Interactions of alachlor with homoionic montmorillonites
1993
BOSETTO, M. | ARFAIOLI, P. | FUSI, P.
The adsorption of the herbicide Alachlor on montmorillonite saturated with different cations (Al, Cu, Ca, Mg NH4, Na, Li, Rb, and Cs) was studied in aqueous suspension. Equilibrium adsorption isotherms at 5° and 22°C fit the Freundlich relationship. A correlation between adsorption and the polarizing power of the exchangeable cation was observed. A decrease in temperature from 22° to 5°C resulted in an increase in adsorption except for Al-, Rb-, and Cs-montmorillonite. The isosteric heats of adsorption were also determined. The interaction of Alachlor with homoionic montmorillonites was also studied by FT-IR spectroscopy in an organic solvent. The results indicated that the molecule is adsorbed on monoionic montmorillonite by a coordination bond, through a water bridge, between C==O groups and the exchangeable cation of the clay. Further, the coordination strength is directly correlated with the polarizing power of the cation. X-ray diffraction analyses showed that the herbicide was able to penetrate the interlayer space of montmorillonite saturated with polyvalent cations. On moderate heating (70°C for 6 h) Alachlor adsorbed on Al-, Cu-, Ca-, Mg-, and NH4-clay is partially decomposed to 2-chloro-2′,6′-diethylacetanilide.
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