Electrochemical deposition and properties of polypyrrole films doped with calcion ligands

doi:10.1016/S0003-2670(99)00353-0

Analytica Chimica Acta

Volume 395, Issues 1–2, 16 August 1999, Pages 65-75

https://doi.org/10.1016/S0003-2670(99)00353-0 Get rights and content

Abstract

The properties of polypyrrole (PPy) film doped with calcion (calcichrome) in the process of electrochemical polymerization from aqueous solutions are presented. The properties of the films were inspected using different electrochemical methods, analysis by energy dispersive X-ray analysis and X-ray diffraction. Since the calcion ligands introduced to the PPy film retain the metal-complexing properties known from the aqueous solutions, it is possible to design calcium-sensitive sensors with an anticipated open-circuit response.

Introduction

Since the discovery of the electrochemical polymerization of conducting polymers (CP), they have attracted wide interest in the field of electrochemistry 1, 2, 3. One of the first and the most investigated conducting polymers, polypyrrole (PPy), can be conveniently prepared by electro-oxidation from aqueous or organic solutions. The polymer is then simultaneously doped by the electrolyte anion. The size and mobility of the doping anions influence the mechanical and electrochemical properties of the film: the open-circuit anionic 4, 5, 6, 7, 8, 9 or cationic 10, 11, 12, 13, 14, 15 response of the conducting polymer film, as well as a fast or slow redox response [16].

A general theoretical model of the open-circuit behavior of CPs, as well as its experimental validation, has been presented 17, 18. A reversible doping/undoping process of PPy films has been employed to obtain chemical sensors that are sensitive to redox species 19, 20, 21 as well as to ions in solution 4, 7, 9. Although neither PPy nor any other CP studied so far are selective enough to be used as membrane materials for ion-selective electrodes, the sensitivity towards both ionic and redox species has been utilized in the construction of all-solid-state potentiometric sensors 13, 22, 23, 24, 25, 26. The intrinsic ionic and/or redox sensitivity of the conducting polymers can offer a wide application of CPs in sensor technology [27]. The introduction of CPs could result in the simplification and integration of the sensors. Such an advance is much awaited especially where the user-friendly, maintenance-free use of a sensor is desirable, for instance in clinical analysis [28]. In a study on the potentiometric properties of PPy film doped with hexaferrocyanate(II), it was shown that the open-circuit properties of such film can be modeled [29]. Another way to obtain PPy films with an expected (cationic) response is to dope them with organic ligands, possessing metal-complexing properties. In this case, even a selective response can be observed [15].

This report describes the electrochemical preparation of PPy films in aqueous solution containing a calcion (calcichrome) anion with a molecular weight >1000 as a dopant, and the electrochemical properties of such films. In analytical chemistry, calcion was used as a specific reagent for calcium. It allows the determination of calcium even if a large excess of Mg, Sr and Ba ions were present in the investigated solution [30]. We suppose the complexing properties of the calcion ligands inside the PPy film to be similar to those in aqueous solutions (as was previously shown for another complexing ligands [15]) and the conducting polymer-based ion-selective electrode can be obtained.

Section snippets

Chemicals

Pyrrole (Merck) was purified by double distillation and stored under argon gas at low temperature, and protected from light.

The calcion (calcichrome) with formula C₃₀H₁₄O₂₂N₄S₆Na₅·H₂O p.a. (POCh), and FW = 1108 was used. The pH of saturated solution was 4.5. Prior to electropolymerization, the sodium cations were removed with a DOWEX 50WX8 50/100 ion exchanger.

During electropolymerization, the following calcion solutions were used:

1.
Saturated solution with a pH of about 2 (acidic form of calcion

Electropolymerization of pyrrole from aqueous solutions saturated with calcion

Prior to the electropolymerization of the pyrrole, the CVs were recorded for the saturated solution of calcion (pH = 2) on the bare substrate, Pt or GC electrodes. Fig. 1a shows the recorded curves. The first scan was always anodic from 0 V up to +0.7 V and was almost flat. Next, a cathodic scan was performed up to −0.3 V and a considerably large cathodic current was observed in the negative potential range. An oxidation peak at +0.33 V could be seen during subsequent anodic scans. It is thought that

Conclusions

The PPy films doped with calcion can be obtained in the process of electropolymerization from a saturated solution of calcion in acidic form. The deposition of the film is facilitated by the adsorption of calcion ions both on the substrate and the film itself. The adsorption of calcion on PPy film is much stronger than on the electrode substrate as well as the redox process of calcion being more reversible.

The films after soaking in saturated Ca(OH)₂ are sensitive to calcium ion. This is due to

Acknowledgements

The financial help from the Polish Committee for Scientific Research (KBN), project 3T09A-09514, is gratefully acknowledged. The authors thank Professors Zygmunt Kowalski for his support and encouragement. Mrs. Barbara Trybalska is acknowledged for performing the EDAX analysis Mr. Nigel Kimberley is acknowledged for improving the English in the text.

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Electrochemical deposition and properties of polypyrrole films doped with calcion ligands

Abstract

Introduction

Section snippets

Chemicals

Electropolymerization of pyrrole from aqueous solutions saturated with calcion

Conclusions

Acknowledgements

J. Electroanal. Chem.

Talanta

Talanta

Anal. Chim. Acta

Electrochim. Acta

Anal. Chim. Acta

J. Electroanal. Chem.

J. Electroanal. Chem.

J. Electroanal. Chem.

Talanta

Synth. Mater.

Microchem. J.

Talanta

J. Phys. Chem.