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APPLIED CHEMISTRY Comprehensive Study of the Wavelength Effect on Oxidation Processes of 2-Chloroaniline W. Chu,* C. Y. Kwan, K. H. Chan, and C. W. Wu Department of CiVil and Structural Engineering, Research Centre for EnVironmental Technology and Management, The Hong Kong Polytechnic UniVersity, Hunghom, Kowloon, Hong Kong
The objective of this project is to explore the iron-catalyzed oxidation performance of 2-chloroaniline (2-ClA) under different illumination wavelengths. UV irradiations with different wavelengths at 254, 300, 350, 419 nm, corresponding to UVC, UVB, UVA, and UV-visible banding, respectively, are chosen as the light sources. The oxidation of 2-ClA by different iron-catalyzed oxidation processes, with or without the presence of ultraviolet light and oxalate, was investigated and compared. The performance was compared by means of the initial decay rate and the overall removal percentage. To achieve an in-depth understanding, all the feasible combinations and/or blank systems were investigated: UV radiation only, UV/H2O2, H2O2/Fe2+, H2O2/Fe3+, UV/H2O2/Fe2+, UV/H2O2/Fe3+, UV/H2O2/Fe2+/oxalate (Ox), UV/H2O2/Fe3+/Ox. The initial 2-ClA decay rates and the total removal percentages generally followed the order of UV254 > UV300 > UV350 > UV419. Among all tested processes, UV/H2O2/Fe2+ and UV/H2O2/Fe3+/Ox are suggested to be used for the treatment process of 2-ClA, because both processes are very effective in removing 2-ClA in solution over a wide range of wavelengths. Introduction With the increased development of different industries and rapid population growth, environmental contamination has been getting more and more serious in the past few decades. Specially, the vast amount of industrial and domestic wastewater has heightened public awareness of the severe pollution occurring in natural water resources. The contaminants discharged into rivers or seas may cause not only damage to the marine life but also sickness to human beings. It has been a great concern to develop effective and green methods for wastewater treatment in order to control the release of pollutants into the environment. 2-Chloroaniline (2-ClA), a primary aromatic amine, is a chemical intermediate for the production of azo dyes, petroleum and rubber products, pharmaceuticals, and pesticides.1 2-ClA is suspected to be a carcinogenic chemical and is highly toxic to aquatic life.2 A major toxic effect of chloroaniline is the formation of methemoglobin in erythrocytes, resulting from the oxidation of heme iron from the ferrous to the ferric state.3 It enters the environment through improper disposal of textile industrial effluents or the metabolism or degradation of herbicides used in agriculture.4 A high concentration of 2-ClA has been reported in groundwater near a landfill site containing pharmaceutical organic compounds.5 Conventional biological treatment is not an effective means for the removal of chloroaniline as the biodegradation of chloroaniline either does not occur or is very slow.6 Although 2-ClA is rather inert toward conventional biological treatment, it has been shown to be transformed by sunlight even in the winter due to its UV light absorption property7 or by irradiation with a fluorochemical lamp (wavelengths above 300 nm), resulting in a photodegradation half-life of 11.5 h.8 Recently, advanced oxidation * To whom all correspondence should be addressed. Fax: +85223346389. E-mail:
[email protected].
processes (AOPs), which usually involve the combination of a high oxidation-potential source (i.e., H2O2 or O3) or catalysts such as TiO2 with ultraviolet (UV) radiation,9-11 have become a popular alternative for the transformation and mineralization of a great variety of organic compounds. For example, Winarno and Getoff12 found that the synergic effect of γ-rays and ozone leaded to the most efficient degradation of 2-ClA, followed by the treatments of ozonation/UV254 and then by pure ozonation. Ultraviolet radiation can be divided into UVA (wavelengths of 315-400 nm), UVB (280-315 nm), UVC (200-280 nm), and vacuum UV radiation (100-200 nm). The UV disinfection of water is currently used in the drinking water, wastewater, and aquaculture industries.13 In direct photolysis, the organic compound must absorb the incident light and have a reasonable quantum yield of photodissociation, depending on the light absorptivity of that compound at a specific wavelength and intensity of light. Apart from the UV-assisted treatments mentioned before, the iron-catalyzed oxidation (Fenton reaction) is another efficient AOP which produces hydroxyl radicals through the combination of ferrous ions and hydrogen peroxide. The catalytic effect of Fe2+ in degrading various organic compounds by the Fenton process (Fe2+/H2O2) has been shown to be greatly increased under UV254, sunlight,14 or even visible light irradiation.15 In addition, the use of a Fenton-like system (Fe3+/H2O2) with exposure to UV and visible light was reported by Huston and Pignatello16 and Wu et al.,17 respectively. The presence of UV facilitates the photolysis of the aquated ferric ion (Fe(OH)2+) to yield hydroxyl radicals and generate ferrous ions for a Fenton reaction: hV
Fe(OH)2+ 98 Fe2+ + •OH
(1)
Since the aquated ferric ion is limited to illumination wave-
10.1021/ie060141v CCC: $33.50 © 2006 American Chemical Society Published on Web 04/26/2006
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each lamp is around 10-6 einstein L-1 s-1 according to the manufacturer’s information. Figure 1 shows the setup of the UV reactor. Experimental Procedures. The reaction vessel of all the experiments was a 400 mL quartz column. The pH of the mixture was adjusted by either sodium hydroxide or sulfuric acid, if necessary, to a predetermined pH of 3. Stocks solutions of 2-ClA and iron (i.e., Fe2+ or Fe3+) were mixed together in the reaction vessel. For reactions involving iron oxalate, diluted potassium oxalate and iron solutions were premixed first and stirred for at least 45 min in the dark. 2-ClA was added right before the start of the experiment. The dark reactions were normally initiated by adding diluted hydrogen peroxide. After the quartz column was placed inside the UV reactor, the irradiated reactions were initiated by adding diluted hydrogen peroxide and turning on the preheated UV-light source, simutaneously. The mixture was kept stirring during the reaction to ensure its homogeneity. Exactly 1 mL of sample was taken out of the reaction vessel at a prefixed time, and methanol was added for quenching purposes. 2-ClA was quantified by a Waters HPLC equipped with a Restek pinnacle octylamine column. The mobile phase used was 60% acetonitrile and 40% DDW with a flow rate of 1 mL min-1. Figure 1. Setup of the photochemical reactor.
length,16 the addition of oxalate (Ox) to the UV/Fe3+/H2O2 system has been suggested to increase the quantum yield of ferrous production due to the photoreduction of the highly photosensitive ferrioxalate complex.18,19 Likewise, the use of the ferrous oxalate complex was proved to be capable of further improving the photodegradation of 2,4-D by UV/Fe2+/H2O2.20 The information about the degradation of 2-chloroaniline using photoassisted iron-catalyzed oxidation processes is very limited. This study investigates the degradation of 2-ClA involving different iron-catalyzed oxidation processes including H2O2/Fe2+, H2O2/Fe3+, H2O2/Fe2+/Ox, and H2O2/Fe3+/Ox with or without UV irradiation. Given that wavelengths in both the UV and the visible region can be used to accelerate the treatment processes, it is of special interest to examine the degradation of 2-ClA under illumination at different wavelengths. Methodologies Materials. The model compound, o-2-chloroaniline (2-ClA), with a purity greater than 99% was purchased from SigmaAldrich Laborchemikalien GmbH. Iron(II) sulfate-7-hydrate (FeSO4‚7H2O) and ferric sulfate were bought from Riedel-de Haen, while H2O2 (30% solution) and potassium oxalate (K2C2O4‚H2O) were obtained from British Drug Houses. All stock solutions were prepared in deionized distilled water (DDW), and 2-ClA was prepared at 200 ppm (≈1.57 mM). Ferrous sulfate and ferric sulfate solutions were freshly made in diluted sulfuric acid. The solvents, including methanol and acetonitrile, were HPLC (high-performance liquid chromatography) grade and purchased from Lab-Scan. Sodium hydroxide and sulfuric acid were used for pH adjustment. All chemicals were used as received, without further purification. The Fe2+, Fe3+, H2O2, and oxalate solutions were freshly prepared before each experiment. Photochemical Reactor. The photochemical reactor used in this study is the RPR-200 Rayonet equipped with a cooling fan. All experiments involving UV radiation were carried out in this reactor. Two phosphor-coated lamps were placed symmetrically inside the UV reactor. The available wavelengths for the light source were 254, 300, 350, and 419 nm. The light intensity of
Results and Discussion Dark Reaction. Figure 2 shows the effect of the addition of oxalate, with either Fe2+ or Fe3+, on the degradation of 0.2 mM 2-ClA in 1 mM hydrogen peroxide under dark conditions (i.e., no UV involved). It can be seen that sole H2O2 shows insignificant contribution to the decay of 2-ClA. Although hydrogen peroxide is a strong oxidizing agent, it is not effective in oxidizing the refractory organic when it is used alone. In contrast, the use of Fe2+ together with H2O2 resulted in a twostage degradation of 2-ClA, in which a fast initial stage was followed by a slower second stage. The rapid first stage is likely due to the formation of the highly reactive hydroxyl radical (see eq 2) which has a high oxidation potential of 2.8 V.21
Fe2+ + H2O2 f Fe3+ + •OH + OHk ≈ 70 M-1 s-1 (ref 22) (2) Fe2+ + •OH f Fe3+ + OHk ) 3.2 × 108 M-1 s-1 (ref 23) (3) In the second stage, however, most of the Fe2+ was oxidized to Fe3+, leading to a shortage of ferrous catalyst; in addition, the generation of hydroperoxyl radical (see eqs 4-6), which is less reactive than the hydroxyl radial toward organic compounds, may further reduce the rates in the second stage.
Fe3+ + H2O2 T Fe(HO2)2+ + H+ Keq ) 3.1 × 10-3 M-1 s-1 (ref 24) (4) Fe3+ + Fe(HO2)2+ f Fe2+ + •HO2 k ) 2.7 × 10-3 s-1 (ref 25) (5) Fe3+ + •HO2 f Fe2+ + O2 + H+ k ) 1.2 × 106 M-1 s-1 (ref 26) (6) Theoretically, the hydroperoxyl radical may reduce Fe3+ to Fe2+ for the conventional Fenton reaction. However, from an individual test (as shown in Figure 2 as well), only 5% of 2-ClA was transformed by Fe3+/H2O2 after 30 min of reaction,
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Figure 4. Plot of absorbance values of 0.2 mM of 2-ClA and 1 mM of H2O2 against wavelengths.
Figure 2. Transformation of 0.2 mM of 2-ClA by 1 mM H2O2 with or without iron catalysts in the dark. [Fe2+] ) [Fe3+] ) 0.1 mM; [Ox] ) 1.0 mM.
conditions adopted in this study. It makes up more than 70% of the total ferrous ions in the solution.27 This may minimize the concentration of free ferrous ions in the mixture for the conventional Fenton reaction and, consequently, reduce the reaction rate. This also implies that the generation rate of the hydroxyl radical via the following process is slow:
FeIIC2O4 + H2O2 f FeIII(C2O4)+ + •OH + OH-
(7)
Thus, it can be concluded that ferrous oxalate is catalytically less active than Fe2+ toward hydrogen peroxide in the dark processes. Direct Photolysis and the UV/H2O2 Process. The photodegradation of 0.2 mM 2-ClA by direct photolysis and the UV/ H2O2 process at four different wavelengths is illustrated in Figure 3. Under sole exposure to UV254 radiation at 254 nm, about 35% of 2-ClA was transformed in 30 min. When 1 mM of H2O2 was added to the solution, the overall 2-ClA removal was increased to 52%. By comparing with the dark process, a 160-fold improvement on the initial decay rate was observed when solely H2O2 was used. This enhancement is due to the photolysis of hydrogen peroxide at 254 nm which generates hydroxyl radicals per eq 8: hV
H2O2 98 •OH Figure 3. Decay curves of the direct photolysis of 0.2 mM of 2-ClA in the absence or presence of 1 mM H2O2 at four different UV wavelengths.
suggesting that the generation of Fe2+ through eqs 4 and 5 should be minor in this process. Similarly, the ferrioxalate/H2O2 system did not oxidize 2-ClA effectively. Once the ferrioxalate complex is formed, it is rather stable and Fe2+ can only be generated in the presence of UV light; hence, the Fenton reaction could not be initiated without the presence of Fe2+ in the solution initially. However, upon mixing ferrous oxalate with hydrogen peroxide, 2-ClA was transformed rapidly for the first 5 min with a total removal of 18%, and then, the reaction ceased. It is obvious that the reaction of Fe2+ and H2O2 with the addition of oxalate was slower than that without oxalate. Ferrous ions can readily form complexes with oxalate in the form of mono- and bis-oxalate complexes, FeII(C2O4) and FeII(C2O4)22-, and the speciation is dependent on the oxalate concentration and pH value, at which FeII(C2O4) is the predominant species under the
(8)
As the wavelength of the light source increased from 254 to 300 nm, both the reactions were reduced where the total removal of 2-ClA decreased by 12% and 23% in the solely UV300 and the UV/H2O2 system, respectively. It is known that the efficiency of the photolysis of a compound depends on its capacity to absorb incident light. Referring to Figure 4, the absorbance of either 2-ClA or H2O2 at 254 nm is higher than that at UV300 so 2-ClA and H2O2 are both more reactive toward the radiation of UV254. In addition, UV254 has a higher energy than the other studied wavelengths according to Planck’s blackbody theory. Therefore, the transformation of 2-ClA by direct photolysis with or without H2O2 is more efficient using a shorter wavelength. It can further be justified by using two longer wavelengths at 350 and 419 nm. Both 2-ClA and H2O2 show insignificant absorbance at 350 and 419 nm, meaning that 2-ClA and H2O2 were not photosensitive at these two wavelengths. As such, only a few percent of 2-ClA was removed by direct photolysis or/ and the UV/H2O2 system after 30 min of illumination. This suggests that the direct photolysis of 2-ClA is ineffective and
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Figure 5. Comparisons of various treatments of 0.2 mM of 2-ClA under irradiation at (A) 254, (B) 300, (C) 350, and (D) 419 nm. [Fe2+] ) [Fe3+] ) 0.1 mM; [H2O2] ) [Ox] ) 1.0 mM.
can be ignored at 350 and 419 nm. Even though radical oxidation is very powerful, the photolysis of H2O2 at such long wavelengths can generate only negligible amounts of hydroxyl radicals which is not enough to initiate the transformation of 2-ClA. Iron-Catalyzed Systems. To investigate the UV-associated iron-catalyzed systems, 2-ClA was irradiated at 254, 300, 350, and 419 nm with the following alternatives: H2O2/Fe2+, H2O2/ Fe3+, H2O2/Fe2+/Ox, and H2O2/Fe3+/Ox. The results are demonstrated in Figure 5a-d. Comparing with the dark reactions, the involvement of UV light significantly accelerated all the iron-catalyzed systems. At 254 nm, the initial decay rates were increased 4 and 44 times for ferrous and ferric systems without the addition of oxalate, respectively, where almost all the 2-ClA was decayed within 20 min in both reactions. As mentioned
before, direct photolysis and additional radical oxidation are responsible for such photoenhancement. In addition to the conventional Fenton reaction (Fe2+/H2O2) or the Fenton-like reaction (Fe3+/H2O2), the photodecomposition of H2O2 and the photosensitization of aquated Fe3+ ions (i.e., FeOH2+) become the extra sources of hydroxyl radicals in the presence of UV light. For the two ferric-catalyzed systems, photosensitization allows the generation of Fe2+ for the succeeding Fenton reaction; therefore, an improvement in both the decay rate and removal efficiency was found over the respective dark reactions. As expected, the addition of oxalate increased the initial reaction rate of the treatment of 2-ClA by Fe3+/H2O2 upon UV irradiation. This is because the ligand-to-metal electron transfer28 and the high photosensitivity enable the ferrioxalate complex to generate and recycle Fe2+ faster than the aquated Fe3+ ion.
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Figure 6. Absorption spectrua of Fe2+ and Fe3+ before and after the formation of complexes with oxalate at pH ) 3.0. [Fe2+] ) [Fe3+] ) 0.1 mM; [Ox] ) 1.0 mM.
It is known that once the iron-oxalate complexes are formed, the photosensitivity of these iron complexes become higher than those of free iron.29 Figure 6 shows the absorption spectrum of Fe2+ and Fe3+ before and after the formation of complexes with oxalate. This figure justifies that the photosensitivity of the iron species were improved after complexation with oxalate, where the absorbance significantly increased under different UV wavelengths. It is observed that the UV-illuminated H2O2/Fe2+/Ox system shows a much faster decay of 2-ClA compared to that of the dark reaction, but it is slightly slower than the system without oxalate, a result that is inconsistence with our previous study. Kwan and Chu20 have shown that the degradation of 2,4dichlorophenoxyactic acid by the UV/H2O2/Fe2+ process could be enhanced by the addition of oxalate and that UV irradiation is necessary for speeding up the generation of the hydroxyl radical through the reaction between ferrous oxalate and hydrogen peroxide: hV
FeIIC2O4 + H2O2 98 FeIII(C2O4)+ + •OH + OH- (9) However, the controversial results are likely due to the electrophilic characteristic of the hydroxyl radical toward the functional groups of the two substrates, where 2,4-D consists of a anion -OCH2COO- and 2-ClA possesses a cation -NH3+ in the solution. For the effect of changing wavelength, as seen in Figure 5b, the pattern of all the processes irradiated at 300 nm was similar to that of using 254 nm as the light source, but the performance of the former reactions was comparatively lower so that all the curves shifted to the upper-right direction. The initial decay rate of 2-ClA decreased from 0.3822 to 0.3039 and 0.1324 to 0.0582 min-1 in the Fe2+/H2O2/UV and the Fe3+/H2O2/UV systems, respectively, when using UV300. As discussed earlier, the reaction rate of 2-ClA decay by direct photolysis and UV/H2O2 slowed at UV300 as well. When the wavelength increased to 350 and 419 nm, the curves shifted further, indicating that the reaction rates greatly decreased. It was interesting to note, in the Fe3+/H2O2/UV system, that a two-stage degradation comprising a lag phase followed by a faster stage, was observed, as indicated in Figure 5c and d. This lag phase is probably due to the slow initiation of Fe2+ via photosensitization of FeOH2+. Unlike the irradiation
Figure 7. Effect of wavelength on the initial decay constant.
occurring at shorter wavelengths, FeOH2+ has a smaller absorbance and absorbs very little UV350, which decreases the generation of Fe2+ at the beginning of the reaction. After the first 10 mins, the concentration of 2-ClA started to drop faster due to the accumulation of a high Fe2+ concentration in the mixture. The lag phase associated with 419 nm was even longer, and it took 25 min for the second stage to emerge. Comparison of Initial Decay Constants and Overall Removal Capacities. It was verified that the systems by which degradation of 2-ClA occurs include UV only, UV/H2O2, UV/ H2O2/Fe2+, UV/H2O2/Fe3+, UV/H2O2/Fe2+/Ox, and UV/H2O2/ Fe3+/Ox. The overall process can be described by pseudo-firstorder kinetics until the removal of 2-ClA approaches completion. The decay rate constants were calculated based on the first 15 min of degradation to ensure that the trends can be described by pseudo-first-order kinetics. Figure 7 summarizes the decay rate constants under four different wavelengths in the above systems. In general, a downward trend is found for all curves from 254 to 419 nm. It can be seen that direct photolysis and UV/H2O2 are relatively insignificant pathways compared with the UV-assisted iron-catalyzed systems. No matter if oxalate is added or not, the decay constant is higher when Fe2+ is used as the starting material instead of Fe3+. The difference in rate constant should be attributed to the photosensitization of FeOH2+, which is the rate determining step, to give a ferrous ion and the hydroxyl radical. Balmer and Sulzberger28 pointed out that the rate constant of the Fenton reaction is much faster than that of the photosensitization of FeOH2+. Thus, every ferriccatalyzed reaction has to first go through photosensitization in order to generate Fe2+ for the initiation of the Fenton reaction, which produces hydroxyl radicals in a faster rate. This indirect step hinders the initial reaction rate. The fastest decay constant associated with the UV/H2O2/Fe2+ system decreases linearly with the wavelength as well. This could be ascribed to the fact that the longer the wavelength, the lower the light absorption and the quantum yield of the target compound and the photosensitive species (i.e., H2O2 and FeOH2+). The rate of photodecomposition of 2-ClA by using the Fe3+/H2O2/oxalate/ UV system was also found to be dependent on illumination wavelengths. The initial decay constant decreases with increasing wavelength, in which it increases from 0.0269 min-1 at 419 nm to 0.1875 min-1 at 254 nm. The faster oxidation process
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Figure 8. Effect of wavelength on the overall removal of 2-ClA.
under irradiation of wavelength 254 nm arises mainly from the stronger light absorbance of ferrioxalate complexes comparing to those at 300, 350, and 419 nm, in addition to direct photolysis and the H2O2/UV process. The initial decay rate of 2-ClA by Fe2+/H2O2/oxalate/UV is also found to decrease when the illumination wavelength was increased from 254 to 419 nm. Figure 8 summarizes the overall removal percentages of 2-ClA after 30 min of irradiation at 254, 300, 350, and 419 nm with the above six treatment methods. For direct photolysis and UV/H2O2, the overall 2-ClA removal decreased sharply from 35 and 52% to 3 and 6%, respectively, as the illumination wavelength increased from 254 to 350 nm. The reactions were inactive when 419 nm was used as the light source. For the ferric-catalyzed systems, over 93% 2-ClA was transformed at wavelengths 254, 300, and 350 nm but only 19 and 46% 2-CLA could be removed without and with the addition of oxalate, respectively, as the wavelength increased to 419 nm. The major reason for the difference could be attributed to the photosensitive characteristics of the ferrioxalate complexes, in which the absorbance of ferrioxalate complexes covers a wider range and is higher than that of Fe3+ over the range 220-420 nm, so the photosensitivity of FeOH2+ is more wavelength limited. Hence, the rate of photodecomposition of ferrioxalate would be faster in generating Fe2+ for a higher degradation rate of the organic compounds. On the basis of the comparison of the initial decay constants and the overall removal capacities, it can be concluded that the addition of oxalate imposes a positive photoeffect to the ferric-catalyzed reaction and the corresponding improvement becomes more significant as the illumination wavelength get longer. In the ferrous-catalyzed cases, almost all of the 2-ClA was degraded at all four wavelengths except the one illuminated at 419 nm with oxalate, i.e., 33% of 2-ClA remained. Although the degradation was slightly hindered in the presence of oxalate, the overall removal of 2-ClA percentages were same as those without the oxalate upon UV irradiation at or below 300 nm. Among all the studied treatment methods, only the removal capacity of the UV/H2O2/Fe2+ process is independent of wavelength. Conclusions Under dark conditions, the sole use of hydrogen peroxide or a Fenton-like reagent (i.e., H2O2/Fe3+) for the transformation
of 2-ClA was found to be inefficient. Although the conventional Fenton reaction (i.e., H2O2/Fe2+) showed a fast initial decay, it slowed quickly at the latter stage due to limited transfer of Fe3+ to Fe2+. The presence of UV was found to be capable of enhancing all of the above treatment processes. The performances of the iron-catalyzed photooxidation processes (UV/ H2O2/Fe2+ and UV/H2O2/Fe3+), with or without the addition of oxalate, were found to be wavelength dependent. Hence, the reaction rate of different UV-assisted iron-catalyzed oxidation processes followed the order: UV254 > UV300 > UV350 > UV419. Besides, the overall removal percentage of 2-ClA of most of the mentioned systems decreased with increasing illumination wavelength, except the reaction using ferrous as the starting material (wavelength independent). More than 99% of 2-ClA was removed by UV/H2O2/Fe2+ at all tested wavelengths. However, when oxalate was added to this process, an adverse effect in the reaction rate was observed. It suggests that when ferrous is used as a starting material in treating 2-ClA, using an oxalate solution should be avoided. When ferric ions were used as the starting material (UV/ H2O2/Fe3+), the initial decay rate of 2-ClA was found to be slower than that using ferrous ions. The reaction was greatly retarded when the wavelength was over 350 nm, but the reaction rate was significantly improved in the presence of oxalate at all wavelengths used in this study. Therefore, if ferric is used as the starting material, oxalate is suggested to be added to achieve a higher oxidation performance. Acknowledgment The work described in this paper was supported by a grant from the University Research Fund of the Hong Kong Polytechnic University. Literature Cited (1) IARC. Some aromatic amines, anhraquinones, and nitroso compounds, and inorganic fluorides used in drinking water and dental preparations. Monogr. EVal. Carcinogenic Risk Chem. Humans 1982, 27, 39-61. (2) Yane, L.; Fein, J. B. Experimental study of mineral surface and aqueous aluminum complexation with aniline and 2-chloroaniline. Geochim. Cosmochim. Acta 1998, 62, 2077-2085. (3) Chhabra, R. S.; Thompson, M.; Elwell, M. R.; Gerken, D. K. Toxicity of p-chloroanilines in rats and mice. Food Chem. Toxicol. 1990, 28, 717722. (4) Hargesheimer, E. E.; Coutts, R. T.; Pasutto, F. M. Gas-liquid chromatographic determination of aniline metabolites of substituted urea and carbonate herbicides in aqueous solution. J.sAssoc. Off. Anal. Chem. 1981, 64, 833-840. (5) Holm, J. V.; Ru¨gge, K.; Bjerg, P. L.; Christensen, T. H. Occurrence and distribution of pharmaceutical organic compounds in the groundwater down gradient of a landfill (Grindsted, Denmark). EnViron. Sci. Technol. 1995, 29, 1415-1420. (6) Howard, P. H. Handbook of EnVironmental Fate and Exposure Data for Organic Chemicals. Vol. I. Large Production and Priority Pollutants; Lewis Publishers: New York, 1991. (7) Othmen, K.; Boule, P. Phototransformation of 2,6-dichloroaniline in aqueous solution. J. Photochem. Photobiol. A 1999, 121, 119-123. (8) Kondo, M. Simulation Studies of Degradation of Chemicals in the EnVironment; Office of Health Studies Environ Agency: Tokyo, Japan, 1978. (9) Brillas, E.; Cabot, P. L.; Rodriguez, R. A.; Arias, C.; Garrido, J. A.; Oliver, R. Degradation of the herbicide 2,4-DP by catalyzed ozonation using the O3/Fe2+/UVA system. Appl. Catal. B 2004, 51, 117-127. (10) Aleboyeh, A.; Moussa, Y.; Aleboyeh, H. The effect of operational parameters on UV/H2O2 decolourisation of Acid Blue 74. Dyes Pigm. 2005, 66, 129-134. (11) Willian, C.; Peterlini, W. C.; Pupo, F.; Nogueira, R. F. P. Multivariate analysis of photo-Fenton degradation of the herbicides tebuthiuron, diuron and 2,4-D. Chemosphere 2005, 58, 1107-1116.
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(22) Rigg, T.; Taylor, W.; Weiss, J. The rate constant of the reaction between hydrogen peroxide and ferrous ions. J. Chem. Phys. 1954, 22, 575577. (23) Buton, G. V.; Greenstock, C. L. Critical review of rate constants for reactions of hydrated electrons. J. Phys. Chem. Ref. Data 1988, 17, 513-886. (24) Gallard, H.; De Laat, J.; Legube, B. Spectrophotometric study of the formation of iron (III)-hydroperoxy complexes in homogeneous aqueous solution. Water Res. 1999, 33, 2029-2036. (25) De Laat, J.; Gallard, H. Catalytic decomposition of hydrogen peroxide by Fe(III) in homogeneous aqueous solution: mechanism and kinetic modeling. EnViron. Sci. Technol. 1999, 33, 2726-2732. (26) Bielski, B. H. J.; Cabelli, D. E.; Arudi, R. L. Reactivity of H2O2/ O2- radicals in aqueous solution. J. Phys. Chem. Ref. Data 1985, 14, 10411100. (27) Park, S. B.; Wood, P. M.; Davies, M. J.; Gilbert, B. C.; Whitwood, A. C. A kinetic and ESR investigation of iron(II) oxalate oxidation by hydrogen peroxide and dioxygen as a source of hydroxyl radicals. Free Radical Res. 1997, 27, 447-458. (28) Balmer, M.; Sulzberger, B. Atrazine degradation in irradiated iron/ oxalate systems: effects of pH and oxalate. EnVrion. Sci. Technol. 1999, 33, 2418-2424. (29) Zhou, D.; Wu, F.; Deng, N. S. Fe(III)-oxalate complexes induced photooxidation of diethylstilbestrol in water. Chemosphere 2004, 57, 283291.
ReceiVed for reView February 3, 2006 ReVised manuscript receiVed March 23, 2006 Accepted March 23, 2006 IE060141V
