Degradation of Pentachlorophenol and 2, 4-Dichlorophenol by

Nov 4, 2010 - The mutual promotion of photolysis and laccase-catalysis on removal of dichlorophen from water under simulated sunlight irradiation...
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Environ. Sci. Technol. 2010, 44, 9117–9122

Degradation of Pentachlorophenol and 2,4-Dichlorophenol by Sequential Visible-Light Driven Photocatalysis and Laccase Catalysis LIFENG YIN, ZHENYAO SHEN,* JUNFENG NIU, JING CHEN, AND YANPEI DUAN State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, P. R. China

Received July 27, 2010. Revised manuscript received October 17, 2010. Accepted October 21, 2010.

Chlorophenols (CPs) can be degraded by visible-light driven photocatalysisorlaccasecatalysis.However,previousandpresent studies have shown that neither of the two methods was efficient when being used individually. Low degradation rates were observed for the degradation of pentachlorophenol (PCP) by laccase-catalysis and that of 2,4-dichlorophenol (2,4DCP) by photocatalysis. To remove CPs more completely, a sequentialphotolaccasecatalyticsystemwasdesignedtodegrade PCP and 2,4-DCP mixture in water at the optimal pH value. The results showed that photocatalysis prior to laccase-catalysis (PPL) is a better approach than laccase-catalysis prior to photocatalysis (LPP), eliminating CPs more efficiently and generating lower toxic products. The identified intermediate products consisted of adipic acid, hexanediol, glycol, propylene glycol, hydroquinol, and phthalandione. Based on the products identified, the sequential degradation process was proposed, including the interlace reactions involving quinoid oxidation, reductive dechlorination, and no-enzyme polymerization. Upon reaction optimization, a piston flow reactor (PFR) was designed to treat the continuous feeding of simulated wastewater containing PCP and 2,4-DCP. After a 128 h period of treatment, 87.4-99.5% total concentration of CPs were removed (PPL removed 99.7% PCP and 99.2% 2,4-DCP; LPP removed 95.9% PCP and 78.9% 2,4-DCP).

Introduction Chlorophenols (CPs) including 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP) have been widely used as wood preservative, anticorrosive rust production, fungicides, and pesticides for a long time (1). CPs have strong denaturing effects on organisms such as being irritant to skin and mucous membrane, and being caustic. In addition, previous publications have suggested that CPs are difficult to be degraded by microorganisms and easy to bioaccumulate in human bodies (2, 3). Hence, CPs have been listed as the important priority contaminants with great potential risk to human health in many countries. * Corresponding author phone/fax: +86-10-5880 0398; e-mail: [email protected]. 10.1021/es1025432

 2010 American Chemical Society

Published on Web 11/04/2010

Laccase (EC 1.10.3.2), a multicopper enzyme found in white rot fungi has catalytic activity to dechlorinate and degrade CPs in the presence of oxygen (4). The removal of CPs from wastewater by laccase catalysis has been widely investigated (5-9). However, the degradation efficiency of CPs by laccase catalysis is affected by the substrate specificity of laccase. Although some chlorophenols including 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP, and PCP could be degraded as substrates by laccase-catalysis, there are significant differences among their degradation rates (5, 6, 10, 11). It has been demonstrated that the higher the numbers of chlorine substituents on the phenyl ring, the more difficult the chlorophenol can be degraded, suggesting poor biocompatibility of heavily substituted CPs (12). During the degradation of CPs, another concern is that laccase-catalysis may produce more toxic and/or nonbiodegradable products, even dioxins (13). Clearly, in order to eliminate the parent CPs and their byproducts and thus to remove the toxicities more efficiently and completely, the laccase-catalysis method needs to be modified. One potential alterative is to combine the laccase-catalysis method with other treatment techniques. Photocatalysis, one environmentally friendly water treatment technology, has attracted much attention in recent years. Photocatalysis is a facile method that can remove various organic pollutants including CPs in water (14, 15). Although photocatalysis has been demonstrated to be able to degrade many CPs, this technique still has its limitation. One example is its selectivity (i.e., not all the CPs can be successfully degraded by photocatalytic reaction). Previous studies have shown that the photocatalytic degradation of 2,4-DCP was less efficient compared to that of PCP using TiO2 as the photocatalyst (16). In addition, the efficiency for 2,4-DCP was even lower compared to that of PCP as the concentration of 2,4-DCP increased (17). Photocatalysis has potential to be a good complementation for laccase-catalysis. Actually, some analogous studies have been carried out to improve the degradation efficiency of laccase by assisting with photocatalysis (18, 19). A significant enhancement on the degradation efficiency of trinitrotoluene (TNT) by laccase catalysis was observed by applying a titania-assisted photocatalytic pretreatment under UV light irradiation (18). The decoloration efficiency of immobilized laccase was enhanced by using TiO2 powder as the photocatalyst (19). Nevertheless, investigation on the combination of laccase and visible light driven photocatalyst for the degradation of CPs is rarely reported. In this study, the sequential photolaccase-catalytic treatment for the mixture of 2,4-DCP and PCP in aqueous solution was evaluated. We used a visible light responsive photocatalyst Ti-doped Bi2O3 to conduct the photocatalytic procedure (20). Its catalytic activity for the degradation of CPs has been demonstrated in our previous work (21). In particular, the selected photocatalyst has high activity for degradation of CPs under visible light irradiation and shows great potential of making good use of sunlight. This present study also investigated the different combination of laccase catalysis and photocatalysis to degrade PCP and 2,4-DCP in water. The combined treatment conditions including reaction sequence for sequential treatment, pH value, concentration, and duration time have been studied. Based on these results, the sequential degradation pathways and mechanisms were also proposed.

Experimental Section Reagents and Materials. All chemicals used in the experiments were reagent grade or higher and were used as received VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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without further purification. PCP (98.5%), 2,4-DCP (99.0%), hydrochloric acid, sodium hydroxide, acetic acid, and dipotassium phosphate were obtained from Sinopharm, China. Laccase from Trametes versicolor was supplied by Sigma with activity of 22.6 U/mg. Deionized water was used throughout the experiments. The visible light responsive photocatalyst NTB was prepared via a solvothermal synthesis process. The typical preparation procedure has been addressed in the Supporting Information (SI). Photocatalysis. A single xenon lamp batch photoreactor with a 200 mL vessel was utilized in the heterogeneous photocatalytic process. The reactor vessel consisted of a quartz glass cooling sleeve (250 mm high, 55 mm diameter) sealed at one end and a quartz tube housed inside with an external diameter of 25 mm. The tube was fitted with a xenon lamp (CHF-XM-500W; Trusttech, China) in the reactor center. 1.0 M NaNO2 aqueous solution was used as light filter liquor to screen UV light of λ < 400 nm. The system temperature was controlled by circulating water from a thermostatic water bath (VIVO Itherm-B3; Hamburg, Germany). The initial concentrations of both 2,4-DCP and PCP were both 10 mg/L. The photocatalytic experiments were conducted to evaluate the degradation of CPs and their intermediate products with the concentration range of 0.1-2.0 g/L for the photocatalyst. Prior to irradiation, half an hour of dark adsorption was allowed to establish an adsorptiondesorption balance (control experiments, i.e., without irradiation and without photocatalyst, have been carried out in our previous work (20). Results showed that slight removal was attributed to photolysis and adsorption) and the pH value of the solution was preadjusted to 2.0-10.0 with hydrochloric acid and sodium hydroxide. Continuous stirring (500 rpm) was used throughout the one hour experiments. The sampling interval was 10 min and sampling volume was 1.0 mL. Laccase-Catalysis. The laccase reactor was the same as the photoreactor without xenon lamp. Free laccase catalysis experiments were carried out in the reactor with 5.0-50.0 mg/L laccase in dark. The reaction temperature was controlled at 19-39 °C by a thermostatic water bath. Prior to the experiments, the pH values of the solutions were adjusted to 2.0-10.0 with acetic acid and dipotassium phosphate. The sampling volume, sampling interval time, and stirring speed were the same as those in the photocatalysis process. Both the laccase and the photocatalytic experiments were repeated for three times. Instrument Analysis. The concentrations of CPs in either photolysis or laccase-catalysis reaction were monitored with a high performance liquid chromatography (HPLC; Waters 600, USA) equipped with a Symmetry C18 column. Methanol and 0.1% acetic acid aqueous solution (80:20, volume) were used as the mobilization phase. The UV-vis detector was operating at wavelength of 290 nm. The concentration of total organic carbon (TOC) in the solution was measured with a TOC analyzer (HACH IL550; Loveland, CO). A Finnigan LCQTM DUO ion trap mass spectrometer coupled with the LC was employed to identify the photochemical intermediates. A Symmetry C18 column was used as the LC column. The electrospray ionization (ESI) source was operated in a negative mode. A linear gradient of 0.15% of acetic acid and acetonitrile increased from a ratio of 100:0 to 50:50 at a flow rate of 1.0 mL/min was used to separate CPs and the intermediates. The total analysis time was 35 min. For intermediate products (including low molecular weight acid, alcohol, and aldehyde, etc.) that could not been well measured by LC/MS, a Varian 4000 GC/MS equipped with VF-5 ms column (FactorFour, 30 m × 0.25 mm × 0.25 µm) was used. The column temperature increased from 45 9118

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FIGURE 1. Plug flow reactor (PFR) for combined laccasecatalysis and photocatalysis. to 280 °C linearly. The temperature of sample injector was kept at 120 °C. The products were inferred by MS/MS mode and analyzed by selective ion monitoring (SIM) with their characteristic ions. Toxicity Assessment. A toxicity sensing strain Escherichia coli containing green fluorescent protein (GFP) was constructed to evaluate the toxicity change during the degradation of CPs by photocatalysis and laccase-catalysis (22). The recombinant GFP expression E. coli (JM109, a K strain bacterium that has been modified to minimize recombination and improve the quality of plasmid DNA) was generated by cloning the GFP gene fragment into a kanamycin-resistant plasmid vector (23). E. coli grew in a LB medium at 30 °C for 12-16 h with a shaking rate of 120 rpm. Before application, the E. coli cultures were centrifuged for 5 min at 12 000 rpm, washed three times, and then suspended in a M9 medium (a glucose and mineral salt mixture culture medium for E. coli). A 96-well microliter plate spectrofluorimeter (Tecan Infinite 200; Ma¨nnedorf, Switzerland) was used to monitor the intensity change of the fluorescence on the recombinant E. coli upon exposure to CPs and their products. The CP solution or the resulting reaction solution containing CPs and the intermediate products was added into the 96-well plate spectrofluorimeter for GFP fluorescence measurement. An additional control experiment was conducted without additives. The toxicity changes were determined by the fluorescence intensity of E. coli excited by the irradiation at 488 nm. The emission intensity at λ 520 nm was recorded in the spectrofluorimeter. Plug Flow Reaction. A plug flow reaction (PFR) system was used to conduct the experiments combining both laccase-catalysis and photocatalysis. The detailed reactor layout is shown in Figure 1. To prevent the loss of the catalysts, immobilized laccase and photocatalyst were utilized to perform the entire reaction. The detailed catalyst immobilization procedure is presented in the SI. The PFR reactor was made of polytetrafluorethylene (PTFE, 120 × 250 × 50 mm) with working volume of 500 mL. The reaction space was evenly divided into two chambers, the laccase catalysis chamber and the photocatalysis chamber, each of 250 mL. The photocatalysis chamber was covered with a cutoff filter at 390 nm (SCF-S50-39 L; Sigma Koki, Japan), illuminated by a xenon lamp (CHF-XM-1000W; Trusttech, China) to simulate the sunlight. Five grams of the photocatalyst were laid on a plate in the photocatalysis chamber. The laccase chamber was fitted with an immobilized laccase membrane (100 × 100 mm) supported by a stainless steel stand. In a continuous reaction, the CP solution containing 3.0 mg/L of 2,4-DCP and 5.0 mg/L of PCP was pumped into the two reaction chambers one by one with the flow rate of 1.0 mL/min. Periodically, the solution was sampled from the back of each chamber for analysis. The whole reactor was maintained at 35 ( 2 °C by an aircooling thermostatic apparatus.

Results and Discussion Sequential Treatment of CPs. During the photocatalytic reactions, the reaction rates for 2,4-DCP and PCP were 2.2-5.2 × 10-5 s-1 and 1.6-2.4 × 10-4 s-1 respectively, suggesting a

FIGURE 2. The degradation efficiencies of PCP and 2,4-DCP in different treatment order. distinct PCP selectivity (see SI Figure S3a). On the contrary, the degradation of 2,4-DCP was obviously faster than that of PCP in laccase-catalysis (see SI Figure S3b). The difference might be attributed to fact that the carbocation of PCP is less stable and easier to be reduced by photocatalysis (24) and the high chlorine-substituent made the dechlorination reaction by laccase difficult (9, 25). The complementation of laccase catalysis and photocatalysis can therefore be hypothesized in that visible light photocatalysis was more effective for the degradation of high chlorine substituted phenols such as PCP, whereas laccase catalysis could remove low chlorine substituted phenols efficiently (i.e., 2,4-DCP). Therefore, the combination of laccase and photocatalysis might be suitable for treating CP contaminated water. Based on the kinetics analysis and reaction condition optimization (see the SI), the treatment for a mixture of 2,4DCP and PCP in aqueous solution was designed as a twostep sequential reaction. The CP mixture solution was preadjusted to the optimal pH 4.0 (the best for laccase was obtained on the shortest half-time and highest final removal. The value was slightly lower than that from previous reports (6, 26), which might be due to different source organisms of laccase and buffer surrounding used in our experiments); the optimal doses of laccase (15 mg/L) and photocatalyst (1.0 g/L) were selected to carry out the sequential experiments as well (see the SI). The degradation profiles during the whole reaction are shown in Figure 2. It took 13 h to degrade CPs under the sequences of laccase prior to photocatalysis (LPP) or photocatalysis prior to laccase (PPL). Obviously, the degradation of PCP and 2,4-DCP by photocatalysis was more efficient than that of laccase-catalysis in the first 3 h. However, the degradation rate of 2,4-DCP by laccase-catalysis was higher than that by photocatalysis when the reaction time was extended to 7 h. Besides, the treatment by photocatalysis alone could not remove PCP and 2,4-DCP thoroughly even if the treating time was extended to 13 h. During the next 10 h of the photocatalytic reaction, 2,4-DCP and PCP could only be removed by 4.5% and 6.7%, respectively. Thus, a single catalytic treatment, no matter photocatalysis or laccase-catalysis, could not perform well enough for the complete degradation of CPs. However, the degradation efficiency might be enhanced dramatically by combining the two reactions. A notable removal of CPs was made by the sequential treatments (PPL and LPP) in 13 h. As shown in Figure 2, the PPL treatment is more efficient than the LPP treatment. Almost all of the CPs in the solution could be removed by the PPL sequence. The high efficiency of PPL might result from the pretreatment of photocatalysis that provided biocompatible products for laccase catalysis. These intermediate products were easy to be degraded by laccase catalysis (identification of the products was provided below). Moreover, the reduced

FIGURE 3. The sequential degradation intermediate products and pathway of laccase-catalysis, photocatalysis, and combined reactions. concentrations of 2,4-DCP and PCP were less toxic for laccase, allowing laccase to exhibit higher activity in the degradation of CPs. Sequential Degradation Mechanism and Pathway. The degradation pathways of CPs by visible-light responsive photocatalysis have been proposed in our previous work (20), in which the reductive dechlorination was proposed as the major decomposition route. As shown in Figure 3, the CPs were dechlorinated stepwise (i) into cyclohexanol and cyclohexanone (4), which might be further decomposed into low alcohols, acids and ketones (5). As for laccase-catalysis, the degradation of CPs followed the quinoid oxidation and no-enzyme polymerization pathway that have been described in the literature (6). 2,4-DCP and PCP were oxidized (ii) by laccase-catalysis and transformed into hydroxylated intermediates (6). These intermediates were easy to dechlorinate, forming semiquinones (7) and their dismutated (iii) products, including chlorobenzoquinone and chlorohydroquinone (8). VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 4. Toxicity changes during the photocatalysis, laccase and PPL treatments. Fluorescence (FL) intensity is used to identify the toxicity changes. The weaker the intensity of FL, the more toxic the sample. These semiquinone, chlorobenzoquinone, and chlorohydroquinone could copolymerize or self-polymerize. Some transformed into dioxins and chlorine substituted phenoxyphenol (9). According to the identification of the final products (10, 11, and 12), CPs might undergo at least five reactions: catalytic oxidation, semiquinone dismutation, nonenzyme polymerization, reductive dechlorination, and oxidative ring open reaction. The products formed from photocatalysis might proceed with the laccase-catalysis, and vice versa. However, the products from photocatalysis, including dechlorinated CPs and phenol, were easy to be degraded by laccasecatalysis. In other words, the pretreatment by photocatalysis would improve the biocompatibility of CPs for enzymecatalysis (12, 27). By contrast, the products from laccase reaction, including quinone and hydroquinol, had no advantage in the following degradation by photocatalytic

reaction. This may explain why the degradation efficiency of PPL was better than that of LPP. Change of Toxicity. The toxicity assessment of CPs and its degradation products was carried out on the recombinant GFP expression E. coli. CPs are toxic and their toxicity may change with the treatments by the photocatalytic and laccase reaction due to the formation of intermediates. The toxicity change is difficult to be measured by a model creature that is sensitive to CPs, such as photobacteria and zebrafish (28, 29). Here we employed an E. coli that is insensitive to CPs to monitor new toxins. As shown in Figure 4, E. coli could endure the toxicity of CPs at low concentrations. No colony could be observed in a 5 h culture of the E. coli. Thus, the toxicity changes of the intermediate products could be successfully observed whereas neglecting the toxicity of CPs. In fact, the experiments demonstrated that distinct toxic products for E. coli culture were formed during the single treatment by photocatalysis or laccase-catalysis. After being treated by photocatalysis for 50 min, the toxicity of the solution was reinforced. However, the toxicity was eliminated by further treatment and did not reappear until the end of the degradation. By contrast, the toxicity in the reaction solution by laccase-catalysis was more distinct and longlasting. Even if the toxicity reduced a little in the further reaction, it was maintained at a high level, resulting in ca. 70% loss of GFP expression by E. coli. The results suggested that higher or acuter toxic chemicals (than PCP and 2,4-DCP) were produced and caused the mortality and inhibition of E. coli. It has been reported that dioxin or dibenzofuran could be formed as a byproduct during the photocatalysis and laccase-catalysis (13). In our case, reductive dechlorination, oxidative dechlorination, and polymerization could all occur in the reaction. Generally, the reduced products should be less toxic than CPs. The identified products included adipic acid (LD50, 1900 mg/kg, from RTECS, Registry of toxic effects of chemical substances), hexanediol (20 mL/kg), glycol (10876 mg/kg), propylene glycol (22500 mg/kg), hydroquinol (720 mg/kg), and phthalandione

FIGURE 5. The concentration change of CPs and their TOC by PPL and LPP sequences in PFR for 128 h. 9120

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(1530 mg/kg). They were less toxic than DCP (47 mg/kg) and PCP (27 mg/kg). Hence, the strong toxicant might be produced in an oxidative process rather than a reductive process. As shown in Figure 3, the laccase-catalysis might bring a primary oxidative reaction. Although the sources of toxicity during the laccase-catalysis process have not been clarified, the polymerized CPs, including dioxins, dibenzofurans, and their derivatives (20-120 µg/kg, 1000 times more than CPs), might be the potential contributors. Further experiments on toxicity source clarification are ongoing in our laboratory. Continuous Reaction. Base on the results of batch-type sequential reactions, a plug flow reaction (PFR) system was established to evaluate the long running durability and reliability. Different from the batch-type reaction, the PFR shortened and equalized the retention time of CP feeding in the photocatalysis and laccase-catalysis process. In addition, the catalysts used in PFR were immobilized, stabilized and inactivated partly. Thus, the treatment process and intermediate products might be changed. However, the PPL sequential reaction was always more efficient than the LPP reaction as far as removal rate was concerned. As shown in Figure 5-PPL, the removal rate of CPs was kept at about 99.5% to the end of the 128 h treatment. Furthermore, the PPL are recommended for easy mineralization of CPs (from 2.75 to 0.007 mg/L). The TOC decreased with the transformation of chlorophenols partly owing to the polymerization of products during laccase-catalysis. On the other hand, the mineralization of low molecular weight products brought a nonreversible conversion during the catalytic oxidation process. By contrast, the LPP reaction did not perform very well. Although the removal rate of PCP was satisfactory, only 80% of 2,4-DCP could be removed after the two-step treatment during the whole process. The results coincided with those obtained in the batch-type reactions. Given the immobilization of laccase and photocatalyst, the running efficiency of the PFR system did not decrease significantly in 128 h (the efficiency changes of immobilized laccase are provided in the SI). Although during the latter part of LPP, the activity of immobilized laccase decreased slightly (might be attributed to the high concentrated chlorophenols that damaged the functional activity of laccase 30, 31), the final removal rate was not affected. During the PPL process, the immobilized laccase and photocatalyst did not lose their activity to the end of the reaction. The sequential combining of photocatalysis and laccasecatalysis leads to the efficient removal of chlorophenols and reduces their toxicity in wastewater, which benefits from the products of chlorophenols with enhanced biocompatibility after the photocatalytic process. The sequential process is an interesting and promising technique that has good potential for the application in wastewater treatment. In other respects, the continuous reaction in the PFR system with immobilized catalyst demonstrates the longterm stability of the technique. It can be concluded from the present study that the sequential treatment, especially PPL, is durable and efficient. To some degree, the drawbacks of laccase-catalysis and photocatalysis can be avoided. These results provide scientific basis for the design of pilot-scale PFR for the treatment of CP contaminated wastewater.

Acknowledgments This work was supported by the National Basic Research Program of China (973 Program, 2010CB429003), the National Natural Science Foundation of China (40701166), the National High Technology Research and Development Program (863 Program, 2006AA06Z323), and the Fok Ying-Tong Education Foundation, China (Grant No. 121077).

Supporting Information Available Reagent lists, synthesis procedures, analytical methods, data modeling, and additional experimental results. This material is available free of charge via the Internet at http:// pubs.acs.org.

Literature Cited (1) Pera-Titus, M.; Garcia-Molina, V.; Banos, M. A.; Gimenez, J.; Esplugas, S. Degradation of chlorophenols by means of advanced oxidation processes: A general review. Appl. Catal., B 2004, 47 (4), 219–256. (2) Zhang, X. Y.; Zha, J. M.; Li, W.; Yang, L. H.; Wang, Z. J. Effects of 2,4-dichlorophenol on the expression of vitellogenin and estrogen receptor genes and physiology impairments in chinese rare minnow (Gobiocypris Rarus). Environ. Toxicol. 2008, 23 (6), 694–701. (3) Cooper, G. S.; Jones, S. Pentachlorophenol and cancer risk: Focusing the lens on specific chlorophenols and contaminants. Environ. Health Perspect. 2008, 116 (8), 1001–1008. (4) Murugesan, K.; Chang, Y. Y.; Kim, Y. M.; Jong-Rok, J.; Kim, E. J.; Chang, Y. S. Enhanced transformation of triclosan by laccase in the presence of redox mediators. Water Res. 2010, 44 (1), 298–308. (5) Bhattacharya, S. S.; Karmakar, S.; Banerjee, R. Optimization of laccase mediated biodegradation of 2,4-dichlorophenol using genetic algorithm. Water Res. 2009, 43 (14), 3503–3510. (6) Zhang, J. B.; Liu, X. P.; Xu, Z. Q.; Chen, H.; Yang, Y. X. Degradation of chlorophenols catalyzed by laccase. Int. Biodeterior. Biodegrad. 2008, 61 (4), 351–356. (7) Couto, S. R.; Sanroman, M.; Gubitz, G. M. Influence of redox mediators and metal ions on synthetic acid dye decolourization by crude laccase from Trametes Hirsuta. Chemosphere 2005, 58 (4), 417–422. (8) Bhattacharya, S. S.; Banerjee, R. Laccase mediated biodegradation of 2,4-dichlorophenol using response surface methodology. Chemosphere 2008, 73 (1), 81–85. (9) Bollag, J. M.; Chu, H. L.; Rao, M. A.; Gianfreda, L. Enzymatic oxidative transformation of chlorophenol mixtures. J. Environ. Qual. 2003, 32 (1), 63–69. (10) Leontievsky, A. A.; Myasoedova, N. M.; Baskunov, B. P.; Golovleva, L. A.; Bucke, C.; Evans, C. S. Transformation of 2,4,6trichlorophenol by free and immobilized fungal laccase. Appl. Microbiol. Biot. 2001, 57 (1-2), 85–91. (11) Jeon, J. R.; Murugesan, K.; Kim, Y. M.; Kim, E. J.; Chang, Y. S. Synergistic effect of laccase mediators on pentachlorophenol removal by ganoderma lucidum laccase. Appl. Microbiol. Biotechnol. 2008, 81 (4), 783–790. (12) Gonzalez, L. F.; Sarria, V.; Sanchez, O. F. Degradation of chlorophenols by sequential biological-advanced oxidative process using trametes pubescens and TiO2/UV. Bioresour. Technol. 2010, 101 (10), 3493–3499. (13) Wittsiepe, J.; Kullmann, Y.; Schrey, P.; Selenka, F.; Wilhelm, M. Myeloperoxidase-catalyzed formation of PCDD/F from chlorophenols. Chemosphere 2000, 40 (9-11), 963–968. (14) Gimeno, O.; Carbajo, M.; Lopez, M. J.; Melero, J. A.; Beltran, F.; Rivas, F. J. Photocatalytic promoted oxidation of phenolic mixtures: An insight into the operating and mechanistic aspects. Water Res. 2007, 41 (20), 4672–4684. (15) Yang, S. G.; Fu, H. B.; Sun, C.; Gao, Z. Q. Rapid photocatalytic destruction of pentachlorophenol in F-Si-comodified TiO2 suspensions under microwave irradiation. J. Hazard. Mater. 2009, 161 (2-3), 1281–1287. (16) Robert, D.; Malato, S. Solar photocatalysis: a clean process for water detoxification. Sci. Total Environ. 2002, 291 (1-3), 85–97. (17) Ricotta, A.; Unz, R. F.; Bollag, J. M. Role of a laccase in the degradation of pentachlorophenol. Bull. Environ. Contam. Toxicol. 1996, 57 (4), 560–567. (18) Vohra, M. S.; Tanaka, K. Photocatalytic degradation of nitrotoluene in aqueous TiO2 suspension. Water Res. 2002, 36 (1), 59–64. (19) Peralta-Zamora, P.; Pereira, C. M.; Tiburtius, E. R. L.; Moraes, S. G.; Rosa, M. A.; Minussi, R. C.; Duran, N. Decolorization of reactive dyes by immobilized laccase. Appl. Catal., B 2003, 42 (2), 131–144. (20) Yin, L. F.; Niu, J. F.; Shen, Z. Y.; Chen, J. Mechanism of reductive decomposition of pentachlorophenol by Ti-doped β-Bi2O3 under VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

9121

(21)

(22)

(23)

(24)

(25)

9122

visible light irradiation. Environ. Sci. Technol. 2010, 44 (14), 5581–5586. Yin, L. F.; Niu, J. F.; Shen, Z. Y.; Sun, Y. The electron structure and photocatalytic activity of Ti(IV) doped Bi2O3. Sci. China Chem. 2010, DOI: 10.1007/s11426-010-4008-x. Elvang, A. M.; Westerberg, K.; Jernberg, C.; Jansson, J. K. Use of green fluorescent protein and luciferase biomarkers to monitor survival and activity of arthrobacter chlorophenolicus a6 cells during degradation of 4-chlorophenol in soil. Environ. Microbiol. 2001, 3 (1), 32–42. Hammon, J.; Palanivelu, D. V.; Chen, J.; Patel, C.; Minor, D. L. A green fluorescent protein screen for identification of wellexpressedmembrane proteins from a cohort of extremophilic organisms. Protein Sci. 2009, 18, 121–133. Patel, U. D.; Suresh, S. Dechlorination of chlorophenols using magnesium-palladium bimetallic system. J. Hazard. Mater. 2007, 147 (1-2), 431–438. Wei, D. S.; Houtman, C. J.; Kapich, A. N.; Hunt, C. G.; Cullen, D.; Hammel, K. E. Laccase and its role in production of extracellular reactive oxygen species during wood decay by the brown rot basidiomycete postia placenta. Appl. Environ. Microbiol. 2010, 76 (7), 2091–2097.

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(26) Xu, F. Effects of redox potential and hydroxide inhibition on the pH activity profile of fungal laccases. J. Bio. Chem. 1997, 272 (10), 924–928. (27) Barreto-Rodrigues, M.; Souza, J. V. B.; Silva, E. S.; Silva, F. T.; Paiva, T. C. B. Combined photocatalytic and fungal processes for the treatment of nitrocellulose industry wastewater. J. Hazard. Mater. 2009, 161 (2-3), 1569–1573. (28) Ismailov, A. D.; Pogosyan, S. I.; Mitrofanova, T. I.; Egorov, N. S.; Netrusov, A. I. Bacterial bioluminescence inhibition by chlorophenols. Appl. Biochem. Microbiol. 2000, 36 (4), 404–408. (29) Pavlica, M.; Klobucar, G. I. V.; Vetma, N.; Erben, R.; Papes, D. Detection of micronuclei in haemocytes of zebra mussel and great ramshorn snail exposed to pentachlorophenol. Mutat. Res., Genet. Toxicol. Environ. Mutagen 2000, 465 (1-2), 145– 150. (30) Ahlborg, U. G.; Thunberg, T. M.; Spencer, H. C. Chlorinated phenols: Occurrence, toxicity, metabolism, and environmental impact. Crit. Rev. Toxicol. 1980, 7 (1), 1–35. (31) Geng, F. S.; Wang, X. L.; Tong, J. M.; Liu, H. M. Study of inhibition by pentachlorophenol on human placental alkaline phosphatase. Prog. Biochem. Biophys. 2000, 27 (4), 397–401.

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