Removal of pesticide 2,4-D by conductive-diamond photoelectrochemical oxidation

• 2,4-D can be efficiently degraded by electrolysis with diamond anodes.
• Coupling UV light irradiation to CDEO improve the oxidation of 2,4-D and mineralization.
• Single photolysis does not attain any appreciable oxidation of 2,4-D.
• Important effect of mediated oxidants on the depletion of 2,4-D by photo-electrolysis.

In this work, the removal of pesticide 2,4-D by single photolysis, electrolysis with BDD anode and a combined UV irradiation—electrolysis is studied. Results demonstrate that although photolysis is completely inefficient in the degradation of this pesticide, light irradiation improves significantly the results obtained by single electrolysis, leading to harsher oxidation conditions, which contribute to reduce the number of intermediates and promote mineralization. Electrolysis with diamond electrodes can attain the complete depletion of the pesticide and its mineralization regardless the current density applied and the light irradiation. In comparing the effect of current density, it was found that the process is much efficient operating at 10 mA cm−2, attaining complete mineralization with specific current charges below 10 Ah dm−3, in spite of being detected a lower concentration of oxidants. Under absence of chlorides in the supporting electrolyte main intermediates formed were hydroquinone and 4-chlororesorcinol. Under the presence of this anion, 2-chlorophenol and 4-chlorophenol were also observed at high concentrations. UV irradiation does not modify the intermediates formed although concentration is lower. An oxidation mechanism is proposed in agreement with other works shown in the literature.

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