Preparação e caracterização de filmes de PbO2 sobre diferentes substratos e MnO2 sobre fibra de carbono para aplicação no tratamento eletroquímico de efluentes simulados

Abstract

PbO2 films were grown on different substrates (Ti-Pt, ADE, FC and Pb), at constant current density of 20 mA cm-2, using two methodologies: electrodepositon from 0.1 mol L-1 Pb(NO3)2, 1.7 mmol L-1 LSS and 0.1 mol L-1 HNO3 solution and lead anodization in 3 mol L-1 H2SO4 solution. All PbO2 films presented important characteristics such as: homogeneous and compact morphology, quite uniform growth and good adherence. MnO2-composite film was prepared from electrolytic MnO2 powder [80 % (m/m)], carbon black [10 % (m/m)] e PVDF [10 % (m/m)] and then applied on carbon fibre (FC). The physical and electrochemical properties of these different electrode materials were characterized by scanning electronic microscopy, X-ray diffratometry, linear potential scan and cyclic voltammetry. The PbO2 films obtained by electrodeposition presented mainly the tetragonal phase â-PbO2, while the PbO2 film obtained by anodization presented an oxide mixture with the following phases: tetragonal â-PbO2, orthorhombic á-PbO2, PbO and also PbSO4. The electrolytic MnO2 was obtained mainly with the phase å- MnO2. The Pb/PbO2 electrode presented the best performance regarding OER. Among the electrodes obtained by electrodeposition (Ti-Pt/PbO2, ADE/PbO2 and FC/PbO2), the FC/PbO2 electrode presented higher values of superficial area and overpotential for the OER. The FC/MnO2 did not present good performance regarding OER. The Pb/PbO2 electrode was applied, at constant current density of 5 mA cm-2, in the oxidation of 0.05 mol L-1 Cr3+ ions solution, presenting a conversion efficiency of Cr3+ to Cr6+ ions of 90 %. The FC/PbO2 was also applied in the decolorization of the BR 19 dye solution (100 mg L-1), using a filter-press reactor. A decolorization efficiency of 99.5 % was obtained in the following experimental conditions: flow rate of 7.0 L min-1, current density of 30 mA cm-2 and chloride concentration of 70 mmol L-1. At the end of the oxidation process, a value of the German parameter DFZ 10 times lower than the maximum value (3 m-1) established before discarding in the environment was found.