Alumina em eletrodos de carbono: seu efeito catalítico em eletroanálise

Abstract

This thesis presents a systematic study of the effect of alumina (Al2O3) particles on the surface of glassy carbon electrodes (GCE) in the face of voltammetric and amperometric determinations of several analytes. The electrocatalytic oxidation of catechol (CT), dopamine (DP) and tert-butylhydroquinone (TBHQ) on GCE modified with alumina nanoparticles (Al2O3) synthesized in different structures and morphologies was investigated. The highest electrochemical activity for the oxidation of CT, DP was verified using the polished GCE in suspension of α-Al2O3 in comparison with the surfaces modified with γ- Al2O3 and -Al2O3. In addition, it was found that the effect of the Al2O3 structure is predominant in relation to the effect of the surface area of the particles, being the modification with alumina more stable on GCE than on gold surfaces and on platinum. The high stability of the α-Al2O3 modified GCE surface was attested by amperometric detection of phenolic compounds. The electrochemical oxidation of naproxen (NPX) is demonstrated using the modified GCE with the α-Al2O3 particles and the results obtained were advantageous with increased current and catalytic effect, resulting in a highly sensitive sensor. Together with NPX, voltammetric studies were also carried out for ibuprofen (IBF). Molecular dynamics simulations showed a stronger interaction of NPX than IBF with α-Al2O3 sites. The GCE modified with α-Al2O3 also demonstrated catalytic action in reducing the 2,4,6-trinitrotoluene (TNT) molecule. The three reduction peaks characteristic of TNT were shifted to less negative potentials with improved peak resolution, combined with increased current and analytical sensitivity. The electrochemical reduction of dissolved oxygen was also significantly increased by the presence of α-Al2O3. Finally, it was demonstrated that the residual α-Al2O3 on the GCE surface (commonly used for polishing electrodes) affects the electrochemical parameters of antioxidants (caffeic acid, gallic acid, chlorogenic acid, catechin, rutin and quercetin) and food samples (tea and wine) obtained by voltammetry and used to calculate the antioxidant activity, resulting in discordant values. The results showed a substantial increase in current (and charge) on the GCE modified with α-Al2O3 and the calculated Electrochemical Index (parameter that indicates antioxidant activity) was considerably increased. Thus, it is concluded that the modification of the GCE surface with α-Al2O3 is an interesting strategy to increase the analytical sensitivity and the detectability of the electrode for various electroactive compounds.