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/PbO 2 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 PbO 2 anode. Electrolysis experiments strongly improves that the complete degradation of pesticides occurred in the presence of Na 2 SO 4 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.

Electroanalytical Study of Fungicide Bixafen on Paste Electrode Based on the Thermally Reduced Graphene Oxide Synthesized in Air Conditions and its Determination in River Water Samples

“…The overall voltammetric behavior plausibly suggests that the initial oxidation of bixafen (peak I) is related to the dichlorobenzene moiety of the molecule, resulting in substitution of chlorine atoms with hydroxide groups, thus, forming catechol moiety, which is in agreement with known reactive oxidation pathways of other dichlorobenzene pesticides [37]. The catechol forms a chemically reversible and electrochemically quasi‐reversible redox couple catechol/ o ‐quinone, thus, giving rise to the new voltammetric response at the potential of about +0.12 V [37].…”

“…In the second potential cycle, a new anodic peak at +0.17 V appears (peak II), which is a counterpart of the cathodic peak II’, thus representing electrode transformation of a single redox couple, formed following the initial oxidation of bixafen at +0.79 V (peak I). The voltammetric characteristics of the system II’–II resembles strongly the typical behavior of the o ‐quinone‐catechol quasi‐reversible redox couple [37].…”

Tannery wastewater treatment after activated sludge pre-treatment using electro-oxidation on inactive anodes

“…The electro-oxidation of industrial wastewater has many advantages as simple, high capacity, low cost, easy automation, reduced chemical requirement, less harmful to the environment and high selectivity (Chen 2004;Olvera-Vargas et al 2014). Many kinds of electrodes were used as anode materials in electro-oxidation, such as boron-doped diamond (BDD), and dimensionally stable anodes (DSA) such as IrO 2 and RuO 2 (Rabaaoui et al 2017). Among these electrodes, the use of highly oxygenated inactive anode materials such as SnO 2 and PbO 2 has high oxidation potential for the decomposition of organic contaminants.…”