Abstract:Radiolytic reactions of phenylureas were studied in detail with fenuron model compound in dilute aqueous solutions using pulse radiolysis for detection of the intermediates, gamma radiolysis with UV-Vis and HPLC-MS techniques for analysis of the final products. The kinetics of oxidation was followed by COD, TOC and toxicity measurements. During radiolysis of aerated solutions hydroxyl radical ((•)OH), eaq (-), H(•) and O2 (•-)/HO2 (•) reactive intermediates are produced, the degradation of solute takes place p… Show more
“…in the case of diuron: − O(Cl 2 )C 6 H 2 NHCON(CH 3 ) 2 → − O(Cl 2 )C 6 H 2 N=C=O + HN(CH 3 ) 2 . Similar reaction (isocyanate ion formation) has also been observed in the thermal degradation of diuron [ 6 ] and during the mass spectrometric analysis of irradiated fenuron samples [ 11 ]. Figure 4 Chromatogram of 1 × 10 −4 mol dm −3 diuron solutions.…”
Section: Resultssupporting
confidence: 57%
“…Most of these products were observed also in previous studies where hydroxyl radicals were the initiating reactants [ 4 , 7 , 10 ]. According to Tahmasseb et al [ 4 ] “The disubstitution of the phenyl ring by chlorine atoms reduces its susceptibility towards any electrophylic and/or radical attack which in counterpart makes the attack on the urea N-terminus group more competitive.” However, our results clearly show the predominance of ring hydroxylation reactions for diuron similarly to the reactions with fenuron [ 11 ].…”
Section: Resultsmentioning
confidence: 73%
“…for the chloroanilines the maxima of the bands are around 360 nm [ 15 ]. For fenuron the maximum is at 350 nm [ 11 ]. Therefore, we assign the ~360 nm band to hydroxycyclohexadienyl radical isomers.…”
Section: Resultsmentioning
confidence: 99%
“…To the best of our knowledge, there is only one publication reporting the radiation induced degradation of diuron [ 10 ]. In a previous paper we have already reported on the degradation of fenuron [ 11 ].…”
BackgroundCutting 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.ResultsIrradiation 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.ConclusionThe presence of dissolved oxygen is highly important to achieve efficient ionizing radiation induced degradation of diuron in dilute aqueous solution.
“…in the case of diuron: − O(Cl 2 )C 6 H 2 NHCON(CH 3 ) 2 → − O(Cl 2 )C 6 H 2 N=C=O + HN(CH 3 ) 2 . Similar reaction (isocyanate ion formation) has also been observed in the thermal degradation of diuron [ 6 ] and during the mass spectrometric analysis of irradiated fenuron samples [ 11 ]. Figure 4 Chromatogram of 1 × 10 −4 mol dm −3 diuron solutions.…”
Section: Resultssupporting
confidence: 57%
“…Most of these products were observed also in previous studies where hydroxyl radicals were the initiating reactants [ 4 , 7 , 10 ]. According to Tahmasseb et al [ 4 ] “The disubstitution of the phenyl ring by chlorine atoms reduces its susceptibility towards any electrophylic and/or radical attack which in counterpart makes the attack on the urea N-terminus group more competitive.” However, our results clearly show the predominance of ring hydroxylation reactions for diuron similarly to the reactions with fenuron [ 11 ].…”
Section: Resultsmentioning
confidence: 73%
“…for the chloroanilines the maxima of the bands are around 360 nm [ 15 ]. For fenuron the maximum is at 350 nm [ 11 ]. Therefore, we assign the ~360 nm band to hydroxycyclohexadienyl radical isomers.…”
Section: Resultsmentioning
confidence: 99%
“…To the best of our knowledge, there is only one publication reporting the radiation induced degradation of diuron [ 10 ]. In a previous paper we have already reported on the degradation of fenuron [ 11 ].…”
BackgroundCutting 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.ResultsIrradiation 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.ConclusionThe presence of dissolved oxygen is highly important to achieve efficient ionizing radiation induced degradation of diuron in dilute aqueous solution.
“…Their removal from waters therefore is an important task, which can be achieved through the application of advanced oxidation processes (AOPs). The degradation of monuron (3-(p-chlorophenyl)-1,1-dimethylurea) and phenylurea pesticides in general has been studied using several methods, such as photolysis (Kovács et al, 2016a), gamma-radiolysis (Kovács et al, 2014b;Kovács et al, 2016b). electro-and photo-Fenton processes (Bobu et al, 2006;Oturan et al, 2010), ozonation (Tahmasseb et al, 2002;Kovács et al, 2016a), heterogeneous photocatalysis (Rao et al, 2010;Chu et al, 2012;Solís et al, 2016) or their combinations including photocatalytic ozonation (Bobu et al, 2006;Oturan et al, 2010) Titanium dioxide (TiO2) is generally considered the most adequate photocatalyst, as it is cheap, inert, and it has prominent photocatalytic activity.…”
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