- Email: [email protected]
Synthesis of single-walled carbon nanotubes using hemoglobin-based iron catalyst
CARBON
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Synthesis of single-walled carbon nanotubes using hemoglobin-based iron catalyst Hye-Jin Kim, Eugene Oh, Jaegeun Lee, Kun-Hong Lee
*
Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), san 31, Hyoja-dong, Nam-gu, Pohang, Gyungbuk 790-784, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history:
Hemoglobin (Hb) was used as a catalyst for the growth of single-walled carbon nanotubes
Received 7 June 2011
(SWCNTs). Hb was deposited onto a hydrophilic treated substrate by spin coating method.
Accepted 18 September 2011
After oxidation at 800 °C, protein chains were decomposed and iron oxide nanoparticles
Available online 22 September 2011
remained with an average diameter of 2.29 nm. High quality SWCNTs were synthesized with an average diameter of 1.22 nm. The protein chains prevent iron atoms aggregation and so the size of the nanoparticles is smaller than that from ferritin-like proteins. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1.
Introduction
The electronic properties of single-walled carbon nanotubes (SWCNTs) are strongly related to their diameter and chirality [1,2]. Among many factors that affect the diameter and chirality of SWCNTs, such as growth temperature, gas composition and precursors, the size of catalyst particle has been the most important issue on the growth of SWCNTs [3,4]. Since ferritin, an iron storage protein, was adopted for the precise control of the number of iron atoms as a catalyst for the growth of SWCNTs [5], Co-filled ferritin [6] and DNA-binding proteins from starved cells (Dps) [7,8] have been widely used to synthesize SWCNTs as well as multi-walled carbon nanotubes (MWCNTs) [9–11]. Narrow diameter distribution was achieved by sedimentation velocity centrifugation to separate ferritin according to the size [12]. Dps also yielded SWCNTs with narrow diameter distribution [7]. When using these ferritin-like proteins as a catalyst, discrete catalytic nanoparticles were obtained by placing controllable number of iron atoms into the cores of an empty ferritin [5]. However, the incorporation of iron atoms into the core of an empty ferritin is known to be a multistep process involving the binding and migration of Fe(II) to the ferroxidase site, Fe(II) oxidation, Fe(III) hydrolysis and the nucleation and growth of the mineral core in
iron-containing aqueous solutions [13]. As an effort to avoid this complex process, we introduced iron-containing proteins – hemoglobin (Hb), myoglobin (Mb), or cytochrome c (Cyt c) – as iron catalyst sources, and synthesized MWCNTs [14]. Previously, we demonstrated the catalytic possibility of the nanoparticles derived from three kinds of iron-containing proteins on the growth of MWCNTs. In this paper, we focused on the analysis of the nanoparticles derived from Hb in detail, and they can synthesize not only MWCNTs but SWCNTs by optimizing the experimental conditions.
2.
Experimental
2.1.
Catalyst preparation
Hb from bovine heart (Sigma–Aldrich, H2500) was purchased as lyophilized powders and used without further purification. Hb was dissolved in distilled water at a concentration of 5 mg/ ml at room temperature. For the growth of SWCNTs, a Si wafer with a 300 nm thick thermally grown oxide layer was used as a substrate. The silicon oxide layer was used as a buffer layer to prevent iron silicide formation at the high temperatures used in the growth of carbon nanotubes (CNTs). The substrates were hydrophilic treated using piranha solution
* Corresponding author: Fax: +82 54 279 8298. E-mail address: [email protected] (K.-H. Lee). 0008-6223/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.09.038
CARBON
5 0 (2 0 1 2) 7 2 2–72 6
723
(70 vol.% H2SO4 + 30 vol.% H2O2) for 30 min at 140 °C, followed by sonication twice in distilled water for 15 min, and then blow-dried with nitrogen. Hb was deposited onto the substrates by spin coating method with 2000 rpm for 40 s five times each. After spin coating, the protein chains of Hb were removed by oxidation at 800 °C for 5 min in air.
2.2.
Growth of SWCNTs
SWCNTs were grown by thermal chemical vapor deposition (CVD) using a 1 in. quartz tube furnace. As-prepared substrates were placed in the quartz tube and heated to 750 °C under an argon (500 sccm) atmosphere. After the temperature stabilized, the substrates were reduced in hydrogen (400 sccm) for 10 min. Subsequently, ethylene (100 sccm) was introduced for 20 min, followed by cooling with argon to room temperature.
2.3.
Analysis methods
The iron oxide nanoparticles were characterized with an atomic force microscope (AFM, Veeco, Dimension 3100) and high resolution transmission electron microscope (TEM, JEOL, JEM-2100F). TEM samples were prepared as follows. The nanoparticles-deposited substrate was cut to a 3 mm disk and backside of the disk was dimpled down to about 10– 20 lm at the center of the disk. Then, the disk was Ar ionmilled from the backside until the tiny hole at the center of the disk was made, and then introduced to the TEM chamber. Raman spectroscopy (Jobin–Yvon, LabRam HR) was performed using a 512 nm excitation beam.
3.
Results and discussion
Fig. 1 shows the AFM analysis of the nanoparticles derived from Hb. Hb was deposited onto a hydrophilic treated Si/ SiO2 substrate by spin coating method. Previously, we have reported that the self-assembled monolayer (SAM) films allow Hb to be adsorbed onto them with appropriate density that can initiate the growth of CNTs [14]. However, the SAM film formation process requires a lot of attention. Here, by using spin coating method, Hb was easily deposited on a substrate by optimizing the concentration of Hb-containing solution and the spin coating rate. After deposition on a substrate and oxidation at a high temperature, the protein chains were removed, and only iron atoms remained on the substrate, because Hb consists of carbon, hydrogen, nitrogen, oxygen, sulfur and iron. At high temperature, iron atoms are highly mobile enough to form nanoparticles assembling with iron atoms from nearby other Hbs. As shown in Fig. 1(a), discrete nanoparticles were formed from Hb. The topographic height profile in Fig. 1(b) was mainly used to measure the diameter of the nanoparticles due to the AFM tip convolution in measuring apparent widths. Fig. 1(c) shows the size distribution of the nanoparticles and the histogram was obtained by examination of approximately 100 individual particles. The average diameter of nanoparticles was found to be 2.41 ± 0.66 nm and this value is similar to the smallest size of the nanoparticles obtained
Fig. 1 – (a) AFM image of nanoparticles derived from Hb. (b) AFM height profile along the line in (a). (c) Histogram of diameter distribution of the nanoparticles.
from size-separated ferritin by sedimentation velocity centrifugation at 30,000 rpm for 17 h [12]. When using ferritin as a catalyst carrier, discrete catalytic nanoparticles were obtained by loading iron atoms into the cores of empty ferritin, and later removing organic shells [5,6,11]. Accordingly, the size of the nanoparticles is determined by ferritin loading time or number of loadings. Therefore, it is difficult to load accurate number of iron atoms into the cores, especially small number of iron atoms [5,15]. Unlike ferritin, Hb has defined number of iron atoms per molecule. One Hb molecule contains four heme prosthetic groups that each has an iron atom, i.e., four iron atoms per Hb molecule. This means that more accurate control of the size of catalyst particles is possible, at least in theory, thus more narrow size distribution of synthesized CNTs. Iron oxide nanoparticles are formed by decomposition of protein chains as illustrated in Fig. 2. Since protein chains in each Hb are likely to prevent the iron atoms from aggregation, it is favorable to form smaller diameter nanoparticles as compared with the case of using ferritin.
724
CARBON
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
Fig. 2 – Formation of nanoparticles derived from Hbdeposited substrate by decomposition of protein chains.
TEM analysis confirmed the formation of the nanoparticles derived from Hb. The distribution of the nanoparticles in Fig. 3(a) corresponds to that obtained by AFM, and the high resolution image in the inset shows the lattice fringes of the nanoparticles. The nanoparticles were spherical and crystalline with a diameter of approximately 2 nm. The presence of iron was confirmed by energy dispersive spectroscopy (EDS) in Fig. 3(b).
Fig. 4(a) shows the AFM images of SWCNTs grown from the nanoparticles derived from Hb. The SWCNTs were mostly isolated and not bundled. The diameters of SWCNTs were measured by their heights from topographic profile. The diameter distribution of SWCNTs in Fig. 4(b) was obtained from over 100 individual SWCNTs, and the average diameter of grown SWCNTs was 1.22 ± 0.43 nm. As previous studies on ferritinlike proteins, the diameter of SWCNTs is smaller than the size of the nanoparticles [5,6,8,12]. Because the size of the nanoparticles was measured after oxidation to remove the proteins chains, the measurements indicates the size of oxide nanoparticles. However, the SWCNTs are actually synthesized from iron nanoparticles reduced by hydrogen before the growth of SWCNTs. This makes the difference between the nanoparticles and the SWCNTs in size. Considering that the diameter of a SWCNT is roughly equal to the size of a reduced iron catalyst particle, we used the following equation to estimate the average number of iron atoms per iron catalyst particle. N¼
pqD3 NA 6M
ð1Þ
Where the density of face centered cubic (fcc) iron q = 7.874 g/ cm3, the average diameter of iron catalyst particle D = 1.22 nm, the atomic mass of iron M = 55.845 g/mol and NA is Avogadro’s number. According to this calculation, a
Fig. 3 – (a) TEM image of nanoparticles derived from Hb. The inset shows a high resolution TEM image of one of the nanoparticles. The scale bar is 2 nm. (b) EDS of the nanoparticles.
Fig. 4 – (a) AFM image of SWCNTs. (b) Histogram of diameter distribution of SWCNTs.
CARBON
5 0 (2 0 1 2) 7 2 2–72 6
725
derived from Hb was confirmed by AFM and TEM images. Because Hb has iron atoms in itself, the nanoparticles are formed by assembly of iron atoms from Hb molecules. Since protein chains prevent iron atoms from aggregation during decomposition, smaller size of nanoparticles tends to form. Raman spectroscopic analysis has approved the growth of high quality SWCNTs by using the nanoparticles derived from Hb.
Acknowledgments The authors would like to thank the Ministry of Education, Science and Technology of Korea for its financial support through the second phase BK21 program. This work was also supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MEST) (Grant No. 2011-0000360).
R E F E R E N C E S
Fig. 5 – (a) TEM image of SWCNTs. The scale bar in inset is 5 nm. (b) Raman spectra of SWCNTs grown from Hb.
1.22 nm iron nanoparticle consists of approximately 80 iron atoms. In other words, 20 Hb molecules are assembled to form a 1.22 nm iron nanoparticle because one Hb molecule has four iron atoms. We believe it is possible to accurately control the size of iron catalyst particles by controlling the number of assembled Hb molecules. Such an effort is ongoing in our laboratory. TEM image in Fig. 5(a) clearly shows that SWCNTs are synthesized from discrete catalytic nanoparticles. As-synthesized SWCNTs are mostly isolated as shown in AFM image but they are bundled in the dispersion on TEM grid. Fig. 5(b) shows the Raman spectrum for the SWCNTs obtained from this work. The single peak in the range of the radial breathing mode (RBM) indicates the existence of SWCNTs in our sample. By the relation, d ¼ 248=x
ð2Þ
where d is tube diameter and x is the Raman shift, the peak at 154 cm1 corresponds to SWCNTs with 1.61 nm diameter and this value is in the range of measured diameter by AFM. Also, weak D-band (1344 cm1) and strong G-band (1594 cm1) indicates the synthesis of high quality SWCNTs.
4.
Conclusions
In conclusion, we have synthesized high quality SWCNTs by using Hb as a catalyst. The formation of the nanoparticles
[1] Odom TW, Huang JL, Kim P, Lieber CM. Atomic structure and electronic properties of single-walled carbon nanotubes. Nature 1998;391:62–4. [2] Wildoer JWG, Venema LC, Rinzler AG, Smalley RE, Dekker C. Electronic structure of atomically resolved carbon nanotubes. Nature 1998;391:59–62. [3] Nasibulin AG, Pikhitsa PV, Jiang H, Kauppinen EI. Correlation between catalyst particle and single-walled carbon nanotube diameters. Carbon 2005;43:2251–7. [4] Inoue T, Gunjishima I, Okamoto A. Synthesis of diametercontrolled carbon nanotubes using centrifugally classified nanoparticle catalysts. Carbon 2007;45:2164–70. [5] Li Y, Kim W, Zhang Y, Rolandi M, Wang D, Dai H. Growth of single-walled carbon nanotubes from discrete catalytic nanoparticles of various sizes. J Phys Chem B 2001;105:11424–31. [6] Jeong G-H, Yamazaki A, Suzuki S, Yoshimura H, Kobayashi Y, Homma Y. Cobalt-filled apoferritin for suspended single walled carbon nanotubes growth with narrow diameter distribution. J Am Chem Soc 2005;127:8238–9. [7] Kramer RM, Sowards LA, Pender MJ, Stone MO, Naik RR. Constrained iron catalysts for single-walled carbon nanotube growth. Langmuir 2005;21:8466–70. [8] Jeong G-H, Yamazaki A, Suzuki S, Yoshimura H, Kobayashi Y, Homma Y. Production of single-walled carbon nanotubes with narrow diameter distribution using iron nanoparticles derived from DNA-binding proteins from starved cells. Carbon 2007;45(5):978–83. [9] Zhang Y, Li Y, Kim W, Wang D, Dai H. Imaging as-grown single-walled carbon nanotubes originated from isolated catalytic nanoparticles. Appl Phys A Mater Sci Process 2002;74(3):325–8. [10] Tempel H, Joshi R, Schneider JJ. Ink jet printing of ferritin as method for selective catalyst patterning and growth of multiwalled carbon nanotubes. Mater Chem Phys 2010;121(1– 2):178–83. [11] Bonard J-M, Chauvin P, Klinke C. Monodisperse multiwall carbon nanotubes obtained with ferritin as catalyst. Nano Lett 2002;2(6):665–7. [12] Durrer L, Greenwald J, Helbling T, Muoth M, Riek R, Hierold C. Narrowing SWNT diameter distribution using size-separated ferritin-based Fe catalysts. Nanotechnology 2009;20:355601. [13] Yang X, Chen-Barrett Y, Arosio P, Chasteen ND. Reaction paths of iron oxidation and hydrolysis in horse spleen and
726
CARBON
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
recombinant human ferritins. Biochemistry 1998;37(27):9743–50. [14] Kim H-J, Oh E, Lee J, Shim D-S, Lee K-H. Synthesis of carbon nanotubes with catalytic iron-containing proteins. Carbon 2011;49(12):3717–22.
[15] Durrer L, Helbling T, Zenger C, Jungen A, Stampfer C, Hierold C. SWNT growth by CVD on ferritin-based iron catalyst nanoparticles towards CNT sensors. Sens Actuators B 2008;132:485–90.
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/carbon
Synthesis of single-walled carbon nanotubes using hemoglobin-based iron catalyst Hye-Jin Kim, Eugene Oh, Jaegeun Lee, Kun-Hong Lee
*
Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), san 31, Hyoja-dong, Nam-gu, Pohang, Gyungbuk 790-784, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history:
Hemoglobin (Hb) was used as a catalyst for the growth of single-walled carbon nanotubes
Received 7 June 2011
(SWCNTs). Hb was deposited onto a hydrophilic treated substrate by spin coating method.
Accepted 18 September 2011
After oxidation at 800 °C, protein chains were decomposed and iron oxide nanoparticles
Available online 22 September 2011
remained with an average diameter of 2.29 nm. High quality SWCNTs were synthesized with an average diameter of 1.22 nm. The protein chains prevent iron atoms aggregation and so the size of the nanoparticles is smaller than that from ferritin-like proteins. Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved.
1.
Introduction
The electronic properties of single-walled carbon nanotubes (SWCNTs) are strongly related to their diameter and chirality [1,2]. Among many factors that affect the diameter and chirality of SWCNTs, such as growth temperature, gas composition and precursors, the size of catalyst particle has been the most important issue on the growth of SWCNTs [3,4]. Since ferritin, an iron storage protein, was adopted for the precise control of the number of iron atoms as a catalyst for the growth of SWCNTs [5], Co-filled ferritin [6] and DNA-binding proteins from starved cells (Dps) [7,8] have been widely used to synthesize SWCNTs as well as multi-walled carbon nanotubes (MWCNTs) [9–11]. Narrow diameter distribution was achieved by sedimentation velocity centrifugation to separate ferritin according to the size [12]. Dps also yielded SWCNTs with narrow diameter distribution [7]. When using these ferritin-like proteins as a catalyst, discrete catalytic nanoparticles were obtained by placing controllable number of iron atoms into the cores of an empty ferritin [5]. However, the incorporation of iron atoms into the core of an empty ferritin is known to be a multistep process involving the binding and migration of Fe(II) to the ferroxidase site, Fe(II) oxidation, Fe(III) hydrolysis and the nucleation and growth of the mineral core in
iron-containing aqueous solutions [13]. As an effort to avoid this complex process, we introduced iron-containing proteins – hemoglobin (Hb), myoglobin (Mb), or cytochrome c (Cyt c) – as iron catalyst sources, and synthesized MWCNTs [14]. Previously, we demonstrated the catalytic possibility of the nanoparticles derived from three kinds of iron-containing proteins on the growth of MWCNTs. In this paper, we focused on the analysis of the nanoparticles derived from Hb in detail, and they can synthesize not only MWCNTs but SWCNTs by optimizing the experimental conditions.
2.
Experimental
2.1.
Catalyst preparation
Hb from bovine heart (Sigma–Aldrich, H2500) was purchased as lyophilized powders and used without further purification. Hb was dissolved in distilled water at a concentration of 5 mg/ ml at room temperature. For the growth of SWCNTs, a Si wafer with a 300 nm thick thermally grown oxide layer was used as a substrate. The silicon oxide layer was used as a buffer layer to prevent iron silicide formation at the high temperatures used in the growth of carbon nanotubes (CNTs). The substrates were hydrophilic treated using piranha solution
* Corresponding author: Fax: +82 54 279 8298. E-mail address: [email protected] (K.-H. Lee). 0008-6223/$ - see front matter Crown Copyright Ó 2011 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2011.09.038
CARBON
5 0 (2 0 1 2) 7 2 2–72 6
723
(70 vol.% H2SO4 + 30 vol.% H2O2) for 30 min at 140 °C, followed by sonication twice in distilled water for 15 min, and then blow-dried with nitrogen. Hb was deposited onto the substrates by spin coating method with 2000 rpm for 40 s five times each. After spin coating, the protein chains of Hb were removed by oxidation at 800 °C for 5 min in air.
2.2.
Growth of SWCNTs
SWCNTs were grown by thermal chemical vapor deposition (CVD) using a 1 in. quartz tube furnace. As-prepared substrates were placed in the quartz tube and heated to 750 °C under an argon (500 sccm) atmosphere. After the temperature stabilized, the substrates were reduced in hydrogen (400 sccm) for 10 min. Subsequently, ethylene (100 sccm) was introduced for 20 min, followed by cooling with argon to room temperature.
2.3.
Analysis methods
The iron oxide nanoparticles were characterized with an atomic force microscope (AFM, Veeco, Dimension 3100) and high resolution transmission electron microscope (TEM, JEOL, JEM-2100F). TEM samples were prepared as follows. The nanoparticles-deposited substrate was cut to a 3 mm disk and backside of the disk was dimpled down to about 10– 20 lm at the center of the disk. Then, the disk was Ar ionmilled from the backside until the tiny hole at the center of the disk was made, and then introduced to the TEM chamber. Raman spectroscopy (Jobin–Yvon, LabRam HR) was performed using a 512 nm excitation beam.
3.
Results and discussion
Fig. 1 shows the AFM analysis of the nanoparticles derived from Hb. Hb was deposited onto a hydrophilic treated Si/ SiO2 substrate by spin coating method. Previously, we have reported that the self-assembled monolayer (SAM) films allow Hb to be adsorbed onto them with appropriate density that can initiate the growth of CNTs [14]. However, the SAM film formation process requires a lot of attention. Here, by using spin coating method, Hb was easily deposited on a substrate by optimizing the concentration of Hb-containing solution and the spin coating rate. After deposition on a substrate and oxidation at a high temperature, the protein chains were removed, and only iron atoms remained on the substrate, because Hb consists of carbon, hydrogen, nitrogen, oxygen, sulfur and iron. At high temperature, iron atoms are highly mobile enough to form nanoparticles assembling with iron atoms from nearby other Hbs. As shown in Fig. 1(a), discrete nanoparticles were formed from Hb. The topographic height profile in Fig. 1(b) was mainly used to measure the diameter of the nanoparticles due to the AFM tip convolution in measuring apparent widths. Fig. 1(c) shows the size distribution of the nanoparticles and the histogram was obtained by examination of approximately 100 individual particles. The average diameter of nanoparticles was found to be 2.41 ± 0.66 nm and this value is similar to the smallest size of the nanoparticles obtained
Fig. 1 – (a) AFM image of nanoparticles derived from Hb. (b) AFM height profile along the line in (a). (c) Histogram of diameter distribution of the nanoparticles.
from size-separated ferritin by sedimentation velocity centrifugation at 30,000 rpm for 17 h [12]. When using ferritin as a catalyst carrier, discrete catalytic nanoparticles were obtained by loading iron atoms into the cores of empty ferritin, and later removing organic shells [5,6,11]. Accordingly, the size of the nanoparticles is determined by ferritin loading time or number of loadings. Therefore, it is difficult to load accurate number of iron atoms into the cores, especially small number of iron atoms [5,15]. Unlike ferritin, Hb has defined number of iron atoms per molecule. One Hb molecule contains four heme prosthetic groups that each has an iron atom, i.e., four iron atoms per Hb molecule. This means that more accurate control of the size of catalyst particles is possible, at least in theory, thus more narrow size distribution of synthesized CNTs. Iron oxide nanoparticles are formed by decomposition of protein chains as illustrated in Fig. 2. Since protein chains in each Hb are likely to prevent the iron atoms from aggregation, it is favorable to form smaller diameter nanoparticles as compared with the case of using ferritin.
724
CARBON
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
Fig. 2 – Formation of nanoparticles derived from Hbdeposited substrate by decomposition of protein chains.
TEM analysis confirmed the formation of the nanoparticles derived from Hb. The distribution of the nanoparticles in Fig. 3(a) corresponds to that obtained by AFM, and the high resolution image in the inset shows the lattice fringes of the nanoparticles. The nanoparticles were spherical and crystalline with a diameter of approximately 2 nm. The presence of iron was confirmed by energy dispersive spectroscopy (EDS) in Fig. 3(b).
Fig. 4(a) shows the AFM images of SWCNTs grown from the nanoparticles derived from Hb. The SWCNTs were mostly isolated and not bundled. The diameters of SWCNTs were measured by their heights from topographic profile. The diameter distribution of SWCNTs in Fig. 4(b) was obtained from over 100 individual SWCNTs, and the average diameter of grown SWCNTs was 1.22 ± 0.43 nm. As previous studies on ferritinlike proteins, the diameter of SWCNTs is smaller than the size of the nanoparticles [5,6,8,12]. Because the size of the nanoparticles was measured after oxidation to remove the proteins chains, the measurements indicates the size of oxide nanoparticles. However, the SWCNTs are actually synthesized from iron nanoparticles reduced by hydrogen before the growth of SWCNTs. This makes the difference between the nanoparticles and the SWCNTs in size. Considering that the diameter of a SWCNT is roughly equal to the size of a reduced iron catalyst particle, we used the following equation to estimate the average number of iron atoms per iron catalyst particle. N¼
pqD3 NA 6M
ð1Þ
Where the density of face centered cubic (fcc) iron q = 7.874 g/ cm3, the average diameter of iron catalyst particle D = 1.22 nm, the atomic mass of iron M = 55.845 g/mol and NA is Avogadro’s number. According to this calculation, a
Fig. 3 – (a) TEM image of nanoparticles derived from Hb. The inset shows a high resolution TEM image of one of the nanoparticles. The scale bar is 2 nm. (b) EDS of the nanoparticles.
Fig. 4 – (a) AFM image of SWCNTs. (b) Histogram of diameter distribution of SWCNTs.
CARBON
5 0 (2 0 1 2) 7 2 2–72 6
725
derived from Hb was confirmed by AFM and TEM images. Because Hb has iron atoms in itself, the nanoparticles are formed by assembly of iron atoms from Hb molecules. Since protein chains prevent iron atoms from aggregation during decomposition, smaller size of nanoparticles tends to form. Raman spectroscopic analysis has approved the growth of high quality SWCNTs by using the nanoparticles derived from Hb.
Acknowledgments The authors would like to thank the Ministry of Education, Science and Technology of Korea for its financial support through the second phase BK21 program. This work was also supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MEST) (Grant No. 2011-0000360).
R E F E R E N C E S
Fig. 5 – (a) TEM image of SWCNTs. The scale bar in inset is 5 nm. (b) Raman spectra of SWCNTs grown from Hb.
1.22 nm iron nanoparticle consists of approximately 80 iron atoms. In other words, 20 Hb molecules are assembled to form a 1.22 nm iron nanoparticle because one Hb molecule has four iron atoms. We believe it is possible to accurately control the size of iron catalyst particles by controlling the number of assembled Hb molecules. Such an effort is ongoing in our laboratory. TEM image in Fig. 5(a) clearly shows that SWCNTs are synthesized from discrete catalytic nanoparticles. As-synthesized SWCNTs are mostly isolated as shown in AFM image but they are bundled in the dispersion on TEM grid. Fig. 5(b) shows the Raman spectrum for the SWCNTs obtained from this work. The single peak in the range of the radial breathing mode (RBM) indicates the existence of SWCNTs in our sample. By the relation, d ¼ 248=x
ð2Þ
where d is tube diameter and x is the Raman shift, the peak at 154 cm1 corresponds to SWCNTs with 1.61 nm diameter and this value is in the range of measured diameter by AFM. Also, weak D-band (1344 cm1) and strong G-band (1594 cm1) indicates the synthesis of high quality SWCNTs.
4.
Conclusions
In conclusion, we have synthesized high quality SWCNTs by using Hb as a catalyst. The formation of the nanoparticles
[1] Odom TW, Huang JL, Kim P, Lieber CM. Atomic structure and electronic properties of single-walled carbon nanotubes. Nature 1998;391:62–4. [2] Wildoer JWG, Venema LC, Rinzler AG, Smalley RE, Dekker C. Electronic structure of atomically resolved carbon nanotubes. Nature 1998;391:59–62. [3] Nasibulin AG, Pikhitsa PV, Jiang H, Kauppinen EI. Correlation between catalyst particle and single-walled carbon nanotube diameters. Carbon 2005;43:2251–7. [4] Inoue T, Gunjishima I, Okamoto A. Synthesis of diametercontrolled carbon nanotubes using centrifugally classified nanoparticle catalysts. Carbon 2007;45:2164–70. [5] Li Y, Kim W, Zhang Y, Rolandi M, Wang D, Dai H. Growth of single-walled carbon nanotubes from discrete catalytic nanoparticles of various sizes. J Phys Chem B 2001;105:11424–31. [6] Jeong G-H, Yamazaki A, Suzuki S, Yoshimura H, Kobayashi Y, Homma Y. Cobalt-filled apoferritin for suspended single walled carbon nanotubes growth with narrow diameter distribution. J Am Chem Soc 2005;127:8238–9. [7] Kramer RM, Sowards LA, Pender MJ, Stone MO, Naik RR. Constrained iron catalysts for single-walled carbon nanotube growth. Langmuir 2005;21:8466–70. [8] Jeong G-H, Yamazaki A, Suzuki S, Yoshimura H, Kobayashi Y, Homma Y. Production of single-walled carbon nanotubes with narrow diameter distribution using iron nanoparticles derived from DNA-binding proteins from starved cells. Carbon 2007;45(5):978–83. [9] Zhang Y, Li Y, Kim W, Wang D, Dai H. Imaging as-grown single-walled carbon nanotubes originated from isolated catalytic nanoparticles. Appl Phys A Mater Sci Process 2002;74(3):325–8. [10] Tempel H, Joshi R, Schneider JJ. Ink jet printing of ferritin as method for selective catalyst patterning and growth of multiwalled carbon nanotubes. Mater Chem Phys 2010;121(1– 2):178–83. [11] Bonard J-M, Chauvin P, Klinke C. Monodisperse multiwall carbon nanotubes obtained with ferritin as catalyst. Nano Lett 2002;2(6):665–7. [12] Durrer L, Greenwald J, Helbling T, Muoth M, Riek R, Hierold C. Narrowing SWNT diameter distribution using size-separated ferritin-based Fe catalysts. Nanotechnology 2009;20:355601. [13] Yang X, Chen-Barrett Y, Arosio P, Chasteen ND. Reaction paths of iron oxidation and hydrolysis in horse spleen and
726
CARBON
5 0 ( 2 0 1 2 ) 7 2 2 –7 2 6
recombinant human ferritins. Biochemistry 1998;37(27):9743–50. [14] Kim H-J, Oh E, Lee J, Shim D-S, Lee K-H. Synthesis of carbon nanotubes with catalytic iron-containing proteins. Carbon 2011;49(12):3717–22.
[15] Durrer L, Helbling T, Zenger C, Jungen A, Stampfer C, Hierold C. SWNT growth by CVD on ferritin-based iron catalyst nanoparticles towards CNT sensors. Sens Actuators B 2008;132:485–90.