Electrocatalytic dechlorination of atrazine

Abstract

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a photosynthetic inhibitor that is used in large quantities for weed control in corn and sorghum, is dechlorinated in aqueous solution upon electrolysis at a reticulated vitreous carbon cathode in the presence of noble-metal catalysts. Electrocatalytic hydrogenolysis to 2-ethylamino-4-isopropylamino-s-triazine occurs in quantitative yield, and is most efficient with palladium-based catalysts. Current efficiency increases with atrazine and catalyst concentration, and decreasing current density. A previously unobserved phenomenon with Pd catalysts is that current must be passed for a certain time before dechlorination commences. This lag time is explained in terms of the palladium lattice absorbing a finite amount of hydrogen before catalytically active hydrogen atoms appear on the catalyst surface.Résumé : Soumise à une électrolyse en solution aqueuse, au niveau d'une cathode de carbone vitreuse et réticulée et en présence de catalyseurs de métaux nobles, l'atrazine (la 2-chloro-4-éthylamino-6-isopropylamino-s-triazine), un inhibiteur de la photosynthèse utilisé en grandes quantités pour contrôler les mauvaises herbes dans le maïs et dans le shorgo, subit une déchloration. L'hydrogénolyse électrocatalytique en 2-éthylamino-4-isopropylamino-s-triazine se produit avec un rendement quantitatif et les catalyseurs à base de palladium sont les plus efficaces. L'efficacité de courant augmente avec les concentrations d'atrazine et de catalyseur et elle diminue avec la densité du courant. Avec les catalyseurs de Pd, il se produit un phénomène qui n'a pas été observé antérieurement; on doit faire passer le courant pour un certain temps avant que la déchloration ne débute. On explique ce décalage dans le temps en fonction d'une absorption dans un premier temps d'une quantité finie d'hydrogène par le réseau du palladium qui précéderait l'apparition d'atomes d'hydrogène catalytiquement actifs à la surface du catalyseur.

Electrocatalytic Hydrogenation of 4-Chlorophenol on the Glassy Carbon Electrode Modified by Composite Polypyrrole/Palladium Film

“…The use of ECH for the dechlorination of chloroaromatic compounds is potentially advantageous compared with traditional techniques such as adsorption on activated carbon or incineration. Recent studies have shown that the dechlorination of 4-CP (4-chlorophenol) by electrocatalytic hydrogenation on a palladized carbon cloth and of chlorophenoxy acetic acids on palladium-loaded carbon felt can be performed with good efficiencies. − According to the literature, , the mechanism of the electrocatalytic hydrogenolysis of a carbon−halogen bond involves the steps described in eqs 1−4 …”

“…Because of its strong ability to intercalate hydrogen in its lattice, the palladium is the most common catalyst for ECH. It was shown to be much more effective in promoting the dechlorination reaction than platinum and Raney nickel. , Usually, a high degree of dispersity and the large surface areas of palladium are desirable for the ECH process. High surface areas of many conducting polymers favored their use as supporting materials for the development of new electrocatalysts .…”

“…Recent studies have shown that the dechlorination of 4-CP (4-chlorophenol) by electrocatalytic hydrogenation on a palladized carbon cloth and of chlorophenoxy acetic acids on palladium-loaded carbon felt can be performed with good efficiencies. [1][2][3] According to the literature, 3,4 the mechanism of the electrocatalytic hydrogenolysis of a carbon-halogen bond involves the steps described in eqs 1-4.…”

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“…For chemical degradation of atrazine, many new techniques have been explored. These include photocatalytic degradation (Minero et al, 1996), advanced oxidation (Arántegui et al, 1995), Electrocatalytic dechlorination (Monson et al, 1998;Stock and Bunce, 2002), and reductive degradation by the use of zero-valent iron (Dombek et al, 2001), and Fenton reactions (Arnold et al, 1995). Chemical methods for atrazine breakdown was done with the help of Fenton's reagent (Larson et al, 1991).…”

Environmental significance of atrazine in aqueous systems and its removal by biological processes: an overview

“…Various new techniques that have been proposed and explored for the destruction of chlorinated triazine herbicides, in particular atrazine included photocatalytic degradation [61], advanced oxidation [62][63][64][65], Fenton like reactions [66][67], electrocatalytic dechlorination [68] and reductive degradation by the use of zero-valent iron [69][70]. Chemical process using Fenton's reagent was tried to degrade atrazine.…”