Photostabilization of Trifluralin Adsorbed on a Clay Matrix

The photochemical behavior of trifluralin (TF) adsorbed on montmorillonite (Mont), with and without the organic cation thioflavin T (TFT) coadsorbed, is reported. The effect of complexation on the photostability of TF was studied by measuring the reaction rates and photoproduct yields in photolysis experiments and the herbicidal activity of TF in soil samples following exposure to UV light, using oat roots bioassays. In the two complexes (Mont-TF and Mont-TFT-TF) considerable photostabilization of TF was observed, as compared with the herbicide in its free form. The interactions between TF and the clay were studied by Fourier-transform infrared spectroscopy. It is suggested that photostabilization is due to steric hindrance imposed by the clay surface to the cyclization step of the photochemical reaction.