The surface of glassy carbon (GC) electrode has been modified by oxidation of L-cysteine. The covalent modified GC electrode with L-Cysteine has been studied, according the supporting electrolyte used. Favourable interactions between the L-cysteine film and DA enhance the current response compared to that at the Nafion GC and bare GC electrodes, achieving better performances than those other electrodes. This behaviour was as result of the adsorption of the cysteine layer film, compact and uniform formation; depending on L-cysteine solution (phosphate buffer or chloridric acid supporting electrolyte) used for modifying GC surface. In cyclic voltammetric measurements, modified electrodes can successfully separate the oxidation/reduction DA peaks in different buffer solutions, but an evident dependence in the response was obtained as function of pH and modified electrode. The modified electrode prepared with L-cysteine/HCl solution was used to obtain the calibration curve and it exhibited a stable and sensitive response to DA. The results are described and discussed in the light of the existing literature.

In this work, the role of chloride with respect to the oxygen evolution reaction by using BDD and Pt/Ti anodes was investigated to understand the performance of both anodes for the electrochemical treatment of a real sample of wastewater, with lower organic load, generated at Federal University of Rio Grande do Norte. Bulk experiments were performed under real discharged effluent conditions (pH and conductivity) in order to verify the applicability of direct and mediated electrochemical oxidation by applying 2.5 and 5.0 mA cm−2. Results clearly showed that, a partial elimination of chemical oxygen demand (COD) was achieved, depending on applied current density. Using Pt/Ti, by applying 2.5 and 5.0 mA cm−2, COD removal efficiencies of 25.2% and 30.49% were obtained. Under the same conditions, a minor COD removal was achieved by using BDD electrode. However, the removal efficiencies were improved when Cl-mediated oxidation approach was employed, obtaining 63.7% and 60% for Pt/Ti by applying 2.5 and 5.0 mA cm−2, respectively; while for BDD electrode, COD removals were about 15% and 47%, under the same conditions. These figures are in agreement with the polarization curves obtained, where it was possible to confirm that the concentration of halide in solution increases the importance of Cl2/oxy-chloro radicals system depending on the electrocatalytic material and this behavior plays an important role in relation with the oxygen evolution reaction, influencing on the efficiency of electrochemical approach adopted