The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

Zuzana Morávková,Patrycja Bober,Ivana Šeděnková

doi:10.3390/app10062091

Abstract

There are several types of aniline oligomers that can be formed in the early stages of aniline oxidation: linear oligomers with repeating units joined in para positions, and various branched and polycyclic oligomers, being the two most important groups. The fraction of these different oligomeric groups depends upon the reaction conditions of aniline oxidation. The aim of this study was to analyze the first products of the chemical and electrochemical oxidation of aniline at the (starting) pH 1 and 7, in order to specify the conditions of the formation of phenazine-like oligomers, and to test the theory that they have an important role in polyaniline film formation. We have confirmed that phenazine-like oligomers do not form at pH 1, neither in the chemical nor the electrochemical oxidation of aniline; however, they form in both chemical and electrochemical oxidation of aniline at pH 7. Phenazine-like oligomers are thus definitely not necessary intermediates for PANI film formation, not even in the chemical polymerization of aniline. Finally, the redox behavior of phenazine-like oligomers was demonstrated in a medium at pH 1.

Highlights

Polyaniline (PANI) is one of the most studied conducting polymers
In order to compare the chemical and electrochemical oxidation of aniline as reliably as possible, we have brought some typical conditions of chemical oxidation to our electrochemical experiment, and vice versa
The chemical oxidation of aniline, on the other hand, is initiated in media with acidity varying from ca pH 2 to 8 [17,24]

Summary

Introduction

Polyaniline (PANI) is one of the most studied conducting polymers It has a wide range of applications, including wastewater processing [1,2], catalysis [2], sensing [3,4,5,6], biomedical [5,7,8], optical [9] and electrochemical [9,10,11,12,13] applications. Many of these areas require PANI in the form of a thin film. In neutral or basic media, ortho-coupling becomes possible in addition to para-coupling, which leads to a formation of a mixture of various AO structures [19,20,22,23]

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Conclusion