Reinvestigation of the Role of Humic Acid in the Oxidation of Phenols

Nov 18, 2013 - Humic acid (HA) affects the oxidation of phenolic compounds by permanganate, but the role of HA in the oxidation of phenols by permanga...
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Reinvestigation of the Role of Humic Acid in the Oxidation of Phenols by Permanganate Bo Sun,†,‡ Jing Zhang,‡ Juanshan Du,‡ Junlian Qiao,† and Xiaohong Guan*,† †

State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 20092, P. R. China ‡ State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, P. R. China S Supporting Information *

ABSTRACT: Humic acid (HA) affects the oxidation of phenolic compounds by permanganate, but the role of HA in the oxidation of phenols by permanganate is far from clear. The mechanisms by which HA influences the oxidation of phenols by permanganate at pH 5.0−9.0 were systematically examined in this study. The presence of HA enhanced the oxidation of phenolic compounds by permanganate at pH ≤7.0, with greater enhancement at lower pH values. The presence of HA facilitated the in situ formation of MnO2, implying the importance of reductive moieties of HA in this reaction. This was supported by the finding that HA preoxidized by ozone showed enhancements in the oxidation of phenols by permanganate at pH 5.0−6.0 smaller than those seen with pristine HA. The good correlation between HA-induced improvement in the oxidation rates of phenols by permanganate and those by preformed colloidal MnO2 at pH 5.0 confirmed that contribution of MnO2 formed in situ for the oxidation of phenols under this condition. The differences in the influence of Na2S2O3 and HA on the oxidation of phenol by permanganate revealed the fact that the continuous generation of fresh MnO2 and stabilization of the MnO2 formed in situ by HA were crucial for the HA-induced enhancement of the oxidation of phenols by permanganate at pH ≤7.0. The consumption of permanganate by HA and the poor oxidation ability of in situ-generated MnO2 under alkaline conditions resulted in the slightly negative effect of HA on the degradation rates of phenols by permanganate at pH >7.0.

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INTRODUCTION Many phenolic compounds such as phenol, 2-chlorophenol (2CP), 2,4-dichlorophenol (2,4-DCP), and trichlorophenol are potentially harmful to organisms1 and human health and thus have been designated priority pollutants by the U.S. Environmental Protection Agency (EPA) since 1979.2 Recently, the increasingly frequent occurrence of some endocrine-disrupting chemicals (EDCs) in the aquatic environment reported in various studies3−5 has also raised concerns about their adverse effects on aquatic ecology and risks to human health.6 Many EDCs containing a phenolic moiety, such as bisphenol A (BPA), triclosan (TCS), estrone (E1), 17β-estradiol (E2), estriol (E3), 2,4-DCP, and 4-n-nonylphenol (4-n-NP), have been detected in surface water.4,7 Various chemical oxidants, such as free chlorine,8 chlorine dioxide,9 ozone,10 Fenton reagent,11 ferrate,12 sulfate radicals,13−15 and permanganate,1 can be applied in removing phenols in drinking water and wastewater treatment. Among these oxidants employed to degrade the aqueous phenols, permanganate as a green oxidant16 is preferred for its venerable virtues of easy handling, relatively low cost, effectiveness, comparative stability over a wide pH range, and no formation of chlorinated or brominated byproducts during its application.17,18 Permanganate was reported to be effective for © 2013 American Chemical Society

degrading various phenolic compounds (BPA, TCS, E1, E2, E3, 2,4-DCP, etc.)19−22 and other emerging contaminants (ciprofloxacin, lincomycin, and carbamazepine).23 Surprisingly, compared to the oxidation kinetics obtained in synthetic water under the same condition, tap water, filtered natural water, and wastewater accelerated the oxidation of BPA, TCS, and estrone by permanganate, although they had natural permanganate demand.19,24,25 Humic substances (HS) are ubiquitous in natural waters, and their presence may cause the gap between the oxidation behavior of phenolic compounds in pure water and that in natural waters. Therefore, we investigated the influence of humic acid (HA), one major fraction of HS, on the oxidation of phenol by permanganate and found that the oxidation of phenol by permanganate could be enhanced by the presence of HA at pH 4.0−8.0. The oxidation of phenol was accelerated by the highnominal molecular weight (NMW) fractions of HA at pH 7.0 to a greater extent than by the low-NMW fractions of HA.17 Further study was conducted to show that the influence of HAs Received: Revised: Accepted: Published: 14332

April 4, 2013 November 14, 2013 November 18, 2013 November 18, 2013 dx.doi.org/10.1021/es404138s | Environ. Sci. Technol. 2013, 47, 14332−14340

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(99% pure) were purchased from Acros. HA (industry pure) was obtained from Sigma-Aldrich and purified by repeated pH adjustment, precipitation, and centrifugation to remove ash, humin, and fulvic acid, completely following the procedure described by Kilduff and Weber.32 The KMnO4 crystals and purified HA were dissolved in Milli-Q water to make 50 mM and 2.06 g/L (as DOC) stock solutions, respectively. The stock solutions of phenols (5 mM) were freshly prepared for each set of experiments by dissolving a measured quantity of phenols in Milli-Q water to avoid air oxidation and volatilization. The stock solution of sodium thiosulfate (0.2 M) as a scavenger/ reductant of oxidants was prepared in Milli-Q water. Methanol (HPLC grade) and formic acid (GR grade) were purchased from Merck (Darmstadt, Germany) for the chemical analysis. A stable colloidal MnO2 stock solution was prepared following the procedure described by Perez-Benito et al.33 In brief, a mixture of 20 mL of KMnO4 (50 mM) and 1.875 mL of Na2S2O3 (0.2 M) was diluted to 1 L with doubly distilled water, which was gently mixed to homogenize the solution. Then a dark-brown solution was obtained, remaining transparent and stable for several months. The reaction that took place under these conditions could be described by eq 1:

of different origins on the oxidation of phenol and 2-CP by permanganate at pH 7.0 was strongly dependent on HAorigin.1 Jiang et al.19,20 also reported that the presence of HA can improve the oxidation of TCS by permanganate at pH 5.0−7.0 and the oxidation of BPA by permanganate at pH 9.0.22 HA enhanced the oxidation of phenols by permanganate at pH ≤7.0, and the enhancement was greater at lower pH values. In addition, the HA-induced improvement in the oxidation of phenols by permanganate was strongly dependent on the amount and position of chlorine substituents on the aromatic ring. Shao et al.25 also reported that the promotive effects of HA on the oxidation of phenolic EDCs by permanganate were dependent on the structure of EDCs, consistent with our observations. Figure 1 also reveals that the presence of HA slightly decreased the oxidation rate constants of phenols at pH ≥8.0, indicating that HA played a role under

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RESULTS AND DISCUSSION Influence of HA on the Oxidation of Phenols. A previous study1 showed that the kinetics of oxidation of phenols by permanganate followed a generalized second-order rate law. When the concentration of permanganate is present in 10-fold excess, the oxidation rate of phenols can be simplified to eq 2. 14334

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Figure 2. Variation of UV−vis spectra during the course of the reactions (a) between KMnO4 and phenol, (b) between KMnO4 and phenol in the presence of HA, and (c) between KMnO4 and phenol in the presence of Na2S2O3 (10 μM). Reaction conditions: [phenol]0 = 5 μM, [KMnO4]0 = 50 μM, and [HA]0 = 1.0 mg/L as DOC.

Figure 3. (a) Influence of HA or preoxidized HA on the oxidation of phenol by KMnO4 at pH 5.0 and 6.0. [HA]0 = 1.0 mg/L as DOC (without preoxidation). (b) Influence of Na2S2O3 applied at different modes on the oxidation of phenol by permanganate at pH 6.0. The kinetics of oxidation of phenol by permanganate in the absence or presence of HA is also present in this figure as a reference. Reaction conditions: [phenol]0 = 5 μM, and [KMnO4]0 = 50 μM.

conclude that HA played a role in the oxidation of phenolic compounds by permanganate different from that of other ligands like pyrophosphate and EDTA. The influence of the pristine HA and HA preoxidized by ozone on the oxidation kinetics of phenol by permanganate at pH 5.0−6.0 was compared, as shown in Figure 3a. Obviously, the promotive effects of HA were weakened after preoxidation by ozone, confirming that the oxidizable moieties in HA were crucial for the influence of HA on the oxidation of phenols by permanganate. Furthermore, the rate of phenol removal by permanganate in the presence of ozone-treated HA was still faster than that in the absence of HA, ascribed to the incomplete elimination of the electron donating capacity of HA.35 Because ozonation of HA could result in a decrease in the molecular weight and aromaticity but an increase in the levels of carboxylic acids and ketones and the O/C ratio in HA,36 the weakening of the promotive effects of HA after preozonation agreed well with the results reported in our previous studies.1,17 Interaction of Phenol with Preformed MnO2. Following the practice of Jiang et al.,19 we also employed ex situ-prepared

alkaline conditions different from that under acidic and/or neutral conditions. The Reductive Property of HA Promotes the Formation of MnO2 in the Oxidation of Phenol by Permanganate. Panels a and b of Figure 2 show the online scanning of UV−vis spectra at 250−800 nm (where phenol and its oxidation products do not absorb) during the course of reactions between permanganate and phenol over the pH range of 5.0−9.0 in the absence or presence of HA. The nonspecific absorbance at 4000 Da, as shown in Figure S6 of the Supporting Information. Šmejkalová et al.47 stated that phenols could interact with HA, and the level of binding increased with an increasing fraction of the undissociated form of phenols in solution. Thus, the acceleration of the oxidation of phenol by permanganate in the initial stage of the reaction at pH ≤7.0 due to the HA−phenol interaction may exist but be masked by the strong reactivity of MnO2 formed in situ. Because the pKa of phenol is 9.99, 90.7% of phenol is undissociated at pH 9.0. The influence of HA on the oxidation of 2,6-DCP, which is completely dissociated at pH 9.0 (pKa = 6.78), by permanganate at pH 9.0 was further examined, as shown in Figure S7 of the Supporting Information. Obviously, the presence of HA at concentrations of up to 10 mg/L did not accelerate the oxidation of 2,6-DCP by permanganate at pH 9.0 in the initial reaction stage, further

suggesting the similar mechanisms of oxidation of phenols by permanganate and MnO2. Figure 5b reveals that the influence of chlorine substituents on the susceptibility of the oxidation of phenols by permanganate and MnO2 generally follows this sequence: Cl at the ortho position ≫ Cl at the para position > Cl at the meta position. All phenols employed in this study are almost undissociated at pH 5.0 because the smallest pKa of those of these phenolic compounds is 5.99 (2,4,6-TCP). Thus, intramolecular hydrogen bonding exists in the phenols with chlorine substituents at the ortho position. Zhang et al.44 demonstrated that the intramolecular hydrogen bonding plays a decisive role in determining the reactivity of the O−H bonds for ortho-substituted phenols. The lengths of the hydrogen bonds vary from 2.342 to 2.408 Å, generally increasing with the increase in the amount of ortho-substituted chlorines.46 As a result, the intramolecular hydrogen bond shifts the redox potential of the phenols to lower potentials and facilitates the oxidation of phenols. Therefore, the rates of oxidation of phenols by permanganate and MnO2 increase with an increase in the amount of ortho-substituted chlorines like 2,4-DPC and 2,4,6-TCP at pH 5.0. The phenoxy radical could be generated in the initial step of the oxidation of phenols by an eletrophilic attack on the phenolic group, and then the phenoxy radical was quickly consumed by subsequent oxidation reactions.31,45 Ring substituents that stabilize phenoxy radicals accelerate the reaction because the transition-state structure bears more resemblance to the product.31 All chlorine substituents are σelectron acceptors that decrease the stability of the phenoxy radical by decreasing the electron density in the aromatic ring. Chlorine substituents in ortho and para positions are π-electron donors, which provide electron density and stabilize the phenoxy radical by resonance interaction. Thus, the phenols with chlorine at the para position are more susceptible to being oxidized by permanganate and MnO2 than those with chlorine at the meta position. Consequently, HA enhances the oxidation of phenols with ortho-substituted chlorines by permanganate more significantly than that of phenols with meta-substituted chlorines. Role of HA in the Oxidation of Phenols by Permanganate under Alkaline Conditions. A close inspection of the influence of HA (1.0 mg/L as DOC) on the kinetics of oxidation of phenol by permanganate at pH 8.0− 9.0 revealed that the presence of HA increased the initial rate of 14338

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(3) Ternes, T. A. Occurrence of drugs in German sewage treatment plants and rivers. Water Res. 1998, 32 (11), 3245−3260. (4) Kolpin, D.; Furlong, E.; Meyer, M.; Thurman, E. M.; Zaugg, S.; Barber, L.; Buxton, H. Pharmaceuticals, hormones, and other organic wastewater contaminants in US streams, 1999−2000: A national reconnaissance. Environ. Sci. Technol. 2002, 36 (6), 1202−1211. (5) Heberer, T. Occurrence, fate, and removal of pharmaceutical residues in the aquatic environment: A review of recent research data. Toxicol. Lett. 2002, 131 (1), 5−17. (6) Pickering, A. D.; Sumpter, J. P. Peer Reviewed: Comprehending endocrine disruptors in aquatic environments. Environ. Sci. Technol. 2003, 37 (17), 331−336. (7) Kuch, H. M.; Ballschmiter, K. Determination of endocrinedisrupting phenolic compounds and estrogens in surface and drinking water by HRGC-(NCI)-MS in the picogram per liter range. Environ. Sci. Technol. 2001, 35 (15), 3201−3206. (8) Deborde, M.; von Gunten, U. Reactions of chlorine with inorganic and organic compounds during water treatmentkinetics and mechanisms: A critical review. Water Res. 2008, 42 (1), 13−51. (9) Hoigné, J.; Bader, H. Kinetics of reactions of chlorine dioxide (OClO) in waterI. Rate constants for inorganic and organic compounds. Water Res. 1994, 28 (1), 45−55. (10) Gimeno, O.; Carbajo, M.; Beltrán, F. J.; Rivas, F. J. Phenol and substituted phenols AOPs remediation. J. Hazard. Mater. 2005, 119 (1), 99−108. (11) Georgi, A.; Schierz, A.; Trommler, U.; Horwitz, C.; Collins, T.; Kopinke, F.-D. Humic acid modified Fenton reagent for enhancement of the working pH range. Appl. Catal., B 2007, 72 (1), 26−36. (12) Jiang, J.-Q.; Lloyd, B. Progress in the development and use of ferrate (VI) salt as an oxidant and coagulant for water and wastewater treatment. Water Res. 2002, 36 (6), 1397−1408. (13) Anipsitakis, G. P.; Dionysiou, D. D. Degradation of organic contaminants in water with sulfate radicals generated by the conjunction of peroxymonosulfate with cobalt. Environ. Sci. Technol. 2003, 37 (20), 4790−4797. (14) Saputra, E.; Muhammad, S.; Sun, H.; Patel, A.; Shukla, P.; Zhu, Z.; Wang, S. α-MnO2 Activation of Peroxymonosulfate for Catalytic Phenol Degradation in Aqueous Solutions. Catal. Commun. 2012, 26, 144−148. (15) Liang, H.; Sun, H.; Patel, A.; Shukla, P.; Zhu, Z.; Wang, S. Excellent performance of mesoporous Co3O4/MnO2 nanoparticles in heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions. Appl. Catal., B 2012, 127, 330−335. (16) Singh, N.; Lee, D. G. Permanganate: A green and versatile industrial oxidant. Org. Process Res. Dev. 2001, 5 (6), 599−603. (17) He, D.; Guan, X.; Ma, J.; Yu, M. Influence of different nominal molecular weight fractions of humic acids on phenol oxidation by permanganate. Environ. Sci. Technol. 2009, 43 (21), 8332−8337. (18) Rodríguez, E.; Majado, M. E.; Meriluoto, J.; Acero, J. L. Oxidation of microcystins by permanganate: Reaction kinetics and implications for water treatment. Water Res. 2007, 41 (1), 102−110. (19) Jiang, J.; Pang, S. Y.; Ma, J. Oxidation of triclosan by permanganate (Mn(VII)): Importance of ligands and in situ formed manganese oxides. Environ. Sci. Technol. 2009, 43 (21), 8326−8331. (20) Jiang, J.; Pang, S. Y.; Ma, J. Role of ligands in permanganate oxidation of organics. Environ. Sci. Technol. 2010, 44 (11), 4270−4275. (21) Jiang, J.; Pang, S. Y.; Ma, J.; Liu, H. Oxidation of Phenolic Endocrine Disrupting Chemicals by Potassium Permanganate in Synthetic and Real Waters. Environ. Sci. Technol. 2012, 46 (3), 1774− 1781. (22) Du, J.; Sun, B.; Zhang, J.; Guan, X. Parabola-Like Shaped pHRate Profile for Phenols Oxidation by Aqueous Permanganate. Environ. Sci. Technol. 2012, 46 (16), 8860−8867. (23) Hu, L.; Martin, H. M.; Arce-Bulted, O.; Sugihara, M. N.; Keating, K. A.; Strathmann, T. J. Oxidation of carbamazepine by Mn(VII) and Fe(VI): Reaction kinetics and mechanism. Environ. Sci. Technol. 2009, 43 (2), 509−515.

confirming that the interaction between HA and undissociated phenols contributes to the acceleration of the oxidation of phenols by permanganate in the initial stage under alkaline conditions. Environmental Implications. This study showed that the influence of HA on the oxidation of phenols by permanganate was ascribed primarily to the reductive properties of HA, which enhanced the in situ generation of MnO2, and it was more reactive toward phenols at pH ≤7.0 but less reactive at pH >7.0 and second to the complexing ability of HA, which could stabilize the formed MnO2 and inhibit its precipitation. Furthermore, HA could combine with the undissociated phenols and enhance the density of the electron cloud of phenol, which could result in the enhancement of the oxidation of phenol by permanganate at the initial stage of the reaction. The results of this study indicated that the influence of HA on the oxidation of phenols by permanganate was strongly related to the reductive and complexing property of HA, which should be considered in water treatment when employing permanganate to remove phenolic contaminants. Clarifying the role of HA in the oxidation of phenols by permanganate is also beneficial to the development of the HA-enhanced permanganate oxidation process for the removal of phenolic contaminants, especially under acidic conditions. Methyl-, methoxy-, chloro-, and nitro-substituted phenols have been identified in rainwater in the range of micrograms per liter,38 and the pH of today’s rainwater is generally in the range of 5.5−6.0. Thus, combining permanganate and a trace amount of high-molecular mass HA fractions would be a favorite method of removing phenols from rainwater. The results of this study also elucidated the importance of MnO2 formed in situ in permanganate oxidation as an oxidant under acidic conditions. Great efforts will be taken to clarify the properties and structures of MnO2 formed in situ in the future.

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ASSOCIATED CONTENT

S Supporting Information *

One text and seven figures. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +86-21-65980956; fax: +86-21-65986313; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Foundation of the State Key Laboratory of Pollution Control and Resource Reuse (PCRRY11001), the Shanghai Rising-Star Program (12QA1403500), and the National Natural Science Foundation of China (21077029). We thank the anonymous reviewers and the editor for their valuable comments and suggestions to improve the quality of this paper.

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REFERENCES

(1) He, D.; Guan, X.; Ma, J.; Yang, X.; Cui, C. Influence of humic acids of different origins on oxidation of phenol and chlorophenols by permanganate. J. Hazard. Mater. 2010, 182 (1), 681−688. (2) Keith, L.; Telliard, W. ES&T special report: Priority pollutants: Ia perspective view. Environ. Sci. Technol. 1979, 13 (4), 416−423. 14339

dx.doi.org/10.1021/es404138s | Environ. Sci. Technol. 2013, 47, 14332−14340

Environmental Science & Technology

Article

(24) Yang, J. J. Determination of trace permanganate and oxidation of bisphenol A by permanganate. M.S. Dissertation, Harbin Insitute of Technology, Harbin, China, 2008, pp 32−35. (25) Shao, X. L.; Jun, M.; Yang, J. J.; Li, X. C.; Gang, W. Effect of humic acid on the oxidation of phenolic endocrine disrupting chemicals by permanganate. J. Water Supply: Res. Technol.AQUA 2010, 59 (5), 324−334. (26) Peretyazhko, T.; Sposito, G. Reducing capacity of terrestrial humic acids. Geoderma 2006, 137 (1), 140−146. (27) Matthiessen, A. Determining the redox capacity of humic substances as a function of pH. Vom Wasser 1995, 84, 229−235. (28) Aeschbacher, M.; Graf, C.; Schwarzenbach, R. P.; Sander, M. Antioxidant properties of humic substances. Environ. Sci. Technol. 2012, 46 (9), 4916−4925. (29) Xu, L.; Xu, C.; Zhao, M.; Qiu, Y.; Sheng, G. D. Oxidative removal of aqueous steroid estrogens by manganese oxides. Water Res. 2008, 42 (20), 5038−5044. (30) Lin, K.; Liu, W.; Gan, J. Oxidative removal of bisphenol A by manganese dioxide: Efficacy, products, and pathways. Environ. Sci. Technol. 2009, 43 (10), 3860−3864. (31) Ulrich, H. J.; Stone, A. T. The oxidation of chlorophenols adsorbed to manganese oxide surfaces. Environ. Sci. Technol. 1989, 23 (4), 421−428. (32) Kilduff, J.; Weber, W. J., Jr. Transport and separation of organic macromolecules in ultrafiltration processes. Environ. Sci. Technol. 1992, 26 (3), 569−577. (33) Perez-Benito, J. F.; Arias, C.; Amat, E. A kinetic study of the reduction of colloidal manganese dioxide by oxalic acid. J. Colloid Interface Sci. 1996, 177 (2), 288−297. (34) Freeman, F.; Kappos, J. C. Permanganate ion oxidations. 15. Additional evidence for formation of soluble (colloidal) manganese dioxide during the permanganate ion oxidation of carbon-carbon double bonds in phosphate-buffered solutions. J. Am. Chem. Soc. 1985, 107 (23), 6628−6633. (35) Wenk, J.; Aeschbacher, M.; Salhi, E.; Canonica, S.; von Gunten, U.; Sander, M. Chemical oxidation of dissolved organic matter by chlorine dioxide, chlorine, and ozone: Effects on its optical and antioxidant properties. Environ. Sci. Technol. 2013, 47, 11147−11156. (36) Yu, M.; Kim, Y.; Han, I.; Kim, H. Characterization of humic substances isolated from Han River water and change in the structural and chemical characteristics by ozonation. Environ. Technol. 2005, 26 (9), 1033−1042. (37) Jiang, L.; Huang, C.; Chen, J.; Chen, X. Oxidative transformation of 17β-estradiol by MnO2 in aqueous solution. Arch. Environ. Contam. Toxicol. 2009, 57 (2), 221−229. (38) Stone, A. T. Reductive dissolution of manganese (III/IV) oxides by substituted phenols. Environ. Sci. Technol. 1987, 21 (10), 979−988. (39) Ehlers, G. A.; Rose, P. D. An integrated anaerobic/aerobic bioprocess for the remediation of chlorinated phenol-contaminated soil and groundwater. Water Environ. Res. 2006, 78 (7), 701−709. (40) Liu, C.; Zhang, L.; Li, F.; Wang, Y.; Gao, Y.; Li, X.; Cao, W.; Feng, C.; Dong, J.; Sun, L. Dependence of sulfadiazine oxidative degradation on physicochemical properties of manganese dioxides. Ind. Eng. Chem. Res. 2009, 48 (23), 10408−10413. (41) Liu, C.; Zhang, L.; Feng, C.; Wu, C.; Li, F.; Li, X. Relationship between oxidative degradation of 2-mercaptobenzothiazole and physicochemical properties of manganese (hydro) oxides. Environ. Chem. 2009, 6 (1), 83−92. (42) Klausen, J.; Haderlein, S. B.; Schwarzenbach, R. P. Oxidation of substituted anilines by aqueous MnO2: Effect of co-solutes on initial and quasi-steady-state kinetics. Environ. Sci. Technol. 1997, 31 (9), 2642−2649. (43) Laha, S.; Luthy, R. G. Oxidation of aniline and other primary aromatic amines by manganese dioxide. Environ. Sci. Technol. 1990, 24 (3), 363−373. (44) Zhang, Q.; Qu, X.; Wang, H.; Xu, F.; Shi, X.; Wang, W. Mechanism and thermal rate constants for the complete series reactions of chlorophenols with H. Environ. Sci. Technol. 2009, 43 (11), 4105−4112.

(45) Graham, N.; Jiang, C.; Li, X. Z.; Jiang, J. Q.; Ma, J. The influence of pH on the degradation of phenol and chlorophenols by potassium ferrate. Chemosphere 2004, 56 (10), 949−956. (46) Urynowicz, M. A. In situ chemical oxidation with permanganate: Assessing the competitive interactions between target and nontarget compounds. Soil Sediment Contam. 2007, 17 (1), 53−62. (47) Šmejkalová, D.; Spaccini, R.; Fontaine, B.; Piccolo, A. Binding of phenol and differently halogenated phenols to dissolved humic matter as measured by NMR spectroscopy. Environ. Sci. Technol. 2009, 43 (14), 5377−5382.

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