Anodic Oxidation of Chlorinated Pesticides on BDD and PbO2 Electrodes: Kinetics, Influential Factors and Mechanism Determination

Abstract

In this work, the removal of two pesticides 1, 2- dichlorobenzene and 1, 4- dichlorobenzene by electrolysis using BDD and Pb/PbO2 as anodes is studied. Different operating conditions and factors affecting the treatment process including anode material, applied current density, supporting electrolyte and initial pH value were studied and optimized. Results demonstrate, as expected, that the influence of the anode material used on the degradation of pesticides was very significant in all cases. Infact electrolysis with diamond electrodes can attain the complete depletion of the pesticide and its mineralization faster than with PbO2 anode. Electrolysis experiments strongly improves that the complete degradation of pesticides occurred in the presence of Na2SO4 as conductive electrolyte at current density equals 20 mA cm-2. Acidic pH would accelerate dichlorobenzene degradation, whereas alkaline condition showed negative effects. The disappearance of the pesticides followed a pseudo-first-order kinetics. Reversed-phase chromatography allows detecting Catechol, 2-chlorophenol and Pyrogallol as primary aromatic intermediates of 1,2-DCB and Hydroquinone, Benzoquinone and 4-chlorophenol for 1,4-DCB. Dechlorination of these products gives chloride ions Cl-. Ion-exclusion chromatography reveals the presence of maleic, formic, fumaric, malonic, glyoxylic, acetic and oxalic acid. An oxidation mechanism is proposed in agreement with other works shown in the literature.