温泉科学（J. Hot Spring Sci.），62，182‑187（2012）

原著

Electro-synthesis and Electrochromism of Conducting
Polymer Polypyrrole in Volcanic Spring Water
Yu INNAMI1） and Hiromasa GOTO1）*(Received Aug. 24, 2011, Accepted Aug. 31, 2012)

天然火山性水における導電性高分子ポリピロールの電解合成とエレクトロクロミズム
印南 雄1)，後藤博正1)*

要旨

火山性天然水を電解液として用い，導電性高分子ポリピロールの電解合成を行った．得られたポリマーの紫外可視吸収スペクトル，電子スピン共鳴，電気電導度を測定し，これらの測定結果から高分子鎖に電気伝導を行うキャリアが発生していることが分かった．火山性天然水中に含まれるアニオン種が重合時に電解質として機能するとともに，重合後のポリマーのドーパントとなり，電気伝導に寄与したと思われる．
キーワード：温泉水，電気化学，紫外可視吸収スペクトル，電子スピン共鳴

Abstract
Electrochemical synthesis of polypyrrole in natural volcanic water was carried out.
Ultraviolet-visible (UV-vis) absorption spectroscopy, electron spin resonance (ESR), andelectrical conductivity measurement for the polymer were performed, and the results conﬁrm
generation of charge carrier in the polymer. Anionic species in the volcanic water play a roleof electrolyte for the electropolymerization, and the anions as dopants contribute electricalconduction of the polymer.
Key words : Electrochemistry, Electron spin resonance (ESR), Hot spring water, Ultravioletvisible (UV-vis) absorption spectroscopy1)

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Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba,Ibaraki 305‑8573, Japan. 1）筑波大学数理物質系 〒305‑8573 つくば市天王台 1‑1‑1．*Corresponding
author：E-mail gotoh@ims.tsukuba.ac.jp, FAX 029‑853‑5128.

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1． Introduction
Volcanic hot spring water (VW) has been familiar topeople in the world (Deetjen, 1988). The composition ofVW depends on the district. VW generally contains
anions such as SO42− and Cl− . The anions in the VW canfunction as electrolyte. Especially, sulfate ions play arole of dopants of conducting polymers (ChiuLicona-Sánchez., 2005 ;, 2011). Therefore, the VW is appli-cable for electrochemistry. The VW also contains metalcations such as Fe2+, Fe3+ and/or Zn2+. These metal cat-Fig. 1 Fundamental scheme of electrochemical poly merization.

ions might aid polymerization reactions as catalysts.
Conducting polymers have been synthesized with 1) chemical method by using catalysts oroxidizers (Hino2006 ; Phang and Kuramoto, 2009 ; Cao., 1992) and 2) electrochemical

method. Especially, synthetic procedure of electrochemical polymerization is quite simple. As
shown in Fig. 1, the electrochemical polymerization is generally carried out by application ofvoltage between two electrodes in the electrolyte solution containing monomer. The resultant
polymer is generally obtained on the anode (positive electrode) as thin films. Additionally,reference electrode is employed in the polymerization cell to monitor the voltage.
In the previous study, we synthesized polyaniline in the VW by chemical oxidative polymerization (Goto, 2010). In this research, we tried to obtain conducting polymer polypyrrole (Hara2003 ; Matsubara, 2004 ; Lu, 2006) by using VW with electrochemical method,and examined its properties. The polymer thus obtained showed electrochromism (color of thepolymer is tunable by applying voltage in the VW (Goto, 2007) and electrical conductivity. Theseresults imply a possibility of application of VW for electrolytes, and the resultant electroactive
polymer may be used as an ion sensor for VW.

2． Experimental
2．1

Materials
Pyrrole as a monomer was purchased from Tokyo Chemical Industry (TCI) Co., Ltd. andused without further puriﬁcation. The transparent indium tin oxide (ITO) coated glass (9Ω/cm2)
was employed for anode in the polymerization. VW from Owakudani hot spring in Kanagawa
Prefecture was employed in this research. The sample water was obtained on Feb. 16, 2009. TheVW was puriﬁed before using by ﬁltration with a qualitative ﬁlter paper. Multi-channel type
induced plasma coupling (ICP) analysis was carried out at the Chemical Analysis Division of Research Facility Center for Science and Technology of University of Tsukuba. The ICP analysis
revealed that the VW contains Li, Be, B, Na, Mg, Al, Si, S, Ca, Mn, Fe, Zn, Sr and Ba.
2．2TechniqueFourier transform infrared spectra (FT-IR) of the polymer were taken with a Jasco FT-IR

300 spectrometer by the KBr method. Ultraviolet-visible (UV-Vis) absorption spectroscopy meas183

印南雄，後藤博正

温泉科学

urements were carried out at room temperature by using a Hitachi U-2000 spectrometer with aquartz cell. Electrochemical polymerization was carried out in VW using Eco chemie μAutolab
type III. The three electrode system consists of an ITO glass working electrode, a calomel electrode as a reference electrode, and a platinum wire as a counter electrode. Electron spinresonance (ESR) measurement of the polymer in solid state was carried out with a Jeol JES TE200 spectrometer. The electrical conductivity of the polymer was measured at room temperature using Mitsubishi Lowrester-GP MCTP-T610 with MCP-TP06P probe by the DC four-pointprobe method.
2．
3Polymerization
Polymerization of pyrrole in water medium has been carried out by using surfactant(Amaike and Yamamoto, 2006), and template polymerization was conducted (McCullough,2009). In this study, electro-polymerization is carried out in the VW without use of surfactant.
The electrochemical polymerization was performed in the VW solution of 0.1 M pyrrole byrepeated potential cycling at a scan rate of 10 mV/s with saturated calomel electrode (SCE) as areference electrode at room temperature (25 ℃). After three repeating scan, thick dark brown
ﬁlm appeared on the ITO glass. Pyrrole is not highly reactive in β position. However, crosslinking is partly considerable. Thus, polypyrrole has an straight-chain structure mainly (Fig. 2). The
polymer thus obtained is abbreviated as PPy(VW).
The PPy(VW) film was insoluble in organic solvents. Thus, the molecular weight of thePPy(VW) couldnʼt be measured, it might be estimated to be ＜10000 ().

n3． Results and Discussion
3．1

FT-IR absorption spectroscopy
Figure 3 shows an FT-IR absorption spectrum of PPy(VW) scaled from the ITO substrate.

The absorption band at 3411 cm−1 which corresponds to N‑H stretching was observed in Fig. 3.
The polymer also shows the absorption band of a framework vibration of a pyrrole unit at 1622
cm−1. These results indicate that pyrrole was polymerized in the VW under acid condition. Theabsorption band associated with C‑H bending vibration was also observed at 1140 cm−1. Thisband would disappear if the polymer formed a network structure completely. Therefore, PPy(VW)
yielded mainly a straight-chain structure and partially a network structure.
3．2

UV‑Vis absorption spectroscopy
Figure 4 shows UV‑Vis absorption spectra of PPy (VW) film. The electrospectroscopic

measurements were carried out in the monomer-free VW solution for the PPy(VW) on ITO glassFig. 2184

Polymerization of pyrrole in VW.

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working electrode. The electrochemical cell contains the working electrode, an SCE referenceelectrode, and a platinum wire counter electrode. The potential was switched from −0.25 V to0.75 V and 0.75 V to −0.25 V (vs. SCE). In Fig. 4 (a), the doping band around 750 nm increases inan oxidative process. On the other hand, the doping band decreases in a reduction process(Fig. 4 (b)). These doping and dedoping processes were attributed to the dopants such as SO42−Fig. 3FT‑IR absorption spectrum of PPy(VW).

Fig. 4 UV‑Vis spectra of PPy(VW) ﬁlm on ITO glass at the potential (a) from −0.25 V to 0.75 V(oxidation process), and (b) from 0.75 V to −0.25 V (vs. SCE) (reduction process).

Fig. 5PPy(VW) ﬁlm images at the potential of 0.75 V (a) and −0.25 V (b) (vs SCE).

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印南雄，後藤博正

温泉科学Fig. 6ESR spectrum of PPy(VW) at room temperature.

and HSO4− in the VW. Figure 5 shows the ﬁlm images in oxidized state and reduced state. Thepolymer changes in color by applied voltage (oxidized form, 0.75 V, black ; reduced form, −0.25
V, brown), indicating change in electronic state of the polymer in the VW is observable by visible inspection. Therefore, the VW can be useful as electrolyte solution for electroactive polymers.
Further study might enable to detect ions in VW with redox process of the electroactivepolymers.
3．3

ESR spectroscopy and electrical conductivity
ESR spectroscopy of PPy(VW) was measured at room temperature. Figure 6 shows ESR

spectrum of PPy(VW). The spectrum displays a symmetrical shape with ＝2.0034. This signal isdue to a presence of charge carrier such as polarons (radical cations in the polymer) along thepolymer chain. The electrical conductivity of the PPy(VW) ﬁlm was to be 1.3×10−1 S/cm, implying
the PPy(VW) ﬁlm shows moderate electrical conductivity as a conducting polymer.

4． Conclusion
Polypyrrole was electrochemically synthesized in the VW. The polymer thus obtainedshows electrochromism. The redox state of the polymer in the VW can be detected through not
only color but also change in potential during electrochemical measurements. This result might
open for possibilities toward application of natural resources in electrochemistry. This study is anew trial for synthesis of polymers in the VW, and an unprecedented attempt in the ﬁelds ofmaterials science. Our future subject is synthesis of natural polymers in VW. In this step,synthesis of conjugated polymer in VW was successfully carried out.

Acknowledgments
The author thanks Hakone Hot Spring Spa Supply Co. Ltd. (Kanagawa Prefecture, Japan)
for generously providing the hot spring water sample. The author is grateful to the Engineering
Workshop of University of Tsukuba for glasswork and the Analysis Center for the ICP measurements.
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