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Abstract
The kinetics of the reduction of colloidal MnO2 by glyphosate has been investigated spectrophotometrically in an aqueous and micellar (cetyltrimethylammonium bromide, sodium lauryl sulfate) media. The reaction follows first-order kinetics with respect to colloidal MnO2 in both the aqueous and micellar media. The rate of oxidation increases with increase in [glyphosate] in the lower concentration range but becomes independent at its higher concentrations. The addition of both the anionic (NaLS) and cationic (CTAB) micelles increased the rate of reduction of colloidal MnO2 by glyphosate while the nonionic TX-100 micelles did not influence the rate of reaction. In both aqueous and micellar media, the oxidation of glyphosate occurs through its adsorption over colloidal MnO2 surface. The reaction in micellar media was treated by considering the pseudophase model. The values of reaction rates and binding constants in the presence of micelles were determined.
Highlights
Manganese is the eleventh most abundant element in the earth crust and is among the important micronutrients for all micro-organisms
All the kinetic experiments were run under the first-order reaction condition in which the concentrations of surfactant and glyphosate were kept in large excess over [MnO2]
It was observed that the rate constant decreases with increase in concentration of colloidal manganese dioxide This decrease in rate constant may be due to the flocculation of the colloidal MnO2 particles
Summary
Manganese is the eleventh most abundant element in the earth crust and is among the important micronutrients for all micro-organisms. Manganese (III, IV) oxide minerals are thermodynamically stable in the oxygenated environments. These oxide particles in earth crust and in natural water are susceptible for reduction by humic acid and organics [1,2,3,4]. Glyphosate (N-phosphonomethylglycine) is an aminophosphonic analogue of the natural amino acid, glycine. It is a postemergence nonselective broad spectrum herbicide extensively used in agriculture for the control of many annual and perennial weeds [12]. Surfactants aggregates mimic enzyme structurally and functionally, and, the study in CTAB and SDS micelles will be helpful in understanding the mechanism of degradation of herbicide in humic and biological media. The observed data will be helpful in the determination and interpretation of the fate of herbicide after its dispersal in the environment
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