Photocatalytic degradation of organophosphate and phosphonoglycine pesticides using TiO2 immobilized on silica gel.

The photocatalytic degradation of the three pesticides acephate, dimethoate, and glyphosate in water has been investigated using UV light and TiO2 immobilized on silica gel as photocatalyst. Results show that the pesticides can be efficiently degraded by the UV/TiO2 system used in the study. Complete (100%) decomposition of dimethoate and glyphosate was attained within 60 min of irradiation, while total degradation of acephate occurred after 105 min of photocatalytic treatment. Acephate and dimethoate decomposition followed the Langmuir-Hinshelwood apparent first-order degradation kinetics, suggesting the photocatalytic nature of pesticide disappearance, whereas glyphosate decomposition was governed by both adsorption and photocatalytic reactions. Evolution of heteroatoms at their highest oxidized states such as SO(4)(2-), NO(3)(-), and PO(4)(3-) ions provides evidence that pesticide degradation occurred primarily through photocatalytic oxidation reactions. Non-detection of toxic intermediates such as methamidophos and omethoate that have been reported in other studies demonstrates rapid destruction of the pesticides into harmless byproducts using the system.