clay and norflurazone

The study aimed to reduce leaching of the hydrophobic herbicide norflurazon (4-chloro-5-methylamino-2-(alpha,alpha, alpha)-trifluoro-m-tolylpyridazin-3-(2H)-one) by adsorbing it on clays or organo-clays. The surface of the clay mineral montmorillonite was modified from hydrophilic to hydrophobic by preadsorbing it with organic cations, of which thioflavin-T (TFT) at a loading corresponding to (5)/(8) of the cation-exchange capacity of the clay mineral yielded the highest affinity of adsorption of norflurazon. Pillared clay (PC) used without organic cations exhibited enhanced affinity for norflurazon adsorption, much higher than that of montmorillonite or sepiolite. Fourier transform infrared (FTIR) results showed interactions between aromatic moieties of preadsorbed TFT and the herbicide. Stronger interaction of the herbicide with a clay mineral or organo-clay corresponded to its slower release. Formulations prepared on the basis of montmorillonite-TFT and PC were more effective in reducing herbicide leaching in soil columns in comparison to the commercial formulation, whereas the herbicidal efficiencies were comparable.

Topics: Aluminum Silicates; Bentonite; Clay; Herbicides; Pyridazines; Solubility; Spectroscopy, Fourier Transform Infrared

Photostable formulations of the herbicide norflurazon [4-chloro-5-(methylamino)-2-(alpha,alpha, alpha-trifluoro-m-tolyl)pyridazin-3-(2H)-one] were achieved by adsorbing it on pillared clay or on montmorillonite preadsorbed with the organic cation thioflavin T (TFT). Diffuse reflectance Fourier transform infrared spectra showed the existence of strong interactions between the aromatic moieties of preadsorbed TFT and the herbicide, particularly after irradiation. The photostabilization of norflurazon obtained with TFT-clay was mainly due to energy transfer from the herbicide to the organic cation via pi-pi interactions. An additional mechanism is the lower production of radicals from the clay when the clay mineral surface is covered with the organic cation. These radicals are responsible for the enhanced photodegradation observed when norflurazon was irradiated in the presence of untreated montmorillonite.

Topics: Aluminum Silicates; Bentonite; Clay; Herbicides; Light; Photochemistry; Pyridazines; Solubility; Spectroscopy, Fourier Transform Infrared