Electrocatalytic properties of PbO2 and SnO2 in the oxidation of the phenoxy acid herbicide 2,4,5 trichlorophenoxyacetic acid (2,4,5-T)

The phenoxyalkanoic acids (2,4,5-T between them) are systemic herbicides widespread in streams and groundwater. These pesticides were classified by the World Health Organization (WHO) as class II toxics, whose maximum concentration for drinking water must be not greater than 100 ppb. Until now, the elimination studies of phenoxyalkanoic acids from aqueous solutions have been restricted to the oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) by using several advanced oxidation processes (AOP’s) but not considering the electrochemical methods. Therefore, in this work the electrochemical degradation of 2,4,5-T in aqueous media on PbO2 and SnO2 anodes under different experimental conditions was investigated. The experiments were carried out using a two compartment electrochemical cell with the auxiliar electrode separated from reaction compartment by a porcelain pot and under galvanostatic conditions. The electrolyzed solution was periodically analyzed for 2,4,5-T and oxidation byproducts by HPLC, GC-MS, UV, DQO and TOC techniques. The anodic oxidation of 2,4,5-T in 0.5 M H2SO4 at 298 K was better observed on SnO2 (70%) than on Pb/PbO2 (50%) anodes at same conditions of applied current density (20 mA cm-2). This oxidation percentage of 2,4,5-T on SnO2 increased until 83% at 30 mA cm-2 with the scarce formation of two aromatic intermediates (2,4,5-threechloropenol: 2,4,5-TCP and 2,5-dihydroxyhydroquinone: 2,5-DHHQ) which seem to disappear through the formation of malonic and acetic acids to give CO2 as final oxidation product. In this work, the influence of the pH and temperature of the electrooxidation were also studied