and T. Suga, “Transmission electron microscopy investigation of fullerene nanowhiskers and needle-like precipitates formed by using C60 and (η2-C60)Pt(PPh3)2,” Journal of Materials Research, vol. 19, no. 8, pp. 2410–2414, 2004. View at Publisher · View at Google Scholar · View at Scopus
  25. K. Miyazawa and T. Suga, “Transmission electron microscopy investigation of tubular and capsular needlelike crystals of C60 produced by the liquid-liquid interfacial precipitation method,” Journal of Materials Research, vol. 19, no. 11, pp. 3145–3148, 2004. View at Publisher · View at Google Scholar · View at Scopus
  26. M. Sathish, K. Miyazawa, and T. Sasaki, “Preparation and characterization of Ni incorporated fullerene nanowhiskers,” Diamond and Related Materials, vol. 17, no. 4-5, pp. 571–575, 2008. View at Publisher · View at Google Scholar · View at Scopus
  27. V. Z. Mordkovich, A. G. Umnov, T. Inoshita, and M. Endo, “Observation of multiwall fullerenes in thermally treated laser pyrolysis carbon blacks,” Carbon, vol. 37, no. 11, pp. 1855–1858, 1999. View at Publisher · View at Google Scholar · View at Scopus
  28. Y. Saito, T. Yoshikawa, M. Okuda et al., “Carbon nanocapsules encaging metals and carbides,” Journal of Physics and Chemistry of Solids, vol. 54, no. 12, pp. 1849–1860, 1993. View at Scopus
  29. Y. Saito, “Nanoparticles and filled nanocapsules,” Carbon, vol. 33, no. 7, pp. 979–988, 1995. View at Scopus
  30. A. T. Balaban, D. J. Klein, and X. Liu, “Graphitic cones,” Carbon, vol. 32, no. 2, pp. 357–359, 1994. View at Scopus
  31. H. Terrones, “Curved graphite and its mathematical transformations,” Journal of Mathematical Chemistry, vol. 15, no. 1, pp. 143–156, 1994. View at Publisher · View at Google Scholar · View at Scopus
  32. H. Terrones, T. Hayashi, M. Muñoz-Navia et al., “Graphitic cones in palladium catalysed carbon nanofibres,” Chemical Physics Letters, vol. 343, no. 3-4, pp. 241–250, 2001. View at Publisher · View at Google Scholar · View at Scopus
  33. B. O. Boskovic, V. Stolojan, R. U. A. Khan, S. Haq, and S. R. P. Silva, “Large-area synthesis of carbon nanofibres at room temperature,” Nature Materials, vol. 1, no. 3, pp. 165–168, 2002. View at Publisher · View at Google Scholar · View at Scopus
  34. M. Endo, Y. A. Kim, T. Hayashi et al., “Structural characterization of cup-stacked-type nanofibers with an entirely hollow core,” Applied Physics Letters, vol. 80, no. 7, pp. 1267–1269, 2002. View at Publisher · View at Google Scholar · View at Scopus
  35. Y. A. Kim, T. Hayashi, Y. Fukai, M. Endo, T. Yanagisawa, and M. S. Dresselhaus, “Effect of ball milling on morphology of cup-stacked carbon nanotubes,” Chemical Physics Letters, vol. 355, no. 3-4, pp. 279–284, 2002. View at Publisher · View at Google Scholar · View at Scopus
  36. M. Endo, Y. A. Kim, M. Ezaka et al., “Selective and efficient impregnation of metal nanoparticles on cup-stacked-type carbon nanofibers,” Nano Letters, vol. 3, no. 6, pp. 723–726, 2003. View at Publisher · View at Google Scholar · View at Scopus
  37. C. Kim, Y. J. Kim, Y. A. Kim et al., “High performance of cup-stacked-type carbon nanotubes as a Pt-Ru catalyst support for fuel cell applications,” Journal of Applied Physics, vol. 96, no. 10, pp. 5903–5905, 2004. View at Publisher · View at Google Scholar · View at Scopus
  38. K. Saito, M. Ohtani, and S. Fukuzumi, “Electron-transfer reduction of cup-stacked carbon nanotubes affording cup-shaped carbons with controlled diameter and size,” Journal of the American Chemical Society, vol. 128, no. 44, pp. 14216–14217, 2006. View at Publisher · View at Google Scholar · View at Scopus
  39. Q. Liu, W. Ren, Z. G. Chen et al., “Semiconducting properties of cup-stacked carbon nanotubes,” Carbon, vol. 47, no. 3, pp. 731–736, 2009. View at Publisher · View at Google Scholar · View at Scopus