Materials Letters 92 (2013) 157–160

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Materials Letters

0167-57

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Preparation of carpenterworm-like polyaniline/carbon nanotubesnanocomposites with enhanced electrochemical property

Haosen Fan a,b, Ning Zhao a,n, Hao Wang a, Xiaofeng Li a, Jian Xu a,n

a Beijing National Laboratory for Molecular Sciences, Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR Chinab School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen, 518055, PR China

a r t i c l e i n f o

Article history:

Received 6 August 2012

Accepted 12 October 2012Available online 22 October 2012

Keywords:

Carbon nanotubes

Carpenterworm-like

Nanocomposites

Polyaniline

Spectroscopy

7X/$ - see front matter Crown Copyright & 2

x.doi.org/10.1016/j.matlet.2012.10.048

esponding authors. Tel./fax: þ86 10 8261 96

ail addresses: zhaoning@iccas.ac.cn (N. Zhao)

a b s t r a c t

Carpenterworm-like multidimensional architectures of polyaniline/multi-walled carbon nanotubes

(PANI–MWNTs), with a diameter of about 2.5 mm and consisting of many interlaced PANI nanorods

on the surface of MWNTs, were successfully synthesized in a mixture of ethanol and water. Chemical

structure and composition of the prepared PANI–MWNTs nanocomposites were characterized by

Fourier transform infrared (FTIR) spectroscopy, ultraviolet and visible spectroscopy (UV–vis), X-ray

diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It has been found that the concentration

of ethanol in the solution plays a critical role in controlling the morphology of the resultant

nanocomposites. The obtained carpenterworm-like PANI–MWNTs nanocomposites exhibit enhanced

electrochemical behavior in comparison with MWNTs and PANI, indicating a potential application in

electrode material of supercapacitors or secondary batteries.

Crown Copyright & 2012 Published by Elsevier B.V. All rights reserved.

1. Introduction

Carbon nanotubes, due to their special structure and excellentmechanical and electrical properties, have aroused great interestsfor developing new class of multifunctional composites in thepast two decades [1]. In recent years, nanocomposites of carbonnanotubes and conducting polymers have aroused many researchinterests due to the special synergistic effect by combining theexcellent properties of both components [2]. Among the variousstructural conducting polymers, polyaniline (PANI) has beenconsidered to be the most prospective in application because ofits excellent properties such as easy to synthesis, good environ-mental stability and outstanding electrical properties [3,4]. Todate, many attempts such as in-situ polymerization [5], electro-chemical method [6], microemulsion [7] and one-pot synthesis[8], have been made to integrate PANI and carbon nanotubes toobtain nanocomposites with excellent properties. In a generalway, single or multi-walled carbon nanotubes are usually treatedin a strong inorganic acid by a liquid phase oxidation procedure tointroduce oxygen containing groups (carboxyl, hydroxyl, or epoxygroups) on the carbon nanotubes [9–11]. These oxygenatedfunctional groups greatly improve the dispersability of carbonnanotubes in aqueous solutions or organic solvents, which helpsto get a homogeneous dispersion for preparing nanocomposites of

012 Published by Elsevier B.V. All

67.

, jxu@iccas.ac.cn (J. Xu).

PANI and carbon nanotubes with the assist of active groups incarbon nanotubes [12–14].

Although nanocomposites of PANI and carbon nanotubes weregenerally prepared in aqueous solutions [15], the influence of thesolvent composition on the morphology of the product had rarelybeen studied yet. Herein, we report a novel approach to preparecarpenterworm-like PANI–MWNTs nanocomposites using a mixtureof ethanol and H2O as solvent. It has been found that the concen-tration of ethanol in the solution plays a critical role in determiningthe morphology. Electrochemical property of carpenterworm-likePANI–MWNTs nanocomposites exhibits enhanced electrochemicalbehavior because of the hierarchical structure and synergistic effectof both components.

2. Experiment

Aniline (ANI, Beijing Chemical Co.) was distilled under reducedpressure. Ammonium persulfate (APS, Sinopharm Chemical ReagentCo.), commercial multi-walled carbon nanotubes (MWNTs, 20–40 nmin diameter, 5–15 mm in length, purity Z95 wt%, Shenzhen NanotechPort Co., Ltd.), and other reagents of A. R. grade were used withoutfurther treatment.

Before the preparation of PANI–MWNTs nanocomposites,MWNTs were treated by 3 M HNO3 and 30% H2O2 solutionsequentially according to previously reported method [9]. Then20 mg treated MWNTs powder was added into mixed solvent(containing 1 M HClO4) of 40 mL deionized water and 10 mLethanol. After ultrasonicated for 10 min at room temperature,

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H. Fan et al. / Materials Letters 92 (2013) 157–160158

ANI (0.2 mmol) was added into above solution for 30 min. 10 mLaqueous solution of APS (0.1 mmol) was added in one portion andfollowed by stirring for 1 h. Then the reaction system was left atthe stationary state for 12 h at room temperature. The resultingproduct was filtered and washed with water and methanolseveral times. Finally, the product was dried at 80 1C in an ovenfor 24 h.

The morphology of PANI–MWNTs was examined by a HitachiS4800 field emission scanning microscope (SEM) and a JEOL JEM-2200FS transmission electron microscope (TEM). Fourier transforminfrared spectroscopy (FTIR) was measured and recorded on aBruker Equinox 55 spectrometer in the range of 400–4000 cm�1.The ultraviolet and visible spectroscopy (UV–vis) spectrum wasmeasured on a Shimadzu 1601PC UV–vis spectrophotometer.X-ray diffraction (XRD) pattern was recorded on a Rigaku D/max2400 Diffractometer using Cu-Ka (l¼1.5418 A) radiation (40 kV,200 mA). X-ray photoelectron spectroscopy (XPS) analysis wascarried out on a ESCALab220i-XL electron spectrometer from VGScientific. Al-Ka radiation was used as the X-ray source andoperated at 300 W. Cyclic voltammetries (CV) were measuredby a Zahner IM6 electrochemical working station in 0.1 M HClsolution.

3. Results and discussion

The morphology of the as-synthesized PANI–MWNTs nanocom-posites was shown in Fig. 1. Uniformly structured carpenterworm-like PANI–MWNTs nanocomposites with a diameter of about 200 nmwere obtained. From the highly magnified SEM and TEM images, itcan be seen that the surface of the MWNTs is covered by lots ofinterlaced PANI nano-protuberances with dozens of nanometers inheight. Therefore, a core–shell structured PANI–MWNTs nanocompo-sites were obtained with carbon nanotubes as core and PANI nano-protuberances as shell.

Fig. 1. SEM (a and b) and TEM (c and d) images of the c

The typical FTIR spectrum of the PANI–MWNTs nanocompo-sites is shown in Fig. 2a, which is in good according withpreviously reported result [16]. The weak absorption at3061 cm�1 is attributed to the N–H stretching vibration of PANImain chains. The strong peaks at 1578 and 1502 cm�1 areascribed to the C¼C stretching vibration of the quinonoid andbenzenoid rings, respectively. Besides, the characteristic peaks at1292, 1176 and 848 cm�1 are assigned to the C–N stretchingvibration of the benzene ring, C¼N stretching modes and the out-of-plane vibration in the 1, 4-disubstituted benzene ring. For theUV–vis spectrum (Fig. 2b), two obvious adsorptions centeredabout 430 and 800 nm are attributed to the p–pn transition inthe benzenoid rings and quinoid rings, respectively, indicatingPANI in its emeraldine salt form [17]. Fig. 2c exhibits the XRDpattern of PANI–MWNTs nanocomposite. The crystalline peakscentered at 201 and 251 are assigned to (020) and (200) reflectionsof PANI in its emeraldine salt form [18]. Quantitative analysis ofchemical elements on the surface is investigated by XPS measure-ment (Fig. 2d). The survey spectrum shows three major peaks at532, 401, and 285 eV, corresponding to O1s, N1s, and C1sphotoemission, respectively.

Fig. 3 shows the morphologies of PANI–MWNTs nanocompositesprepared in the mixed solvents with different proportions ofethanol. It is interesting that the concentration of ethanol has aprofound effect on the morphology of the resultant PANI–MWNTsnanocomposits. When only water was used as solvent, core–shellstructured PANI–MWNTs nanocomposites with PANI nanoparticlesdecorated on MWNTs surface is obtained (Fig. 3a). A similarcarpenterworm-like structure can be obtained as mixed solventwith 10 vol% of ethanol in water is used (Fig. 3b). The morphology iscomparable to that shown in Fig. 1, which prepared from solutionwith ethanol to water of 2:8. It is obvious that the carpenterworm-like structure (Fig. 3b) has a larger specific area than that shown inFig. 3a. Further increase the concentration of ethanol to 40% willlead to the formation of porous PANI nanostructures covered on

arpenterworm-like PANI–MWNTs nanocomposites.

Fig. 2. (a) FTIR, (b) UV–vis, (c) XRD, and (d) XPS analysis of the carpenterworm-like PANI–MWNTs nanocomposites.

Fig. 3. SEM images of the PANI–MWNTs nanocomposites synthesized with different volume ratios of ethanol to H2O: (a) 0; (b) 1: 9; (c) 4:6 and (d) 6: 4.

H. Fan et al. / Materials Letters 92 (2013) 157–160 159

MWNTs (Fig. 3c) and there are almost no PANI nanostructures onthe surface of MWNTs when the content of ethanol in the solventreaches 60% (Fig. 3d). The results indicate that certain amount ofethanol in the solvent is favorable for the formation of PANI nano-protrusions on the surface of MWNTs. As is well known, ethanol hasdifferent polarity and surface tension in comparison with H2Oowing to its amphiphilic molecular structure. When the solventchanges with certain volume ratios, the surface energy of theproducts and the molecular interactions between the products

and solvents may also change in the reaction solution. Therefore,the morphology of polymerized PANI on the surface of MWNTs willchange at different volume ratios of solvent.

Fig. 4 exhibits the CV curves of MWNTs, PANI and variousPANI–MWNTs prepared at a scan rate of 5 mV s�1 in 1 M H2SO4

solution with the potential range of �0.2–0.8 V. Compared withMWNTs and PANI, PANI–MWNTs nanocomposites exhibit largercurrent density response. The improved electrochemical perfor-mance can be ascribed to the hierarchical structure and the

Fig. 4. CV curves of MWNTs, PANI and carpenterworm-like PANI–MWNTs nano-

composites at the scan rate of 5 mV s�1.

H. Fan et al. / Materials Letters 92 (2013) 157–160160

synergistic effect between MWNTs and PANI by combining thehigh conductivity of MWNTs with good redox properties of PANI.PANI–MWNTs electrode shows two couples of obvious redoxpeaks in CV curve, in which a pair of redox peaks (C1/A1) areattributed to the redox transition of PANI from leucoemeraldine(semiconducting state) to polaronic emeraldine form (conductingsate) and another pair (C2/A2) are due to the transformation fromemeraldine to pernigraniline [19], respectively.

4. Conclusion

In summary, carpenterwprm-like multidimensional structuredPANI–MWNTs nanocomposite with interlaced PANI nano-protuberances on MWNTs surface were chemically synthesizedin the mixture solvent of ethanol and water. The chemicalstructure and composition of as-synthesized PANI–MWNTs nano-composite were characterized by FTIR, UV–vis, XRD and XPS. Thesynthetic parameter, such as the volume ratio of ethanol to H2O,

plays an important in controlling the morphologies and sizes ofPANI–MWNTs nanocomposite. The proposed method indicatesthat this is a facile and effective strategy for the fabrication ofhierarchical PANI–MWNTs nanocomposite. CV curves indicatethat PANI–MWNTs nanocomposite exhibits enhanced electroche-mical activity in comparison with each component of PANI andMWNTs. We hope such a hierarchical PANI–MWNTs nanocompo-site may find applications in electrode material of supercapacitoror secondary batteries.

Acknowledgments

This work was supported by the National Natural ScienceFoundation of China (NSFC) (Grant Nos. 50821062, 21121001).We acknowledge Beijing Municipal Commission of Education forthe special fund for the Disciplines and Postgraduate EducationConstruction project.

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