Construção de eletrodos de grafite: aplicação em processos eletroquímicos ambientais

Abstract

This work studies the construction of different configurations of electrodes based on graphite from commercial/common battery for application in the electrochemistry production of H2O2 by oxygen reduction reaction (ORR) and degradation of dye methyl orange (MO) in acidic medium (K2SO4 0.1 mol L-1, pH 2.0). The electrolysis were conducted in an electrochemical cell of single compartment composed for working electrode (graphite), rhodium wire being counter-electrode and Ag/AgCl a reference electrode. In the electrogeneration of H2O2 tests was applied constant potential in the range of -0.4 a -2.0 V (vs. Ag/AgCl) at 0.2 bar of O2(g), 20 oC under constant stirred. The maximum production of H2O2 was 117 mg L-1 in 90 min. of electrolysis when applied the potential of -1.6 V (vs. Ag/AgCl). The degradation process of MO dye (100 mg L-1) was under the same conditions of H2O2 production; however the applied potential was -1.0 V (vs. Ag/AgCl). The color removal of the MO dye was of ~15 and 64% when submitted to the process of anodic oxidation and electrogenerated H2O2 only respectively, nevertheless when the magnetite (Fe3O4) nanoparticles (NPs) were added (0.2 mmol) as heterogeneous catalyst, i.e.; electro-Fenton process (EF), the color removal of the MO dye was 87% in 90 min. of electrolysis. The kinetics of removal color of the degradation processes was of pseudo-fist order and the apparent kinetic constant (kapp) was maximal for heterogeneous EF process. The Fe3O4 NPs was recycled over four electrolysis consecutives, and there was a small decrease in the catalytic efficiency, due to loss in the wash after each process. The graphite electrode was submitted to a cronoamperometric test and the study of linear scanning voltammetry (LV) showed that after 10 h, the electrode was electrochemically stable and may be considered a viable and promising material for electrocatalytic applications.