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Purification of carbon nanofibers with hydrogen peroxide
Synthetic Metals 139 (2003) 39–42
Purification of carbon nanofibers with hydrogen peroxide Weon-Kyung Choia, Soo-Gil Parka,*, H. Takahashib, Tae-Hwan Choc a
Department of Industrial Chemistry Engineering, Chungbuk National University, 48 Gaesin-dong, Cheongju 361-763, South Korea b Department of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628, Japan c Department of Industrial Chemistry, Dankook University, 29 Anseo-dong, Cheonan 330-714, South Korea Received 20 September 2002; received in revised form 23 September 2002; accepted 1 December 2002
Abstract As-prepared carbon nanofibers (CNFs) contained some carbonaceous impurities of amorphous carbon and incompletely grown carbon nanofibers. Removal of those impurities using hydrogen peroxide as a reducing agent was carried out. Amorphous carbon synthesized in carbon nanofiber preparation and incompletely grown carbonaceous materials were distinctly removed in this purification process performed in hydrogen peroxide. The morphological changes of as-prepared and hydrogen peroxide treated carbon nanofibers were investigated by FESEM and TEM observations. After that purification, amorphous carbons were markedly removed by reduction and carbon nanofibers without carbonaceous impurities were obtained successfully. The X-ray diffraction results show that the purification method using hydrogen peroxides was very stable for carbon nanostructures. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Carbon nanofibers; Purification; Hydrogen peroxide
1. Introduction Carbonaceous materials are found in a variety forms such as graphite, diamond, carbon fibers, etc. In recent times, carbon nanofibers (CNFs), fullerenes and carbon nanotubes are discovered kinds of carbonaceous materials and have many interests in various applications [1–3]. Especially carbon fibers represent an important class of graphite-related materials from both a scientific and commercial views. Currently, carbon nanofibers have been noted as feasible materials for various fields such as hydrogen storage media, semi-fuel cell application, etc. [4–9]. While, all the carbon nanofibers and nanostructured carbonaceous products include impurities such as amorphous carbon, carbon nanoparticles, catalytic metals and incompletely grown carbons. Many researchers tried to get rid of the impurities contained in nanostructured carbon products by various methods and the successful results were reported [10–13]. By means of the purification, the high purity carbon nanofibers obtained could be applied in a field of science and technology. A method of purification was carried out in a gas phase or a liquid phase which could effectively remove the co-residual carbonaceous impurities of by-products or * Corresponding author. Tel.: þ82-43-261-2492; fax: þ82-43-273-8221. E-mail address: [email protected] (S.-G. Park).
catalyst metal. Purification of carbon nanofibers performed in an acid system could remove metal catalytic particles and carbonaceous contamination was eliminated by reducing agent of oxygen or ozone gas. High purity carbon nanofibers was obtained and improved character of the purified carbon nanofibers have been studied [14]. In this study, we try to remove carbonaceous impurities except carbon nanofiber with hydrogen peroxide. Until now, the removal of carbonaceous impurities was proposed using the reduction with oxygen gas and ozone gas as a very effective method [11,15–17], while that purification needs detail controls for oxidation of carbonaceous impurities except carbon nanofibers and some apparatus. For the purpose of simpler purification, we introduce the new purification method by liquid solution using hydrogen peroxide. It is a very effective and simpler way to remove carbonaceous impurities without carbon nanofibers than other purification ways performed by gases and do not need various apparatus. The aim of the present report is to discuss and explain the purification of carbonaceous impurities contained in the as-prepared carbon nanofibers using hydrogen peroxide as a reducing agent. Using FE-SEM and TEM the morphological changes were scanned for as-prepared and purified carbon nanofibers. The stability of crystalline structure of carbon nanofibers was examined by X-ray diffraction.
0379-6779/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(03)00081-X
40
W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
It is well known that the carbonaceous impurities were cogenerated on the growth of carbon nanofibers. To obtain pure carbon nanofibers except carbonaceous impurities, purification method was applied for as-prepared carbon nanofibers. Fig. 1a and b shows the images of the untreated carbon
nanofibers and the hydrogen peroxide treated one, respectively. The effects of hydrogen peroxide treatment were evaluated by comparing with FE-SEM images before and after purification. The raw materials used in this study also have included some of carbonaceous impurities as shown in Fig. 1a. By means of this SEM image, it is known that the synthesized carbon nanofiber with diameter ca. 100 nm and carbonaceous impurities with irregular shapes were distributed entirely. The length of most of the carbon nanotubes was over 1 mm with curved form and carbonaceous impurities were stuck to the surface of carbon nanofibers. Changed external morphology after hydrogen peroxide treatment of carbon nanofibers could be evaluated by comparing with Fig. 1a and b. The purified carbon nanofibers with hydrogen peroxide showed much clearer and tidier image than as-prepared one and the impurities stuck to untreated carbon nanofibers were removed outstandingly. While it was known that the hydrogen peroxide treatment did not affect the carbon nanotubes but carbonaceous impurities were removed by the reduction of carbonaceous elements. For the determination of detailed structure and high magnification, the untreated and purified samples were studied by TEM. Fig. 2a and b shows low and high magnification TEM images of untreated samples of carbon nanofibers and amorphous carbon particles called as impurities. From these images it could be seen that impurities were stuck to the surface of carbon nanofibers and distributed to
Fig. 1. SEM images of: (a) as-prepared carbon nanofibers; (b) 40 h hydrogen peroxide treated carbon nanofibers.
Fig. 2. TEM images of as-prepared carbon nanofibers obtained: (a) low magnification; (b) high magnification.
2. Experimental As a raw material, ca. 50 mg of as-prepared carbon nanofibers were introduced into a round flask and then put 90 8C commercial hydrogen peroxide of 300 ml in that flask. The raw material and hydrogen peroxides were heated and refluxed with magnetic stirring at 90 8C for 40 h. After hydrogen peroxide treatment, treated samples were cooled off for enough time under room temperature and filtered with polymer filter paper with 0.45 mm of pore size. Then the purified carbon nanofibers were washed in distilled water for five times and filtered carbon nanofibers attached to filter paper were dried at 50 8C for 50 h. Morphological observations of as-prepared and purified carbon nanofibers in hydrogen peroxide were performed by FE-SEM and TEM measurements. Crystallographic changes of as-prepared carbon nanofibers and hydrogen peroxide treated carbon nanofibers were carried out using X-ray ˚ , 30 kV, 30 mA). diffractometer (l ¼ 1:541 A
3. Results and discussion
W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
41
Fig. 4. XRD patterns of: (a) as-prepared carbon nanofibers; (b) hydrogen peroxide treated carbon nanofibers.
4. Conclusion
Fig. 3. TEM images of hydrogen peroxide treated carbon nanofibers obtained: (a) low magnification; (b) high magnification.
all over the samples. Also, the incompletely synthesized carbonaceous materials called as impurities were distributed on the whole low magnification TEM image. Morphological changes of hydrogen peroxide treated carbon nanofibers were evaluated by TEM images presented in Fig. 3a and b. In TEM images of Fig. 3a and b, carbonaceous impurities of amorphous carbon nanoparticles and incompletely grown carbonaceous materials disappeared and pure carbon nanofibers existed after this treatments. In spite of impurities disappearance, carbon nanofibers remained in the original form without morphological transformation. The result of the purified sample explained the oxidation of carbonaceous elements except carbon nanofibers in hydrogen peroxide because the carbon oxides (gas phases of CO2 or CO) could disperse out easily. In this result, it could explain that this purification method using hydrogen peroxide did not affect carbon nanofibers but removed carbonaceous impurities effectively. These results suggest strongly that carbonaceous contaminations except carbon nanofibers were eliminated by hydrogen peroxide treatment. Fig. 4 shows the X-ray diffraction patterns of as-prepared carbon nanofibers and hydrogen peroxide treated carbon nanofibers. The obtained X-ray diffraction patterns are very similar to each other. These results suggest that the crystallographic changes of carbon nanofibers did not occur in hydrogen peroxide treatment. It can be explained that the purification of carbon nanofibers using hydrogen peroxides did not affect the crystalline structure of carbon nanofibers.
In this study, we have investigated a purification method on carbon nanofibers with hydrogen peroxides. The treatment was a very simple procedure using commercial hydrogen peroxide as reducing agents. Carbonaceous impurities originating from the preparation procedure were evidently eliminated and pure carbon nanofibers without contaminations were obtained. Despite severe oxidation of carbonaceous impurities, the purified carbon nanofibers were very stable without crystalline changes. As shown earlier, the new purification method for removal of carbonaceous impurities was succeeded effectively in a simple apparatus like those reported using oxygen of ozone. Also, carbonaceous impurities were removed without the oxidation of carbon nanofibers easily and purified carbon nanofibers show stable crystalline structure. Therefore, the purification method of carbonaceous impurities using hydrogen peroxide was effective and this treatment should be the suggested purification method to obtain pure carbon nanofiber.
References [1] R. Sato, G. Dresselhaus, M.S. Dresselhaus, Physical Properties of Carbon Nanotubes, Imperial College Press, Singapore, 1998. [2] M.S. Dresselhaus, G. Dresselhaus, J. Electroceram. 1 (3) (1997) 273. [3] P.J.F. Harris, Carbon Nanotubes and Related Structures, Cambridge University Press, Cambridge, 1999. [4] R.R. Bessette, M.G. Medeiros, C.J. Patrissi, C.M. Deschenes, N.C. LaFratta, J. Power Sources 96 (2001) 240. [5] H.M. Cheng, Q.H. Yang, C. Liu, Carbon 39 (2001) 1447. [6] Y.Y. Fan, B. Liao, M. Liu, Y.L. Wei, M.Q. Lu, H.M. Cheng, Carbon 37 (1999) 1649. [7] J.Y. Hwang, S.H. Lee, K.S. Sim, J.W. Kim, Synth. Met. 126 (2002) 81. [8] R. Strobel, L. Jorissen, T. Schliermann, V. Trapp, W. Schutz, K. Bohmhammel, G. Wolf, J. Garche, J. Power Sources 84 (1999) 221. [9] M. Shiraishi, T. Takenobu, A. Yamada, M. Ata, H. Kataura, Chem. Phys. Lett. 358 (2002) 213. [10] A. Bougrine, A. Naji, J. Ghanbaja, D. Billaud, Synth. Met. 104 (1999) 2480.
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W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
[11] K. Hernadi, A. Fonseca, J.B. Nagy, D. Bernaerts, J. Lucas, A. Riga, Synth. Met. 77 (1996) 31. [12] K.B. Shelimov, R.O. Esenaliev, A.G. Rinzler, C.B. Huffman, R.E. Smalley, Chem. Phys. Lett. 282 (1998) 429. [13] C. Seker, C. Subramanian, Vacuum 47 (1996) 1289. [14] H.S. Youn, H. Ryu, T.-H. Cho, W.-K. Choi, Int. J. Hydrogen Energy 27 (2002) 937.
[15] J.F. Colmer, P. Piedigrosso, A. Fonseca, J.B. Nagy, Synth. Met. 103 (1999) 2482. [16] L.P. Biro, N.Q. Khanh, Z. Vertesy, Z.E. Horvath, Z. Osvath, A. Koos, J. Gyulai, A. Kocsonya, Z. Konya, X.B. Zhang, G. Van Tendeloo, A. Fonseca, J.B. Nagy, Mater. Sci. Eng. 19 (2002) 9. [17] T. Jeong, W.Y. Kim, Y.B. Hahn, Chem. Phys. Lett. 344 (2001) 18.
Purification of carbon nanofibers with hydrogen peroxide Weon-Kyung Choia, Soo-Gil Parka,*, H. Takahashib, Tae-Hwan Choc a
Department of Industrial Chemistry Engineering, Chungbuk National University, 48 Gaesin-dong, Cheongju 361-763, South Korea b Department of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628, Japan c Department of Industrial Chemistry, Dankook University, 29 Anseo-dong, Cheonan 330-714, South Korea Received 20 September 2002; received in revised form 23 September 2002; accepted 1 December 2002
Abstract As-prepared carbon nanofibers (CNFs) contained some carbonaceous impurities of amorphous carbon and incompletely grown carbon nanofibers. Removal of those impurities using hydrogen peroxide as a reducing agent was carried out. Amorphous carbon synthesized in carbon nanofiber preparation and incompletely grown carbonaceous materials were distinctly removed in this purification process performed in hydrogen peroxide. The morphological changes of as-prepared and hydrogen peroxide treated carbon nanofibers were investigated by FESEM and TEM observations. After that purification, amorphous carbons were markedly removed by reduction and carbon nanofibers without carbonaceous impurities were obtained successfully. The X-ray diffraction results show that the purification method using hydrogen peroxides was very stable for carbon nanostructures. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Carbon nanofibers; Purification; Hydrogen peroxide
1. Introduction Carbonaceous materials are found in a variety forms such as graphite, diamond, carbon fibers, etc. In recent times, carbon nanofibers (CNFs), fullerenes and carbon nanotubes are discovered kinds of carbonaceous materials and have many interests in various applications [1–3]. Especially carbon fibers represent an important class of graphite-related materials from both a scientific and commercial views. Currently, carbon nanofibers have been noted as feasible materials for various fields such as hydrogen storage media, semi-fuel cell application, etc. [4–9]. While, all the carbon nanofibers and nanostructured carbonaceous products include impurities such as amorphous carbon, carbon nanoparticles, catalytic metals and incompletely grown carbons. Many researchers tried to get rid of the impurities contained in nanostructured carbon products by various methods and the successful results were reported [10–13]. By means of the purification, the high purity carbon nanofibers obtained could be applied in a field of science and technology. A method of purification was carried out in a gas phase or a liquid phase which could effectively remove the co-residual carbonaceous impurities of by-products or * Corresponding author. Tel.: þ82-43-261-2492; fax: þ82-43-273-8221. E-mail address: [email protected] (S.-G. Park).
catalyst metal. Purification of carbon nanofibers performed in an acid system could remove metal catalytic particles and carbonaceous contamination was eliminated by reducing agent of oxygen or ozone gas. High purity carbon nanofibers was obtained and improved character of the purified carbon nanofibers have been studied [14]. In this study, we try to remove carbonaceous impurities except carbon nanofiber with hydrogen peroxide. Until now, the removal of carbonaceous impurities was proposed using the reduction with oxygen gas and ozone gas as a very effective method [11,15–17], while that purification needs detail controls for oxidation of carbonaceous impurities except carbon nanofibers and some apparatus. For the purpose of simpler purification, we introduce the new purification method by liquid solution using hydrogen peroxide. It is a very effective and simpler way to remove carbonaceous impurities without carbon nanofibers than other purification ways performed by gases and do not need various apparatus. The aim of the present report is to discuss and explain the purification of carbonaceous impurities contained in the as-prepared carbon nanofibers using hydrogen peroxide as a reducing agent. Using FE-SEM and TEM the morphological changes were scanned for as-prepared and purified carbon nanofibers. The stability of crystalline structure of carbon nanofibers was examined by X-ray diffraction.
0379-6779/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(03)00081-X
40
W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
It is well known that the carbonaceous impurities were cogenerated on the growth of carbon nanofibers. To obtain pure carbon nanofibers except carbonaceous impurities, purification method was applied for as-prepared carbon nanofibers. Fig. 1a and b shows the images of the untreated carbon
nanofibers and the hydrogen peroxide treated one, respectively. The effects of hydrogen peroxide treatment were evaluated by comparing with FE-SEM images before and after purification. The raw materials used in this study also have included some of carbonaceous impurities as shown in Fig. 1a. By means of this SEM image, it is known that the synthesized carbon nanofiber with diameter ca. 100 nm and carbonaceous impurities with irregular shapes were distributed entirely. The length of most of the carbon nanotubes was over 1 mm with curved form and carbonaceous impurities were stuck to the surface of carbon nanofibers. Changed external morphology after hydrogen peroxide treatment of carbon nanofibers could be evaluated by comparing with Fig. 1a and b. The purified carbon nanofibers with hydrogen peroxide showed much clearer and tidier image than as-prepared one and the impurities stuck to untreated carbon nanofibers were removed outstandingly. While it was known that the hydrogen peroxide treatment did not affect the carbon nanotubes but carbonaceous impurities were removed by the reduction of carbonaceous elements. For the determination of detailed structure and high magnification, the untreated and purified samples were studied by TEM. Fig. 2a and b shows low and high magnification TEM images of untreated samples of carbon nanofibers and amorphous carbon particles called as impurities. From these images it could be seen that impurities were stuck to the surface of carbon nanofibers and distributed to
Fig. 1. SEM images of: (a) as-prepared carbon nanofibers; (b) 40 h hydrogen peroxide treated carbon nanofibers.
Fig. 2. TEM images of as-prepared carbon nanofibers obtained: (a) low magnification; (b) high magnification.
2. Experimental As a raw material, ca. 50 mg of as-prepared carbon nanofibers were introduced into a round flask and then put 90 8C commercial hydrogen peroxide of 300 ml in that flask. The raw material and hydrogen peroxides were heated and refluxed with magnetic stirring at 90 8C for 40 h. After hydrogen peroxide treatment, treated samples were cooled off for enough time under room temperature and filtered with polymer filter paper with 0.45 mm of pore size. Then the purified carbon nanofibers were washed in distilled water for five times and filtered carbon nanofibers attached to filter paper were dried at 50 8C for 50 h. Morphological observations of as-prepared and purified carbon nanofibers in hydrogen peroxide were performed by FE-SEM and TEM measurements. Crystallographic changes of as-prepared carbon nanofibers and hydrogen peroxide treated carbon nanofibers were carried out using X-ray ˚ , 30 kV, 30 mA). diffractometer (l ¼ 1:541 A
3. Results and discussion
W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
41
Fig. 4. XRD patterns of: (a) as-prepared carbon nanofibers; (b) hydrogen peroxide treated carbon nanofibers.
4. Conclusion
Fig. 3. TEM images of hydrogen peroxide treated carbon nanofibers obtained: (a) low magnification; (b) high magnification.
all over the samples. Also, the incompletely synthesized carbonaceous materials called as impurities were distributed on the whole low magnification TEM image. Morphological changes of hydrogen peroxide treated carbon nanofibers were evaluated by TEM images presented in Fig. 3a and b. In TEM images of Fig. 3a and b, carbonaceous impurities of amorphous carbon nanoparticles and incompletely grown carbonaceous materials disappeared and pure carbon nanofibers existed after this treatments. In spite of impurities disappearance, carbon nanofibers remained in the original form without morphological transformation. The result of the purified sample explained the oxidation of carbonaceous elements except carbon nanofibers in hydrogen peroxide because the carbon oxides (gas phases of CO2 or CO) could disperse out easily. In this result, it could explain that this purification method using hydrogen peroxide did not affect carbon nanofibers but removed carbonaceous impurities effectively. These results suggest strongly that carbonaceous contaminations except carbon nanofibers were eliminated by hydrogen peroxide treatment. Fig. 4 shows the X-ray diffraction patterns of as-prepared carbon nanofibers and hydrogen peroxide treated carbon nanofibers. The obtained X-ray diffraction patterns are very similar to each other. These results suggest that the crystallographic changes of carbon nanofibers did not occur in hydrogen peroxide treatment. It can be explained that the purification of carbon nanofibers using hydrogen peroxides did not affect the crystalline structure of carbon nanofibers.
In this study, we have investigated a purification method on carbon nanofibers with hydrogen peroxides. The treatment was a very simple procedure using commercial hydrogen peroxide as reducing agents. Carbonaceous impurities originating from the preparation procedure were evidently eliminated and pure carbon nanofibers without contaminations were obtained. Despite severe oxidation of carbonaceous impurities, the purified carbon nanofibers were very stable without crystalline changes. As shown earlier, the new purification method for removal of carbonaceous impurities was succeeded effectively in a simple apparatus like those reported using oxygen of ozone. Also, carbonaceous impurities were removed without the oxidation of carbon nanofibers easily and purified carbon nanofibers show stable crystalline structure. Therefore, the purification method of carbonaceous impurities using hydrogen peroxide was effective and this treatment should be the suggested purification method to obtain pure carbon nanofiber.
References [1] R. Sato, G. Dresselhaus, M.S. Dresselhaus, Physical Properties of Carbon Nanotubes, Imperial College Press, Singapore, 1998. [2] M.S. Dresselhaus, G. Dresselhaus, J. Electroceram. 1 (3) (1997) 273. [3] P.J.F. Harris, Carbon Nanotubes and Related Structures, Cambridge University Press, Cambridge, 1999. [4] R.R. Bessette, M.G. Medeiros, C.J. Patrissi, C.M. Deschenes, N.C. LaFratta, J. Power Sources 96 (2001) 240. [5] H.M. Cheng, Q.H. Yang, C. Liu, Carbon 39 (2001) 1447. [6] Y.Y. Fan, B. Liao, M. Liu, Y.L. Wei, M.Q. Lu, H.M. Cheng, Carbon 37 (1999) 1649. [7] J.Y. Hwang, S.H. Lee, K.S. Sim, J.W. Kim, Synth. Met. 126 (2002) 81. [8] R. Strobel, L. Jorissen, T. Schliermann, V. Trapp, W. Schutz, K. Bohmhammel, G. Wolf, J. Garche, J. Power Sources 84 (1999) 221. [9] M. Shiraishi, T. Takenobu, A. Yamada, M. Ata, H. Kataura, Chem. Phys. Lett. 358 (2002) 213. [10] A. Bougrine, A. Naji, J. Ghanbaja, D. Billaud, Synth. Met. 104 (1999) 2480.
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W.-K. Choi et al. / Synthetic Metals 139 (2003) 39–42
[11] K. Hernadi, A. Fonseca, J.B. Nagy, D. Bernaerts, J. Lucas, A. Riga, Synth. Met. 77 (1996) 31. [12] K.B. Shelimov, R.O. Esenaliev, A.G. Rinzler, C.B. Huffman, R.E. Smalley, Chem. Phys. Lett. 282 (1998) 429. [13] C. Seker, C. Subramanian, Vacuum 47 (1996) 1289. [14] H.S. Youn, H. Ryu, T.-H. Cho, W.-K. Choi, Int. J. Hydrogen Energy 27 (2002) 937.
[15] J.F. Colmer, P. Piedigrosso, A. Fonseca, J.B. Nagy, Synth. Met. 103 (1999) 2482. [16] L.P. Biro, N.Q. Khanh, Z. Vertesy, Z.E. Horvath, Z. Osvath, A. Koos, J. Gyulai, A. Kocsonya, Z. Konya, X.B. Zhang, G. Van Tendeloo, A. Fonseca, J.B. Nagy, Mater. Sci. Eng. 19 (2002) 9. [17] T. Jeong, W.Y. Kim, Y.B. Hahn, Chem. Phys. Lett. 344 (2001) 18.