Estudo voltamétrico da oxidação e eletropolimerização da anilina sobre eletrodo de carbono vítreo

Abstract

This work carried out a voltammetric study for the oxidation and electropolymerization of aniline (ANI) in aqueous electrolytes on the glassy carbon electrode (GCE). Different experimental conditions were explored, such as: different voltammetric techniques, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV), applied potential window, scanning speed, pre-treatment of the surface of the GCE, ANI concentration, nature and pH of the supporting electrolyte. Regarding the oxidation of ANI, the electrochemical data indicated an anodic mechanism controlled by diffusion of several steps, all dependent on the pH of the supporting electrolyte. Oxidation initially occurred in the anilinium group with the removal of an electron and a proton and the formation of an intermediate radical cation. These electrogenerated radical cations formed dimers and other electroactive byproducts. The oxidation mechanism of ANI on GCE was revisited in the literature and discussed. The diffusion coefficient of ANI was established in sulfuric acid as 1.14 x 10-5 cm2 s-1 and phosphate buffer as 7.82 x 10-6 cm2 s-1. SWV was explored for detection and quantification of ANI and under optimized conditions an analytical proposal was achieved in phosphate buffer, in a concentration range 0.10 to 2.11 umol L-1, limit of detection (LOD) of 0.12 umol L-1 and limit of quantification (LOQ) of 0.40 umol L-1. The voltammetric data also demonstrated the electropolymerization of ANI and the deposition of the polyaniline film (PANI) on the GCE, under different experimental conditions, mainly from a concentration of 5.00 mmol L-1 of the monomer and in the extended potential window (- 0.20 to + 1.40 V). The voltammetric data from ANI and PANI presented here will also be explored as teaching material for physical-chemistry, electrochemistry and electroanalytical subjects at the Department of Chemistry at UFRPE and two practical class scripts were also developed and presented here.