Ionizing radiation induced degradation of diuron in dilute aqueous solution

Abstract

Background: Cutting edge technologies based on Advanced Oxidation Processes (AOP) are under development for the elimination of highly persistent organic molecules (like pesticides) from water matrices. Among them, ionizing radiation treatment represents a promising technology that requires no additives and can be easily adapted to an industrial scale. In these processes several reactive species are produced, mainly powerful oxidizing radicals inducing the degradation. This paper investigates the reactions taking place in dilute aqueous solutions of a hazardous pollutant (diuron) during irradiation. Results: Irradiation of aqueous diuron solutions resulted in effective degradation of the solute mainly due to the reactions of hydroxyl radicals formed in water radiolysis. Hydroxyl radical reacts with diuron with a second order rate constant of (5.8 ± 0.3) × 109 mol-1 dm3 s-1. The main reaction is addition to the ring forming hydroxycyclohexadienyl radical. 30 - 50% of hydroxyl radical reactions induce dechlorination. Reactions with the methyl groups or with the α-amino group have low contribution to the transformation. The presence of dissolved oxygen enhances the rate of degradation; one hydroxyl radical on average induces five-electron oxidations. The high oxidation rate is attributed to the reaction of some of the primarily formed organic radicals with dissolved O2 and the subsequent reactions of the peroxy radicals. Conclusion: The presence of dissolved oxygen is highly important to achieve efficient ionizing radiation induced degradation of diuron in dilute aqueous solution.