Synthesis and Physical Characterization of Carbon Nanotubes Coated

by Conducting Polypyrrole

AFARIN Bahrami1,2,a , Z. A. Talib1,b*, W. Mahmood Mat Yunus1,

Kasra Behzad1, Nayereh Soltani1 1Department of Physics, Science Faculty, Universiti Putra Malaysia, 43400 UPM Serdang,

Selangor, Malaysia.

2Islamic Azad University, Eslam Shahr Branch, Iran

aafarin.bah@gmail.com, b* zainalat@science.upm.edu.my

Keywords: Conducting polymer; Carbon nanotubes; Thermal stability; Electrical Conductivity

Abstract: This study describes the preparation of polypyrrole multiwall carbon nanotube

(PPy/MWNT) composites by in situ chemical oxidative polymerization. Various ratios of

functionalized MWNTs are dispersed in the water, and PPy are then synthesized via in-situ

chemical oxidative polymerization on the surface of the carbon nanotubes. The morphology of the

resulting complex nanotubes (MWNT-PPY) was characterized by field-emission scanning electron

microscopy (FESEM). The conductivity of each composite showed a maximum in the temperature

scale of 120 – 160 0C and then decreased dramatically with the increase of temperature. The

resultant PPy/MWNT nanotubes enhanced electrical conductivity and thermal stability of

nanocomposite compared to PPy which was strongly influenced by the feed ratio of pyrrole to

MWNTs.

Introduction

Conducting polymers have been received great attention owing to their high conjugated length

and metal-like conductivity as well reversible chemical and physical properties by doping/dedoping

process [1]. On the other hand CNTs received great attention owing to their extraordinary properties

such as excellent Young’s modulus, good flexibility, and high electrical and thermal conductivity

[2, 3]. Polypyrrole (PPy), one of the most important conducting polymers, have potential

applications in batteries, supercapacitors, sensors microwave shielding and corrosion protection [4-

7]. In order to increase the physical properties of PPy, various composites of PPy have been

synthesized. Carbon nanotubes are of interest for composite materials because of their good

electronic and mechanical properties and high stability. Composites of PPy and carbon nanotubes

have been prepared by chemical or electrochemical oxidation [8,9]. In this paper, we report in situ

chemical synthesis of polypyrrole multiwalled carbon nanotube (PPy/MWNT) nanocomposite by

direct oxidation of pyrrole in the presence of different weight percentage of MWNT. Field-emission

scanning electron microscopy (FESEM) studies indicate that MWNT could be coated with PPy. The

effect of the temperature on the electrical conductivity of the resulting samples between room

temperature and 190 0C has been investigated. The thermal stability of nanocomposite samples has

been also studied.

Experimental Procedure

In this study, the pyrrole monomer (Fluka, >97 %) was distilled prior to use and stored at 4 0C.

The as prepared carboxylic functionalized multiwall carbon nanotubes (Nanostructure &

Amorphous Materials, 95 %) and ferric chloride 6-hydrate (HmbG chemical, granulated pure) were

of analytical grade and used without further purification. The diameter and length of f-MWNT were

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about 10 – 20 nm and 20 µm, respectively. Polypyrrole-coated MWNTs were synthesized by in situ

polymerization of pyrrole on MWNTs. Functionalized MWNTs with necessary weight ratio were

dispersed in distilled water and sonicated for 4 hours to obtain well dispersed suspensions. This

enhanced the disaggregation of any nanotubes bundles. Thereafter, a calculated amount of pyrrole

was added into this solution and stirred for 0.5 h. FeCl3.6H2O was added drop wise to the above

solution with constant stirring at ambient temperature. The mixture was stirred again for 1h. The

Fe3+

/pyrrole molar ratio was 2.3. After the reaction was over, the precipitated MWNTs/PPy powder

was filtered by conventional method. The PPy/f-MWNT nanocomposite samples were then washed

with distilled water and methanol several times until the filtrate obtained was colorless. The

nanocomposite samples obtained in powder form were vacuum dried at 40 °C for 24 hours. The

samples were then grounded into fine powder and pressed into pellets. Six samples were prepared

by means of this process. The weight percentage of MWNTs in the MWNT/PPy nanocomposite

was 0, 4, 8, 12, 16 and 20 wt%. We illustrate the coating process in Scheme 1. As can see PPy was

formed slowly and spontaneously deposited on the surface of the f-MWCNTs to form PPy-coated

MWNTs.

A)

B)

Scheme 1: Schematic representation of the process of coating MWNTs with PPy. Carboxylic functionalized

MWNT (A); functionalized nanotubes were coated with PPy (B).

Result and Discussions

Figs. 1a to 1c show FESEM (Nova NanoSEM 30 series) images of the purified MWNTs, the PPy

formed by in-situ chemical polymerization without MWNT, and the PPy/MWNT nanocomposite

formed by electropolymerization. These figures show that the diameter of CNTs has been increased

by in-situ chemical polymerization of pyrrole monomer onto the MWNT as it was expected and

confirms the presence of CNTs inside the composite. In addition, it is obvious that coated CNTs

inside the composite did not have any particular direction and they are connected to each other by

means of polymer with different angles.

Advanced Materials Research Vol. 364 51

Fig. 1, FESEM image of; (a) the PPy without MWNT, (b) the purified MWNTs and (c) the

PPy/MWNT nanocomposite

Fig. 2, The plots of DC conductivity for pure PPy and PPy with different percentage of MWNT vs.

temperature during the heating

52 Nanomaterials

The conductivities of pure PPy and different PPy/MWNT nanocomposite prepared by chemical

polymerization have been measured using four point probe method. The temperature dependence of

conductivity was measured in the scale of about 30 – 190 oC, and plotted in Fig. 2. As can be seen

from this figure, the conductivities of the samples increase with the temperature increase initially

due to the semiconductor property of the polymers [10, 11]. After reaching a maximum in the

temperature scale of 120 – 160 0C, the conductivities decreased dramatically because the structures

of the polymers were decomposed by heating.

The room temperature conductivity of the MWNT/PPy nanocables versus weight percentage of

carbon nanotubes has been sketched in Fig. 3. It is obvious that the conductivity of the nanocable

increases rapidly with increasing MWNT weight percentage. The room temperature (300 K)

conductivity of the PPy is 1.72 S/cm; however, for a 20 wt% composite, it is 9.88 S/cm. The

increase in σ (300 K) as a function of the MWNT mass fraction is usually due to the introduction of

conducting MWNT paths to the polymer, or owed to the charge transfer from PPy to MWNTs and

the improvement of the compactness of PPy by MWNTs [12, 13].

Fig. 3, Room temperature conductivity of PPy/MWNT nanocomposites as a function of MWNT

content.

The thermogravimetric analyzer measurements (TGA) were carried out to investigate the thermal

stability of the MWNTs, PPy and MWNT–PPy nanotubes. Fig. 4 shows that, MWNTs were

comparatively more stable and did not show dramatic decomposition in the temperature range of

30–750 0C and about 18% mass loss was observed due to the present functional groups. The thermal

stability of MWNT–PPy nanotubes increased with the decrease of the feeding mass ratio of pyrrole

to MWNTs. This indicates that the carbon nanotubes can improve the thermal stability of MWNT–

PPy nanotubes. At higher mass ratio of polypyrrole, the trend of the decomposition curve of

MWNT–PPy nanotubes was similar to that of PPy.

Advanced Materials Research Vol. 364 53

Fig. 4, The thermogravimetric analyzer measurements of the MWNTs, PPy and MWNT–PPy

nanotubes.

Conclusion

The PPy-MWNT composite films can be synthesized chemically. Heating the PPy samples leads

to the destruction of the oxidized species of the polymer, and finally, the polymer decomposed into

a carbonaceous material. The results also show MWNT can increase the thermal stability of PPy. It

can be also concluded that doping of PPy with MWNT increases the conductivity of the

nanocomposite which is mainly due to the introduction of conducting paths in the polymer matrix.

The TGA graphs show that the thermal stability of PPy/MWNT nanocomposite improves with

increasing the feeding mass ratio of MWNT inside polypyrrole conducting polymer matrix.

References

[1] T. A. Skotheim Ed. Marcel Dekker: Handbook of Conducting polymers (Marcel Dekker, New

York, 1986 and 1998)

[2] S. Iijima: Nature, Vol. 354 (1991), p. 56-58

[3] R. H. Baughman, A. A. Zakhidov and W. A. de Heer: Science Vol. 297(2002), p.787-792

[4] J.M. Pernaut, and J.R. Reynolds: J. Phys. Chem. Vol. 17 (2000), p. 4080-4090

[5] M.K. Ram, O. Yavuz, and M. Aldissi: Synth. Met. Vol. 151 (2005), p. 77-84

[6] C.W. Lin, B.J. Hwang and C.R. Lee: Mater. Chem. Phys. Vol. 55 (1998), p. 139-144

[7] J.W. Goodwin, G.M. Markham and B. J. Vinent: Phys. Chem. Vol. 101 (1998), p. 1961-1967

[8] Y. Yu, C. Ouyang, Y. Gao, Z. Si, W. Chen, Z. Wang and G. Xue: J. Polym. Sci. Pol. Chem.

Vol. 43, p. 6105-6115

[9] H. Arami, M. Mazloumi, R. Khalifezadeh, Sh. Hojjati and S. K. Sadrnezhad: Mater Lett. Vol.

61 (2007), p. 4412-4415

[10] J.H. Fan, M.X. Wan, D.B. Zhu, B.H. Chang, Z.W. Pan and S.S. Xe: J.Appl. Polym. Sci. Vol.

74 (1999), p. 2605-2618

[11] P. Fedorko and V. Skakalova: Synth. Met. 94 (1998), p. 279-283

[12] Li X, Wu B, Huang J, Zhang J, Liu Z and Li H: Carbon vol.41 (2002), p. 1670-1673

[13] R. Gangopadhyay, A. De, J. Euro Polym. vol. 35 (1999), p. 1985-1992

54 Nanomaterials

Nanomaterials 10.4028/www.scientific.net/AMR.364 Synthesis and Physical Characterization of Carbon Nanotubes Coated by Conducting Polypyrrole 10.4028/www.scientific.net/AMR.364.50

DOI References

[1] T. A. Skotheim Ed. Marcel Dekker: Handbook of Conducting polymers (Marcel Dekker, New York, 1986

and 1998).

doi:10.1016/0379-6779(86)90124-4 [2] S. Iijima: Nature, Vol. 354 (1991), pp.56-58.

doi:10.1038/354056a0 [4] J.M. Pernaut, and J.R. Reynolds: J. Phys. Chem. Vol. 17 (2000), pp.4080-4090.

doi:10.1021/jp994274o [5] M.K. Ram, O. Yavuz, and M. Aldissi: Synth. Met. Vol. 151 (2005), pp.77-84.

doi:10.1016/j.synthmet.2005.03.021 [6] C.W. Lin, B.J. Hwang and C.R. Lee: Mater. Chem. Phys. Vol. 55 (1998), pp.139-144.

doi:10.1016/S0254-0584(98)00087-X [9] H. Arami, M. Mazloumi, R. Khalifezadeh, Sh. Hojjati and S. K. Sadrnezhad: Mater Lett. Vol. 61 (2007),

pp.4412-4415.

doi:10.1016/j.matlet.2007.02.015 [10] J.H. Fan, M.X. Wan, D.B. Zhu, B.H. Chang, Z.W. Pan and S.S. Xe: J. Appl. Polym. Sci. Vol. 74 (1999),

pp.2605-2618.

http://dx.doi.org/10.1002/(SICI)1097-4628(19991209)74:11<2605::AID-APP6>3.0.CO;2-R [11] P. Fedorko and V. Skakalova: Synth. Met. 94 (1998), pp.279-283.

doi:10.1016/S0379-6779(98)00015-0 [12] Li X, Wu B, Huang J, Zhang J, Liu Z and Li H: Carbon vol. 41 (2002), pp.1670-1673.

http://dx.doi.org/10.1016/S0008-6223(03)00124-6 [13] R. Gangopadhyay, A. De, J. Euro Polym. vol. 35 (1999), p.1985-(1992).

doi:10.1016/S0014-3057(99)00008-7