Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes as ion-to-electron transducer in polymer membrane-based potassium ion-selective electrodes

doi:10.1016/j.jelechem.2009.06.005

Journal of Electroanalytical Chemistry

Volume 633, Issue 1, 1 August 2009, Pages 246-252

https://doi.org/10.1016/j.jelechem.2009.06.005 Get rights and content

Abstract

Negatively charged multi-walled carbon nanotubes (MWCNTs) were used as dopants in the electrochemical synthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The resulting electroactive film, PEDOT(CNT), was used as ion-to-electron transducer (solid contact) in potassium ion-selective electrodes (K⁺-ISEs) based on plasticized PVC membrane containing valinomycin as neutral ionophore. Potentiometric measurements were carried out to study the analytical performance of solid-contact K⁺-ISEs, the influence of dissolved O₂ and CO₂ on the potential of the electrodes, and the formation of the interfacial aqueous film. The prepared electrodes were also characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The experimental results showed that PEDOT(CNT) has the capability to function as solid contact in fabrication of K⁺-ISEs. These electrodes, based on PEDOT(CNT) as ion-to-electron transducer, showed high sensitivity and selectivity to K⁺ ion which can be related to the plasticized PVC-based ion-selective membrane containing valinomycin. The stability of the electrode potential, however, was found to depend on the conducting substrate used for deposition of the PEDOT(CNT) film. Results from the CV and EIS revealed that the PEDOT(CNT) contact exhibits high redox capacitance that is favorable for a solid contact.

Introduction

Potentiometric ion sensors, or ion-selective electrodes (ISEs), are the most frequently used chemical sensors in analytical applications in medical, environmental, and industrial analysis [1], [2], [3], [4]. As an analytical device, ISE offers many advantages such as selectivity, fast response, simple analytical procedure, and relatively low cost. The necessity of robust, maintenance-free, and reliable ISEs led to the invention of the so called coated-wire electrode (CWE) which is a polymeric membrane-based all-solid-state ISE [5], [6]. However, the configuration of CWE involves some drawbacks such as drift in the electrode potential due to the high charge-transfer resistance and low double-layer capacitance at the interface between the electrically conducting substrate and the ionically conducting ion-selective membrane (ISM) [7], [8]. To solve this problem, solid-contact ISEs were fabricated by using a layer with mixed electronic and ionic conductivity to act as ion-to-electron transducer between the ISM and the solid substrate [9]. The excellent and unique properties of the electrically conducting polymers (ECPs) make them attractive materials that can function as ion-to-electron transducers in solid-contact ISEs [10], [11], [12]. Poly(3,4-ethylenedioxythiophene) (PEDOT), is one of the most interesting conducting polymers that has been used for this purpose [8], [13], [14].

On the other hand, carbon nanotubes (CNTs) with remarkable structural, electrical, mechanical, and thermal properties have generated a considerable interest since being discovered by Iijima in 1991 [15]. It has been shown that incorporating CNTs into a polymer matrix enhances the mechanical and electrical properties of the original polymer [16], [17], [18]. Another important application of CNTs was incorporating them in electrochemical transducers in the fabrication of biosensing devices [19], [20]. The ability of CNTs to function as gas, pressure, temperature, and mass sensors has been demonstrated [21]. Carbon nanotubes have also been used as the ion-to-electron transducing layer in ISEs [22], [23]. The procedure used to prepare these electrodes, however, was tedious and time consuming. Also other carbon-based materials with high surface area have successfully been used for the same purpose [24], [25].

The aim of this study was to combine the properties of conducting polymers and carbon nanotubes to prepare a composite that can be used as ion-to-electron transducer in poly (vinyl chloride) (PVC)-based ion-selective electrodes. The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with negatively charged multi-walled carbon nanotubes (MWCNT) was electrochemically synthesized to prepare the composite material PEDOT(CNT) that was coated with a PVC-based K⁺-selective membrane containing valinomycin as neutral carrier. The electrochemical properties of PEDOT(CNT) film and the analytical performance of the K⁺-ISEs based on this film as ion-to-electron transducer were studied using different techniques.

Section snippets

Chemicals

The monomer 3,4-ethylenedioxythiophene (EDOT; >97%) was obtained from Bayer AG. Multi-walled carbon nanotubes (MWCNTs) with 10–30 nm diameter and purity >90%, were purchased from Sun Nanotech Co. Ltd. (Jiangxi, China). The carbon nanotubes (CNTs) were first refluxed in 3 M nitric acid for 48 h in order to purify them and to create the negatively charged groups (mainly carboxylic groups) on them. The number of defects and functional groups, which affect the electrical and structural properties of

Sensitivity and selectivity of all-solid-state K⁺-ISEs

The GC/PEDOT(CNT)/K⁺-ISM, GC/PEDOT(Cl)/K⁺-ISM, and GC/K⁺-ISM electrodes were prepared as described in Section 2.2. After conditioning in 0.01 M KCl for 2 days, the electrodes were calibrated in 10⁻¹–10⁻⁷ M and then back to 10⁻¹ M KCl solutions. The reference electrode was Ag/AgCl/3 M KCl with a salt bridge containing 1 M lithium acetate. As can be seen in Fig. 1a, the different types of K⁺-ISEs give linear response in the activity range 10⁻¹–10⁻⁶ M of K⁺ ion. The GC/PEDOT(CNT)/K⁺-ISM electrode shows

Conclusions

Poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically synthesized using negatively charged multi-walled carbon nanotubes as doping ions. The resulting PEDOT(CNT) composite was used as the solid contact in all-solid-state potassium ion-selective electrode (K⁺-ISE) by applying a PVC-based potassium ion-selective membrane (K⁺-ISM) on the composite. Results from the potentiometric measurements show that K⁺-ISEs based on PEDOT(CNT) as the ion-to-electron transducer are sensitive to K⁺ in

Acknowledgments

The authors thank Prof. Carita Kvarnström for the RAMAN measurement. Financial support from the Åbo Akademi University Foundation is gratefully acknowledged. This work is part of the activities of the Åbo Akademi Process Chemistry Centre within the Finnish Centre of Excellence Program (2000–2011) by the Academy of Finland.

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Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes as ion-to-electron transducer in polymer membrane-based potassium ion-selective electrodes

Abstract

Introduction

Section snippets

Chemicals

Sensitivity and selectivity of all-solid-state K+-ISEs

Conclusions

Acknowledgments

Anal. Chim. Acta

Electrochim. Acta

Pharm. Chem. J.

Anal. Sci.

Anal. Chem.

Ion-Sel. Electrode Rev.

Anal. Chem.

Anal. Chem.

Chem. Eur. J.

Electroanalysis

Electroanalysis

Talanta

Sens. Actuators B

Nature

Appl. Phys. Lett.

Sensitivity and selectivity of all-solid-state K⁺-ISEs