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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

Ye, Peng, Lemley, Ann T.
Journal of agricultural and food chemistry 2008 v.56 no.21 pp. 10200-10207
carbaryl, insecticide residues, mecoprop, paraquat, herbicide residues, soil pollution, remediation, chemical degradation, electrodes, electrical treatment, hydrogen peroxide, iron, montmorillonite, slurries, adsorption, sorption isotherms
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.