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Controlling the carbon nanotube type with processing parameters synthesized by floating catalyst chemical vapour deposition
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 1039–1043
www.materialstoday.com/proceedings
ICN3I-2017
Controlling the carbon nanotube type with processing parameters synthesized by floating catalyst chemical vapour deposition Manishkumar D. Yadava, Kinshuk Dasguptab*, Ashwin W. Patwardhana, Jyeshtharaj B. Joshia a
Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400019, India b Materials Group, Bhabha Atomic Research Centre, Mumbai 400085,India
Abstract Single and multi-walled carbon nanotubes have been synthesized by floating catalyst chemical vapour deposition technique. Methane, argon, ferrocene and sulphur were used as carbon source, inert gas, catalyst and promoter, respectively. The types of carbon nanotubes (single or multi-walled) were governed by a variety of experimental factors: the ferrocene flow rate, methane flow rate, sulfur flow rate, argon flow rate and reaction temperature. The optimization of the process parameters was carried out to find the parameter 'islands' for the selective formation of single or multiwalled carbon nanotubes. The characterization was carried out by transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. A high hydrogen flow rate, low methane flow rate and high sulfur flow rate were crucial factors for selective synthesis of single walled carbon nanotubes. This work provides methodology for optimization of processing parameters for synthesizing high purity single or multi walled carbon nanotubes. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017). Keywords:floating catalyst; ferrocene; Raman spectroscopy; transmission electron microscopy
*
Corresponding Author; Tel: +91 22 25594951; Fax: +91 22 25505151; Email:[email protected]
2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017).
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M.D. Yadav et al. / Materials Today: Proceedings 18 (2019) 1039–1043
1. Introduction Since 1991, carbon nanotubes (CNTs) have been the centre of attraction of scientist and engineers across the globe. Various high-end promising applications of CNTs, such as, energy storage, water purification, composites, etc have been achieved in past decade[1]. Various methods, such as, laser ablation, arc discharge, chemical vapour deposition(CVD) are reported for the synthesis of CNTs[2]. Among the aforementioned techniques, CVD is the most amenable and scalable method for the synthesis of CNTs at large scale. Floating catalyst chemical vapour deposition (FC-CVD) is one of the techniques among CVD, where catalyst precursor and hydrocarbon enter the reactor simultaneously[3]. Metallocenes, such as, ferrocene, cobaltocene etc are catalyst precursor reported in literature. Various carbon sources with high decomposition temperature, such as, methane, hexane, xylene, toluene, benzene as well as that with low decomposition temperature such as acetone, ethylene glycol, ethanol, butanol etc have been used for the synthesis of CNTs. Industrial scale synthesis of both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) is achieved as per the required application. SWCNTs are mainly utilized in electronics industries[4] while MWCNTs are mainly utilized for composite based applications[5]. Though plethora of literature exists for synthesis of SWCNTs and MWCNTs separately, recipe for the synthesis of both MWCNTs and SWCNTs in a single reactor is still missing. Present work reports synthesis of both SWCNTs and MWCNTs using FC-CVD technique is a single reactor by tuning operating conditions such as inert gas flow rate and concentration of growth promoters. 2. Experimental 2.1 Materials Methane and argon were supplied by Six Sigma Gases India Pvt. Ltd with a purity of 99.999%. Ferrocene (98 %) and sulfur (99.998%) were procured from Sigma Aldrich, USA and were used without further purification. The mass flow rates of gases were regulated using three Aalborg mass flow controllers (MFCs). 2.2 Methods CNT synthesis was carried out by thermocatalytic decomposition of methane in presence of ferrocene and sulfur as catalyst precursor and growth promoters respectively. Two zone horizontal tubular furnace equipped with quartz tube (i.d. 38 mm, length 1200 mm) were utilized for the synthesis of both single and multi-walled carbon nanotubes. Ferrocene and sulfur were placed in alumina boat in one of the heating zone. The catalyst precursor was heated to 393 K in Ar atmosphere subsequently the temperature of second zone was raised to the reaction temperature i.e 1273 K. Methane was purged into the reactor at 10 - 30 sccm for about 30 minutes after which purging was terminated. The synthesized CNTs were collected from the walls of the reactor and subsequently cleaned using dilute hydrochloric acid in order to remove the excess catalyst particles. Samples were dried using vacuum over for 12 h and used for further characterization. The processing parameters utilized for synthesis of MWCNT and SWCNT is shown in Table 1. Table 1. Synthesis conditions for MWCNT and SWCNT Parameters
MWCNT
SWCNT
Methane flow rate(sccm)
40
10
Argon gas flow rate (sccm)
250
800
Promoter
----
Sulfur
Synthesis temperature (K)
1273
1273
Synthesis pressure (atm)
1
1
M.D. Yadav et al. / Materials Today: Proceedings 18 (2019) 1039–1043
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3. Result and Discussion 3.1 Transmission Electron Microscopy CNTs were characterized using transmission electron microscopy(TEM) [JEM2100 (JEOL Inc.)] with accelerating voltage of 200 kV. Figure 1A and 1 B illustrate the TEM images of MWCNTs and SWCNTs respectively. It can be observed that clusters of nanotubes are formed with uniform diameter distribution. Over 50 nanotubes were analyzed using TEM images in order to get diameter distribution. The outer diameter of MWCNTs formed is in the range of 3.5 to 20 nm while in case of SWCNTs it is in the range of 0.8 to 1.3 nm.
Fig. 1. TEM image of MWCNTs (A) and SWCNTs (B) along with diameter distribution
3.2 Raman spectroscopy In order to characterize crystallinity of the CNTs synthesized, Raman spectroscopy was used (WITec GmbH , 514 nm Ar-Ne laser). Raman spectrum provides signatures peaks/bands for distinguishing single-walled and multiwalled CNTs. As shown in Figure 2A MWCNTs depicts peaks at 1345 cm-1, 1570 cm-1 and 2685 cm-1 corresponding to D, G and 2D band respectively. Similarly Figure 2B depicts peaks at 178.8 cm-1, 1593.3 cm-1 and 2680 cm-1 corresponding to radial breathing mode(RBM), G and 2D band respectively. The intensity ratio of D and G band is a measure of quality of CNTs synthesized. In case of MWCNTs ID/IG corresponds to 0.7 while in case of SWCNTs it corresponds to less than 0.01. Presence of RBM peaks in Figure 2B confirms the presence of SWCNTs. CNT diameter and RBM wave numbers are correlated using following correlation.
ω RBM =
A +B (1) d
Where, A and B are constants with values 234 and 10 cm-1 respectively. The outer diameter of SWCNTs calculated using equation (1) is 1.17 nm which is in consistency with TEM images.
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1593.3
1570
Intensity (a.u.)
Intensity (a.u.)
1345
2685
2680.7
213.2 178.8 300
800
1300
1800
2300
Raman Shift (cm-1)
2800
3300
0
500
1000
1500
2000
2500
3000
Raman Shift (cm-1)
Fig. 2.Raman spectrum of (A) MWCNT and (B) SWCNT with laser 514 nm laser wavelength
4. Discussion The formation mechanisms of MWCNT and SWCNT have been explained schematically in Figure 3.
Fig. 3. Schematic of formation of MWCNTs and SWCNTs using FC-CVD
The growth mechanism of CNTs both MWCNTs and SWCNTs have been studied in great detail by various groups[6-8]. The growth process can be divided into four steps. First step includes mass transfer of carbon source from bulk to the surface of active catalyst site. Subsequently adsorption of carbon source on the active site followed by surface reaction in order to form carbon, hydrogen and other intermediates. Carbon formed during surface reaction undergoes bulk diffusion into the catalyst nanoparticles. As per the supersaturation level of the catalyst particles at the given conditions precipitation of carbon takes place in the form of nanotube. In present work, a mixture of ferrocene, hydrocarbon and sulfur (in case of SWCNT) is purged into a reactor maintained at 1000 0C. Catalyst particles i.e iron nanoparticles are formed due to thermochemical decomposition of ferrocene[9]. Iron nanoparticles act as the active sites for the growth of CNTs. In order to control the formation of either SWCNTs or MWCNTs, control over the size of iron nanoparticles is must. CNT diameters are directly related to the size of catalyst nanoparticles. In order to synthesize SWCNTs or MWCNTs selectively, agglomerations of iron
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1043
nanoparticles must be controlled. Addition of sulfur along with ferrocene provides a protective layer around the catalyst nanoparticles which aids in decelerating the aggolomeration formation of iron nanoparticles[10]. Hence, sulfur coated iron nanoparticles forms selectively SWCNTs, while in absence of sulfur MWCNTs are formed predominantly. As shown in Table 1, in case of MWCNTs synthesis argon flow rate was maintained about 250 sccm while in case of SWCNTs it is about 800 sccm. Increase in inert gas flow rate has been reported to reduce the diameter of CNTs formed. Since, higher flow rate decreases the residence time of catalyst particles inside the reactor which helps in reducing agglomeration of catalyst particles. 5. Conclusions We have developed protocols for selective synthesis of MWCNT and SWCNT in same reactor by tuning the processing parameters in continuous manner using FC-CVD. We found that sulfur is an essential growth promoter required during synthesis of SWCNT. In addition, inert gas flow rate is an important parameter in order to synthesize MWCNTs or SWCNTs selectively. Characterization reports such as Raman spectrum and TEM confirm formation of high quality of CNTs using FC-CVD. Present approach opens up a new way in synthesizing both SWCNT and MWCNT in a single reactor using simple and easily scalable FC-CVD method. References [1] R.H. Baughman, A.A. Zakhidov, W.A. De Heer, Science, 297 (2002) 787-792. [2] M.D. Yadav, K. Dasgupta, A.W. Patwardhan, J.B. Joshi, Industrial & engineering chemistry research, 56 (2017) 12407-12437. [3] Y. Xu, Y. Ma, Y. Liu, S. Feng, D. He, P. Haghi-Ashtiani, A. Dichiara, L. Zimmer, J. Bai, The Journal of Physical Chemistry C, (2018). [4] J. Lefebvre, J. Ding, Z. Li, P. Finnie, G. Lopinski, P.R. Malenfant, Accounts of chemical research, 50 (2017) 2479-2486. [5] K. Sun, P. Xie, Z. Wang, T. Su, Q. Shao, J. Ryu, X. Zhang, J. Guo, A. Shankar, J. Li, Polymer, 125 (2017) 50-57. [6] D. Conroy, A. Moisala, S. Cardoso, A. Windle, J. Davidson, Chemical engineering science, 65 (2010) 2965-2977. [7] C. Bower, O. Zhou, W. Zhu, D. Werder, S. Jin, Applied Physics Letters, 77 (2000) 2767-2769. [8] K.A. Shah, B.A. Tali, Materials Science in Semiconductor Processing, 41 (2016) 67-82. [9] A. Barreiro, S. Hampel, M.H. Rümmeli, C. Kramberger, A. Grüneis, K. Biedermann, A. Leonhardt, T. Gemming, B. Büchner, A. Bachtold, The Journal of Physical Chemistry B, 110 (2006) 20973-20977. [10] S.-H. Lee, J. Park, H.-R. Kim, J. Lee, K.-H. Lee, RSC Advances, 5 (2015) 41894-41900.
ScienceDirect Materials Today: Proceedings 18 (2019) 1039–1043
www.materialstoday.com/proceedings
ICN3I-2017
Controlling the carbon nanotube type with processing parameters synthesized by floating catalyst chemical vapour deposition Manishkumar D. Yadava, Kinshuk Dasguptab*, Ashwin W. Patwardhana, Jyeshtharaj B. Joshia a
Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400019, India b Materials Group, Bhabha Atomic Research Centre, Mumbai 400085,India
Abstract Single and multi-walled carbon nanotubes have been synthesized by floating catalyst chemical vapour deposition technique. Methane, argon, ferrocene and sulphur were used as carbon source, inert gas, catalyst and promoter, respectively. The types of carbon nanotubes (single or multi-walled) were governed by a variety of experimental factors: the ferrocene flow rate, methane flow rate, sulfur flow rate, argon flow rate and reaction temperature. The optimization of the process parameters was carried out to find the parameter 'islands' for the selective formation of single or multiwalled carbon nanotubes. The characterization was carried out by transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. A high hydrogen flow rate, low methane flow rate and high sulfur flow rate were crucial factors for selective synthesis of single walled carbon nanotubes. This work provides methodology for optimization of processing parameters for synthesizing high purity single or multi walled carbon nanotubes. © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017). Keywords:floating catalyst; ferrocene; Raman spectroscopy; transmission electron microscopy
*
Corresponding Author; Tel: +91 22 25594951; Fax: +91 22 25505151; Email:[email protected]
2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanotechnology: Ideas, Innovations & Initiatives-2017 (ICN:3i2017).
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M.D. Yadav et al. / Materials Today: Proceedings 18 (2019) 1039–1043
1. Introduction Since 1991, carbon nanotubes (CNTs) have been the centre of attraction of scientist and engineers across the globe. Various high-end promising applications of CNTs, such as, energy storage, water purification, composites, etc have been achieved in past decade[1]. Various methods, such as, laser ablation, arc discharge, chemical vapour deposition(CVD) are reported for the synthesis of CNTs[2]. Among the aforementioned techniques, CVD is the most amenable and scalable method for the synthesis of CNTs at large scale. Floating catalyst chemical vapour deposition (FC-CVD) is one of the techniques among CVD, where catalyst precursor and hydrocarbon enter the reactor simultaneously[3]. Metallocenes, such as, ferrocene, cobaltocene etc are catalyst precursor reported in literature. Various carbon sources with high decomposition temperature, such as, methane, hexane, xylene, toluene, benzene as well as that with low decomposition temperature such as acetone, ethylene glycol, ethanol, butanol etc have been used for the synthesis of CNTs. Industrial scale synthesis of both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) is achieved as per the required application. SWCNTs are mainly utilized in electronics industries[4] while MWCNTs are mainly utilized for composite based applications[5]. Though plethora of literature exists for synthesis of SWCNTs and MWCNTs separately, recipe for the synthesis of both MWCNTs and SWCNTs in a single reactor is still missing. Present work reports synthesis of both SWCNTs and MWCNTs using FC-CVD technique is a single reactor by tuning operating conditions such as inert gas flow rate and concentration of growth promoters. 2. Experimental 2.1 Materials Methane and argon were supplied by Six Sigma Gases India Pvt. Ltd with a purity of 99.999%. Ferrocene (98 %) and sulfur (99.998%) were procured from Sigma Aldrich, USA and were used without further purification. The mass flow rates of gases were regulated using three Aalborg mass flow controllers (MFCs). 2.2 Methods CNT synthesis was carried out by thermocatalytic decomposition of methane in presence of ferrocene and sulfur as catalyst precursor and growth promoters respectively. Two zone horizontal tubular furnace equipped with quartz tube (i.d. 38 mm, length 1200 mm) were utilized for the synthesis of both single and multi-walled carbon nanotubes. Ferrocene and sulfur were placed in alumina boat in one of the heating zone. The catalyst precursor was heated to 393 K in Ar atmosphere subsequently the temperature of second zone was raised to the reaction temperature i.e 1273 K. Methane was purged into the reactor at 10 - 30 sccm for about 30 minutes after which purging was terminated. The synthesized CNTs were collected from the walls of the reactor and subsequently cleaned using dilute hydrochloric acid in order to remove the excess catalyst particles. Samples were dried using vacuum over for 12 h and used for further characterization. The processing parameters utilized for synthesis of MWCNT and SWCNT is shown in Table 1. Table 1. Synthesis conditions for MWCNT and SWCNT Parameters
MWCNT
SWCNT
Methane flow rate(sccm)
40
10
Argon gas flow rate (sccm)
250
800
Promoter
----
Sulfur
Synthesis temperature (K)
1273
1273
Synthesis pressure (atm)
1
1
M.D. Yadav et al. / Materials Today: Proceedings 18 (2019) 1039–1043
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3. Result and Discussion 3.1 Transmission Electron Microscopy CNTs were characterized using transmission electron microscopy(TEM) [JEM2100 (JEOL Inc.)] with accelerating voltage of 200 kV. Figure 1A and 1 B illustrate the TEM images of MWCNTs and SWCNTs respectively. It can be observed that clusters of nanotubes are formed with uniform diameter distribution. Over 50 nanotubes were analyzed using TEM images in order to get diameter distribution. The outer diameter of MWCNTs formed is in the range of 3.5 to 20 nm while in case of SWCNTs it is in the range of 0.8 to 1.3 nm.
Fig. 1. TEM image of MWCNTs (A) and SWCNTs (B) along with diameter distribution
3.2 Raman spectroscopy In order to characterize crystallinity of the CNTs synthesized, Raman spectroscopy was used (WITec GmbH , 514 nm Ar-Ne laser). Raman spectrum provides signatures peaks/bands for distinguishing single-walled and multiwalled CNTs. As shown in Figure 2A MWCNTs depicts peaks at 1345 cm-1, 1570 cm-1 and 2685 cm-1 corresponding to D, G and 2D band respectively. Similarly Figure 2B depicts peaks at 178.8 cm-1, 1593.3 cm-1 and 2680 cm-1 corresponding to radial breathing mode(RBM), G and 2D band respectively. The intensity ratio of D and G band is a measure of quality of CNTs synthesized. In case of MWCNTs ID/IG corresponds to 0.7 while in case of SWCNTs it corresponds to less than 0.01. Presence of RBM peaks in Figure 2B confirms the presence of SWCNTs. CNT diameter and RBM wave numbers are correlated using following correlation.
ω RBM =
A +B (1) d
Where, A and B are constants with values 234 and 10 cm-1 respectively. The outer diameter of SWCNTs calculated using equation (1) is 1.17 nm which is in consistency with TEM images.
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1593.3
1570
Intensity (a.u.)
Intensity (a.u.)
1345
2685
2680.7
213.2 178.8 300
800
1300
1800
2300
Raman Shift (cm-1)
2800
3300
0
500
1000
1500
2000
2500
3000
Raman Shift (cm-1)
Fig. 2.Raman spectrum of (A) MWCNT and (B) SWCNT with laser 514 nm laser wavelength
4. Discussion The formation mechanisms of MWCNT and SWCNT have been explained schematically in Figure 3.
Fig. 3. Schematic of formation of MWCNTs and SWCNTs using FC-CVD
The growth mechanism of CNTs both MWCNTs and SWCNTs have been studied in great detail by various groups[6-8]. The growth process can be divided into four steps. First step includes mass transfer of carbon source from bulk to the surface of active catalyst site. Subsequently adsorption of carbon source on the active site followed by surface reaction in order to form carbon, hydrogen and other intermediates. Carbon formed during surface reaction undergoes bulk diffusion into the catalyst nanoparticles. As per the supersaturation level of the catalyst particles at the given conditions precipitation of carbon takes place in the form of nanotube. In present work, a mixture of ferrocene, hydrocarbon and sulfur (in case of SWCNT) is purged into a reactor maintained at 1000 0C. Catalyst particles i.e iron nanoparticles are formed due to thermochemical decomposition of ferrocene[9]. Iron nanoparticles act as the active sites for the growth of CNTs. In order to control the formation of either SWCNTs or MWCNTs, control over the size of iron nanoparticles is must. CNT diameters are directly related to the size of catalyst nanoparticles. In order to synthesize SWCNTs or MWCNTs selectively, agglomerations of iron
M.D. Yadav et al. / Materials Today: Proceedings 18 (2019) 1039–1043
1043
nanoparticles must be controlled. Addition of sulfur along with ferrocene provides a protective layer around the catalyst nanoparticles which aids in decelerating the aggolomeration formation of iron nanoparticles[10]. Hence, sulfur coated iron nanoparticles forms selectively SWCNTs, while in absence of sulfur MWCNTs are formed predominantly. As shown in Table 1, in case of MWCNTs synthesis argon flow rate was maintained about 250 sccm while in case of SWCNTs it is about 800 sccm. Increase in inert gas flow rate has been reported to reduce the diameter of CNTs formed. Since, higher flow rate decreases the residence time of catalyst particles inside the reactor which helps in reducing agglomeration of catalyst particles. 5. Conclusions We have developed protocols for selective synthesis of MWCNT and SWCNT in same reactor by tuning the processing parameters in continuous manner using FC-CVD. We found that sulfur is an essential growth promoter required during synthesis of SWCNT. In addition, inert gas flow rate is an important parameter in order to synthesize MWCNTs or SWCNTs selectively. Characterization reports such as Raman spectrum and TEM confirm formation of high quality of CNTs using FC-CVD. Present approach opens up a new way in synthesizing both SWCNT and MWCNT in a single reactor using simple and easily scalable FC-CVD method. References [1] R.H. Baughman, A.A. Zakhidov, W.A. De Heer, Science, 297 (2002) 787-792. [2] M.D. Yadav, K. Dasgupta, A.W. Patwardhan, J.B. Joshi, Industrial & engineering chemistry research, 56 (2017) 12407-12437. [3] Y. Xu, Y. Ma, Y. Liu, S. Feng, D. He, P. Haghi-Ashtiani, A. Dichiara, L. Zimmer, J. Bai, The Journal of Physical Chemistry C, (2018). [4] J. Lefebvre, J. Ding, Z. Li, P. Finnie, G. Lopinski, P.R. Malenfant, Accounts of chemical research, 50 (2017) 2479-2486. [5] K. Sun, P. Xie, Z. Wang, T. Su, Q. Shao, J. Ryu, X. Zhang, J. Guo, A. Shankar, J. Li, Polymer, 125 (2017) 50-57. [6] D. Conroy, A. Moisala, S. Cardoso, A. Windle, J. Davidson, Chemical engineering science, 65 (2010) 2965-2977. [7] C. Bower, O. Zhou, W. Zhu, D. Werder, S. Jin, Applied Physics Letters, 77 (2000) 2767-2769. [8] K.A. Shah, B.A. Tali, Materials Science in Semiconductor Processing, 41 (2016) 67-82. [9] A. Barreiro, S. Hampel, M.H. Rümmeli, C. Kramberger, A. Grüneis, K. Biedermann, A. Leonhardt, T. Gemming, B. Büchner, A. Bachtold, The Journal of Physical Chemistry B, 110 (2006) 20973-20977. [10] S.-H. Lee, J. Park, H.-R. Kim, J. Lee, K.-H. Lee, RSC Advances, 5 (2015) 41894-41900.