Asulam or methylsulfanilyl-carbamate, an herbicide, and diazinon or 2-isopropyl-4-methylpyrimidyl-6-diethylthiophosphate, an insecticide, were photocatalytically degradaded over TiO2. Their limit values in waste water set by the Japanese Environmental Agency, viz. 2000 ppb (μg/l) for asulam and 50 ppb for diazinon, were reached within 9 or 30 minutes, respectively, under our conditions when the initial concentration was 23 ppm (mg/l; asulam) or 52 ppm (diazion). A degradation scheme of asulam is tentatively suggested on the basis of the identification of some intermediate aromatic products. Complete mineralization was attained by prolonged irradiation, however it was more difficult to achieve in the case of diazinon. Organic sulfur was easily oxidized to sulfate. Ammonium ions were rapidly formed from the amine and carbamide functionalities of asulam, and more slowly from the nitrogen atoms of the pyrimidyl moiety of diazinon. The phosphate ions produced from the organophosphorous insecticide remained partly absorbed on the photocatalyst, especially on anatase. Previous results concerning the favorable effect of an ozone pretreatment upon the TOC elimination are confirmed for diazinon.
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