COMPOSITES SCIENCE AND TECHNOLOGY Composites Science and Technology 67 (2007) 811–816 www.elsevier.com/locate/compscitech

Gamma radiation induced distribution of gold nanoparticles into carbon nanotube-polyaniline composite Kwang-Pill Lee

a,b,*

, Anantha Iyengar Gopalan a,b,c, Padmanabhan Santhosh a, Se Hee Lee a,b, Young Chang Nho d

a

d

Department of Chemistry Graduate School, Kyungpook National University, Daegu 702-701, South Korea b Nano Practical Application Center, Daegu 704-230, South Korea c Department of Industrial Chemistry, Alagappa University, Karaikudi-630 003, Tamil Nadu, India Radioisotope/Radio Application Team, Korea Atomic Energy Research Institute, Daejon 305-600, South Korea Received 31 October 2005; accepted 29 December 2005 Available online 10 October 2006

Abstract Composites of single-wall nanotubes, polyaniline and gold nanoparticles were prepared by a one pot synthesis using c-radiation as source for initiation of polymerization and generation of Au nanoparticles. The nanocomposites were characterized for the structure, morphology and electronic properties through X-ray diffraction analysis (XRD), Fourier transform infra red spectroscopy (FT-IR), field emission transmission microscopy (FETEM) and UV–visible spectroscopy. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Nanocomposites; D. Transmission electron microscopy (TEM); D. X-ray diffraction (XRD); D. Infrared (IR) spectroscopy; D. Optical microscopy

1. Introduction Carbon nanotubes (CNTs) are being the focus of current research due to their special mechanical and electronic properties [1,2]. Electrically conducting polymers, the ‘‘fourth generation polymeric materials’’, are receiving importance in modern technology as they find applications in optical, microelectronic devices, sensors, catalysts, drug delivery, energy storage systems, electrochromic display devices, light emitting devices, etc. [3–6]. Recent research interest has been focused on the preparation of nanomaterials/nanocomposites involving the combination of carbon nanotubes (CNTs), conducting polymers and metal nanoparticles by employing various methodologies such as solgel process, self-assembly, electrochemical and chemical methods [7–11]. * Corresponding author. Address: Department of Chemistry Graduate School, Kyungpook National University, Daegu 702-701, South Korea. Tel.: + 82 539505901; fax: + 82 539528104. E-mail address: [email protected] (K.-P. Lee).

0266-3538/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2005.12.030

Polyaniline (PANI) one of the most important conducting polymer has been extensively studied primarily owing to its high electrical conductivity upon doping combined with its environmental stability [12], unique dopability [13], electrochromism [14], variable electrical conductivity, ease of preparation, etc. Preparation of PANI-CNT composite with enhanced electronic properties has been reported [15,16]. Recently, attaching metal nanoparticles on the surfaces of nanotubes or to sidewalls to obtain hybrid nanocomposite is gaining interest. Such nanocomposites find applications in devices such as catalysts for fuel cells [17], transistors [18], logic gates [19] and sensors [20]. A search for the method to prepare CNT/nanoparticle composites has now been an important goal for many researchers [21–23]. Various approaches for the preparation of CNT/nanoparticle composite were reported, such as, physical evaporation, chemical reaction with functionalized CNTs and electroless deposition methods [23–26].

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Wet chemical treatment methods were used to activate the surface of CNTs for linking metal nanoparticles to them. Jiang et al. [27] attached gold nanoparticles to nitrogen-doped multi-wall carbon nanotubes. Au nanoclusters were attached to single wall nanotubes (SWNT) via thioamide interaction at carboxyl group-modified SWNT surfaces. Apart from this method, other methods were also tried [28,29]. Functionalized Au nanoparticles were attached on non-covalently functionalized CNTs [30]. Polymer coated CNTs were prepared using template synthesis [31]. However, all these methods that have been used for the synthesis of nanocomposites consisted of two steps; covalent or non-covalent functionalization of CNTs and the reduction of metal ions to result nanocomposites [32]. As an initiation route, radiolysis provides several advantages over conventional chemical methods. The main advantage stems from the absence of using an additional agent (like oxidizing agent) in the polymerization medium. c-Radiation has been applied extensively in initiating polymerization reactions, grafting polymer chains onto polymeric backbones, modifying polymer blends, and in preparing interpenetrating polymer networks. Nanocomposites of Pt–Ru nanoparticles and electronically conducting polymers were effective for anode catalysts in direct methanol fuel cell (DMFC) applications [33]. Pt nanoparticles of the order of 2–2.5 nm were loaded onto CNTs using the sulfonic acid functionalization of CNTs [34]. PANI/Au nanoparticles composite were synthesized and used as glucose sensor [35]. A non-volatile plastic digital memory device was fabricated based on nanofibers of PANI decorated with Au nanoparticles [36]. The reports reveal that the composites consisting of CNT, PANI and Au nanoparticles can find applications as sensor or electrocatalyst. To the best of our knowledge, a single step or one pot synthesis of preparation of nanocomposite, comprising of CNT, conducting polymer and Au nanoparticles has not been reported so far. The method received important as it reduces the number of steps including complex sequence of processes for making the nanocomposites. Also, the nanocomposites will be free from impurities from each step. In the present work, we have established a one pot synthesis of SWNT-PANI-Au nanocomposites using c-radiation as source for initiation of polymerization and generation of Au nanoparticles in the medium consisting of SWNTs. The nanocomposites prepared were characterized for morphology and electronic properties.

2. Experimental 2.1. Materials Aniline (Aldrich) was distilled and used. Single-wall carbon nanotubes (SWNTs) obtained from CNT Co., Ltd. Incheon, Korea were rinsed with double-distilled water and dried. Cetyltrimethyl ammonium bromide, auric acid,

hydrochloric acid of analytical grade from Aldrich were used as received. 2.2. Preparation of PANI–SWNT–Au nanoparticles composite In a typical synthesis of the nanocomposite, a solution of aniline in 1 M HCl (10 mM), 0.005 g SWNT in 0.5 M CTAB was added and sonicated for 1 h. To this, 0.04 mM HAuCl4 in 1 M HCl was added. Nitrogen gas was bubbled through the above solution (30 min) to remove oxygen and then the solution was irradiated by c-ray (Co-60 source) to a total dose of 3 kGy under atmospheric pressure and room temperature. After c-irradiation, precipitation occurred. The precipitate (SWNT–PANI–Au nanocomposites) was filtered and washed with 1 M HCl until the filtrate became colorless. The composite was then dried under dynamic vacuum at room temperature. 2.3. Characterization Fourier transform infrared (FT-IR) spectrum of the composite was recorded using a Bruker IFS 66v FTIR spectrophotometer in the region 400–4000 cm1 using KBr pellets. The morphology of the composite was examined by field emission transmission microscope (FETEM) – JOEL JEM-2000EX with a field emission gun operated at 200 kV. UV–visible spectrum was recorded using Shimadzu UV–visible spectrophotometer. A Ds-Advanced Burker AXS Diffractometer was employed using a CuÆKa source to obtain XRD spectrum of the composite. The spectrum was scanned from 2h = 0° to 80°. The amount of gold nanoparticles in the composite was determined though inductively coupled plasma-mass spectrometry (ICP-MS VG Elemental-Plasma Quad 3). 3. Results and discussion We have successfully prepared nanocomposites comprising of single wall carbon nanotube-polyaniline-Au (SWNT–PANI–Au–NC) by a one pot synthesis. SWNT– PANI–Au–NC was prepared by irradiating c-ray to a solution consisting of SWNT, aniline and HAuCl4 in 0.5 M CTAB and 1 M HCl. Interestingly, we have neither used a conventional oxidizing agent like ammonium persulphate for polymerization of aniline nor used a reducing agent for generating Au nanoparticles from HAuCl4. Polymerization of aniline and formation of Au nanoparticles were simultaneously achieved in the presence of c-irradiation. It is to be noted that after the c-irradiation of the solution consisting of HAuCl4, SWNT and aniline, green colored precipitate was formed. At the first instance, it was felt that the green precipitate might be polyaniline (PANI) in its emaraldine salt form [37]. Field emission transmission micrograph (FETEM) analysis of the precipitate (details are provided later) indicated the presence of Au nanoparticles along with PANI and SWNT. Hence, we confirmed that

K.-P. Lee et al. / Composites Science and Technology 67 (2007) 811–816

SWNT–PANI–Au–NC was obtained by the simple one step synthesis using c-irradiation. Few more information was obtained about the formation of SWNT–PANI–Au–NC by performing additional experiments. Irradiation of c-ray of a solution consisting of SWNT and aniline for a similar period as used for the preparation of SWNT–PANI–Au–NC did not produce any precipitate or color change. Also, there was no precipitation or coloration, when the solution consisting of HAuCl4 and aniline was kept for a similar period that was used for the preparation of SWNT–PANI–Au–NC. The first experiment demonstrated that PANI was not formed through polymerization of aniline by c-irradiation. The second experiment clarified that HAuCl4 did not oxidize aniline to result PANI under the experimental conditions used in the studies. Hence, we have concluded that formation of PANI and Au nanoparticles occurred simultaneously when a mixture of HAuCl4, SWNT and aniline was irradiation by c-radiation. Considering the details from our trial experiments the following tentative mechanism is proposed. c-radiation

þ   H2 O ƒƒƒƒ! e aq ; H3 O ; H ; H2 ; OH ; H2 O2

e aq

þ Au

Au

II

Cl2 4

III

Cl 4

! Au

II

þ 2C6 H5 NH2 !

C6 H5 NHþ 2

ð1Þ

Cl2 4

ð2Þ 2C6 HNHþ 2

þ Au

þ Aniline ƒƒƒƒƒƒ! polyaniline polymerization solvated e aq

ð0Þ

þ 4Cl



ð3Þ ð4Þ

Formation of and other species is well established [38]. The produced solvated electrons e aq have strong reducing capabilities to convert higher valent metal ions to lower valent or zero valent metal (Eq. (2)). We propose Eq. (3) for the reduction of AuII to Au0. This proposal is arrived from the fact that a solution containing aniline and SWNT could not be polymerized under our experimental conditions. Hence, AuII ions play an important role in forming PANI. Also, a solution containing HAuCl4 and aniline did not yield PANI. This observation indicated that the reduction of AuIII to AuII (or) Au0 did not occur in the absence of c-radiation. Once, aniline radical cation are formed, dimerization and subsequent reactions with aniline resulted PANI (Eq. (4)) [39]. The chloride ion formed (Eq. (3)) act as a dopent for PANI [40].

813

The present approach of preparation of SWNT–PANI– Au–NC has few distinct advantages. (i) Nucleation of Au nanoparticles and polymerization occurred simultaneously, (ii) the functional groups in PANI chains hold Au nanoparticles, (iii) PANI chains can wrap or cover the surface of SWNT as a sheath or layer and Au nanoparticles may be decorated in the SWNT–PANI composite. The results obtained on the morphology, electronic state and structure of SWNT–PANI–Au–NC are detailed below. 3.1. Morphology Presence of Au nanoparticles in the green precipitate obtained after c-irradiation of a mixture of SWNT, aniline and HAuCl4 was clearly evident from the analysis of the precipitate through field emission transmission microscopy (FETEM). Fig. 1 presents the FETEM pictures of the nanocomposite. The presence of Au nanoparticles with an average size of 5 nm can be witnessed from FETEM pictures. The dark spots in FETEM image are the Au nanoparticles. It is to be noted that Au nanoparticles are anchored or decorated on the walls of SWNT coated with a layer of PANI. It is also likely that a portion of Au nanoparticles may be entrapped in the layer of PANI that could not be noticed on the surface of SWNT. In general, FETEM micrograph of the precipitate obtained after cirradiation of a mixture of SWNT, aniline and HAuCl4 informed the simultaneous formation of PANI and Au0 nanoparticles. It is to be noted that surface of SWNT could not hold Au0 nanoparticles due to its hydrophobic nature. Hence, we believe that Au0 nanoparticles are preferentially adsorbed or anchored on PANI. Also, there can be an electrostatic interaction between the sites in PANI and Au0 atom [36]. These types of electrostatic interactions may be the reason for the absence of significant aggregation of Au0 nanoparticles on the surface of SWNT/PANI [41]. Further, the amount of Au nanoparticles in the SWNT– PANI–Au–NC was determined though ICP-MS and was found to be 0.68 lg. The conductivity of the SWNT– PANI–Au–NC as determined by the conventional twopoint probe method (1.38 S m1) is higher than that of pristine PANI [42] and SWNT/PANI composite [43].

Fig. 1. FETEM images showing the anchoring of gold nanoparticles onto SWNT/PANI composite prepared by c-radiation; (a) and (b) SWNT–PANI– Au–NC under different magnification, (c) magnified part of one gold nanoparticles (Scale bar: 100 nm (a), 20 nm (b) and 5 nm (c)). Wt. of SWNT: 0.005 g; [aniline]: 10 mM; [HAuCl4]: 0.04 mM.

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3.2. X-ray diffraction Results from X-ray diffraction analysis support the presence of PANI and Au0 and SWNT nanoparticles in the nanocomposites, SWNT–PANI–Au–NC. XRD pattern (Fig. 2) of nanocomposite is reflective of the presence of Au nanoparticles, PANI and SWNT in it. The Bragg reflection patterns appearing at 2h  38° (1 1 1), 42° (2 0 0), 64° (2 2 0) and 78° (3 1 1) are indexed for the face-centered cubic, fcc structure of gold nanoparticles [44,45]. The diffraction peak around 2h  27° corresponds to (0 0 2) G phase of SWNT [46]. The peak centered at 2h  25° is ascribed to the periodicity of the PANI chain [47]. 3.3. FT-IR spectroscopy FT-IR spectrum (Fig. 3) of the SWNT–PANI–Au–NC is presented. The spectral characteristic of SWNT–PANI– Au–NC mainly resembles PANI (Fig. 3, inset). FT-IR spectrum of SWNT–PANI–Au–NC exhibits absorption band

3000 2000

(200)

4000

40 20 0 10

30 20 40 2 Theta (deg)

(220) (311)

1000 PANI Au

20

60 40 2 Theta (deg)

80

Fig. 2. XRD pattern of SWNT–PANI–Au–NC prepared using c-radiation method. Wt. of SWNT: 0.005 g; [aniline]: 10 mM; [HAuCl4]: 0.04 mM (inset: XRD pattern of pristine PANI; [aniline] = 10 mM).

40

1.2

26

1109

28

1588

30

24 4000

3000 2000 1000 Wavenumbers (cm-1)

25

0.5

0.8

1110

1720 1600

0.3 0.2 0.1

0.6 0.4

20

b

0.4

1.0

1492

30

32

3400

% Transmittance

35

34

3399

% Transmittance

36

Presence of Au nanoparticles in the SWNT–PANI–Au– NC was further confirmed by UV–visible spectroscopy. Fig. 4b represents the UV–visible spectrum of the SWNT– PANI–Au–NC in DMF. For a comparative purpose, SWNT/PANI composite was performed by intimate mixing of SWNT and PANI and UV–visible spectrum of the SWNT/PANI composite is presented (Fig. 4a). SWNT/ PANI composite shows a broad band around 580 nm, characteristics of bipolaronic transition of PANI [39]. On the other hand, UV–visible spectrum of SWNT–PANI–Au– NC showed a broad band around 530 nm. Normally, surface plasmon resonance absorption of Au nanoparticles appears as a sharp peak at 530 nm [50]. It is well established that surface plasmon resonance band of Au nanoparticles is sensitive to environment [51]. Au nanoparticles that are anchored in PANI chains may have a different environment (bound to protonated imine sites) than existing as isolated Au nanoparticles. Also, PANI would provide a dielectric medium that may be different for the Au nanoparticles in aqueous/organic medium. Hence, the position of plasmon resonance peak of Au nanoparticles and its intensity are expected to change. Significant changes in the absorption intensity and peak position of plasmon resonance absorption of Au nanoparticles were witnessed by Shin et al. [52], when Au nanoparticles were encapsulated in polypyrrole matrix.

Abs.

0

3.4. UV–visible spectroscopy

Abs.

Intensity (AU)

60

Intensity (AU)

(112)

corresponding to the stretching of quinoid (1600 cm1) and benzenoid ring (1494 cm1), stretching of –NH (3400 cm1), aromatic C–H in plane bending (1110 cm1) [48]. Besides, a band around 1720 cm1 that corresponds to C@O stretching mode of the carboxyl groups is present which informs the c-radiation induced shorting of SWNT [49]. These spectral bands signify the formation of the nanocomposite through c-radiation induced polymerization of mixture of SWNT, aniline and HAuCl4.

a

0 300 400 500 600 700 800 900 Wavelength (nm)

0.2

1494

b 15 4000

3000

2000

a

0 400 1000

Wavenumbers (cm-1)

Fig. 3. FT-IR spectrum of SWNT–PANI–Au–NC prepared by c-radiation. Wt. of SWNT: 0.005 g; [aniline]: 10 mM; [HAuCl4]: 0.04 mM (inset: FT-IR spectrum of PANI-HCl; [aniline]: 10 mM).

500 600 700 Wavelength (nm)

800

Fig. 4. UV–visible spectrum of (a) SWNT/PANI (intimate mixing) and (b) SWNT/PANI–Au–NC prepared by c-radiation; Wt. of SWNT: 0.005 g; [aniline]: 10 mM; [HAuCl4]: 0.04 mM (inset: UV–visible spectrum of (a) pristine PANI-HCl and (b) Au nanoparticles in aqueous medium).

K.-P. Lee et al. / Composites Science and Technology 67 (2007) 811–816

In the present case, for the SWNT–PANI–Au–NC, the band around 530 nm is broader. We expect that the band around 570 nm that corresponds to bipolaronic state of PANI might be merged with plasmon resonance band of Au nanoparticles. There is also a possibility that formation of nanocomposite might diminish the plasmon resonance band of Au nanoparticles. Alternatively, the strong absorption band of PANI appearing nearer to the plasmon resonance could cause merging of the two bands to result a broad band. Previously, Selvan et al. [53] observed a diminishing of plasmon resonance band of Au nanoparticles by the strong absorption of polypyrrole in polypyrrole-Au nanocomposites. 4. Conclusions One pot synthesis of a nanocomposite comprising of SWNT, polyaniline and Au nanoparticles was successfully established by c-irradiation. This method can be extended for multi-various combinations of conducting polymers and metal nanoparticles to prepare newer nanocomposites. These nanocomposites are expected to find applications as catalysts, sensors and in microelectronic devices. Acknowledgements This work was supported by the Nuclear R&D program, Ministry of Science and Technology, Korea. The authors acknowledge the help of Korea Basic Science Institute, Daejon, South Korea, for recording the FETEM photographs and Kyungpook National University Center for Scientific Instrument. References [1] Iijima S. Helical microtubules of graphitic carbon. Nature 1991;354:56–8. [2] Ebbesen TW, Lezec HJ, Hiura H, Bennett JW, Ghaemi HF, Thio T. Electrical conductivity of individual carbon nanotubes. Nature 1996;382:54–6. [3] Kraft A. Organic field-effect transistors – the breakthrough at last. Chem Phys Chem 2001;2:163–5. [4] Holtz JH, Asher SA. Polymerized colloidal crystal hydrogel films as intelligent chemical sensing materials. Nature 1997;389:829–32. [5] Heeger AJ. Semiconducting and metallic polymers: the fourth generation of polymeric materials. J Phys Chem B 2001;105:8475–91. [6] Pernaut JM, Reynolds JR. Use of conducting electroactive polymers for drug delivery and sensing of bioactive molecules, A redox chemistry approach. J Phys Chem B 2000;104:4080–90. [7] Manners I. Materials science: putting metals into polymers. Science 2001;294:1664–6. [8] Breimer MA, Yevgeny G, Sy S, Sadik OA. Incorporation of metal nanoparticles in photopolymerized organic conducting polymers: a mechanistic insight. Nano Lett 2001;1:305–8. [9] Lu Y, Yang Y, Sellinger A, Lu M, Huang J, Fan H, et al. Selfassembly of mesoscopically ordered chromatic polydiacetylene/silica nanocomposites. Nature 2001;410:913–7. [10] Boal AK, Ilhan F, DeRouchey JE, Albrecht TT, Russell TP, Rotello VM. Self-assembly of nanoparticles into structured spherical and network aggregates. Nature 2000;404:746–8.

815

[11] Mu Y, Liang H, Hu J, Jiang L, Wan L. Controllable Pt nanoparticle deposition on carbon nanotubes as an anode catalyst for direct methanol duel cells. J Phys Chem B 2005;109:22212–6. [12] Camelet JL, Lacorix JC, Aeiyach S, Chaneching K, Lacaze PC. Electrosynthesis of adherent polyaniline films on iron and mild steel in aqueous oxalic acid medium. Synth Met 1998;93:133–42. [13] Paul EW, Ricco AJ, Wrighton WS. Resistance of polyaniline films as a function of electrochemical potential and the fabrication of polyaniline-based microelectronic devices. J Phys Chem 1985;89: 1441–7. [14] Salaneck WR, Haung WS, Lundstrom I, Macdiarmid AG. A twodimensional-surface ‘state diagram’ for polyaniline. Synth Met 1986;13:291–7. [15] Liu J, Tian S, Knoll W. Properties of polyaniline/carbon nanotube multilayer films in neutral solution and their application for stable low-potential detection of reduced b-nicotinamide adenine. Langmuir 2005;21:5596–9. [16] Cochet M, Maser WK, Benito AM, Callejas MA, Martı´nez MT, Benoit JM, et al. Synthesis of a new polyaniline/nanotube composite: ‘‘in-situ’’ polymerisation and charge transfer through site-selective interaction. Chem Commun 2001:1450–1. [17] Che GL, Lakshmi BB, Martin CR, Fisher ER. Metal-nanoclusterfilled carbon nanotubes: catalytic properties and possible applications in electrochemical energy storage and production. Langmuir 1999;15:750–8. [18] Postma HW, Teepen T, Yao Z, Grifoni M, Dekker C. Carbon nanotube single-electron transistors at room temperature. Science 2001;293:76–9. [19] Bachtold A, Hadley P, Nakanishi T, Dekker C. Logic circuits with carbon nanotube transistors. Science 2001;294:1317–20. [20] Lim SH, Wei J, Lin J, Li Q, Kuayou J. A glucose biosensor based on electrodeposition of palladium nanoparticles and glucose oxidase onto Nafion-solubilized carbon nanotube electrode. Biosens Bioelectron 2005;20:2341–6. [21] Kong J, Chapline MG, Dai HJ. Functionalized carbon nanotubes for molecular hydrogen sensors. Adv Mater 2001;13:1384–6. [22] Bezryadin A, Lau CN, Tinkham M. Quantum suppression of superconductivity in ultrathin nanowires. Nature 2000;404:971–4. [23] Li W, Liang C, Zhou W, Qiu J, Zhou Z, Sun G, et al. Preparation and characterization of multiwalled carbon nanotube-supported platinum for cathode catalysts of direct methanol fuel cells. J Phys Chem B 2003;107:6292–9. [24] Liu J, Rinzler AG, Dai HJ, Hafner JH, Bradley RK, Boul PJ, et al. Fullerene pipes. Science 1998;280:1253–6. [25] Azamian BR, Coleman KS, Davis JJ, Hanson N, Green MLH. Directly observed covalent coupling of quantum dots to single-wall carbon nanotubes. Chem Commun 2002:366–7. [26] Xue B, Chen P, Hong Q, Lin JY, Tan KL. Growth of Pd, Pt, Ag and Au nanoparticles on carbon nanotubes. J Mater Chem 2001: 2378–81. [27] Jiang K, Eitan A, Schadler LS, Ajayan PM, Siegel RW. Selective attachment of gold nanoparticles to nitrogen-doped carbon nanotubes. Nano Lett 2003;3:275–7. [28] Sun J, Gao L. Development of a dispersion process for carbon nanotubes in ceramic matrix by heterocoagulation. Carbon 2003;41:1063–8. [29] Sun J, Gao L, Li W. Colloidal processing of carbon nanotube/ alumina composites. Chem Mater 2002;14:5169–72. [30] Chen RJ, Zhan YG, Wang DW, Dai HJ. Noncovalent sidewall functionalization of single-walled carbon nanotubes for protein immobilization. J Am Chem Soc 2001;123:3838–9. [31] Carrillo A, Swartz JA, Gamba JM, Kane RS, Chakrapani N, Wei BQ, et al. Noncovalent functionalization of graphite and carbon nanotubes with polymer multilayers and gold nanoparticles. Nano Lett 2003;3:1437–40. [32] Choi HC, Shim M, Bangsaruntip S, Dai HJ. Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes. J Am Chem Soc 2002;124:9058–9.

816

K.-P. Lee et al. / Composites Science and Technology 67 (2007) 811–816

[33] Choi JH, Kim YM, Lee JS, Cho KY, Jung HY, Park YJ, et al. A polyaniline supported PtRu nanocomposite anode and a Pd-impregnated nanocomposite Nafion membrane for DMFCs. Solid State Ionics 2005;176:3031–4. [34] Waje MM, Wang X, Li W, Yan Y. Deposition of platinum nanoparticles on organic functionalized carbon nanotubes grown in situ on carbon paper for fuel cells. Nanotechnology 2005;16: 395–400. [35] Ma Y, Li N, Yang C, Yang X. One-step synthesis of water-soluble gold nanoparticles/polyaniline composite and its application in glucose sensing. Colloids Surf A 2005;269:1–6. [36] Tseng RJ, Huang J, Ouyang J, Kaner RB, Yang Y. Polyaniline nanofiber/gold nanoparticle nonvolatile memory. Nano Lett 2005;5:1077–80. [37] Huang WS, Humphrey BD, MacDiarmid AG. Polyaniline, a novel conducting polymer. Morphology and chemistry of its oxidation and reduction in aqueous electrolytes. J Chem Soc Faraday Trans 1986;82:2385–400. [38] Remita H, Lampre I, Mostafavi M, Balanzat E, Bouffard S. Comparative study of metal clusters induced in aqueous solutions by c-rays, electron or C6+ ion beam irradiation. Rad Phys Chem 2005;72:575–86. [39] Wen TC, Sivakumar C, Gopalan A. In situ, UV–vis spectroelectrochemical studies on the initial stages of copolymerization of aniline with diphenylamine-4-sulphonic acid. Electrochim Acta 2001;46: 1071–85. [40] Morales GM, Llusa M, Miras MC, Barbero C. Effects of high hydrochloric acid concentration on aniline chemical polymerization. Polymer 1997;38:5247–50. [41] Gunter PLJ, Niemantsverdriet JW, Ribeiro FH, Somorjai GA. Surface science approach to modelling supported catalysts. Catal Rev Sci Eng 1997;39:77–168. [42] Zhou Y, He BL, Zhou WJ, Huang J, Li XH, Wu B, et al. Electrochemical capacitance of well-coated single-walled carbon

[43] [44]

[45]

[46]

[47] [48]

[49]

[50]

[51]

[52]

[53]

nanotube with polyaniline composites. Electrochim Acta 2004;49: 257–62. Huang JE, Li XH, Xu JC, Li HL. Well-dispersed single-walled carbon nanotubes/polyaniline composite films. Carbon 2003;41:2731–6. Joint Committee on Powder Diffraction Standards, Diffraction data file: JCPDS International Center for Diffraction Data: Swarthmore, PA 1991. Leff DV, Brandt L, Heath JR. Synthesis and characterization of hydrophobic, organically soluble gold nanocrystals functionalized with primary amines. Langmuir 1996;12:4723–30. Terrones N, Hsu WK, Schilder A, Terrones H, Grobert N, Hare JP. Novel nanotubes and encapsulated nanowires. Appl Phys A 1998;66: 307–17. Moon YB, Cao Y, Smith P, Heeger AJ. X-ray scattering from crystalline polyaniline. Polymer Commun 1989;30:196–9. Sun Y, MacDiarmid AG, Epstein AJ. Polyaniline: synthesis and characterization of pernigraniline base. J Chem Soc Chem Commun 1990:529–30. Chen J, Hamon MA, Hu H, Chen Y, Rao AM, Eklund PC, et al. Solution properties of single-walled carbon nanotubes. Science 1998;282:95–8. Huang H, Yang X. One-step, shape control synthesis of gold nanoparticles stabilized by 3-thiopheneacetic acid. Colloids Surfaces A 2005;255:11–7. Mirkin CA. Programming the assembly of two- and three-dimensional architectures with DNA and nanoscale Inorganic building blocks. Inorg Chem 2000;39:2258–72. Shin HJ, Hwang IW, Hwang YN, Kim D, Han SH, Lee JS, et al. Comparative investigation of energy relaxation dynamics of gold nanoparticles and gold-polypyrrole encapsulated nanoparticles. J Phys Chem B 2003;107:4699–704. Selvan ST, Hayakawa T, Nogami M, Moller M. Block copolymer mediated synthesis of gold quantum dots and novel gold-polypyrrole nanocomposites. J Phys Chem B 1999;103:7441–8.