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Photodegradation of Isoproturon in Water by Several Adavanced Oxidation Processes
Abstract
The paper deals with the study of the Isoproturon degradation and mineralization in water by four Advanced Oxidation Processes (AOP): UV/H2O2, UV/H2O2/Fe(II) (photo-Fenton), UV/TiO2, and UV/H2O2/TiO2 (anatase). All the degradation experiments have been done in a quartz glass photoreactor (V= 0.5 L ) equipped with a UV lamp having an incident photonic flux of 5x10-6 Es/s. The initial concentration of the Isoproturon aqueous solution was 5x10-5 mol/L. The concentrations of the unreacted substrate and of some intermediates have been determined by HPLC analysis. The Total Organic Carbon (TOC) measurements have been performed with a TOC analyzer Shimadzu model TOC 5000A. The optimal parameters have been identified for each process. The main conclusion from the obtained results is that the most effective is the photo - Fenton process. Using doses of 0.5 mmol/L H2O2 and 0.05 mmol/L Fe (II) the Isoproturon is almost completely removed after only 15 minutes, while TOC is reduced by 88.78 % after 60 minutes of irradiation.
... This substance fights mono-and dicotyledonous plants. It is a component of preparations used mainly in the protection of cereals (Del Pilar et al. 2001;Bobu et al. 2005). Diuron is a substituted herbicide based on derivatives of urea. ...
The EU directive 2013/39/EU has incorporated four biocidal compounds as priority substances: diuron, isoproturon, cybutryne, and terbutryn. The research was undertaken to determine the concentration of biocides in surface waters in three locations in southern Poland: the Wisła River in Kraków, the Wisłoka River in Mielec, and the drainage ditch draining water from arable fields located near Mielec. Environmental samples were taken in two series: winter (February) and spring (May and June). The analyses were carried out using gas chromatography with mass spectrometry. The seasonality of biocides in surface waters was observed. In winter samples, the concentrations were below MQL, while in spring, they ranged from a few to several dozen nanograms per liter. The highest concentrations of all analyzed compounds were recorded in water taken from the Wisła River. According to directive 2013/39/EU, the maximum allowable concentration was exceeded only in the case of cybutryne in water from the Wisła, both in May and in June. The assessment of the toxicity with the tested compounds was defined based on the Environmental Risk Assessment method. Low risk was estimated for diuron and isoproturon, while moderate risk for terbutryn and cybutryne.
... La décroissance de la cinétique observée au-delà de 4 mg/L s'expliquerait par une trop grande concentration en catalyseur qui affecte la diffusion de la lumière dans la solution à traiter impliquant ainsi la diminution de la cinétique de dégradation ou par l'agrégation des particules de TiO2 à de fortes concentrations, causant une diminution du nombre de sites de surface active ( Parra et al., 2001 ;Mehrvar et al., 2002;Wong et Chu, 2003 ;Deepika et al., 2005). Les travaux respectifs de Kamel et Tahar (1998), Daneshvar et al. (2003), Sakkas et al. (2004), Bobu et al. (2005), Eslami et al. (2007 confirment cette tendance pour la famille de pesticides apparentée au diazinon. ...
The treatment of pesticides is a necessity in view of the stability and toxicity of the pesticides that generate them. The objective of this work is to study the degradation of picloram in aqueous medium under UV irradiation. It is a selective and systemic herbicide that can control woody plants and broadleaf weeds. The irradiations were carried out using a mercury vapor lamp of wavelength λ = 365 nm. A high performance liquid chromatograph equipped with a UV / visible detector was used to analyze the samples. The degradation of picloram in aqueous medium was carried out by direct photolysis and photocatalysis. In direct photolysis, a low rate of product degradation (6.9 %) was obtained after 225 min of irradiation. Photolysis in the presence of a catalyst (TiO2) accelerated the degradation of the molecule. Experiments demonstrating the effect of the concentration of the catalyst showed that the optimum concentration corresponding to a maximum degradation of picloram is 4 mg / L (62.68 %). The study of the influence of the pH of the solution on the degradation indicates that the molecule degrades better in an acid medium (pH = 5) with a rate of 62 % in 225 min
European Scientific Journal October 2017 edition Vol.13, No.30 ISSN: 1857 – 7881 (Print) e - ISSN 1857- 7431
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of irradiation. Apparent order 1 degradation kinetics were observed in all cases.
... Scheme1. Structure of isoproturon Therefore, it is important to understand the fate of this herbicide in the environment in order to assess its environmental impact.Several authors have investigated the photodegradationofisoproturon in aqueous solution [3][4][5][6].In recent decades, different strategies have been developed for removal of pollutants from water and a great deal of interest has been devoted to photocatalytic degradation of isoproturon by semiconductor compounds [7][8][9][10][11][12][13][14][15]. Photocatalytic treatmentofisoproturonover TiO 2 /Al-MCM-41 and TiO 2 /HY composite systemsusing solar light is reported to be very efficient in the destruction of the herbicide [7,8]. ...
The photocatalytic degradation of isoproturon, a persistent toxic herbicide, was investigated in the presence of natural iron oxide and oxalic acid and under UV irradiation. The influence of the relevant parameters such as the pH and the iron oxide and oxalic acid concentrations has been studied. The presence of natural iron oxide and oxalic acid in the system effectively allow the degradation of isoproturon, whereas the presence of t-butyl alcohol adversely affects the phototransformation of the target pollutant, thus indicating that an OH radical initiated the degradation mechanism. The degradation mechanism of isoproturon was investigated by means of GC-MS analysis. Oxidation of both the terminal N-(CH3)2 and isopropyl groups is the initial process leading to N-monodemethylated (NHCH3), N-formyl (N(CH3)CHO), and CHCH3OH as the main intermediates. The substitution of the isopropyl group by an OH group is also observed as a side process.
Natural organic matter (NOM) is a heterogeneous complex of organic materials and is ubiquitous in natural aquatic systems. The amount of NOM in the environment is continuously increasing because of global warming and/or changes in precipitation patterns and has negative impact on drinking water as it produces an undesirable colour and as a vector for the introduction of contaminants. For these reasons, several technologies have been proposed to address the impact of NOM in aqueous systems. Among these, advanced oxidation processes (AOPs) refer to oxidation processes that result in the formation of highly reactive radical species. This chapter presents an overview of recent research studies dealing with photon-activated AOPs for the removal of NOM and emerging contaminants in water.
The paper reports the results of an investigation aimed to find out the number and the chemical structures of byproducts which form during the reactions occurring in aqueous solution between two very common disinfectants, sodium hypochlorite (NaClO) and chlorine dioxide (ClO2), and two herbicides widely used in agriculture and frequently found in groundwaters: ametryn and isoproturon. Under controlled experimental conditions [T=20°C, pH=7, reaction-time = 48h, herbicide/disinfectant molar ratios: 0.05 and 0.05×10−2], ametryn reactions with chlorine dioxide much slower than with sodium hypochlorite, whereas the opposite trend has been observed for isoproturon. In any case, however, the higher the reagents concentration the faster the reactions. As for reaction byproducts, they have been detected by HPLC and identified by HPLC-MS. In particular, ametryn (R-S-CH3) reaction with NaClO gives rise to the consecutive formation of four derivatives: the sulphoxide (R-SO-CH3), the sulphone (R-SO2-CH3), the sulphonate ester (R-O-SO2-CH3) and its hydrolysis product (R-OH). Within the fixed reaction time (48h), ametryn reaction with ClO2 forms only the sulphoxide derivative (R-SO-CH3). As for isoproturon, it reacts with both oxidants forming aromatic-ring substituted derivatives. In particular, during the reactions with NaClO and ClO2, four and two (chlorinated and/or hydroxylated) derivatives are respectively formed.
Physicochemical pre-treatment for the destruction of two non-biodegradable herbicides (metobromuron and isoproturon) were conducted by different advanced oxidation processes, i.e. the systems UV/TiO2, UV/TiO2/H2O2, Fe3+/H2O2, and UV/Fe3+/H2O2. The degradation rates were always higher for the photo-Fenton reactions when compared with the heterogeneous photocatalytic systems. Optimal concentrations of Fe3+ and H2O2 for the abatement of both herbicides in the photo-Fenton system were found. During the phototreatment, experiments were made to obtain information concerning the evolution of: (a) organic carbon and initial compound concentration, (b) the oxidation state, (c) ions, (d) the toxicity, (e) the biodegradability, and (f) the chemical nature of the intermediates. These analysis show that the solution resulting from the photodegradation of metobromuron is not appropriate for a biological treatment, probably due to the formation and the accumulation in the bulk of bromide intermediates, which are highly bio-recalcitrant. In contrast, the solution resulting from the phototreatment of isoproturon is biologically compatible and its complete mineralization can be performed by biological means. A combined photo-Fenton and biological flow reactor for the degradation of isoproturon was operated in continuous mode at laboratory scale. In this coupled system, 100% of the initial concentration of isoproturon and 95% of TOC were removed. Some field experiments under direct sunlight were carried out at the Plataforma Solar de Almeria in Spain. The obtained results demonstrated that the solar catalytic treatment is effective for the purification of water contaminated by the herbicides under study.
The degradation of metobromuron (MB), isoproturon (IP), chlortoluron (CT), and chlorbromuron (CB) in heterogeneous photocatalytic solution via TiO2 was studied in detail. The influence of parameters such as TiO2 and herbicide concentration has been investigated and the optimal conditions for the abatement of the herbicides were found. The primary degradation of the herbicides was measured by HPLC analysis. A systematic study of their photodegradation has been made to assess structure–photoreactivity relationships. Correlation analysis showed that photoreactivity is associated with the molecular dipolar moment dependent on the differences in electronegativity of the substituents in the aromatic ring of each herbicide. The effect of the molecular charge distribution encoded in the dipolar moment was confirmed calculating electrostatic potential contour maps. It was also found that photoreactivity is inverse to the adsorption capability of these compounds on TiO2. Indeed, as confirmed in this paper, the extent of adsorption is not necessarily decisive in the evolution of the photochemical process and the photocatalytic reactions can occur independently of the degree of adsorption of the herbicides on TiO2.
After a previous study in which the considered oxidant was ozone (Part I), a laboratory investigation has been carried out to study the degradation of the herbicide isoproturon during its reaction with another oxidant, i.e. chlorine, in aqueous solution (Part II; this paper). The specific aim was to identify the by-products formed. The effects of pH and the presence of bromide ions were studied. Reactions have been carried out at room temperature, in phosphate buffered aqueous solutions, at four pHs (6, 7, 8 and 9). By-products identification was first performed using relatively high initial reagent concentrations which were analytically convenient ([isoproturon] = 40 mg/l, [HClO + ClO-] = 160 mg Cl/l, [Br-] = 80 mg/l). In follow-up studies, the by-products identified during this preliminary step were searched for when using concentration values closer to those actually encountered at real water treatment plants ([isoproturon] = 0.4 and 0.004 mg/l, [HClO + ClO-] = 1.6 mg Cl/l, [Br-] = 0.8 and 0.008 mg/l). Under all of the studied conditions, the results showed that isoproturon is completely degraded and that it decays much faster in the presence of bromide. The pH has a negligible influence when bromide ions are absent. On the contrary, if bromide ions are present, the isoproturon decay is slower at higher pH values. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses have led to the identification of several by-products as a result of simultaneous oxidation and substitution reactions, both occurring on the aromatic ring of the herbicide. However, the more abundant by-products are those resulting from the oxidation of the isoproturon aromatic ring. As far as halogenated by-products are concerned, the higher the bromide ion concentration the higher the ratio of brominated to chlorinated by-products. On the basis of the analytical results, a pathway for isoproturon degradation under the studied conditions is proposed.
Heterogeneous photocatalysed degradation of a herbicide derivative, N-(4-isopropylphenyl)-N',N'-dimethylurea (Isoproturon, 1) was investigated in aqueous suspensions of titanium dioxide by monitoring the change in absorption intensity and depletion in Total Organic Carbon content as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO(2) and in the presence of electron acceptors such as hydrogen peroxide (H(2)O(2)), potassium bromate (KBrO(3)) and potassium persulphate (K(2)S(2)O(8)) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts. An attempt was made to identify the degradation product through GC-MS analysis technique.
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