Electrochemical and vibrational properties of single-walled carbon nanotubes in hydrochloric acid solutions

doi:10.1016/j.diamond.2004.12.016

Diamond and Related Materials

Volume 14, Issues 3–7, March–July 2005, Pages 873-880

https://doi.org/10.1016/j.diamond.2004.12.016 Get rights and content

Abstract

Raman spectroscopy and cyclic voltammetry (CV) are used for the investigation of the oxidation–reduction processes of single-wall carbon nanotubes (SWNTs) films in an HCl 0.5 M solution. In the potential ranges (+100; +800) and (0; +1500) mV vs. saturated calomel electrode (SCE), the oxidation–reduction reactions of SWNT films, in both aqueous and semi-aqueous HCl 0.5M solutions, are reversible and irreversible, respectively. At potentials higher than +1000 mV vs. SCE, SWNTs break in fragments of different sizes. A post-treatment with an alkaline solution results in a partial restoration of the SWNTs. The functionalization of SWNTs with polydiphenylamine (PDPA) is presented as an application of the reversible oxidation–reduction reactions of nanotubes in an HCl 0.5 M solution. In order to differentiate between a deposition of successive layers of the polymer and a functionalization process, a spectroelectrochemical study of the deposition of polypyrrole (PPY) on SWNT films was carried out, too.

Introduction

The investigation of the chemical functionalization of single-wall carbon nanotubes (SWNTs) is an inciting subject for fundamental research as well as for technological applications. Recently, we showed that the physical properties of polymer-functionalized SWNTs depend on the preparation method [1]. This originates from the oxidation–reduction processes of SWNTs which take place in the polymerization medium. We note that the acid medium is often used to the synthesis of conducting polymers.

In this paper, we show that in the scanning ranges (+100; +800) and (0; +1500) mV vs. saturated calomel electrode (SCE), modifications induced by cyclic voltammetry (CV) in SWNT films immersed both in aqueous and semi-aqueous HCl 0.5 M solutions have a reversible and irreversible character, respectively. Taking into account the reversible character of oxidation–reduction reaction of the SWNT film in semi-aqueous HCl 0.5 M solution, another goal of this work is the functionalization of carbon nanotubes with polydiphenylamine (PDPA). To elucidate if the electropolymerization of diphenylamine on SWNTs results in a deposition of successive layers of the polymer on nanotube film or a functionalization process, the electrosynthesis of polypyrrole (PPY) on SWNTs film has also been studied.

Section snippets

Experimental

We used SWNTs produced by the electric arc technique [2]. To study the electrochemical properties of SWNT films deposited on an Au support, we applied both the potentiostatic method and cyclic voltammetry. The two electrochemical methods were performed in a conventional three-electrode one-compartment cell. The working electrode was a SWNT film deposited on a 25 mm² Au plate. The auxiliary electrode consisted of a spiral Pt wire. The potential of the working electrode was measured by reference

Results and discussions

Fig. 1 shows the 24th cyclic voltammetry curve recorded on an Au electrode alone and coated with a SWNTs film. In both cases, two redox systems are identified. In the first case, according with Eq. (1), the oxidation peak, located at +1320 mV vs. SCE, indicates the formation of a monolayer of gold oxide:2Au+3H₂O-6e^- → Au₂O₃+6H⁺Two reduction peaks, at +400 and +1200 mV vs. SCE, are recorded on the Au electrode. For the same number of cycles carried out on the SWNT film, one observes a reduction

Conclusions

The main results are summarized as follows: i) in the potential ranges (+100; +800) and (0; +1500) mV vs. SCE, the oxidation–reduction reactions of SWNT films, in both aqueous and semi-aqueous HCl 0.5 M solutions, are reversible and irreversible, respectively; ii) at potentials higher than +1000 mV vs. SCE, we observe SWNTs breakage into fragments of different length, some of them like closed-shell fullerenes; iii) the electropolymerization of DPA in semi-aqueous HCl solution on the SWNTs film

Acknowledgments

SWNTs have been provided by the “Groupe de Dynamique des Phases Condensées” of the University of Montpellier II.

This work was performed in the frame of the Scientific Cooperation between the Laboratory of Crystalline Physics of the Institute of Materials, Nantes, and the Laboratory of Optics and Spectroscopy of the National Institute of Materials Physics, Bucharest. A part of this work was supported in the frame of a European program COMELCAN (HRPN-CT-2000-00128) and other by the Grant no. 45

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