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Carbon rods with hexa-branched structure and their formation mechanism
Journal Pre-proofs Carbon Rods with Hexa-Branched Structure and their Formation Mechanism Qian Zhang, Fengjian Yang, Jikuan Zhao, Qingqing Zhang, Xiangfang Wu, Jianhua Yu, Lifeng Dong PII: DOI: Reference:
S0167-577X(19)31830-0 https://doi.org/10.1016/j.matlet.2019.127198 MLBLUE 127198
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
13 October 2019 28 November 2019 17 December 2019
Please cite this article as: Q. Zhang, F. Yang, J. Zhao, Q. Zhang, X. Wu, J. Yu, L. Dong, Carbon Rods with HexaBranched Structure and their Formation Mechanism, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet. 2019.127198
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Carbon Rods with Hexa-Branched Structure and their Formation Mechanism Qian Zhang a, *, Fengjian Yang a, Jikuan Zhao b, Qingqing Zhang a, Xiangfang Wu a, Jianhua Yu a, *, Lifeng Dong a, c, *
a College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China b College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China c Department of Physics, Hamline University, Saint Paul, MN, 55104, United States of America
ABSTRACT In this paper, hexa-branched carbon rods are synthesized by chemical vapor deposition (CVD) method, in which copper particles and acetylene are used as catalyst and carbon source, respectively. The most critical step is to disperse copper catalyst particles uniformly in carbon matrix, which is obtained by heat treatment of cross-linked polyacrylamide (PAM). The matrix structure effectively prevents the aggregation of catalyst particles during CVD process. Hexa-branched carbon rods have six pieces of sub-carbon rods with diameters ranging from 2 to 4 μm. The growth mechanism of hexa-branched carbon rods is discussed briefly.
Keywords: Carbon rods; Hexa-branched; Microstructure; Formation mechanism; Chemical vapor deposition 1
1. Introduction Carbon is widely distributed on earth and has several allotropes, including diamond, carbon nanotubes, and carbon fibers with different properties due to their different structures. Especially since the discovery of carbon nanotubes in 1991 [1], many researchers have devoted to the controlled synthesis of one-dimensional carbon materials, such as carbon nanotubes and carbon fibers. Carbon fibers have many advantages and can be widely used in various applications of military and civil industries. For example, carbon fibers can be used as promising candidate materials for flexible and wearable electronics, including sensors [2-6] and flexible supercapacitors [7-9]. Furthermore, structural complexity of carbon fibers can expand their application domains and optimize their applications, and thus the investigation on structural diversity of carbon fibers/nanotubes has been widely carried out. Three-dimensional branched structure of carbon fibers can enhance electron transport in electronic materials [10-11] and mechanical properties of matrix [12-13]. In this paper, carbon rods with a novel structure are synthesized by a catalytic chemical vapor deposition method, each of which comprises of six pieces of sub-carbon rods on the same copper catalyst particle. 2. Experimental All the chemical reagents utilized in this paper are of analytical grade. 15 g acrylamide monomer was dissolved in 140 mL deionized water at 70 ° C in a N2 atmosphere for 30 min, and 10 mL K2S2O8 solution (3.7×10-4 M) was added dropwise to initiate the polymerization process. The solution was stirred for another 3 h in a N2 atmosphere, 135 mL deionized water 2
was then added, and polyacrylamide (PAM) solution (5 wt.%) was obtained after continuous stirring in water bath for 12 h. 30 mL polyacrylamide solution (5 wt.%), 1.264 mL formaldehyde solution (37 wt.%), and 45 mL deionized water were mixed, and then 0.464 g resorcinol and 3.27 g CuCl2·2H2O were added into the mixture solution above and stirred for 2 h. The solution was transferred into an 80 mL steel autoclave, and kept for 15 h at 130 °C. Then, the intermediate product was annealed at 800 °C under nitrogen atmosphere (50 mL/min) for 2 h to obtain copper/carbon matrix catalyst precursor. The utilization of formaldehyde-resorcinol cross-linkers can facilitate the construction of three-dimensional gel to confine the formation of Cu particles. The catalyst precursor was treated by hydrogen at 300 °C for 10 min, and then acetylene was introduced and hexa-branched carbon rods started to grow. The reaction temperature and reaction time were 300 °C and 20 min, respectively. The product was characterized via X-ray diffraction (XRD, Rigaku, D-max-gA), energy dispersive spectrometer (EDS, X-MAXN, Oxford), scanning electron microscopy (SEM, JSM-6700F) and transmission electron microscopy (TEM, JEM-2100Plus). 3. Results and discussion Generally, catalyst particles tend to aggregate during CVD process, which results in the growth of carbon fibers with nonuniform diameters. To solve this problem, carbon matrix was used as a substrate to disperse and fix copper particles. Fig.1 shows FESEM and TEM images of hexa-branched carbon rods, in which each piece of carbon rods is named as sub-carbon rod. As shown in Fig. 1a, hexa-branched carbon rods scatter uniformly inside every grids of the 3
matrix. Each branched carbon rod (Fig. 1b) consists of six pieces of sub-carbon rods on each individual catalyst particle. More importantly, the synthesis of hexa-branched structure of carbon rods has great reproducibility. The yield is around 6 g hexa-branched carbon rods per gram of copper catalyst, and the rods account for about 95 % of the total product through SEM analysis. TEM is utilized to further investigate copper catalyst particles inside hexa-carbon rods (Fig. 1c and 1d), copper catalyst particles appear as hexahedron with six facets for catalytic growth of sub-carbon rods. Although the profiles of two catalyst particles in Fig. 1c and 1d are different, both possess cubic shapes due to different incident angles of electron beam onto the samples. The formation of polyhedron catalyst particles within carbon rods is closely related to the effect of acetylene adsorption on the surface of copper catalyst particles at the beginning of carbon rod growth [14-15].
Fig.1 FESEM images (a, b) and TEM images (c, d) of hexa-branched carbon rods. 4
Fig.2 XRD patterns of catalyst in carbon matrix and hexa-branched carbon rods in carbon matrix. Fig. 2 presents XRD patterns of products. There are three sharp peaks at 43.30 °, 50.43 ° and 74.13 °, which correspond to crystal planes (111), (200) and (220) of copper ( pdf file No.04-0836 ), respectively. The broad peak ranging from 20 ° to 30 ° results from amorphous carbon matrix and carbon rods. Carbon rods are more like polymer structure than pure inorganic carbon ones, in which they may consist of C=C, CH2, and CH3 groups [14-15]. SEM images of copper catalyst particles in carbon matrix are shown in Fig. 3a and 3b. Backscattered electron image is shown in Fig. 3b, in which lots of bright dots can be observed. Those bright dots with high intensity of backscattered electron signals can be metal copper particles since the atomic numbers of copper and carbon are 29 and 6, respectively. Different from copper catalyst particles insides carbon rods, these copper particles in carbon matrix have irregular near-spherical shape. According to crystal growth principles, high-index facets of catalyst particles grow faster than low-index facets, so that low-index facets tend to form the surfaces of the crystal. These catalyst particles tend to agglomerate and form quasi-spherical or ellipsoidal particles. Hansen et al reported that reversible dynamic shape 5
changes of copper particles occurred at 220 °C in response to the changes in gaseous environment [16]. Wang et al also observed that a variation in the area ratio of {100} to {111} results in shape change of particles [17]. Accordingly, in this study, shape changes in copper catalyst particles can be caused by surface reconstruction, and the driving force is the change of surface energy induced by the adsorption of acetylene on different exposed crystal facets of copper catalyst [14]. To further confirm elemental compositions of these bright dots in Fig. 3b, EDS elemental analysis was employed, and EDS elemental mappings are shown in Fig. 3d and 3e, which corresponding SEM image is shown in Fig. 3c. EDS mapping shows that copper catalyst particles with a diameter of 1 to 3 μm are scattered and fixed uniformly in carbon matrix, which is consistent with the diameter of sub-carbon rods in hexa-branched carbon rods. In this case, copper catalyst particles do not agglomerate even at high reaction temperature, which confirms that hexa-branched carbon rods are synthesized.
Fig. 3 SEM images (a, b) of metal copper catalyst particles in carbon matrix. SEM image (c) and corresponding EDS elemental mappings (d, e) of metal copper catalyst particles in 6
carbon matrix. As shown in Fig. 4, a growth model is proposed to elaborate the role of carbon matrix in the growth of hexa-branched carbon rods, which includes two steps during the synthesis. Firstly, copper chloride is mixed uniformly with cross-linked PAM. By means of heat treatment under nitrogen atmosphere, cross-linked PAM is converted to amorphous carbon matrix with grids structure, and copper catalyst particles are formed and inlaid on the wall of carbon matrix. After hydrogen pre-treatment, the surface of copper catalyst particles is reduced to possess high catalytic activity for the growth of sub-carbon rods. Secondly, six pieces of sub-carbon rods grow on the same catalyst particle when acetylene is introduced into reactor.
Fig.4 Growth model of hexa-branched carbon rods. Accordingly, the growth process of carbon rods on copper catalyst particles under low reaction temperature, including hexa-branched carbon rods, can be explained with vapor-facet-solid (VFS) growth mechanism [15], in which V, F and S represent the adsorption of gaseous carbon source, the diffusion of carbon atoms along the facets of copper catalyst particles and the precipitation process of carbon rods. For this growth mechanism, acetylene molecules decompose into carbon atoms and/or atom clusters on certain facets of copper catalyst particles; After diffusion of carbon atoms and/or atom clusters to other facets, six 7
pieces of carbon rods start to grow simultaneously, and hexa-branched carbon rods are obtained. 4. Conclusion In this study, high yield of hexa-branched carbon rods were synthesized by CVD method. Through inlaying metal copper particles inside the wall of carbon matrix, the aggregation of catalyst particles was prevented and six pieces of sub-carbon rods were formed on the same catalyst particle. The formation mechanism of hexa-branched carbon rods was discussed briefly. Acknowledgments This work was financially supported by the International Science & Technology Cooperation Program of China (2014DFA60150), the National Natural Science Foundation of China (21776147), and the Shandong Natural Science Foundation (ZR2012EMM006). L. F. Dong also thanks financial support from the Malmstrom Endowment Fund at Hamline University. References [1] S. Iijima, Nature 354 (1991) 56-58. [2] Y. Cheng, R. Wang, J. Sun, et al., Adv. Mater. 27 (2015) 7365-7371. [3] C. Wang, X. Li, E. Gao, et al., Adv. Mater. 28 (2016) 6639-6639. [4] Q. Wang, M.Q. Jian, C. Wang, et al., Adv. Funct. Mater. 27(2017) 1605657 [5] C. Wang, K.L. Xia, M. Zhang, et al., ACS Appl. Mater. Inter. 9 (2017) 39484-39492. [6] Y. Li, Y.A. Samad, K. Liao, J. Mater. Chem. A 3 (2015) 2181-2187. [7] C. Wang, M. Zhang, K. Xia, et al., ACS Appl. Mater. Inter. 9 (2017) 13331-13338. 8
[8] H. Wang, C. Wang, M. Jian, et al., Nano Res. 11 (2018) 2347-2356. [9] P. Luan, N. Zhang, W. Zhou, et al., Adv. Funct. Mater. 26 (2016) 8178-8184. [10] S. Darbari, Y. Abdi, S. Mohajerzadeh, Sens. Actuators, A, 167(2) (2011) 389-397. [12] X.Q. Liang, F. Wang, M.H. Chen, et al., Ceram. Int., 44(14) (2018) 16791-16798. [13] K.L. Zhang, Y.J. Li, X.W. He, et al., Compos. Sci. Technol., 167 (2018) 1-6. [14] X. Jian, M. Jiang, Z.W. Zhou, et al., Carbon 48 (2010) 4535-4541. [15] Y. Ma, X. Sun, N.J. Yang, et al., Chem. Eur. J. 21 (2015) 12370-12375. [16] P.L. Hansen, J.B. Wagner, S. Helveg, et al., Science 295 (5562) (2002) 2053-2055. [17] Z.L. Wang. J. Phys. Chem. B 104 (2000) 1153-1175.
Hexa-branched carbon fibers are synthesized by chemical vapor deposition method.
The key step is to disperse copper catalyst particles uniformly in carbon matrix.
The growth mechanism of hexa-branched carbon fibers is discussed briefly.
Qian Zhang: Conceptualization, Writing - Review & Editing, Funding acquisition. Fengjian Yang: Writing - Original Draft, Validation, Software. Jikuan Zhao: Resources. Qingqing Zhang：Investigation. Xiangfang Wu：Investigation. Jianhua Yu：Investigation, Validation. Lifeng Dong：Supervision，Funding acquisition.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 9
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
10
S0167-577X(19)31830-0 https://doi.org/10.1016/j.matlet.2019.127198 MLBLUE 127198
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
13 October 2019 28 November 2019 17 December 2019
Please cite this article as: Q. Zhang, F. Yang, J. Zhao, Q. Zhang, X. Wu, J. Yu, L. Dong, Carbon Rods with HexaBranched Structure and their Formation Mechanism, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet. 2019.127198
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Carbon Rods with Hexa-Branched Structure and their Formation Mechanism Qian Zhang a, *, Fengjian Yang a, Jikuan Zhao b, Qingqing Zhang a, Xiangfang Wu a, Jianhua Yu a, *, Lifeng Dong a, c, *
a College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China b College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China c Department of Physics, Hamline University, Saint Paul, MN, 55104, United States of America
ABSTRACT In this paper, hexa-branched carbon rods are synthesized by chemical vapor deposition (CVD) method, in which copper particles and acetylene are used as catalyst and carbon source, respectively. The most critical step is to disperse copper catalyst particles uniformly in carbon matrix, which is obtained by heat treatment of cross-linked polyacrylamide (PAM). The matrix structure effectively prevents the aggregation of catalyst particles during CVD process. Hexa-branched carbon rods have six pieces of sub-carbon rods with diameters ranging from 2 to 4 μm. The growth mechanism of hexa-branched carbon rods is discussed briefly.
Keywords: Carbon rods; Hexa-branched; Microstructure; Formation mechanism; Chemical vapor deposition 1
1. Introduction Carbon is widely distributed on earth and has several allotropes, including diamond, carbon nanotubes, and carbon fibers with different properties due to their different structures. Especially since the discovery of carbon nanotubes in 1991 [1], many researchers have devoted to the controlled synthesis of one-dimensional carbon materials, such as carbon nanotubes and carbon fibers. Carbon fibers have many advantages and can be widely used in various applications of military and civil industries. For example, carbon fibers can be used as promising candidate materials for flexible and wearable electronics, including sensors [2-6] and flexible supercapacitors [7-9]. Furthermore, structural complexity of carbon fibers can expand their application domains and optimize their applications, and thus the investigation on structural diversity of carbon fibers/nanotubes has been widely carried out. Three-dimensional branched structure of carbon fibers can enhance electron transport in electronic materials [10-11] and mechanical properties of matrix [12-13]. In this paper, carbon rods with a novel structure are synthesized by a catalytic chemical vapor deposition method, each of which comprises of six pieces of sub-carbon rods on the same copper catalyst particle. 2. Experimental All the chemical reagents utilized in this paper are of analytical grade. 15 g acrylamide monomer was dissolved in 140 mL deionized water at 70 ° C in a N2 atmosphere for 30 min, and 10 mL K2S2O8 solution (3.7×10-4 M) was added dropwise to initiate the polymerization process. The solution was stirred for another 3 h in a N2 atmosphere, 135 mL deionized water 2
was then added, and polyacrylamide (PAM) solution (5 wt.%) was obtained after continuous stirring in water bath for 12 h. 30 mL polyacrylamide solution (5 wt.%), 1.264 mL formaldehyde solution (37 wt.%), and 45 mL deionized water were mixed, and then 0.464 g resorcinol and 3.27 g CuCl2·2H2O were added into the mixture solution above and stirred for 2 h. The solution was transferred into an 80 mL steel autoclave, and kept for 15 h at 130 °C. Then, the intermediate product was annealed at 800 °C under nitrogen atmosphere (50 mL/min) for 2 h to obtain copper/carbon matrix catalyst precursor. The utilization of formaldehyde-resorcinol cross-linkers can facilitate the construction of three-dimensional gel to confine the formation of Cu particles. The catalyst precursor was treated by hydrogen at 300 °C for 10 min, and then acetylene was introduced and hexa-branched carbon rods started to grow. The reaction temperature and reaction time were 300 °C and 20 min, respectively. The product was characterized via X-ray diffraction (XRD, Rigaku, D-max-gA), energy dispersive spectrometer (EDS, X-MAXN, Oxford), scanning electron microscopy (SEM, JSM-6700F) and transmission electron microscopy (TEM, JEM-2100Plus). 3. Results and discussion Generally, catalyst particles tend to aggregate during CVD process, which results in the growth of carbon fibers with nonuniform diameters. To solve this problem, carbon matrix was used as a substrate to disperse and fix copper particles. Fig.1 shows FESEM and TEM images of hexa-branched carbon rods, in which each piece of carbon rods is named as sub-carbon rod. As shown in Fig. 1a, hexa-branched carbon rods scatter uniformly inside every grids of the 3
matrix. Each branched carbon rod (Fig. 1b) consists of six pieces of sub-carbon rods on each individual catalyst particle. More importantly, the synthesis of hexa-branched structure of carbon rods has great reproducibility. The yield is around 6 g hexa-branched carbon rods per gram of copper catalyst, and the rods account for about 95 % of the total product through SEM analysis. TEM is utilized to further investigate copper catalyst particles inside hexa-carbon rods (Fig. 1c and 1d), copper catalyst particles appear as hexahedron with six facets for catalytic growth of sub-carbon rods. Although the profiles of two catalyst particles in Fig. 1c and 1d are different, both possess cubic shapes due to different incident angles of electron beam onto the samples. The formation of polyhedron catalyst particles within carbon rods is closely related to the effect of acetylene adsorption on the surface of copper catalyst particles at the beginning of carbon rod growth [14-15].
Fig.1 FESEM images (a, b) and TEM images (c, d) of hexa-branched carbon rods. 4
Fig.2 XRD patterns of catalyst in carbon matrix and hexa-branched carbon rods in carbon matrix. Fig. 2 presents XRD patterns of products. There are three sharp peaks at 43.30 °, 50.43 ° and 74.13 °, which correspond to crystal planes (111), (200) and (220) of copper ( pdf file No.04-0836 ), respectively. The broad peak ranging from 20 ° to 30 ° results from amorphous carbon matrix and carbon rods. Carbon rods are more like polymer structure than pure inorganic carbon ones, in which they may consist of C=C, CH2, and CH3 groups [14-15]. SEM images of copper catalyst particles in carbon matrix are shown in Fig. 3a and 3b. Backscattered electron image is shown in Fig. 3b, in which lots of bright dots can be observed. Those bright dots with high intensity of backscattered electron signals can be metal copper particles since the atomic numbers of copper and carbon are 29 and 6, respectively. Different from copper catalyst particles insides carbon rods, these copper particles in carbon matrix have irregular near-spherical shape. According to crystal growth principles, high-index facets of catalyst particles grow faster than low-index facets, so that low-index facets tend to form the surfaces of the crystal. These catalyst particles tend to agglomerate and form quasi-spherical or ellipsoidal particles. Hansen et al reported that reversible dynamic shape 5
changes of copper particles occurred at 220 °C in response to the changes in gaseous environment [16]. Wang et al also observed that a variation in the area ratio of {100} to {111} results in shape change of particles [17]. Accordingly, in this study, shape changes in copper catalyst particles can be caused by surface reconstruction, and the driving force is the change of surface energy induced by the adsorption of acetylene on different exposed crystal facets of copper catalyst [14]. To further confirm elemental compositions of these bright dots in Fig. 3b, EDS elemental analysis was employed, and EDS elemental mappings are shown in Fig. 3d and 3e, which corresponding SEM image is shown in Fig. 3c. EDS mapping shows that copper catalyst particles with a diameter of 1 to 3 μm are scattered and fixed uniformly in carbon matrix, which is consistent with the diameter of sub-carbon rods in hexa-branched carbon rods. In this case, copper catalyst particles do not agglomerate even at high reaction temperature, which confirms that hexa-branched carbon rods are synthesized.
Fig. 3 SEM images (a, b) of metal copper catalyst particles in carbon matrix. SEM image (c) and corresponding EDS elemental mappings (d, e) of metal copper catalyst particles in 6
carbon matrix. As shown in Fig. 4, a growth model is proposed to elaborate the role of carbon matrix in the growth of hexa-branched carbon rods, which includes two steps during the synthesis. Firstly, copper chloride is mixed uniformly with cross-linked PAM. By means of heat treatment under nitrogen atmosphere, cross-linked PAM is converted to amorphous carbon matrix with grids structure, and copper catalyst particles are formed and inlaid on the wall of carbon matrix. After hydrogen pre-treatment, the surface of copper catalyst particles is reduced to possess high catalytic activity for the growth of sub-carbon rods. Secondly, six pieces of sub-carbon rods grow on the same catalyst particle when acetylene is introduced into reactor.
Fig.4 Growth model of hexa-branched carbon rods. Accordingly, the growth process of carbon rods on copper catalyst particles under low reaction temperature, including hexa-branched carbon rods, can be explained with vapor-facet-solid (VFS) growth mechanism [15], in which V, F and S represent the adsorption of gaseous carbon source, the diffusion of carbon atoms along the facets of copper catalyst particles and the precipitation process of carbon rods. For this growth mechanism, acetylene molecules decompose into carbon atoms and/or atom clusters on certain facets of copper catalyst particles; After diffusion of carbon atoms and/or atom clusters to other facets, six 7
pieces of carbon rods start to grow simultaneously, and hexa-branched carbon rods are obtained. 4. Conclusion In this study, high yield of hexa-branched carbon rods were synthesized by CVD method. Through inlaying metal copper particles inside the wall of carbon matrix, the aggregation of catalyst particles was prevented and six pieces of sub-carbon rods were formed on the same catalyst particle. The formation mechanism of hexa-branched carbon rods was discussed briefly. Acknowledgments This work was financially supported by the International Science & Technology Cooperation Program of China (2014DFA60150), the National Natural Science Foundation of China (21776147), and the Shandong Natural Science Foundation (ZR2012EMM006). L. F. Dong also thanks financial support from the Malmstrom Endowment Fund at Hamline University. References [1] S. Iijima, Nature 354 (1991) 56-58. [2] Y. Cheng, R. Wang, J. Sun, et al., Adv. Mater. 27 (2015) 7365-7371. [3] C. Wang, X. Li, E. Gao, et al., Adv. Mater. 28 (2016) 6639-6639. [4] Q. Wang, M.Q. Jian, C. Wang, et al., Adv. Funct. Mater. 27(2017) 1605657 [5] C. Wang, K.L. Xia, M. Zhang, et al., ACS Appl. Mater. Inter. 9 (2017) 39484-39492. [6] Y. Li, Y.A. Samad, K. Liao, J. Mater. Chem. A 3 (2015) 2181-2187. [7] C. Wang, M. Zhang, K. Xia, et al., ACS Appl. Mater. Inter. 9 (2017) 13331-13338. 8
[8] H. Wang, C. Wang, M. Jian, et al., Nano Res. 11 (2018) 2347-2356. [9] P. Luan, N. Zhang, W. Zhou, et al., Adv. Funct. Mater. 26 (2016) 8178-8184. [10] S. Darbari, Y. Abdi, S. Mohajerzadeh, Sens. Actuators, A, 167(2) (2011) 389-397. [12] X.Q. Liang, F. Wang, M.H. Chen, et al., Ceram. Int., 44(14) (2018) 16791-16798. [13] K.L. Zhang, Y.J. Li, X.W. He, et al., Compos. Sci. Technol., 167 (2018) 1-6. [14] X. Jian, M. Jiang, Z.W. Zhou, et al., Carbon 48 (2010) 4535-4541. [15] Y. Ma, X. Sun, N.J. Yang, et al., Chem. Eur. J. 21 (2015) 12370-12375. [16] P.L. Hansen, J.B. Wagner, S. Helveg, et al., Science 295 (5562) (2002) 2053-2055. [17] Z.L. Wang. J. Phys. Chem. B 104 (2000) 1153-1175.
Hexa-branched carbon fibers are synthesized by chemical vapor deposition method.
The key step is to disperse copper catalyst particles uniformly in carbon matrix.
The growth mechanism of hexa-branched carbon fibers is discussed briefly.
Qian Zhang: Conceptualization, Writing - Review & Editing, Funding acquisition. Fengjian Yang: Writing - Original Draft, Validation, Software. Jikuan Zhao: Resources. Qingqing Zhang：Investigation. Xiangfang Wu：Investigation. Jianhua Yu：Investigation, Validation. Lifeng Dong：Supervision，Funding acquisition.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 9
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
10