Passivação de eletrodos cerâmicos à base de de oxidos não estequiométricos de titânio utilizados no tratamento eletroquimico de efluentes farmacêuticos

In order to develop new techniques for wastewater treatment which are less expensive and more suitable for refractory and/or toxic organic compounds, electrochemical advanced oxidation processes (EAOP) have been developed rapidly since the 1980s [1]. The interest in the improvementof EAOP's technologies is justified by very fast degradation kinetics, the high oxidizing hydroxyl radicals energy and their reactivity, as well as by their non-selective behavior to wards the recalcitrant molecules [2]. Actually, boron-doped diamond electrodes (BDD) are the best-known anode material for electro-oxidation because of their high chemical stability and the complete mineralization of organic pollutants; however, the high cost and scarcity of the substrate suitable for this use limit its application on a large scale. For that reason, different studies have been searching for new materials that could replace the BDD, such as electrodes made from non-stoichiometric titanium oxides (whose empirical formula is TinO2n-1, with n≥3), which exhibit high electrical conductivity at room temperature, good corrosion resistance and good chemical stability [2]. Nevertheless, it was verified that the effectiveness of mineralization of antibiotics over time –using this material during the electrochemical oxidation experiments–decreased significantly, possibly due to the formation of an adherent and less conductive thin layer on the surface of the electrode, thereby reducing the amount of active sites capable of allowing the generation of hydroxyl radials. In this study, we are interested in the surface passivation characterization of these electrodes and the other electrochemical reactions which can occur between the electrode and the electrolyte containing the pollutant. The analyses are conducted using different characterization techniques in situ as cyclic voltammetry and linear scanning, chronoamperometry and electrochemical impedance spectroscopy.