Adsorption and photo-reactivity of bensulfuron-methyl on homoionic clays

The adsorption and photolysis of the herbicide bensulfuron-methyl on homoionic Na (super +) -, Ca (super 2+) - and Fe (super 3+) -montmorillonite and kaolinite clays were studied. The Freundlich adsorption coefficient, Kf, measured from isotherms on clays followed the order Na (super +) < Ca (super 2+) < Fe (super 3+) . Montmorillonite showed a greater adsorptive capacity than kaolinite. Analysis of Fourier transform IR spectra of bensulfuron-methyl adsorbed on clay suggested probable bonding interactions between bensulfuron-methyl and homoionic clays. The photolysis rate of herbicide adsorbed on homoionic clay surfaces was quite slow to its free state and decreased in the order Na (super +) > Ca (super 2+) > Fe (super 3+) , indicating that adsorption may have prevented photolysis.