In this work, we evaluated the performance of the Ti/RuO2-TiO2 and Ti/RuO2-IrO2-TiO2 electrodes as electrocatalytic materials in the degradation of the insecticide imidacloprid (ICP). The temperature and current density operating parameters were investigated, and the degradation was followed by measurements of TOC and by UV-Vis spectroscopy. The complete oxidation de ICP (100% mineralization) was achieved by applying 40 mA cm−2 when Ti/RuO2-TiO2 or Ti/RuO2-IrO2-TiO2 were used at 60°C during 2 or 3 h electrolysis, consuming 33.3 kWh m−3 and 47.5 kWh m−3 of energy, respectively. Raising the temperature promoted a significant change in the results compared to those obtained at 25°C. TOC removal, mineralization current efficiency and electric charge data indicated a system operating under mass transport control. The ICP absorption spectra showed suppression of the peak at 265 nm and increasing the peak at 214 nm, with the electrolysis time, indicating breakdown of the insecticide's molecular structure and formation of short chain compounds, before its complete mineralization. Degradation process occurred via direct anodic oxidation and Cl2-mediated oxidation. The study showed that the electrochemical degradation process using DSA anodes is feasible and can be a good alternative for removing the insecticide in water or sewage treatment plants.
Pyriproxyfen (PPF) is a juvenile hormone agonist used in agriculture and in combating Aedes aegypti. In this work, for the first time, a study of electrochemical oxidation (EO) of this insecticide is reported, which involved the degradation of a commercial formulation of PPF on boron-doped diamond (BDD) electrode. pH conditions influenced the process; after 360 min of electrolysis the COD removals were 88.1% (pH 3.0), 78.9% (pH 5.0), 65.5% (pH 7.0), 76.7% (pH 9.0) and 80.0% (pH 11.0). The increase in applied current density favored the COD removal and the S 2 O 8 2generation. At 20, 40 and 60 mA cm -2 , the COD removal was 88.1%, 90.0% and 91.0% and the S 2 O 8 2production was 0.15, 0.26 and 0.35 mmol l -1 , respectively. The COD removal process occurred via •OH and other oxidants as S 2 O 8 2− and SO 4 -• , and it was more efficient at the lowest current density (20 mA cm -2 ), which removed 88.1% COD with the lowest energy consumption (25.2 kWh m -3 ). Chromatographic (GC-MS and IC) data showed that the EO removed 37% PPF and formed short chain carboxylic acids as final organic by-products. EO with DDB seems to be an appropriate approach to be applied to degrade PPF in contaminated environmental samples.
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