Removal of the pesticide methamidophos from aqueous solutions by electrooxidation using Pb/PbO2, Ti/SnO2, and Si/BDD electrodes

The anodic oxidation of methamidophos (MMD), a highly toxic pesticide used worldwide, was studied in a sodium sulfate aqueous solution on Pb/PbO2, Ti/SnO2, and Si/BDD (boron doped diamond) electrodes at 30 degrees C. Under galvanostatic conditions, it was observed that the performance of the electrode material is influenced by pH and current density as shown by HPLC and ATR-FTIR analysis of MMD and its oxidation products along the electrolysis. It was found that MMD degradation using Pb/PbO2 in acid media (pH 2.0 and 5.6) generates formaldehyde as the main product of the reaction giving evidence of an indirect mineralization mechanism. Under the same conditions, Ti/SnO2 showed poor formaldehyde production compared to the Pb/PbO2 electrode. On Si/BDD electrodes formaldehyde production was not observed, instead the ATR-FTIR results showed the formation of phosphate as the reaction progressed suggesting a complete MMD mineralization on this electrode. In addition, HPLC results showed that the electrode efficiency is also dependent on the applied current density. This current density influence is remarkably clear on the Si/BDD electrodes where it was evident that the most efficient current density toward a complete MMD mineralization was reached with the application of 50 mA/cm(2).