Iodosulfuron degradation by TiO2 photocatalysis: Kinetic and reactional pathway investigations (original) (raw)
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Analytical Chemistry, 2006
In the present study, HPLC/ESI-MS and stopped-flow HPLC/ 1 H NMR methods were developed and applied to separate and characterize the byproducts arising from TiO 2 -catalyzed photodegradation of the herbicide iodosulfuron methyl ester (IOME) in aqueous solution under UV irradiation. Prior to identification, irradiated solutions of IOME (200 and 1000 mg‚L -1 ) were concentrated by solid-phase extraction using two cartridges: Isolute C 18 and Isolute ENV + . Analytical separation was achieved on a C 18 reversed-phase column with ACN/H 2 O (HPLC/MS) or ACN/D 2 O (HPLC/NMR) as mobile phase and a linear gradient with a chromatographic run time of 35 min. The combination of UV and MS data allowed the structural elucidation of more than 20 degradation products, whereas 1 H NMR data permitted an unequivocal confirmation of the identities of major products and the differentiation of several positional isomers, in particular, the hydroxylation isomers. The obtained results permitted us to propose a possible degradation scheme and to put in evidence the presence of privileged sites for the attack of OH radicals.
Photocatalytic degradation of sulfonylurea herbicides in aqueous TiO2
Applied Catalysis B: Environmental, 2002
The degradation of two sulfonylurea (Sus) herbicides, cinosulfuron and triasulfuron, has been investigated in aqueous solutions containing TiO 2 suspensions as photocatalyst. Cinosulfuron and triasulfuron have been rapidly transformed with different kinetic orders (1 and 1/2, respectively). The calculated quantum efficiencies (φ) of both Sus have been found similar (0.73%). Intermediate products were identified using HPLC-UV or HPLC-MS analyses. A photocatalytic degradation pathway has been proposed, leading to cyanuric acid as a final product. This molecule is known as resistant to all oxidation technologies.
Journal of Photochemistry and Photobiology A: Chemistry, 2003
The photocatalytic degradations of six sulfonylurea herbicides have been investigated in aqueous solutions containing TiO 2 suspensions as photocatalyst, in order to assess influence of various parameters, such as adsorption, initial concentration and photon flux on the photocatalytic process. Results show that adsorption is an important parameter controlling the apparent kinetic order of the degradation (either one in the case of associative adsorption or a half in the case of dissociative adsorption). In respect to the Langmuir-Hinshelwood model, the photocatalytic reaction is favoured by a high concentration. A higher efficiency is observed under the lower photon fluxes, the limiting factor being the electron-hole pair recombinations.
Photocatalytic transformation of sulfonylurea herbicides over irradiated titanium dioxide particles
Colloids and Surfaces A-physicochemical and Engineering Aspects, 1999
The heterogeneous photocatalytic transformation of two sulfonylurea herbicides (chlorsulfuron and thifensulfuron methyl ) has been investigated in aerated aqueous suspensions of TiO 2 particles at pH 7, under UV A irradiation. The evolution of intermediate and end products of the process has been monitored by using liquid and ion chromatography, as well as total organic carbon measurements. Key intermediates have been identified by employing liquid chromatography coupled with mass spectrometry and/or matching with real standards. Under photocatalytic conditions the (hetero)aromatic moieties of the herbicides are destroyed very rapidly. This evidence is confirmed by the fast degradation of 4-chlorobenzenesulfonamide under the same conditions. The s-triazine ring is almost quantitatively transformed to cyanuric acid. By contrast, hydrolytic processes occurring in the natural environment lead to the aromatic sulfonamides as persistent intermediates. A mechanism explaining the experimental results is presented.
Journal of Hazardous Materials, 2005
Heterogeneous photocatalysed degradation of two selected pesticide derivatives such as indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) has been investigated in aqueous suspensions of titanium dioxide by monitoring the change in substrate concentration employing UV spectroscopic analysis technique and depletion in total organic carbon (TOC) content as a function of irradiation time. The degradation kinetics was studied under different conditions such as pH, types of TiO 2, substrate and catalyst concentration, and in the presence of electron acceptor such as hydrogen peroxide (H 2 O 2) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 showed comparatively highest photocatalytics. The pesticide derivative, indole-3-acetic acid was found to degrade slightly faster than indole-3-butyric acid.
Materials Science Forum, 2005
Semiconductor mediated photocatalysed degradation of an anthraquinone dye Remazol Brilliant Blue R under sunlight and artificial light source has been investigated in aqueous suspensions of titanium dioxide by monitoring the change in absorption intensity as a function of irradiation time under a variety of conditions. The degradation kinetics were 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 ammonium persulphate (NH 4 ) 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 under UV light, whereas Hombikat UV100 was better under sunlight as compared with other photocatalysts. The degradation products were analysed by GC-MS technique and probable pathways for the formation of products are proposed. #
Journal of Xenobiotics
Photodegradation (photolysis) causes the breakdown of organic pesticides molecules by direct or indirect solar radiation energy. Flucetosulfuron herbicide often encounters water bodies. For this reason, it is important to know the behavior of the compound under these stressed conditions. In this context, photodegradation of flucetosulfuron, a sulfonylurea-based herbicide, has been assessed in aqueous media in the presence of photocatalyst TiO2 and photosensitizers (i.e., H2O2, humic acid, and KNO3) under the influence of ultraviolet (UV) irradiation. The influence of different water systems was also assessed during the photodegradation study. The photodegradation followed the first-order reaction kinetics in each case. The metabolites after photolysis were isolated in pure form by column chromatographic method and characterized using the different spectral data (i.e., XRD, IR, NMR, UV-VIS, and mass spectrometry). The structures of these metabolites were identified based on the spect...
Nanomaterials
The determination of reaction pathways and identification of products of pollutants degradation is central to photocatalytic environmental remediation. This work focuses on the photocatalytic degradation of the herbicide Imazapyr (2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl) pyridine-3-carboxylic acid) under UV-Vis and visible-only irradiation of aqueous suspensions of CaxMnOy-TiO2, and on the identification of the corresponding degradation pathways and reaction intermediates. CaxMnOy-TiO2 was formed by mixing CaxMnOy and TiO2 by mechanical grinding followed by annealing at 500 °C. A complete structural characterization of CaxMnOy-TiO2 was carried out. The photocatalytic activity of the hetero-nanostructures was determined using phenol and Imazapyr herbicide as model pollutants in a stirred tank reactor under UV-Vis and visible-only irradiation. Using equivalent loadings, CaxMnOy-TiO2 showed a higher rate (10.6 μM·h−1) as compared to unmodified TiO2 (7.4 μM·h−1) for Imazapyr de...
Journal of The American Society for Mass Spectrometry, 2003
The photocatalytic degradation of the organophosphorus insecticide diazinon in aqueous suspensions has been studied by using titanium dioxide as a photocatalyst. The degradation of the insecticide was a fast process and included the formation of several intermediates that were identified using GC/ion-trap mass spectrometry with EI or CI in positive and negative ionization mode and HPLC/electrospray-QqTOF mass spectrometry. Since primarily hydroxy derivatives were identified in these aqueous suspensions, the mechanism of degradation was probably based on hydroxyl radical attack. The initial oxidative pathways of the degradation of diazinon involved the substitution of sulfur by oxygen on the P=S bond, cleavage of the pyrimidine ester bond, and oxidation of the isopropyl group. Exact mass measurements of the derivatives allowed the elemental formula of the molecules to be determined confidently. Similarities to the metabolic pathways occurring in living organisms were observed.