Scientia Iranica F (2013) 20(6), 2382{2385

Sharif University of TechnologyScientia Iranica

Transaction F: Nanotechnologywww.scientiairanica.com

Research Note

Synthesis of novel carbon nanostructures through thesolvothermal route

P. Zarabadi-Poora, A. Badiei�;a and A.A. Youse�b

a. School of Chemistry, College of Science, University of Tehran, Tehran, Iran.b. Department of Plastic Materials Processing and Engineering, Iran Polymer and Petrochemical Institute, Tehran, Iran.

Received 6 April 2013; received in revised form 3 June 2013; accepted 21 September 2013

KEYWORDSCarbon nanotubes;Solvothermal;Ferrocene;Chlorinated solvents.

Abstract. Novel morphologies of carbon nanotubes obtained through the solvothermalreaction of various chlorinated solvents in the presence of various catalysts are described.The reaction mixture, including C2Cl4 as solvent and ferrocene as catalyst, exhibited mostinteresting novel arrangements of carbon nanotubes. Therefore, more characterizations,such as Raman spectroscopy and thermogravimetry analysis, were performed on thementioned sample for further investigation into the novel pine-tree-like morphology ofcarbon nanostructures.c 2013 Sharif University of Technology. All rights reserved.

1. Introduction

The remarkable discovery of Iijima [1], in 1991, whichpresented carbon nanotubes to scientists, caused anexponential growth of attention to CNTs for undertak-ing detailed research. CNTs became fascinating dueto their unique and extraordinary physical, electronicand thermal properties [2]. The current synthesismethods of CNTs are classi�ed into the followingmethods: arc discharge [1], laser ablation [3], chemicalvapor deposition [4-6], solvothermal [7] etc. To thebest of our knowledge, one active research area is thedevelopment of synthesis methods for the production ofCNTs, considering three main objectives; synthesis ofCNTs with desired properties, reduction of productioncosts and large scale production. The solvothermalmethod seems to be a promising approach to thelow temperature synthesis of carbon nanotubes, whichis under development. An important date in the

*. Corresponding author. Tel.: +98 21 61112614;Fax: +98 21 66495291E-mail addresses: pzarabadip@khayam.ut.ac.ir (P.Zarabadi-Poor), abadiei@khayam.ut.ac.ir (A. Badiei),a.youse�@ippi.ac.ir (A.A. Youse�)

timeline of solvothermal synthesis of carbon nanotubesis 1998, when Qian and his co-workers reported theapplication of a Wurtz-like reaction for the synthesisof diamond powder via the solvothermal reduction ofcarbon tetrachloride by metallic sodium in the presenceof Ni-Co alloy [8]. Wang et al. presented a novelbenzene thermal route, following previous e�orts, onthe solvothermal synthesis of CNTs [9]. The reactionmixture consisted of C2Cl4, benzene, and di�erentcatalysts. Their proposed mechanism is similar tothe one reported by Jiang et al. [7]. It is seen thatusing Fe-Au catalysts leads to the production of carbonnanotubes, while using Ag ends in the formation ofcarbon nanorods. In 2008, Shen et al. [10] proposeda new deposition method for the synthesis of CNTs,based on decomposition of CCl4, in the presenceof ferrocene and through a free radical productionpathway.

According to our knowledge, further studies onsynthesis parameters, such as di�erent catalysts andsolvents in various amounts, are still required. Inthis paper, we intend to report the e�ect of addingco-catalysts, such as FeCl3.6H2O, CoCl2.6H2O andNiCl2.6H2O, to the reaction mixture to investigate thee�ect of bimetallic catalysts on the reaction product.

P. Zarabadi-Poor et al./Scientia Iranica, Transactions F: Nanotechnology 20 (2013) 2382{2385 2383

The e�ect of changing the CCl4 with other chlorinatedsolvents such as dichloromethane, tetrachloroethyleneand chloroform was also investigated.

2. Experimental

2.1. MaterialsCarbon tetrachloride (CCl4), tetrachloroethylene(C2Cl4), chloroform (CHCl3), ferrocene (FeCp2),iron(III) chloride hexahydrate, cobalt(II) chloride hex-ahydrate, nickel(II) chloride hexahydrate and ethanolwere purchased from Merck and used as received.

2.2. SynthesisThe synthesis procedure was similar to [10] with slightmodi�cation. Ferrocene was dissolved in 25 ml ofthe desired solvent. Then, 0.2 g of the desiredcatalyst was added to the reaction mixture. For bi-metallic reaction mixtures, appropriate amounts ofFeCl3.6H2O, CoCl2.6H2O or NiCl2.6H2O were mixedwith FeCp2 before adding to the reaction mixture in1:1 molar ratio and a total weight of 0.2 g. In the caseof examination of the e�ect of di�erent solvents, anappropriate amount of ferrocene was dissolved in thementioned solvents. Then, the reaction mixture wastransferred into a stainless steel autoclave and kept at180�C for 24 h. Afterward, the black precipitate was�ltered o� and washed several times with ethanol anddistilled water. The list of synthesized samples, alongwith their corresponding synthesis condition, is givenin Table 1.

2.3. CharacterizationsScanning Electron Microscopy (SEM) was carried outon a LEO 1455VP instrument. Raman spectra wererecorded using a Brucker SENTERRA Raman mi-croscope equipped with a 785 nm laser and CCDdetector. Thermogravimetric analysis (TGA) wasperformed on a Q50 instrument of Thermal Analysis(TA) from ambient temperature to 800�C with theramp rate of 10�C/min. The N2 adsorption-desorptionisotherms were measured on a BELSORP mini-II at-196�C. All samples were degassed at 100�C beforemeasurement.

Table 1. List of synthesized samples at reactiontemperature of 180�C and reaction time of 24 h.

Sample Catalyst Solvent

S1 FeCl3/FeCp2 CCl4S2 CoCl2/FeCp2 CCl4S3 NiCl2/FeCp2 CCl4S4 FeCp2 C2Cl4S5 FeCp2 CHCl3S6 FeCp2 CH2Cl2

3. Results and discussions

The SEM images of as-synthesized S1, S2, and S3 sam-ples are given in Figure 1. It is observed that additionof metal salts to the reaction mixture not only doesnot improve the production of carbon nanotubes, butalso dramatically diminishes the presence of tubularstructures. The main formed structures are sphericaland in a bulky shape.

Since the spherical particles are formed and notubular structure is observed, it is proposed that thecleavage of ferrocene and subsequent formation ofspherical particles occurred, but further decompositionof the solvent and cyclopentadien rings did not occurto provide carbon feedstock for the growth of carbonnanotubes.

The SEM images of as-synthesized S4, S5, andS6 samples are given in Figure 2. Replacing the CCl4with C2Cl4 exhibits the most interesting structures.

Figure 1. SEM images of a) S1, b) S2, and c) S3 samples.

Figure 2. SEM images of a) S4, b) S5, and c) S6 samples.

2384 P. Zarabadi-Poor et al./Scientia Iranica, Transactions F: Nanotechnology 20 (2013) 2382{2385

It is obviuos in Figure 2(a) that tubular stucturesformed in the product di�erent from previusly reportedstructures for the CCl4/ferrocene system. Herein, anovel arrangment of carbon nanotubes is observed inthe form of pine-tree-like or rami�ed structures with anaverage outer diameter of � 350 nm and closed ends.

It is also observed that there are long CNTs,as it is the main stem having shorter CNT growthprependicular to the main stem that is making therami�ed structure. Figure 2(b) and (c) show thatchloroform/ferrocene and dichloromethane/ferrocenesystems did not produce tubular structures. Theformer system's main product consisted of sheet-likestructures, however, the latter produced thinner sheetsthat formed ower-like structures.

It should be mentioned that among the testedsystems, only the C2Cl4/ferrocene system providedtubular stuctures and, therefore, is favored in our fu-ture research. Then, furthor characterization were per-formed on the synthesized sample. Figure 3 providesthe Raman spectrum of the mentioned sample. Twomain characteristic peaks of carbonecous structures areobvious in the spectrum. The D-band that correspondsto disordered structures is observed at 1340 cm�1, andthe G-band indicates that the graphitized sp2 carbon-carbon bonds are observed at around 1600 cm�1.

Figure 4 shows the TGA curve of the C2Cl4sample that is used to evaluate the yield of carbonnanotube production. Three weight loss regions canbe attributed to this curve. The �rst small weight lossoccurred from ambient temperature to 150�C, whichis attributed to the removal of physically adsorbedvolatiles. Then, the main weight loss is observed,which can be attributed to the removal of carboneceousmaterials. It shows that 60% of the sample wasremoved. Finally, it can be observed that almost 40%of sample weight remained after heating to 800�C. Thisash content can be referred to the remaining materialsin the sample, such as remaining catalysts etc.

The N2 adsorption-desorption isotherms of the

Figure 3. Raman spectrum of S4 sample.

Figure 4. TGA curve of S4 sample.

Figure 5. N2 adsorption-desorption isotherms of S4sample.

C2Cl4 sample is given in Figure 5. It is similar to thetype III IUPAC standard isotherm, which correspondsto the presence of porousity in the material with specialadsorbate-adsorbant interaction. The observed openhysteresis loop indicates that desorption of adsorbednitrogen molceules cannot have taken place at themeasurement temperature.

The calculated speci�c surface area is 52 m2/g,which is dramatically lower in comparison with pre-viously reported values by Shen et al. [10] for theCCl4/ferrocene system (413 m2/g). Considering theTGA observation on high ash content, besides thesigini�cant lowering of speci�c surface area, it canbe proposed that metallic species formed during thesolvothermal process and remained in the sample.

4. Conclusion

Di�erent solvothermal systems, consisting of variousmetal ions or chlorinated solvents, have been examinedfor the synthesis of carbon nanotubes. Adding FeCl3,NiCl2 and CoCl2 introduced a negative e�ect on thesynthesis of carbon nanotubes and, then, no tubular

P. Zarabadi-Poor et al./Scientia Iranica, Transactions F: Nanotechnology 20 (2013) 2382{2385 2385

structure formed. The C2Cl4/ferrocene system pro-duced carbon nanotubes with novel interesting arrange-ments consisting of pine-like or rami�ed structures.Using CHCl3 and CH2Cl2 instead of CCl4 also resultedin non-tubular structures and is not favored for carbonnanotube production. So, further characterizationswere undertaken on the synthesized sample in theC2Cl4/ferrocene system by Raman, N2 adsorption-desorption measurements and TGA for more detailedinvestigation to provide basic information for futurestudies. These investigations revealed that tubularstructures were successfully synthesized and that prob-ably catalysts or carbonaceous nano and microparticlesexist in the product. Therefore, it can be proposedthat the suggested reaction mechanism changed byaltering the catalyst or reaction solvent. Probably, thepresence of C2Cl4 and oxygen in the reaction mixturecaused the formation of iron species, which remainedin the product, and were initially observed as high ashcontent. At this point of time, further investigation ofthe C2Cl4/ferrocene system is being undertaken by ourresearch group to obtain more explanations regardingthe e�ect of di�erent parameters on the properties ofsynthesized materials.

Acknowledgment

The authors would like to thank the research councilof the University of Tehran for its �nancial support.

References

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5. Zarabadi-Poor, P. and Badiei, A. \Synthesis of car-bon nanotubes using metal -modi�ed nanoporous sil-icas', In Carbon Nanotubes-Growth and Applications,Naraghi, M., Ed., pp. 59-74, InTech, Rijeka (2011).

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Biographies

Pezhman Zarabadi-Poor was born in 1983, inQazvin, Iran. He obtained his diploma from NationalOrganization for Development of Exceptional Talents(NODET) in 1995, his BS degree in Applied Chemistryfrom Bu-Ali Sina University, Hamedan, Iran, and hisMS and PhD degrees in Inorganic Chemistry fromthe University of Tehran, Iran. His research interestsinclude synthesis, characterization and application ofnovel nanomaterials such as mesoporous silica materi-als and carbon nanotubes.

Alireza Badiei was born in Iran, in 1965. He receivedBS and MS degrees in Chemistry and Inorganic Chem-istry from Tarbiat Moallem University, Tehran, Iran,in 1988 and 1991, respectively, and his PhD degree inthe synthesis and modi�cation of nanoporous materialsfrom Laval University, Quebec, Canada, in 2000. He iscurrently Associate Professor in the Chemistry Depart-ment of Tehran University, Iran. His research interestsinclude nanoporous materials synthesis, modi�cationand its applications.

Ali Akbar Youse� was born in Iran, in 1965. Heobtained his BS degree in Pure Chemistry from Cham-ran University, Ahwaz, Iran, in 1987, his MS degree inOrganic Polymer Chemistry from Kharazmi University,Tehran, Iran, in 1991, and his PhD degree in ChemicalEngineering on the rheology of polymer modi�ed as-phalts from Laval University, Quebec, Canada, in 1999.He is currently Faculty Member and Professor at theIran Polymer and Petrochemical Institute.