Feb 2, 2017 - walled carbon nanotubes grow under low pressure hydrogen, air, and ... with other nanomaterial including carbon nanohorn had attained.
Fullerenes, Nanotubes and Carbon Nanostructures
ISSN: 1536-383X (Print) 1536-4046 (Online) Journal homepage: http://www.tandfonline.com/loi/lfnn20
Multi-walled carbon nanotubes grow under low pressure hydrogen, air, and argon ambient by arc discharge plasma M. S. Roslan, K. T. Chaudary, Z. Haider, M. S. Aziz & J. Ali To cite this article: M. S. Roslan, K. T. Chaudary, Z. Haider, M. S. Aziz & J. Ali (2017) Multiwalled carbon nanotubes grow under low pressure hydrogen, air, and argon ambient by arc discharge plasma, Fullerenes, Nanotubes and Carbon Nanostructures, 25:4, 269-272, DOI: 10.1080/1536383X.2017.1285287 To link to this article: http://dx.doi.org/10.1080/1536383X.2017.1285287
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Date: 26 April 2017, At: 18:33
FULLERENES, NANOTUBES AND CARBON NANOSTRUCTURES 2017, VOL. 25, NO. 4, 269–272 http://dx.doi.org/10.1080/1536383X.2017.1285287
Multi-walled carbon nanotubes grow under low pressure hydrogen, air, and argon ambient by arc discharge plasma M. S. Roslana,b, K. T. Chaudarya, Z. Haidera, M. S. Aziza, and J. Alia a Laser Center, Ibnu Sina Institute for Scientific and Industrial Research, (ISI-SIR), Universiti Teknologi Malaysia, Johor Bahru, Malaysia; bCenter for Diploma Studies (CeDS), Unviersiti Tun Hussein Onn Malaysia, Parit Raja, Batu Pahat, Johor Darul Takzim, Malaysia
ABSTRACT
ARTICLE HISTORY
Multi-walled carbon nanotubes (MWCNTs) were grown on cathode deposit by arc discharge plasma under H2, Ar, and air ambient environment. The influence of ambient gas pressure on the structure and physical properties of carbon nanotube were compared. Herein, we highlight the influence of ambient environment and pressure to grow high quality carbon nanotubes. Field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction were used for structural characterization and yield determination. The result revealed that background gas and pressure were crucial factor for growing highly crystalline and highly graphitic with ID/IG ratio 0.237 obtained for MWCNTs’ synthesized in H2 environment with extreme low defects.
Received 20 December 2016 Accepted 18 January 2017
1. Introduction Carbon nanotube is tubular structure of carbon possesses unique physical and electrical properties with superior tensile strength up to 0.15 TPa (1). There have been various reports on different technique used to synthesis MWCNTs including arc discharge (2,3), laser assistance grow (4), thermal growth (5), and chemical vapor deposition (CVD) (6,7). Among these technique, arc discharge promote efficient and simple with fewer defects (8). Arc discharge plasma has widely used to synthesize good quality carbon nanomaterials from 1D single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) to 2D graphene structure. Although the controlling of the nanomaterial become an issue in this process, high quality of CNT for high performance application inherently achievable using this process. Studies show that by altering the and dimension and source type of carbon, ambient environment, and catalyst, favorable CNTs with length and diameter control can be achieved (9). On the other hand, the selection of ambient pressure and temperature becomes the driven force for high yield of crystalline CNTs (10). Thus, arc discharge is preferential method because high temperature can be achieved »2200–2400 K by argon and »3600–3800 K using hydrogen plasma (11) which vaporize carbon and formed mixture of CNTs deposited at cathode. The mixture of carbon nanotube with other nanomaterial including carbon nanohorn had attained attention for many application including supercapacitor (12,13), highly efficient field emission (14), flexible solar cells (15), and high-performance electronics devices (16). MWCNTs are highly conductive with high intrinsic carrier mobility but mechanically flexible thus ideal candidate used for flexible electronics (17) and future flexible devices. In this paper, we reported simple technique
KEYWORDS
Carbon nanotubes; Arc discharge; Electron microscopy; Raman spectroscopy; X-ray diffraction
to synthesize CNTs in single steps using arc discharge plasma in three main conditions; Hydrogen, Argon, and Air, resulting in bundles of high quality carbon nanotubes.
2. Methodology This method was used because it is time efficient and produce high quality MWCNTs. The growth of MWCNTs were performed in controlled stainless steel reaction chamber in terms of flow rate, pressure of gases, and duration of growth time to produce high quality and pristine MWCNTs. The flow rate of hydrogen and argon are fixed (100 sccm) and synthesis time (10 min). Next, the pressures are fixed at 1 mbar. Finally, the MWCNTs grow at cathode deposit was studied as function of different ambient environment and pressure at fixed input current (70 A) and voltage (12 V). The dimension of anode (9 mm outer diameter and 5.5 mm inner diameter) and cathode (12 mm diameter) are constant for all experiments. Figure 1 shows the schematic diagram of the arc discharge reaction chamber used in the experiments. After arc discharge process, cathode deposit with semi-transparent appearance attached on the cathode surface area. Usually, about 400 mg of cathode deposit produce obtained after discharging for 10 minutes and consume about 2.5 cm anode rod. Note that MWCNTs’ deposition at cathode surface area were examined and characterized in this paper.
3. Results and discussion Field emission scanning electron microscopy (FESEM) images shown in Fig. 2 describes the growth morphology of MWCNTs
CONTACT M. S. Roslan sufi@uthm.edu.my Laser Center, Ibnu Sina Institute for Scientific and Industrial Research, (ISI-SIR), Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lfnn. © 2017 Taylor & Francis Group, LLC
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Figure 1. Schematic of arc discharge process to synthesize CNTs inside stainless steel vacuum chamber.
carried at pressure 1 mbar under three different environment: hydrogen, argon, and air. Figure 2(a) shows that the long MWCNTs structure grow in hydrogen environment and loosen. This is the effect of hydrogen gas that prevent from over layer formation of graphitic particles on nanostructure growth area (18). On the other hand, bundle of MWCNTs grow under Ar ambient shown in Fig. 2(b). As reference, the tube structure grow in air ambient shown in Fig. 2(c) also showing reducing of cost for the synthesis MWCNTs. Figure 2 (d–f) show the transmission electron microscope (TEM) images correspond to the same MWCNTs sample grown under different condition. Very fine, well defined straight MWCNTs structure observed from TEM micrographs. In average, air environment grows large tube diameter at »16 nm compared with hydrogen and argon ambient which have tube diameter approximately 13 and 14 nm. Meanwhile the average length for MWCNTs grow in air ambient environment is »587 nm which is much shorter than tube grow under hydrogen and argon which possesses length »661 and »648 nm. Figure 3 displays the Raman spectrum obtained at frequency range from 1200 to 1800 cm¡1 using Argon ion laser with excitation wavelength 514.5 nm. The spectrum shows rise of two prominent bands at 1350 and 1580 cm¡1 correspond to rise of D band and G band. Moreover, there is no apparent signal peak at frequency below
Figure 3. Raman spectrum for MWCNTs synthesized under different environment at pressure 1 mbar.
300 cm¡1 (not shown here). That means single-walled carbon nanotube did not grown under the selected environment. The G band is attributed from vibration of in plane of sp2 orbital indicating rise of highly ordered graphitic structure of MWCNTs while D band recognize as vibration out of plane showing the rise of defects from MWCNTs structure. The clear high intensity G band indicates highly graphitic MWCNTs structure obtained under hydrogen ambient environment. Furthermore, the lower value of full width half maximum (FWHM) in G band associate with the sample grown in hydrogen environment indicate improvement of structural quality of MWCNTs (19). The intensity ratio between D and G bands noted as ID/IG presents the quality of carbon nanotube structure (20). High quality with low disorder structure of MWCNTs grow under hydrogen ambient with ID/IG ratio 0.237. Meanwhile the ID/IG ratio for nanotube grow under argon and air environment both at 0.576 and 0.632. The X-ray diffraction (XRD) patterns of MWCNTs grow in different environment are presented in Fig. 4. The peak
Figure 2. FESEM and TEM micrographs of MWCNTs grow under different environments; hydrogen (a,d) argon (b,e) and air (c,f) at ambient pressure 1 mbar.
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from XRD patterns (nm). From the experimental result, it can be found that the MWCNTs grow under hydrogen ambient environment with smaller diameter has greater d002 and larger g. It indicate hydrogen environment induce small diameter of MWCNTs and harder graphitization. More structural information including crystallite size can be calculated by optimizing FWHM using Debye–Scherer formula using constant K for spherical crystal cubic symmetry (23): L002 D
Figure 4. XRD patterns of MWCNTs grow under different environment at pressure 1 mbar.
observed at 2u D 26 , 42 , 54 , and 78 correspond to the diffraction of planes (002), (101), (004), and (110) of carbon nanotube (JCPDF no. 75–1621) (21). Meanwhile plane (002) correspond to interlayer of graphene rolled between carbon nanotube layer structures. The XRD profile of MWCNTs grow under different ambient environment were analyzed and the structural parameters were determined from corresponding peak (002) profile are listed in Table 1. The intensities of plane (002) are comparable for all MWCNTs grow in different environment. The strong peak observed at diffraction angle 2u D 26 suggests that MWCNTs grow with highly crystalline structure at ambient pressure 1 mbar during arc discharge process. The interlayer or d-spacing can be calculated using Bragg’s law; nλ D 2dsinu
(1)
where d is distance between the planes of graphite layers, n is the order of diffraction, u is the Bragg angle and λ is the wavelength of X-ray radiation used. The calculated d002 spacing of MWCNTs samples is larger when compared with pure graphite (3.3354 A). On the other hand, the degree of graphitization g on the MWCNTs samples can be obtained from Franklin model (22) using approach: gD
0:3440 ¡ d002 0:3440 ¡ 0:3354
(2)
where 0.3440 nm is the interlayer spacing of fully non-graphitized carbon, 0.3354 nm is an interlayer spacing of an ideal crystalline graphite and d002 is calculated interlayer spacing Table 1. The structural parameters of MWNTs based on XRD data for synthesis under different ambient environment.
Environment
FWHM
d002 (A)
L002 (nm)
g
No. of walls
Ar H2 Air
0.77929 0.70236 0.73278
3.435 3.427 3.428
10.61 11.75 11.32
0.0581 0.1512 0.1395
30 34 33
Kλ BðuÞcosu
(3)
where L002 is the crystallite size, B is FWHM, λ is the wavelength, and u refers to diffracted angle. By dividing the number of stacking graphite crystallites with d002 spacing, the number of wall formed by carbon nanotube can be estimated (24). The evolution of the nanotube structure grown under different environment explain the hydrogen as background grows great number of graphene layer with 34 tube walls compared with other environment. Theoretical calculation of XRD patterns of hexagonal graphite and turbostatic carbon have shown that as the curvature of the graphite sheet increase, the FWHM decrease and Bragg angle increase (25). Peaks integration of XRD data as tabulated in Table 1 shows that FWHM for MWCNTs grow under hydrogen ambient is smaller compared with other environment. This is in agreement with theoretical prediction where curvature of graphene layers had increase by forming large number of tube walls in hydrogen ambient as compared with argon and air.
4. Summary In this work, selective condition involving the hydrogen, argon and air as background environments were used to synthesize multi-walled carbon nanotube at ambient pressure 1 mbar. The MWCNTs were prepared by using arc discharge plasma process in vacuum system. The long tube structure and small tube diameter incorporated with low disorder structure with ID/IG ratio 0.237 was achieved under the hydrogen as background gas. Moreover, a significant improvement in the facilitated hydrogen ambient was realized by greater graphitization g and number of walls which enhance mechanical strength with harder graphitization. The comparison of MWCNTs grow under different environments were presented in this work, capable of achieving exceptional MWCNTs structural properties and improve quality of nanotube at certain low ambient pressure. A one step, simple method was adapted for low defects, and highly crystalline bulk production of MWCNTs.
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