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© Applied Science Innovations Pvt. Ltd., India Carbon – Sci. Tech. 8/1(2016)25-31

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RESEARCH ARTICLE Received: 17/10/2015, Accepted: 23/10/2015

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Synthesis and characterization of multiwalled carbon nanotubes using Brassica

Juncea oil as carbon source

S. Kalaiselvan

(A), K. Gopal

(B), S. Karthikeyan

(C, *)

(A) Department of Chemistry, Hindusthan College of Engineering & Technology, Coimbatore,

Tamil Nadu, India.

(B)

Department of Chemistry, Erode Arts & Science College, Erode, Tamil Nadu, India.

(C) Department of Chemistry, Chikkanna Government Arts College, Tirupur, Tamil Nadu, India.

*Corresponding Author

The present work aspire to explore a natural renewable green precursor for the synthesis of Multi-walled

carbon nanotubes (MWCNTs) using methyl esters of Brassica Juncea oil at 650 °C with a flow rate at

20 mL per hour of precursor on Fe-Co supported on silica under N2 atmosphere. The characterization of

the as-grown carbonaceous was analyzed by scanning electron microscopy (SEM), high resolution

transmission electron microscopy (HRTEM), X-ray diffraction, and Raman spectroscopic analysis. We

confirmed that well graphitized with uniform sized multi-walled carbon nanotubes were nicely grown

over Fe-Co bi-metallic catalyst supported on silica at 650 °C.

Keywords: Carbon nanotubes; Spray-pyrolysis; HRTEM; SEM, Raman spectroscopic analysis,

Brassica Juncea ------------------------------------------------------------------------------------------------------------------------------------------------

1. Introduction: Since Iijima’s report in 1991, CNT have been at the foreground in the nanotechnology

forum [1]. It is supposed that the CNT have been discovered 58 years ago, started with the discovery of

50 nm diameter CNT by Russian scientist Radushkevich and Lukyanovich in 1952. These were

followed by Roger Bacon in the late 1950s where he found a curious new carbon fibre along with

straight and hollow tubes of carbon. In the 1976, Morinobu Endo shinshu university japan and

colleagues discovered SWCNT, produced by a vapour-growth technique [2]. From that time onwards

carbon nanotubes viewed as most fascinating nanostructure with nanometer-sized diameter and

micrometer-sized length that exists on the earth, it has attracted intensive theoretical and experimental

interests in past twenty four years, due to its extraordinary structural, mechanical, optical and electrical

properties [3]. There are four principal methods in producing CNTs are laser ablation, arc discharge,

chemical vapor deposition (CVD) and spray pyrolysis [4-7]. Among these, spray pyrolysis method has

been more developed because of its advantages such as large scale production of high quality CNTs,

lower growth temperature, higher yield, lower cost. The key parameters in CNT growth using spray

pyrolysis processes are chemical and physical characteristics of catalyst nano-particles such as their size,

hydrocarbons source, and reacting environment during growth of CNTs. Gaseous hydrocarbon fuels

such as methane, ethylene and acetylene [8-10] have been used for the synthesis of nanostructures

because of their tendency to produce less amorphous carbon during combustion. Higher saturated

hydrocarbons such as liquefied petroleum gas (LPG) were successfully used for the production of multi-

walled CNTs [11]. Aromatic hydrocarbons such as benzene, toluene and xylene [12-14] were also

ASI

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studied as potential carbon sources for CNTs production however they do not seem to offer substantial

advantages over alkanes and alkenes and thus, were not widely used.

Considering the environmental effects and decreasing fossil fuels such as petroleum product and

Gaseous hydrocarbon fuels, these hydrocarbon sources are expected to diminish in the near future.

Therefore, it is inevitable to look for alternative eco-friendly carbon precursors. Recently, there have

been a few reports on the synthesis of CNTs from plant derived carbon precursors such as camphor,

turpentine oil, eucalyptus oil, palm oil, neem oil and carbon nanobeads from Brassica oil [15-20]. Our

research groups have also succeeded in growing CNT from Eco-friendly green bio-hydrocarbons such as

Pine oil, Jactropha curcas oil, Cymbopogen flexuosus oil, Glycine Max oil, Helianthus annuus oil

Madhuca longifolia, Brassica Juncea and Citrus limonum oil [21-28].

In this present work we aim to utilize natural renewable eco friendly Carbon precursor Brassica Juncea

oil obtained from brown Indian mustard seeds belongs to Brassicaceae family of mustard plant to

produce CNTs. It has about 60% monounsaturated fatty acids (42% erucic acid and 12% oleic acid). It

has about 21% polyunsaturated fats (6% the omega-3 alpha-linolenic acid and 15% the omega-6 linoleic

acid), and it has about 12% saturated fats. Using mustard oil (methyl ester of Brassica juncea) CNTs

grown over silica impregnated Fe-Co bi-metallic catalyst by Spray Pyrolysis method and the product are

analyzed qualitatively and quantitatively.

2. Experimental:

2.1 Materials used: Materials used for synthesis of Fe-Co/SiO2 nanocatlyst, Fe(NO3)3.6H2O and

Co(NO3)3.6H2O (iron and cobalt nitrate hexahyrdate) were purchased from Merck, India. The chemicals

were used as received without further purification. Brassica Juncea oil was used after trans-

esterification process using NaOH/CH3OH mixture.

2.2 Preparation of mixture of catalysts: A silica supported Fe-Co bi-metallic catalyst supported on

silica was prepared by wet impregnation method [15]. Appropriate quantities of metal salts (Merck) i.e.

Fe(NO3)3.6H2O and Co(NO3)3.3H2O were dissolved in methanol and mixed thoroughly with methanol

suspension of silica support of particle size 100-150 µm was procured from Merck (India). The solvent

was then evaporated and the resultant cake heated to 90-100 °C for 3 hours, removed from the furnace

and ground in an agate mortar. The fine powders were then calcined for 1 h at 450 °C and then re-

ground before loading into the reactor [29].

2.3 Synthesis and purification of nanotubes: The catalyst was placed on the quartz boat. The boat was

placed in the heating furnace. The carrier gas nitrogen (100 mL/min) was flushed out before switch on

the reaction furnace to remove air and create nitrogen atmosphere. The temperature was raised from

room temperature up to the desired growing temperature. Subsequently, methyl esters of Brassica

Juncea was introduced into the quartz tube through spray nozzle and the flow was maintained using

saline tube at the rate of 0.5 mL/min. The deposition time lasted for 45 minutes at temperature 650 °C.

The reactor was then allowed to cool to room temperature with nitrogen gas flowing. The carbon

product on the silica support was then weighed to determine the carbon yield of the spray pyrolysis. We

define carbon yield here as the functional mass increase (m1-m0)/m0, where m1 and m0 are respectively,

the final mass of the catalyst support with carbon deposit and the initial mass of the catalyst support. Of

course, not all the carbon mass is in the form of MWNTs. Nevertheless, the amount of amorphous

carbon detected in electron microscope images was small and our practical definition of the relative

yield is believed to provide a reasonable assessment of MWNTs production in these experiments. The

yield does not change appreciably as time progressed beyond 45 minutes. The amount of CNTs

produced is proportional to the amount of catalyst used. So, the optimum condition for the synthesis of


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high yield of relatively pure MWNTs of narrow size 15-45 nm were established as reaction temperature

around 650 °C, 80 mg of catalyst substrate, 45 minutes reaction time, 100 mL per minute nitrogen gas

flow and 0.5 mL per minute precursor flow. The as-grown MWNTs were purified by the following

procedure. 40 mg of raw material was added to 20 mL 1N HCl to form an acidic slurry. This slurry was

heated to 60 °C and stirred at 600 rpm. To this heated acidic slurry 20 mL H2O2 was added to form

oxidative slurry that continued to be heated and stirred for 30 minutes. The addition of HCl, H2O2,

subsequent heating and stirring was repeated three more times, each time allowing the heated oxidative

slurry to stir for 30 minutes. Phase separation was allowed to proceed followed by filtering the carbon

phase and washing with 1N HCl and distilled water. The collected sample was dried at 120°C in air for

2 hours.

2.4 CNT characterization: The crystalline structure of as grown CNT samples was characterized by

Raman Spectroscopy. Raman spectra of samples were performed by JASCO NRS- 1500W, green laser

with excitation wavelength 532 nm. X-ray diffraction (XRD) with Cu-K radiation using an automated

X-ray diffractometer (Shimazu Lab XRD-6000). As grown carbon samples surface morphology was

examined using scanning electron microscope (SEM, Hitachi S-4700) and high-resolution transmission

electron microscope (HRTEM, JEOL-3010). For HRTEM studies, the samples were prepared by

sonication of products in isopropanol and few drops of resultant suspension was put onto holey carbon

grid and dried.

3. Results and Discussions:

Figures (1) shows the scanning electron microscopy image of the as-grown carbon nanostructures over

Fe-Co bimetallic catalyst, impregnated in silica at 650 °C under the flow of nitrogen by CVD assisted

spray pyrolysis method. SEM image clearly reveals that CNTs grew nicely on the surface of the silica

particles with heterogeneous diameter.

Figure (1): Scanning electron micrographs of as grown MWCNTs at 650 °C.

The morphologies of the carbon nanostructure deposit obtained were characterized by HRTEM. Dense

rope like carbon nanostructure was grown from the surface of the dark catalyst clusters. A closer look

with higher magnification shows the rope like tubular carbon structure with hollow core, confirming the

formation of CNTs [30]. Figures 2 (a-d) shows the HRTEM images of samples synthesized at 650 °C

using methyl ester of Brassica Juncea oil as carbon source over Fe-Co supported on silica. It clearly

seen from HRTEM measurements that well-graphitized MWCNTs grown from catalytic decomposition

of methyl ester of Brassica Juncea oil at 650 °C with heterogeneous diameter of the tube structure

(Figure 2b). The growth of nanotubes with a bigger diameter due to agglomeration of catalyst particles.


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This finding agrees with experimental results from several authors. It can be observed from HRTEM

images that the nanotubes formed are of multi-walled type composed of around 20 walls and most

graphene layers grow perpendicularly to the growth axis of the tubes. The average outer diameter of the

nanotube ranges from 15-20 nm and inner diameter is about 8 nm (Figure 2c).

(a)

(b)

(c)

(d)

Figure (2): (a, b, c) HRTEM of as grown MWCNTs at 650 °C; (d) HRTEM image of as-grown

MWCNTs with catalyst particle encapsulated at tip (tip growth mechanism).

4. Raman studies: Figure (3) shows the Raman spectra of as-synthesized MWCNTs at 650 oC has three

characteristics peaks are observed at 1342.24 cm-1

, 1572.57 cm-1

and 2686.71 cm-1

(532 nm)

corresponding to D-peak, G- peak and G’-peak. The G peak corresponds to the tangential stretching

(E2g) mode of the highly oriented pyrolytic graphite and suggests the CNTs to be composed of

crystalline graphitic carbon. The D-peak at 1342.24 cm-1

originates from disorder in the sp2-hybridized

carbon and indicates lattice distortions in the curved graphene sheets, tube ends, etc. On the other hand,

band at 2683 cm–1

called the G’-peak and attributed to the overtone of the D-peak. G’-peak originates

from thicker multi-layer carbon nanotubes. The absence of peak under 300 cm-1

shows the absence of

SWCNTs [31]. The IG/ID ratio found as 1.17. This higher ratio value corresponds to a lower proportion

of sp3-like carbon, originates from disorder in the sp

2-hybridized carbon and indicates good

graphitization in the curved graphene sheets, tubes ends etc [32].


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Figure (3): Raman Spectra of as-synthesized MWCNT at 650 oC using spray pyrolysis method.

5. XRD ANALYSIS: The XRD spectrum of as-synthesized MWCNTs was recorded with 2-theta (2θ)

between 10 oC to 80

oC. Figure (4) shows the XRD diffraction pattern of as-synthesized MWCNTs

having three peaks at 26o, 44

o and minor peak at 77

o are identified. At synthesis temperature of about

650 oC, the XRD pattern of MWCNTs was reported to show mainly graphitic reflections at 26

o and 77

o

corresponds to (002) and (112) respectively. Obviously in Figure (4) only two peaks at 26o and 44

o are

prominent. The small peak at 77o suggests presence of Fe3C in the as-synthesized sample. The metal

carbides act as active catalysts in the formation of tubular structure of graphitic carbon [33].

Figure (4): XRD pattern of as-synthesized MWCNTs grown at 650 oC.

6. Conclusions: We accomplished the synthesis of MWCNTs at a temperature of 650 oC using methyl

esters of Brassica Juncea oil on Fe-Co supported on Silica. CNTs morphology and structure were

investigated by SEM, HRTEM, XRD, and Raman spectroscopy. It was found that temperature was

enough to transform hydrocarbon source into carbon nanotubes using plant derived precursor methyl

esters of Brassica Juncea oil with heterogeneous diameter, good quality and yield at this temperature.

Thus we could grow good crystalline MWCNTs at low temperature by spray pyrolysis of methyl ester of

Brassica Juncea without of release of any toxic chemicals.

Acknowledgement: The authors acknowledge the UGC New Delhi for financial support, the Institute

for Environmental and Nanotechnology for technical support and IITM for access to electron

microscopes.


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