S

Oa

Ha

b

c

a

ARRA

KNPW

1

tdeppeTotisttlwipvcse

Hf

0d

Materials Science and Engineering B 176 (2011) 684–687

Contents lists available at ScienceDirect

Materials Science and Engineering B

journa l homepage: www.e lsev ier .com/ locate /mseb

hort communication

rganic/inorganic nanocomposite films based on poly(3-methoxythiophene)nd WO3

ao Yong Yina, Xu Chun Songa,b,∗, Yi Fan Zhengc, Xia Wangb, Zhi Ai Yangb, Rong Mab

Institute of Environmental Science and Engineering, Hangzhou Dinazi University, Hangzhou 310018, PR ChinaDepartment of Chemistry, Fujian Normal University, Fuzhou 350007, PR ChinaCollege of Chemical Engineering & Materials Science, Zhejiang University of Technology, Hangzhou 310014, PR China

r t i c l e i n f o

rticle history:eceived 6 December 2010

a b s t r a c t

Organic/inorganic nanocomposite films based on poly(3-methoxythiophene) (PMOT) and WO3 were pre-

eceived in revised form 27 January 2011ccepted 14 February 2011

eywords:anocomposite films

pared by a consecutive two-step electrochemical method. The products were characterized in detailby scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS) and Fourier-transforminfrared spectroscopies (FTIR). The results show that the PMOT/WO3 nanocomposite films consist of twolayers, the substrate WO3 with 30 nm grains and superstratum PMOT, which average grain size is 60 nm.The obtained PMOT/WO3 nanocomposite films were also characterized by cyclic voltammetry to investi-

ry prond W

oly(3-methoxythiophene)O3

gate their electrochemistthan that of pure PMOT a

. Introduction

Conducting polymers, such as polyaniline, polypyrrole, poly-hiophene and their derivatives, are still of growing interestue to their potentially interesting electrical and optical prop-rties controlled by a simple and reversible doping–dedopingrocess, which allowed these conducting polymer nanomaterialsossibly to be applied in the fields of electromagnetic interfer-nce shielding, electrochromic devices and energy storage [1–4].hese polymers can generally be prepared either by chemicalr by electrochemical polymerization. Among these methods,he electrochemical technique offers several advantages, includ-ng rapidity, simplicity, generation of the polymer in the dopedtate and controlled synthesis of these compounds [5,6]. However,he electrochemical polymerization of thiophene and its deriva-ives in water was not so straightforward, resulting from theirow solubility in water, higher oxidation potential than that of

ater, and strong nucleophilic reactivity of thienyl cation rad-cals with water molecules [7]. Ionic liquids, with the uniquehysicochemical properties, such as negligible vapor pressure, low

olatility, high thermal and electrochemical stability, and ioniconductivity [1,8,9], made themselves favorable electrolytes intuding the electropolymerization of conducting polymers. Forxample, poly(3-methylthiophene), poly(3-hexylthiophene) and

∗ Corresponding author at: Institute of Environmental Science and Engineering,angzhou Dinazi University, Hangzhou 310018, PR China. Tel.: +86 591 87441126;

ax: +86 591 83465376.E-mail address: songxuchunfj@163.com (X.C. Song).

921-5107/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.mseb.2011.02.012

perties which display significant enhancement of electrochemical activityO3 films.

© 2011 Elsevier B.V. All rights reserved.

poly(3-octylthiophene) were successfully synthesized in ionic liq-uids [10].

With the development of nanotechnology, conducting poly-mer/metal oxides nanocomposite films have gained extensiveattention [11,12]. The physicochemical properties of conductingpolymers can be greatly improved by organic–inorganic inter-actions. The polypyrrole (PPy)–inorganic composites, such asPPy/silicon carbon, PPy/tungsten oxide, PPy/Fe2O3 and PPy/Fe3O4composites, have been successfully prepared by Guo et al. [13–15]and Chen et al. [16], which show tunable electrical conduc-tivity in PPy/silicon carbon and PPy/tungsten oxide compositesand enhancement of conductivity in PPy/Fe2O3 and PPy/Fe3O4composites. Organic/inorganic composite membranes based onpolybenzimidazole (PBI) and nano-SiO2 were also prepared,exhibiting improved mechanical properties with the addition(0–15 wt%) of nano SiO2 [17]. Tungsten oxide (WO3), an indi-rect band gap semiconductor, is one such promising electrodematerial for photocatalyses, electrochemical cells, electrochromicand sensor devices [18,19]. The use of conducting polymer andtungsten oxide composite materials as electrodes is of great inter-est to improve the electrochemical properties. Tunable electronicproperties were observed on surface-initiated-polymerization syn-thesized Polyaniline (PANI)/WO3 metacomposites by Zhu et al.[20]. WO3/PANI nanocomposite film was also electrodepositedby cyclic voltammetric technique from a solution of aniline and

tungstic acid. The obtained WO3/PANI film displayed significantenhancement of electrocatalytic activity for iodate reduction anda better stability than that of pure WO3 and PANI films [21].Although great enhancement of physicochemical properties havebeen shown on the polymer/metal oxides nanocomposite, to the

and Engineering B 176 (2011) 684–687 685

binwte(tpv

2

2

mooowtcvet1a

2

apriPPe

i

2

mpTpFicuwtt

3

udFad

H.Y. Yin et al. / Materials Science

est of our knowledge, the electrochemical synthesis and propertynvestigation of poly(3-methoxythiophene)/WO3 (PMOT/WO3)anocomposite films have never been reported before. In thisork, PMOT/WO3 nanocomposite films were prepared using elec-

rochemical method with ionic liquid as electrolyte. Scanninglectronic microscopy (SEM), energy-dispersive X-ray analysisEDS) and Fourier-transform infrared (FTIR) were used to charac-erize the PMOT/WO3 nanocomposite films. The electrochemicalroperties of the PMOT/WO3 films were also investigated by cyclicoltammetry method.

. Experimental

.1. Preparation of the nano-WO3 film

WO3 film was prepared using potentiostatic electrodepositionethod. Deposition electrolytes were prepared by dissolving 0.35 g

f Na2WO4·2H2O in 10 mL of distilled water and adding 0.1 mLf H2O2 with the pH adjusted to 1–2 with HNO3. An indium tinxide (ITO) conducting glass (1 cm × 1 cm) had been pretreatedith ultrasonic cleaning with acetone, anhydrous ethanol and dis-

illed water for 5 min, respectively, and dried in air at 80 ◦C. Theathodic-potentiostatic deposition was performed using a con-entional three-electrode system (CHI660C) with Pt as a counterlectrode and saturated Ag/AgCl as a reference electrode. The elec-rodeposition of WO3 was performed under a voltage of −0.65 V for0 min. After deposition, sample was washed with deionized waternd dried in air at 80 ◦C.

.2. Preparation of the PMOT/WO3 nanocomposite film

PMOT was then deposited on this WO3 film as a second step bypotentiodynamic polymerization method involving scanning theotential repeatedly between −1.0 V and +2.0 V versus a Ag/Ag+

eference electrode at a scan rate of 100 mV/s for three cyclesn 2 M 3-methoxythiophene in 5 ml [BMIM]PF6 (AR, Henan Lihuaharmaceutical Co., Ltd.). After electrochemical polymerization, theMOT/WO3 nanocomposite film was washed with acetone for sev-ral times to remove unreacted monomer and dried in air.

PMOT film was similarly prepared in 2 M 3-methoxythiophenen 5 ml [BMIM]PF6 for comparison.

.3. Characterization

The morphologies were characterized using scanning electronicroscopy (SEM, Hitachi S-4700, 25 kV). The composition of the

roducts was analyzed by energy dispersive X-ray detector (EDS,hermo Noran VANTAG-ESI). FTIR spectra of the products dis-ersed in KBr disks were recorded on a Thermo Nicolet 5700ourier-transform infrared spectrophotometer. The electrochem-cal activities of the films were studied by cyclic voltammetry. Aomputer-controlled CHI 660C electrochemical workstation wassed to obtain cyclic voltammetric, and a scan rate of 100 mV/sas used. The cell setup consisted of films as the working elec-

rode, Ag/Ag+ reference, a Pt counter electrode, and [BMIM]PF6 ashe electrolyte.

. Results and discussion

PMOT/WO3 nanocomposite film was prepared by two consec-

tive electrochemical steps. The potentiostatic curves obtaineduring electrodeposition of WO3 (the first step) are presented inig. 1a. The rising portion of the current-time curve was interpreteds the formation of a monolayer of WO3 on the electrode and theegressive portion was attributed to the growth of the WO3 on top

Fig. 1. (a) Potentiostatic curve during electrodeposition of WO3, (b) SEM image and(c) EDS pattern of WO3 film.

of this monolayer [22]. The morphology of the electrodepositedWO3 film is shown in Fig. 1b. The average size of the WO3 particlesis determined to be about 30 nm. In order to confirm that the nano-WO3 film was effectively coated on the ITO, EDS spectrum wasacquired for sample. The composition microanalysis by SEM/EDSdemonstrated that the nano-WO3 film was only composed of Wand O, which is shown in Fig. 1c.

PMOT was then deposited on the nano-WO3 film as second stepby a potentiodynamic method, in order to complete the formationof the PMOT/WO3 nanocomposite film. The cyclic voltammogramsobtained during polymerization of 3-methoxythiophene (MOT) onWO3 in ionic liquid [BMIM]PF6 are presented in Fig. 2a. The CVcurves revealed that the onset of oxidation of MOT at 0.8 V at thefirst cycle. Repeated cycling resulted in a gradual increases in theonset of oxidation potential and decrease in the current intensity.It was because more and more polymer was formed on the WO3film, thus polymer was more difficultly oxidized. Upon sequentialcycles, there were gradual increases in the current intensity in a

potential range from −0.2 to 0.8 V, which indicated that the filmswere formed on the surface of WO3. The surface morphology of thePMOT/WO3 nanocomposite films is shown in Fig. 2b. The averagesize of the PMOT is determined to be about 60 nm. EDS analysis

686 H.Y. Yin et al. / Materials Science and Engineering B 176 (2011) 684–687

Fs

wna

MCfcFcst

Psag1[

Fig. 3. (a) Cyclic voltammogram during electropolymerization of MOT on ITO sub-strate, (b) SEM image and (c) EDS pattern of the PMOT film.

PMOT/WO3

PMOT

WO3

Tra

nsm

itta

nce(%

)

ig. 2. (a) Cyclic voltammogram during electropolymerization of MOT on WO3 sub-trate, (b) SEM image and (c) EDS pattern of the PMOT/WO3 nanocomposite films.

as employed to determine the composition of the PMOT/WO3anocomposite films. As shown in Fig. 2c, signals of S from PMOTnd W from WO3 are detected through EDS analysis.

The cyclic voltammograms obtained during polymerization ofOT on ITO in ionic liquid [BMIM]PF6 are presented in Fig. 3a. The

V currents for polymerization of MOT on ITO in a potential rangerom 0.8 to 2.0 V were higher than that of MeT on WO3, which indi-ates that the WO3 films provided the small electrical conductivity.ig. 3b shows the SEM image of the PMOT film on ITO substrate. Itan be seen that PMOT products are nanoparticles with an averageize of 60 nm. It was found that substrate had not much effect onhe morphology of the PMOT.

FTIR spectra of similarly prepared WO3, PMOT and theMOT/WO3 films are shown in Fig. 4. As can be seen, the PMOT/WO3pectrum exhibits the main characteristic bands of PMOT. The char-

cteristic peak of the stretching vibration at 1573 cm−1 of C Croups in the thiophene ring can be seen. The peaks at 1442,369 cm−1 may be ascribed to CH3 bending vibrations of the PMOT23]. Two strong bands at 1167 cm−1 in the PMOT were attributed

5001000150020002500300035004000

Wavenumbers(cm-1)

Fig. 4. FTIR spectra of the WO3, PMOT films and PMOT/WO3 films.

H.Y. Yin et al. / Materials Science and En

2.01.51.00.50.0-0.5-1.0-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

cb

a

Cu

rre

nt

(10

-3A

)

tisi

bt[iaeaFmfpioavcaciorchnt

[[

[[[[[[[[[[

Potential/(V vs. Ag/Ag+)

Fig. 5. CV curves of (a) WO3, (b) PMOT and (c) PMOT/WO3 films.

o Ca–H in-plane bending vibrations. An intense peak at 843 cm−1

n PMOT was attributed to C–S stretching vibrations. The W–O bondtretching mode appears as a broad band around 623 cm−1 whichs similar to that of WO3 [24].

The electrochemical properties of the films were characterizedy cyclic voltammetry measurements. Typical cyclic voltamme-ry curves of the prepared films WO3, PMOT and PMOT/WO3 inBMIM]PF6 at a scan rate of 100 mV/s are shown in Fig. 5. As shownn Fig. 5a, the applied triangular potential was varied between −1.4nd 1.8 V and back to −1.4 V. The shape of the curves is typical oflectrochromism in WO3 films [25]. WO3 film was almost colorlesst bleached state (0.4 V), and film was blue at color state (−0.8 V).ig. 5b shows the cyclic voltammogram for PMOT. The voltam-ogram consists of two oxidation peaks, the first around −0.5 V

ollowed by a peak at +0.3 V. On the reverse scan two reductioneaks at −0.5 and −1.1 V can be observed. The PMOT film exhib-

ted different colors during the potential scanning sweep: at thexidized state (E = 1.8 V) the coloration of the film is dark green,nd at the reduced state (E = −1.4 V) it is violet red. The cyclicoltammogram of PMOT/WO3 nanocomposite films displays theharacteristic redox peaks in Fig. 5c. An oxidation peak is observedt 0.7 V, and during the reverse scan a reduction peak at −0.5 Van be observed. The PMOT/WO3 nanocomposite films also exhib-ted different colors during the potential scanning sweep: at thexidized state (E = 1.8 V) the coloration of the film is dark violet

ed, and at the reduced state (E = −1.4 V) it is deep blue. The redoxurrents for the PMOT/WO3 nanocomposite films are considerablyigher than that of the PMOT and WO3 film, and the PMOT/WO3anocomposite film exhibit characteristic electrochromic proper-ies. It is obvious that the significantly enhanced electrochemical

[

[[

[

gineering B 176 (2011) 684–687 687

properties and new electrochromic properties of the PMOT/WO3nanocomposite film, compared with WO3 and PMOT film, may beattributed to its unique structure and interactions between PMOTand WO3.

4. Conclusion

In this paper, the PMOT/WO3 nanocomposite films were pre-pared by two consecutive electrochemical steps. At first the WO3film was grown by a potentiostatic method in tungsten elec-trolytes, and then PMOT was deposited on the WO3 film bya potentiodynamic polymerization method in 2 M solutions of3-methoxythiophene in [BMIM]PF6. Cyclic voltammetric exper-iment results showed that the electrochemical activity of thePMOT/WO3 was significantly improved. The findings showed thatthe PMOT/WO3 nanocomposite films are potential materials forconstructing electronic devices.

Acknowledgments

We wish to acknowledge the financial support from the NationalNatural Science Foundation of China (No. 20873020) and QianjiangPersonal Project of Zhejiang Province (No. 2009R10025).

References

[1] S. Shang, L. Li, X. Yang, et al., J. Colloid Interface Sci. 333 (2009) 415–418.[2] F. Garnier, G. Tourillon, M. Gazard, et al., J. Electroanal. Chem. 148 (1983)

299–303.[3] S. Panero, P. Prosperi, B. Klaptse, et al., Electrochim. Acta 31 (1986) 1597–1600.[4] A. Cihaner, A.M. Önal, J. Electroanal. Chem. 601 (2007) 68–76.[5] Y. Pang, H. Xu, X. Li, et al., Electrochem. Commun. 8 (2006) 1757–1763.[6] E. Naudin, H.A. Ho, S. Branchaud, et al., J. Phys. Chem. B 106 (2002)

10585–10593.[7] A.J. Downard, D. Pletcher, J. Electroanal. Chem. 206 (1986) 147–152.[8] J.H. Davis, P.A. Fox, Chem. Commun. 11 (2003) 1209–1212.[9] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 39 (2000) 3772–3789.10] Y. Pang, X. Li, H. Ding, et al., Electrochim. Acta 52 (2007) 6172–6177.11] M. Ferreira, F. Huguenin, V. Zucolotto, et al., J. Phys. Chem. B 107 (2003)

8351–8354.12] P. Gomez-Romero, Adv. Mater. 13 (2001) 163–174.13] P. Mavinakuli, S. Wei, Q. Wang, et al., J. Phys. Chem. C 114 (2010) 3874–3882.14] J. Zhu, S. Wei, L. Zhang, et al., J. Phys. Chem. C 114 (2010) 16335–16342.15] Z. Guo, K. Shin, A.B. Karki, et al., J. Nanopart. Res. 11 (2009) 1441–1452.16] A. Chen, H. Wang, B. Zhao, et al., Synth. Met. 139 (2003) 411–415.17] H. Pu, L. Liu, Z. Chang, et al., Electrochim. Acta 54 (2009) 7536–7541.18] X.C. Song, Y.F. Zheng, E. Yang, et al., Mater. Lett. 61 (2007) 3904–3908.19] S.H. Baeck, T. Jaramillo, G.D. Stucky, et al., Nano Lett. 2 (2002) 831–834.20] J. Zhu, S. Wei, L. Zhang, et al., J. Mater. Chem. 21 (2011) 342–348.21] B.X. Zou, X.X. Liu, D. Diamondc, et al., Electrochim. Acta 55 (2010) 3915–3920.

22] S. Asavapiriyanent, G.K. Chandler, G.A. Gunawa, J. Electroanal. Chem. 177 (1984)

229–244.23] B. Dong, J. Xu, L. Zheng, et al., J. Electroanal. Chem. 628 (2009) 60–66.24] M. Deepa, A.K. Srivastava, S.N. Sharma, et al., Appl. Surf. Sci. 254 (2008)

2342–2352.25] Y. Pang, Q. Chen, X. Shen, et al., Thin Solid Films 518 (2010) 1920–1924.