Photocatalytic degradation of thiocarbamate herbicide active ingredients in water

It has been shown that a wide range of organic compounds in aqueous solutio ns is photocatalytically oxidized to carbon dioxide in the presence of tita nium dioxide with near-UV radiation. The photocatalytic mineralization of t hiocarbamate derivative pesticides (EPTC, butylate, molinate, vernolate and cycloate) in water by illuminated TiO2 has been studied. The determination of the effects of various kinetic factors on the photocatalytic degradatio n and the determination of the nature of the principal intermediates form p art of the focus of this study. The degradation rate of these thiocarbamate s in a continuous recirculation mode approximates first-order kinetics. It was demonstrated that photocatalyzed degradation of thiocarbamate active in gredients does not occur instantaneously to form carbon dioxide, but throug h the formation of long-lived intermediate species. Photocatalytic intermed iates detected during the degradation of thiocarbamates were identified by GC/MS techniques. Intermediates detected in the photocatalytic oxidation of thiocarbamates in water solutions are in excellent agreement with products identified from the atmospherically important reactions of OH radical with thiocarbamates. Particular attention will be paid to the carbon dioxide fo rmed from the illuminated suspension in order to demonstrate not only appar ent destruction but also complete mineralization. The degradation of a two- component mixture was carried out and compared to results obtained with sin gle-component studies. (C) 1999 Elsevier Science B.V. All rights reserved.