Mechanism of Perchlorate Formation on Boron-Doped Diamond Film Anodes

Abstract

This research investigated the mechanism of perchlorate (ClO(4)(-)) formation from chlorate (ClO(3)(-)) on boron-doped diamond (BDD) film anodes by use of a rotating disk electrode reactor. Rates of ClO(4)(-) formation were determined as functions of the electrode potential (2.29-2.70 V/standard hydrogen electrode, SHE) and temperature (10-40 °C). At all applied potentials and a ClO(3)(-) concentration of 1 mM, ClO(4)(-) production rates were zeroth-order with respect to ClO(4)(-) concentration. Experimental and density functional theory (DFT) results indicate that ClO(3)(-) oxidation proceeds via a combination of direct electron transfer and hydroxyl radical oxidation with a measured apparent activation energy of 6.9 ± 1.8 kJ·mol(-1) at a potential of 2.60 V/SHE. DFT simulations indicate that the ClO(4)(-) formation mechanism involves direct oxidation of ClO(3)(-) at the BDD surface to form ClO(3)(•), which becomes activationless at potentials > 0.76 V/SHE. Perchloric acid is then formed via the activationless homogeneous reaction between ClO(3)(•) and OH(•) in the diffuse layer next to the BDD surface. DFT simulations also indicate that the reduction of ClO(3)(•) can occur at radical sites on the BDD surface to form ClO(3)(-) and ClO(2), which limits the overall rate of ClO(4)(-) formation.

Electrodegradation of ifosfamide and cyclophosphamide at BDD electrode: Decomposition pathway and its kinetics

“…1). A decrease in the current efficiency can also be explained by the formation of oxidants that are weaker than Å OH radicals such as, Cl 2 or HClO/ClO À and which participate in the organic matter oxidation; moreover, these chlorine species can possibly be transformed into chlorine oxospecies [37]. The transformation can be correlated with the chloride disappearance and the possibility of creating perchlorate and chloroorganics in our system.…”

Understanding active chlorine species production using boron doped diamond films with lower and higher sp3/sp2 ratio

“…Recent research has shown that high concentrations of ClO 3 − and ClO 4 − are formed during electrolysis of Cl − solutions when BDD anodes are used [1][2][3][4][5][6][7][8][9]. The relationship between experimental conditions and chlorine speciation has been studied in those works and the most important parameters affecting ClO 3 − and ClO 4 − formation were found to be the mass-transfer rate and the concentration of competitive ions [2,3,5].…”

On the role of salts for the treatment of wastewaters containing pharmaceuticals by electrochemical oxidation using a boron doped diamond anode

“…HClO 4 [39] pharmaceuticals. This is the aim of proposing adequate operating conditions to limit the risk of formation of toxic by-products.…”

“…Since, for an electrical charge of 0. and OH [39]. The high concentration of electrogenerated oxygen species allows the reactions between the intermediate chlorine species and oxygen species to form ClO 4 À .…”

“…Using a BDD anode, besides direct electron transfer reactions, the electro-oxidation pathway of Cl À also includes the chemical oxidation reactions with hydroxyl radicals [33][34][35][36][37][38][39]. The possible pathway is exhibited in reaction scheme (6) listed in Table 1.…”