Environ. Sci. Technol. 2006, 40, 3373-3377
Mechanism and Pathways of Chlorfenapyr Photocatalytic Degradation in Aqueous Suspension of TiO2 YONGSONG CAO,† LEI YI,‡ LU HUANG,§ Y I N G H O U , † A N D Y I T O N G L U * ,† Department of Resource and Environment Science, Shanghai Jiaotong University, Shanghai, China, Hunan Communication Polytechnic College, Changsha, China, and Hunan Research Institute of Chemical Industry, Changsha, China
The light-induced degradation of chlorfenapyr under UV was investigated in aqueous solutions containing TiO2 as photocatalyst. The photocatalytic degradation of chlorfenapyr followed pseudo-first-order degradation kinetics (Ct ) C0e-kt). The study focused on the identification of possible intermediate products during the degradation, using gas chromatography mass-spectrometry (GC-MS) and 1HNMR. Six aromatic intermediates were identified by several techniques during the treatment and some of them were further confirmed by matching authentic standards. Structure analysis of the degradation products suggested two degradation pathways: (1) The aliphatic ether group was cleaved from chlorfenapyr to form pyrrole-alph-carboxylic acid, then the pyrrole group was broken to form 4-chloroglycine; (2) Chlorfenapyr was debrominated and the aliphatic ether group was cleaved from the pyrrole group, which was further broken to form 4-chlorophenylglycine. The glycine was degraded into 4-chlorobenzoic acids, which was further broken into inorganic ions and CO2.
Introduction Some insecticides are considered cumulative and toxic compounds. Their presence as contaminates in aquatic environments may cause serious problems to human beings and other organisms (1-4). Photochemical reactions are important in the realm of wastewater treatment as a technique to remove harmful chemicals from the waste stream (5). Pesticide photocatalysis with TiO2 has been conducted with fine TiO2 particles (Degussa P-25, mean diameter 30 nm) suspended in an aqueous phase (6). To effectively employ photolysis as a water treatment technique, the reaction of the chemical of interest must be thoroughly studied including the subsequent reactions of intermediates. Since complete removal of harmful chemicals is the goal in wastewater treatment, demonstration of formation and elimination of intermediates was required to show that complete remediation had been achieved (5). Hence, both kinetic and mechanistic data are needed to fully understand the photochemical reaction. Chlorfenapyr was developed by the American Cyanamid Company. The IUPAC name is 4-bromo-2-(4-chlorophenyl)* Corresponding author phone : 86-21-64785941(O); fax: 86-2164787938; e-mail:
[email protected]. † Shanghai Jiaotong University, Shanghai. ‡ Hunan Communication Polytechnic College. § Hunan Research Institute of Chemical Industry. 10.1021/es052073u CCC: $33.50 Published on Web 04/13/2006
2006 American Chemical Society
FIGURE 1. Chemical structure of chlorfenapyr. 1-ethoxymethyl-5-(trifluoromethyl)pyrrole-3-carbonitrile. The formula is C15H11BrClF3N2O. It is a white-tan crystalline solid belonging to the pyrrole group of pesticides. Chlorfenapyr is a novel broad-spectrum insecticide-miticide registered in 19 countries for the control of various insects and mite pests on cotton, ornamentals, and a number of vegetable crops. It is effective on species of Heliothis sp., Spodoptera sp., Trichoplusia sp., Pseudoplusia sp., and Tetranychus sp. that are typically resistant to carbamate, organophosphate, and pyrethroid insecticides as well as chitin synthesis inhibitors (7). Since chlorfenapyr is stable and persistent in the environment, there are certain risks of leaching to surface water and seeping into groundwater. Therefore, the investigation of viable remediation treatment of polluted waters from industrial effluents or agriculture runoff containing trace amounts of chlorfenapyr is of environmental interest. Chlorfenapyr structure (Figure 1) contains two parts: a phenyl group and a pyrrole group. Photocatalytic degradation of nitrogen-containing heterocyclic compounds such as pyridine (8), pyrimidine (9-11), S-triazine (12, 13) has been thoroughly investigated. However, to the best of our knowledge, there were few studies on the chlorfenapyr compounds (14). In this paper, we reported photocatalytic degradation of chlorfenapyr for the first time. The objectives were to study the kinetics and identify the main intermediates in order to determine the degradation mechanism.
Experimental Section Chemicals. An analytical standard of chlorfenapyr was supplied by the American Cyanamid, USA. P-25 TiO2 was purchased from Degussa Co. Chlorfenapyr standard solution (1294 mgL-1) was prepared in methanol. Solutions required for preparing a standard curve (0.1294, 0.6470, 1.294, 3.235, 6.470 mgL-1) were prepared from the stock solution by serial dilutions. Methanol was a chromatograph reagent. Other solvents and chemicals used were analytical grade (Shanghai experiment reagent Co., Ltd., China). All aqueous solutions were prepared with distilled-deionized water. Apparatus. All direct photolysis and photocatalysis experiments were conducted using an SGY-photochemical reactor (Nanjing Stonetech. EEC Ltd. Nanjing, China). A quartz cylinder (50 × 450 mm) filled with 500 mL sample solutions was placed inside the reactor and illuminated with monochromatic UV lamps. Special glass filters restricting the transmission of wavelengths at either 300 or 350 nm are available with the photoreactor. A magnetic stirrer was located at the base so that a homogeneous TiO2 suspension could be maintained throughout the reaction. A thermostat was also installed in the reactor to adjust the experimental temperature. HA0.45 µm filters were supplied from Millipore (Bedford, U.S.A.). To elucidate the structures of the intermediates, the concentrated sample solutions were subjected to GC-MS analysis. The GC (Agilent 6890 series) was equipped with a DB-5 capillary column (0.25 mm I. D., 0.32 µm film thickness, 30 cm length) and interfaced directly to the MS (micromass GCT) detector. The MS was operated with electron energy VOL. 40, NO. 10, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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of 70 eV, an electron impact of ionization mode and a source temperature of 220 °C. The GC column was operated in a temperature-programmed mode with an initial temperature of 110 °C held for 2 min and then ramped to 280 °C with a 10 °C min-1 rate. The extracted solution was injected in GCMS in split mode (1:60) with helium as the carrier gas. The degradation compounds were isolated with preparative thin layer chromotography (TLC), and their structures were determined by comparing 1HNMR analysis with Varian INOVA-300 NMR (U.S.A). High Performance Liquid Chromotography (HPLC) Condition and Working Curve. Samples taken at different times of irradiation were filtered through 0.45 µm filters to remove TiO2 particles before analyses by HPLC-UV at 260 nm. The mobile phase was methanol-water (80:20 v/v) with 1 mL min-1 flow rate. The column oven was kept at 30 °C. The volume of the injection was 20 µL. External standard method was adopted. About 0.06 mg standard chlorfenapyr was transferred into a 50 mL volumetric flask, and filled with methanol. Serial dilutions in methanol were made to produce solutions with final concentrations in the range of 0.12946.470 mg L-1. Concentrations of chlorfenapyr were determined and the peak areas of the standards were recorded. The slope and intercept of the calibration graph were obtained by linear regression of peak area versus concentration: y ) ax + b, where a is the slope, b is the intercept, x is the concentration and y is the peak area. The parameters obtained by the selected chromatographic conditions for chlorfenapyr calibration corresponded to: y ) 2765.3 + 61816x, R2 ) 0.9997. The accuracy and precision of analytical method were 99.3% and 99.6%, respectively. The minimum detectable amount of chlorfenapyr was 6.5 × 10-10 g. The minimum detectable concentration was 0.0162 mgL-1.
Results and Discussion Photodegradation Kinetics. The destruction rates of photocatalysis of various organic contaminants over illuminated TiO2 were suggested fitting the Langmuir-Hinshelwood kinetics (15-17). The Langmuir-Hinshelwood rate form is
R)
kKC dc ) dt 1 + KC
(1)
Where R is the oxidation rate of the reactant (mg L-1 min-1), C is the concentration of the reactant (mgL-1), t is the illumination time, k is the reaction rate constant (min-1), and K is the adsorption coefficient of the reactant onto the TiO2 particles (L mg-1). Integration of eq 1 yields eq 2:
()
ln
C0 + K(C0 - C) ) kKt C
(2)
When the initial concentration C0 is a millimolar solution, eq 2 is altered to eq 3
ln
()
C0 ) kKt ) k′t or Ct ) C0e-k′t C
(3)
which expresses a pseudo-first-order reaction (18), where k′ is the apparent photodegradation rate constant. A plot of ln(C0/C) versus time represents a straight line. Its slope equals the apparent first-order rate constant k′. The degradation of chlorfenapyr by either 300 or 350 nm UV irradiation, with and without the presence of TiO2 at 25 °C, was investigated. The initial concentrations of TiO2 and chlorfenapyr were 800 and 50 mg L-1, respectively, at pH 6. All reactions were found to follow a pseudo-first-order kinetic, as shown in Figure 2. There was an excellent linear relationship between lnc (concentration of chlorfenapyr) and t (time). Table 1 listed the values of k and the linear regression 3374
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FIGURE 2. Direct photolysis and photocatalytic degradation of chlorfenapyr using two different monochromatic UV irradiations: 300 and 350 nm. The initial concentrations of chlorfenapyr and TiO2 were 50 and 800 mgL-1, respectively; pH 6,T ) 25 °C.
TABLE 1. Photocatalytic Degradation Kinetic Parameters (rate constants, correlation coefficients, half-life time) of Chlorfenapyr Using Two Different Monochromatic UV Irradiations: 300 and 350 nm UV-300 UV-350 UV-300 + TiO2 UV-350 + TiO2
linear regression equation
T1/2 (min)
R2
ln(C/C0) ) -0.0168t ln(C/C0) ) -0.0120t ln(C/C0) ) -0.0427t ln(C/C0) ) -0.0355t
41.3 57.8 16.2 19.5
0.9960 0.9944 0.9894 0.9876
coefficients for pseudo-first-order kinetics of chlorfenapyr photocatalytic degradation. According to these values the appropriate first-order relationship appeared to fit well. The photocatalysis rate constants (k′) (with TiO2) for 300 and 350 nm were 0.0427 and 0.0355 min-1, which were higher than their corresponding direct photolysis rates (without TiO2) by about 2.5 and 3 times, respectively. This indicated that the chlorfenapyr was mainly oxidized by the hydroxyl radicals generated through the process of photocatalysis or by O2- through direct oxidation. The lamp used in the irradiation experiments produced a narrow line at 300-350 nm UV that generated enough energy to produce TiO2 (e+ h+) (eq 4); h+ could capture HO- of water and produce hydroxyl radical (eq 5). e- could capture O2 of water and produce O2- (eq 6) (19). The low direct photolysis rates were apparently due to the low molar absorptivity of chlorfenapyr at 300 and 350 nm, and the lower energy of the UV irradiation. Besides, the test of chlorfenapyr degradation in the dark (with TiO2, but without the exposure to UV light) showed that variations in chlorfenapyr concentrations during 60 min of mixing were insignificant, suggesting that the adsorption (or loss) of chlorfenapyr onto the surface of the TiO2 particles could be neglected.
TiO2 + hν f TiO2 (e- + h+)
(4)
h+ + OH- f HO•
(5)
e- + O2 f O2-
(6)
Identification of Degradation Compounds. The HPLC analysis revealed that, after few minutes irradiation, some UV absorbing intermediates were present together with the unreacted substrate. All these chromatographic peaks completely disappeared within 120 min irradiation. Given that the decomposition of the organic intermediates is strongly dependent on pH, all experiments were performed on solutions irradiated at a fixed initial pH value. At pH 6,in
FIGURE 3. HPLC chromatograms of chlorfenapy and intermediates obtained from an extract of chlorfenapyr solution after 40 min of irradiation under UV.
FIGURE 4. GC-MS-EI total ion chromatogram obtained from an extract of chlorfenapyr solution after 40 min of irradiation under UV.
TABLE 2. GC-MS-EI Retention Times (tR) and Spectra Characteristics of Chlorfenapyr and its major photoproducts A B C D E F
proposed photodegradation compound
Rt (min)
EI-MS spectrum ions (m/z) (%, abundance)
2-(p-chlorophenyl)-1-ethoxymethyl-5(trifluoromethyl)-pyrroline-3-carbonitrile 4-bromo-2-(p-chlorophenyl)-5(trifluoromethyl)-pyrroline-3-carbonitrile 2-(p-chlorophenyl)-5-(trifluoromethyl)pyrroline-3-carbonitrile 4-bromo-2-(p-chlorophenyl)-pyrroline3-carbonitrile-5-carbonic acid 4-chlorophenylglycine 4-chloro benzoic acid
5.0
330(15), 328(10), 269(10), 214(5), 137(15), 112(30), 77(20), 59(100). 352(25), 350(100), 348(77), 328 (10), 269(5), 249(70), 214 (10), 112(30), 77(20). 272(32), 270(100), 215(29), 112(40), 77 (30), 69(70), 52(20). 328(10), 326(50), 324(30), 280(70), 245(30), 112(30), 77(40). 188(30), 186(100), 143(10), 115(30), 41(30) 156(90), 139(100), 111(80), 75 (70)
particular, the formation of such compounds reached a maximum after about 40 min. The observed HPLC pattern was shown in Figure 3. It is important to note that the number of the observed peaks and their corresponding retention times did not vary in the pH 3-9 interval, suggesting that the reaction intermediates were essentially the same. The identification of byproducts was performed by solidphase extraction (SPE) followed by GC-MS analysis in EI mode. SPE has been demonstrated to be more efficient than traditional liquid-liquid extraction (LLE) in the analysis of water samples containing very polar intermediates resulting from the photocatalytic degradation process (20, 21). The compounds were identified by NIST spectra library and by interpretation of fragment ions. Blank analysis helped us to discard those peaks coming from the sample handling procedure and chromatographic system. Figure 4 showed the total ion chromatogram obtained from a SPE extract of chlorfenapyr solution after 40 min of irradiation. Up to 6 compounds were detected as candidate degradation intermediates. Several peaks were not identified, but they might be regarded as transformation products since their concentrations changed as the function of the reaction time. The molecular ion and spectrometric fragmentation peaks along with their relative abundance for different products
5.7 6.3 6.8 7.6 7.1
were given in Table 2. Products were identified by comparing the MS spectra with corresponding products reported in the library, with similarity higher than 85% to the standard spectra. From these data, we identified the compounds with retention times of 5.5, 7.0, and 7.5 min as chlorfenapyr, 4-chlorobenzoic acid (F), and 4-chlorophenylglycine (E), respectively. These assignments were based on a comparison of retention times and mass spectra to the standard molecules. The compounds appearing at the other retention times required further characterization before a confident identification could be made. These compounds were identified by NIST spectra library and 1HNMR analysis. The compound A appeared at Rt ) 5.0 min in the GC-MS chromatogram was isolated and identified. The major ions in the mass spectra included (m/z, %): 330 (M + 2,15), 328 (M, 10), 269 (10), 214 (5), 137 (15), 112 (ClC6H5+, 30), 77 (C6H5+, 20), and 59 (100). This compound was isolated with preparative TLC, and the structure was determined by comparing 1HNMR analysis with the mass spectral data. The 1HNMR spectra for this compound were (DMSO-D6): δ 7.55 (d, 2H, Ar-H), 7.50 (d, 2H, Ar-H), 7.13 (s, 1H, pyrrole-H), 5.34 (s, 2H, -CH2), 3.45 (q, 2H, -CH2), and 1.31 (t, 3H, -CH3). It might be 2-(p-chlorophenyl)-1-ethoxy methyl-5-(trifluoromethyl)-pyrroline-3-carbonitrile. VOL. 40, NO. 10, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 5. Proposed photocatalytic degradation pathway of chlorfenapyr in suspension of TiO2 irradiated by UV. The compound B appeared at Rt ) 5.7 min in the GC-MS chromatogram, and it was isolated and identified. The major ions in the mass spectra included (m/z, %): 352 (M + 4, 25), 350 (M + 2, 100), 348 (M, 77), 328 (10), 269 (5), 249 (70), 214 (10), 112 (ClC6H5+, 30), and 77 (C6H5+, 20). This compound was isolated with preparative TLC, and the structure was determined by comparing 1H NMR analysis with the mass spectral data. The 1H NMR spectra for this compound were (DMSO-D6): δ 13.41 (s, 1H, N-H), 7.88 (d, 2H, Ar-H), and 7.73 (d, 2H, Ar-H). It might be 4-bromo-2-(p-chlorophenyl)5-(trifluoromethyl)-pyrroline-3-carbonitrile. The compound C appeared at Rt ) 6.3 min in the GC-MS chromatogram, and it was also isolated and identified. The major ions in the mass spectra included (m/z, %): 272 (M + 2, 32), 270 (M, 100), 215 (29), 112 (ClC6H5+, 40),77 (C6H5+, 30), 69 (70), and 52 (20); This compound was isolated with preparative TLC, and the structure was determined by comparing 1HNMR analysis with the mass spectral data. The 1HNMR spectra for this compound were (DMSO-D ): δ 12.81 6 (s, 1H, N-H), 7.80 (d, 2H, Ar-H), 7.65 (d, 2H, Ar-H), and 7.30 (s, 1H, pyrrole-H). It might be 2-(p-chlorophenyl)-5(trifluoromethyl)-pyrroline-3-carbonitrile. The compound D appeared at Rt ) 6.8 min in the GC-MS chromatogram was isolated and identified. The major ions in the mass spectra included (m/z, %): 328 (M + 4, 10), 326 (M + 2, 50), 324 (M, 30), 280 (70), 245 (30), 112 (ClC6H5+, 30), and 77 (C6H5+, 40). This compound was isolated with preparative TLC, and the structure was determined by comparing 1HNMR analysis with the mass spectral data. The 1HNMR spectra for this compound were (DMSO-D ): δ 13.22 6 (s, 1H, N-H), 11.83 (s, 1H, COOH), 7.74 (d, 2H, Ar-H), and 7.68 (d, 2H, Ar-H). It might be 4-bromo-2-(p-chlorophenyl)pyrroline-3-carbonitrile-5-carbonic acid. Proposed Photocatalytic Degradation Pathway. Based upon the structure identification of six intermediates and gas chromatograms derived at different irradiation time, a reaction pathway for the photocatalytic degradation of chlorfenapyr was proposed and described in Figure 5. Figure 5 described two possible reaction pathways leading to the degradation of chlorfenapyr. The first step of the photochemical reaction of chlorfenapyr in water was similar to its base hydrolysis reaction. Namely, the aliphatic ether group was cleaved from the molecule to form 4-bromo-2(p-chlorophenyl)-5-(trifluoromethyl)-pyrroline-3-carbonitrile (B) and aliphatic ether. To produce B from chlorfenapyr, the N-C bond of the pyrrole group should be broken. The 3376
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lamp used in the irradiation experiments produced a narrow line at 300-350 nm UV that corresponds to enough energy to cleave the bond; thus, sufficient energy was available in this system to break the bond. Cleavage of the N-C bond formed an aliphatic ether anion and a cation on basic nitrogen in the cleaved pyrrole group. The anion could abstract a proton from the solvent (water) to form the aliphatic ether. The cation could abstract an OH• or O2-, also from water, to form pyrrole-alph-carboxylic acid (D, 4-bromo-2-(p-chlorophenyl)-pyrroline-3- carbonitrile-5-carbonic acid). Pyrrolealph-carboxylic acid was degraded into pyrrole cation and carbon dioxide. Pyrrole cation could also abstract an OH• or O2- from water, and was broken into glycine (E, 4-chlorophenylglycine). The N-C bond of the glycine was cleaved by irradiation and formed carboxylic acid (F, 4-chlorobenzoic acid) and amine. The formation of the gaseous products was a driving force for this reaction. The second step of the photochemical reaction of chlorfenapyr in water was to form chlorfenapyr cation radical by irradiation and debrominated reaction occurred on the chlorfenapyr cation, resulting in the formation of compound 2-(p-chlorophenyl)-1-ethoxymethyl-5-(trifluoromethyl)-pyrroline-3-carbonitrile (A), The compound A hydrolyzed into 2-(p-chlorophenyl)-5-(trifluoromethyl)-pyrroline-3-carbonitrile (C). To produce A and C from chlorfenapyr, the Br-C and N-C bonds of the pyrrole group should be broken. The lamp used in the irradiation experiments produced a narrow line at 300-350 nm UV that corresponds to enough energy to cleave the bonds; thus, sufficient energy was available in this system to break the bonds. Cleavage of the bond formed aliphatic ether anion, hydrobromic acid, and a cation on basic nitrogen in the cleaved pyrrole group. The anion could abstract a proton from the solvent (water) to form the aliphatic ether. The cation could abstract an OH• or O2-, also from water, to form pyrrole-alph-carboxylic acid. Pyrrole-alphcarboxylic acid was degraded to pyrrole cation and carbon dioxide. Pyrrole cation could also abstract an OH• or O2from water, and was broken into glycine. The N-C bond of the glycine was cleaved by irradiation to form carboxylic acid and amine, as described in the first step.
Acknowledgments This work was supported by the National Natural Science Foundation of China (no. 20377029). Major State Basic Research Development Program of China (973 program no. 2004CB18503). We thank Shanghai University for providing the materials.
Literature Cited (1) Papa, E.; Castiglioni, S.; Gramatica, P.; Nikolayenko, V.; Kayumov, O.; Calamari, D. Screening the leaching tendency of pesticides applied in the Amu Darya Basin (Uzbekistan). Water Res. 2004, 38 (16), 3485-3494. (2) Papadopoulou-Mourkidou, E.; Karpouzas, D. G.; Patsias, J.; Kotopoulou, A.; Milothridou, A.; Kintzikoglou, K.; Vlachou, P. The potential of pesticides to contaminate the groundwater resources of the Axios river basin. Part II. Monitoring study in the south part of the basin. Sci. Total Environ. 2004, 321, 147164. (3) Hernando, M. D.; Ejerhoon, M.; Ferna´ndez-Alba, A. R.; Chisti, Y. Combined toxicity effects of MTBE and pesticides measured with Vibrio fischeri and Daphnia magna bioassays. Water Res. 2003, 37 (17), 4091-4098. (4) Hinton, M. H. Infections and intoxications associated with animal feed and forage which may present a hazard to human health. Vet. J. 2000, 159 (2), 124-138. (5) Ollis, D. F.; Pelizzetti, E.; Serpone, N. Photocatalyzed destruction of water contaminants. Environ. Sci. Technol. 1991, 25 (9), 15221529. (6) Gelover, S.; Mondrago´n, P.; Jime´nez, A. Titanium dioxide solgel deposited over glass and its application as a photocatalyst for water decontamination. J. Photochem. Photobiol. A 2004, 165, 241-246.
(7) Tomlin, C. D. S. The Electronic Pesticide Manual, Version 1.0, 11th ed.; Surrey, U. K., Ed.; British Crop Protection Council: Alton, UK, 1999. (8) Low, G. K. C.; Mcevoy, S. R.; Matthews, R. W. Formation of nitrate and ammonium ions in titanium dioxide mediated photocatalytic degradation of organic compounds containing nitrogen atoms. Environ. Sci. Technol. 1991, 25 (3), 460-467. (9) Horikoshi, S.; Serpone, N.; Yoshizawa, S.; Knowland, J.; Hidaka, H. Photocatalyzed degradation of polymers in aqueous semiconductor suspensions: IV Theoretical and experimental examination of the photooxidative mineralization of constituent bases in nucleic acids at titania/water interfaces. J. Photochem. Photobiol. A 1999, 120 (1), 63-74. (10) Herrmann, J. M.; Guillard, C.; Arguello, M.; Agu ¨ era, A.; Tejedor, A.; Piedra, L.; Ferna´ndez-Alba, A. Photocatalytic degradation of pesticide pirimiphos-methyl: Determination of the reaction pathway and identification of intermediate products by various analytical methods. Catal. Today 1999, 54, 353-367. (11) Jaussaud, C.; Paı¨sse´, O.; Faure, R. Photocatalysed degradation of uracil in aqueous titanium dioxide suspensions: mechanisms, pH and cadmium chloride effects. J. Photochem. Photobiol. A 2000, 130, 157-162. (12) Assabane, A.; Ichou, Y. A.; Tahiri, H.; Guillard, C.; Herrmann, J.-M. Photocatalytic degradation of polycarboxylic benzoic acids in UV-irradiated aqueous suspensions of titania.: Identification of intermediates and reaction pathway of the photomineralization of trimellitic acid (1,2,4-benzene tricarboxylic acid). Appl. Catal., B 2000, 24 (2), 71-87. (13) Ezio, P.; Valter, M.; Claudio, M.; Vilma, C.; Maria, L. T.; Edmondo, P.; Orfeo, Z. Photocatalytic degradation of atrazine and other s-triazine herbicides. Environ. Sci. Technol. 1990, 24 (10), 15591565. (14) Horikoshi, S.; Hidaka, H. Photodegradation mechanism of heterocyclic two-nitrogen containing compounds in aqueous TiO2 dispersions by computer simulation. J. Photochem. Photobiol. A 2001, 141, 201-208.
(15) Ollis, D. F.; Hsiao, C.-Y.; Budiman, L.; Lee, C.-L. Heterogeneous photoassisted catalysis: Conversions of perchloroethylene, dichloroethane, chloroacetic acids, and chlorobenzenes. J. Catal. 1984, 88 (1), 89-96. (16) Al-Ekabi, H.; Serpone, N. Kinetics studies in heterogeneous photocatalysis. I. Photocatalytic degradation of chlorinated phenols in aerated aqueous solutions over titania supported on a glass matrix. J. Phys. Chem. 1988, 92 (20), 5726-5731. (17) Andjelka, T.; Do´ra, M.-G.; Ja´nos, C. Photocatalytic oxidation of the fungicide metalaxyl dissolved in water over TiO2. Water Res. 1999, 33 (6), 1371-1376. (18) Moza, P. N.; Hustert, K.; Feicht, E.; Kettrup, A. Photolysis of imidacloprid in aqueous solution. Chemosphere 1998, 36 (3), 497-502. (19) Chu, W.; Wong, C. C. The photocatalytic degradation of dicamba in TiO2 suspensions with the help of hydrogen peroxide by different near UV irradiations. Water Res. 2004, 38 (4), 10371043. (20) Agu ¨ era, A.; Almansa, E.; Tejedor, A.; Ferna´ndez-Alba, A. R.; Malato, S.; Manuel, I. Maldonado photocatalytic pilot scale degradation study of pyrimethanil and of its main degradation products in waters by means of solid-phase extraction followed by gas and liquid chromatography with mass spectrometry detection. Environ. Sci. Technol. 2000, 34 (8), 1563-1571. (21) Fernadez-Alba, A. R.; Aguera, A.; Contreras, M.; Penuela, G.; Ferrer, I.; Barcelo, D. Comparison of various sample handling and analytical procedures for the monitoring of pesticides and metabolites in ground waters. J. Chromatogr. A 1998, 823, 3547.
Received for review October 19, 2005. Revised manuscript received December 26, 2005. Accepted February 27, 2006. ES052073U
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