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Adsorption Effect on the Degradation of Carbaryl, Mecoprop, and Paraquat by Anodic Fenton Treatment in an SWy-2 Montmorillonite Clay Slurry

Author:
Ye, Peng, Lemley, Ann T.
Source:
Journal of agricultural and food chemistry 2008 v.56 no.21 pp. 10200-10207
ISSN:
0021-8561
Subject:
carbaryl, insecticide residues, mecoprop, paraquat, herbicide residues, soil pollution, remediation, chemical degradation, electrodes, electrical treatment, hydrogen peroxide, iron, montmorillonite, slurries, adsorption, sorption isotherms
Abstract:
The Fenton reaction-based anodic Fenton treatment (AFT) was applied to three widely used organic agrochemicals, carbaryl, mecoprop, and paraquat, in a clay slurry. The adsorption and degradation behaviors of these neutral (carbaryl), anionic (mecoprop), and cationic (paraquat) agrochemicals were studied in a slurry of SWy-2 Na+-montmorillonite clay, and adsorption isotherms were obtained at given experimental conditions. The d spacing (d001) of the clay layer before and after adsorption or degradation was measured by X-ray diffraction (XRD). On the basis of the change of d spacing, molecular disposition at the clay interlayer was inferred: both mecoprop and paraquat form a monolayer sitting flat and parallel to the clay siloxane surfaces. Results show that, due to different adsorption mechanisms, the adsorption effect on chemical degradation by AFT varies with pesticide: strong and tight adsorption of paraquat at the clay interlayer protects paraquat from being attacked by hydroxyl radicals; loosely adsorbed carbaryl or mecoprop is readily degraded. XRD analysis clearly indicates that AFT is capable of effectively degrading interlayer noncationic organic chemicals that are not usually available for biodegradation.
Agid:
741146