Degradation of p-chloroaniline by FeO_3−xH_3−2x/Fe⁰ in the presence of persulfate in aqueous solution

Abstract

Sulfate radical based advanced oxidation processes are promising techniques for the removal of organic compounds in aqueous solutions. In this study, FeO_3−xH_3−2x/Fe⁰ catalyst was prepared and used to activate persulfate (S₂O₈²⁻) for the degradation of p-chloroaniline (PCA). The results showed that nearly complete degradation of PCA was observed within 1 h in the persulfate-FeO_3−xH_3−2x/Fe⁰ system under the following optimized reaction conditions: PCA concentration 0.05 mM, FeO_3−xH_3−2x/Fe⁰ 1 g L⁻¹, persulfate 2.5 mM and pH 7.0. The PCA degradation was higher under acidic conditions when compared to alkaline conditions. A complete removal of the added PCA (0.05 mM) was achieved within 5 min with the addition of 2.5 mM persulfate and 1 g L⁻¹ FeO_3−xH_3−2x/Fe⁰ at pH 3.0. FeO_3−xH_3−2x/Fe⁰ catalyst was prepared by the calcination of Fe⁰ at 200 °C. The morphology of the catalyst was investigated with X-ray diffraction patterns (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared spectra (FTIR). The results demonstrated that the catalyst surface was mainly composed of hematite γ-Fe₂O₃ and goethite (α-FeOOH).

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1 Introduction

With the increasing growth of the world population and the strong development of various industries, environmental contamination has also increased tremendously in the last few decades, especially in water resources. The use of fertilizers, pesticides, herbicides, etc. in modern agriculture and disposal of untreated wastes in lakes, rivers and seas are the major contributors to water pollution.¹ Aromatic amines such as p-chloroaniline (PCA) are one of the most toxic pollutants present in the effluent of many industries. PCA has been widely used as raw material in many industries such as plastic, paint, dye manufacturing, pesticides, rubber chemicals, antioxidants and pharmaceuticals.^2,3 PCA considered as an important environmental pollutant and may be detrimental to aquatic lives and human health as a result of their toxicity, persistence, and transformation into hazardous intermediates.^4,5

Recently, sulfate radical based advanced oxidation processes (AOPs) have become promising processes due to its high degradation efficiency of organic contaminants.^6–8 SO₄˙⁻ has higher standard reduction potential (2.5–3.1 V) as compared to ˙OH (1.8–2.7 V).⁹ The high redox potential enables the successful mineralization of numerous organic compounds to carbon dioxide and mineral acids.¹⁰ Sulfate radicals are highly reactive to degrade organic contaminants as compared to ˙OH radical. The stability of sulfate radicals is higher than the hydroxyl radical and therefore sulfate radicals are capable of moving larger distances in the sub-surface. Sulfate radicals reveal a higher redox potential than hydroxyl radicals at neutral pH and both radicals show similar reduction potentials under acidic conditions.^6,11 Sulfate radical acts as more efficient oxidant than hydroxyl radical because of its better selectivity for oxidation.^12,13 Persulfate can be activated to generate a powerful oxidant known as sulfate radicals by means of heat energy, UV light or transition metal ions.¹⁴ Co(II) and Ag(II) can also be used to activate persulfate to produce SO₄˙⁻ but their applications for the treatment of water have significantly restricted due to high cost of silver and adverse effect of cobalt on human health. Therefore, it is strongly needed to develop a new catalyst for the activation of persulfate.¹⁵ Zero valent iron (ZVI) is gaining increasing popularity for the remediation of various toxic and hazardous contaminants. ZVI is current metal of choice because it is good reducing agent, readily available, non-hazardous and inexpensive.^16–18 Due to the strong reducing capacity and ability of ZVI to alter its valence state into more favorable forms for sorption and reductive precipitation, it has also been successfully used for the remediation of contaminants from water. Previous studies have also reported the degradation of phenol and molinate by reactive oxygen species generated by the reaction of oxygen and ZVI.^19–23 Zero valent iron was also used as an alternative source of Fe²⁺ through the oxidation of ZVI to activate persulfate.^14,24 ZVI oxidation by oxygen generates oxide layer which decreased the reactivity of ZVI. To maintain or enhance the catalytic activity of ZVI, different procedures have been reported in previous studies.^25,26 Moura et al.^27,28 prepared a composite mechanical alloying of Fe⁰ and Fe₃O₄ and observed the high activity of catalyst for the decomposition of H₂O₂ due to electron-transfer process from metal to magnetite.

Fe³⁺ + 1e⁻ → Fe²⁺ E⁰ = 0.771 V (1)

F⁰ − 2e⁻ → Fe²⁺ E⁰ = −0.440 V (2)

F⁰ − 2Fe³⁺ → 3Fe²⁺ E⁰ = 1.21 V (3)

Based on above mentioned redox potential, galvanic cells are created by composite of iron oxide coated ZVI in which ZVI acts as cathode and iron oxides act as anode. Due to transfer of electron from ZVI to iron oxides at the metal/oxide interface, the catalytic activity of the composite may be enhanced.

The main objective of this study was to investigate the activation of persulfate by FeO_3−xH_3−2x/Fe⁰ and produce highly reactive sulfate radicals to decompose PCA in aqueous solution. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) was applied to investigate the surface properties of FeO_3−xH_3−2x/Fe⁰. In this study the stability of catalyst was also assessed in the degradation of PCA. This study also evaluated the effects of initial pH (pH = 3.0–11.0) and performance of catalyst on the degradation of PCA.

2 Materials and methods

2.1 Chemicals

All chemicals used in this study were reagent grade and ultrapure water produced by a Millipore milli-Q system. Sodium persulfate (>99.0%), sodium thiosulfate pentahydrate (>99.0%), concentrated sulfuric acid (H₂SO₄, >98.0%) and sodium hydroxide (NaOH, >96.0%) were purchased from Tianjin Kermel Chemical Reagent Co. Ltd (Tianjin China). p-Chloroaniline (C₆H₆ClN, >99.5%), zero valent iron and methanol (CH₃OH, >99.9%) were obtained from Sigma-Aldrich USA.

2.2 Preparation of catalyst

The catalyst was prepared by previous reported method. ZVI was calcined at 200 °C for different times (10, 20, 30, 60 and 120 min) and the results revealed that sample calcined at 30 min showed higher activity (Fig. 1). The activity of catalyst increased rapidly with cycling times (Fig. 2). The sample was used repeatedly 3 times, after that the catalyst was filtered, washed with water, and dried at 70 °C for 2 h. A yellow color FeO_3−xH_3−2x/Fe⁰ catalyst was obtained.²⁹ This catalyst was used in all the experiments.

Fig. 1 Degradation of PCA in persulfate–ZVI system. ZVI was calcined at 200 °C for different times: (a) 15 min, (b) 30 min, (c) 60 min, (d) 120 min. [PCA]₀ = 0.05 mM; [PS]₀ = 2.5 mM; [ZVI] = 1 g L⁻¹; pH = 7.0.

Fig. 2 Cyclic degradation of PCA in persulfate–ZVI system. ZVI was calcined at 200 °C for 30 min, (1) first run, (2) second run, (3) third run, [PCA]₀ = 0.05 mM; [PS]₀ = 2.5 mM; [ZVI] = 1 g L⁻¹; pH = 7.0.

2.3 Characterization of catalyst

The surface morphology was analyzed by using EVO LS10 (Car Zeiss) scanning electron microscope (SEM) being operated at an acceleration voltage of 10 kV and equipped with an Oxford Energy 400 X-ray energy dispersive spectrometer (EDS, INCA Energy). X-ray powder diffraction (XRD) pattern was obtained on a diffractometer with Cu KR radiation (D8 ADVANCE, Bruker). The infrared spectra were recorded on a Fourier transform infrared (FTIR) spectrophotometer. The spectra were obtained from 400 to 4000 wave numbers (cm⁻¹) using a Vector 33 (Bruker, German).

2.4 Procedures and analysis

Stock solutions of PCA (10 mM) and persulfate (50 mM) were prepared in deionized water prior to each batch experiment. The initial pH of the solution was 7.0. The pH values of all solutions were adjusted with 1 M sodium hydroxide (NaOH) or sulfuric acid (H₂SO₄). All of the reactions were carried out in 250 mL Erlenmeyer flasks operated as completely mixed batch reactor systems. Reaction mixtures were obtained by mixing an appropriate amount of PCA (0.5 mL, 0.05 mM) from stock solution and added in deionized water (94.5 mL) on a rotary shaker at 125 rpm and 25 °C. After 10 min, 0.5 mL solution was collected from the reactor to determine the initial PCA concentration and then predetermined amount of FeO_3−xH_3−2x/Fe⁰ particles were added followed by the addition of sodium persulfate (5 mL, 2.5 mM). At regular time intervals, the sample aliquots were taken from flasks and filtered through 0.45 μm membrane. After filtration all samples were quenched immediately with sodium thiosulfate, to stop the chemical oxidation reaction.

The concentration of PCA in the aqueous phase was measured by HPLC (Shimadzu LC-20) equipped with UV detector at 254 nm. The HPLC column used was a reversed-phase C₁₈ column (250 mm × 4.6 mm) and the temperature of the column was maintained at 40 °C. The mobile phase used was methanol–water (70 : 30, v/v) with a flow-rate at 0.7 mL min⁻¹. The concentration of Fe²⁺ was determined colorimetrically using a UV-vis spectrophotometer at 510 nm after adding 1,10-phenanthroline to form a colored complex of Fe²⁺–phenanthroline.³⁰ Persulfate ion was determined by iodometric titration with sodium thiosulfate.³¹ The pH values were measured using a Shanghai Leici E-201-C pH meter.

3 Results and discussion

3.1 Characterization of catalyst

Fig. 3 shows the SEM image of FeO_3−xH_3−2x/Fe⁰. Fig. 4(a–c) shows the X-ray diffraction patterns (XRD) of Fe⁰, Fe⁰-200, and FeO_3−xH_3−2x/Fe⁰, respectively. Fig. 4b clearly showed that calcination at 200 °C did not affect the crystallinity of zero valent iron. XRD patterns of Fe⁰-200 showed similar peaks with zero valent iron. The XRD of FeO_3−xH_3−2x/Fe⁰ showed that characteristics peaks of zero valent iron disappeared and new peaks appeared, which are assigned to γ-Fe₂O₃ (2θ = 31.12°, 33.7°, 43.7°, 58.21°, 63.2°) (Fig. 4c). Fig. 5a shows the Fe2p peaks at binding energies of 711.2 and 725.1, with a shake up satellite at 718.9 eV. The dominant peaks at 711.2 and 725.1 can be assigned to Fe in γ-Fe₂O₃. The signal at 718.9 eV is characteristic of γ-Fe₂O₃. FTIR measurement was done to further investigate the surface layer composition (Fig. 5b). The results showed that Fe⁰-200R spectrum was relatively different from the spectrum of Fe₂O₃ and Fe⁰. The peaks of 1634 and 3433 cm⁻¹ were allotted to the O–H bending and stretching of water.^29,32 The Fe–OH bond was observed at 1022 cm⁻¹.³³ The peak of 884 cm⁻¹ was allotted to α-FeOOH, this shows the existence of FeOOH in the sample.³⁴ The peaks of 584 and 453 cm⁻¹ showed the extending vibration of Fe–O for γ-Fe₂O₃. FTIR analysis shows that the iron oxide outer layer was composed of γ-Fe₂O₃ and α-FeOOH. The results show that the catalyst had a core–shell like structure and the shell was mixture of γ-Fe₂O₃ and α-FeOOH. The catalyst was denoted by FeO_3−xH_3−2x/Fe⁰.

Fig. 3 SEM image of FeO_3−xH_3−2x/Fe⁰.

Fig. 4 XRD patterns of different iron species: (a) Fe⁰, (b) Fe⁰-200, (c) FeO_3−xH_3−2x/Fe⁰.

Fig. 5 (a) XPS spectrum of FeO_3−xH_3−2x/Fe⁰ Fe2p. (b) FTIR spectra: (a) Fe⁰, (b) FeO_3−xH_3−2x/Fe⁰, (c) Fe₂O₃.

3.2 PCA degradation with different catalysts

The batch experiments were conducted to investigate the degradation of PCA without oxidants under oxygenated and deoxygenated conditions at pH 7. The results revealed that ZVI has significant effects on PCA degradation where 54% PCA degradation was observed, while 35% of PCA was degraded by FeO_3−xH_3−2x/Fe⁰ under oxygenated conditions (Fig. 6). γ-Fe₂O₃ also has no significant effect on the degradation of PCA in the presence of oxygen. In contrast, ZVI showed no significant degradation while 70% PCA degradation was observed by FeO_3−xH_3−2x/Fe⁰ in deoxygenated system. These observations indicated that catalytic mechanism of FeO_3−xH_3−2x/Fe⁰ was different from ZVI. The previous work showed that the degradation of pollutants increased with the generation of reactive oxygen species in the presence of ZVI and oxygen which cause oxidative degradation of contaminants.^20,35 Many galvanic cells produced by FeO_3−xH_3−2x/Fe⁰ where FeO_3−xH_3−2x/Fe⁰ act as anode and ZVI act as cathode. Due to the presence of reactive oxygen species, the electron transfer from Fe⁰ to Fe³⁺ was established.²⁷ In oxygenated system, it was possible that oxygen stalled the electron-transfer process by trapping electrons, causing the lower reaction activity of FeO_3−xH_3−2x/Fe⁰ as compared to deoxygenated system.

Fig. 6 PCA degradation of without PS with air (1) ZVI, (2) FeO_3−xH_3−2x/Fe⁰ (3) γ-Fe₂O₃, and under deoxygenated conditions: (4) ZVI (5) FeO_3−xH_3−2x/Fe⁰. Catalyst (1 g L⁻¹), pH = 7.0.

3.3 Effect of different iron catalyst in the presence of persulfate

The generation of sulfate radical is seriously affected by different forms of iron in aqueous solution. The experiments were conducted to explore the comparison of PCA degradation by using different iron catalyst in the presence of persulfate. Fig. 7 shows that persulfate-FeO_3−xH_3−2x/Fe⁰ system has the best performance in PCA degradation as compared to other system. The degradation of PCA can reach 97% in the persulfate-FeO_3−xH_3−2x/Fe⁰ system within 1 h. However, no appreciable PCA degradation was observed by γ-Fe₂O₃ and Fe³⁺–persulfate system. A slow removal of PCA (45%) was achieved by the combined α-FeOOH–persulfate process after 2 h. As shown in Fig. 7, 65% PCA degradation was observed in persulfate–ZVI process. Interestingly, within 10 min, highest PCA degradation rate was observed in the γ-Fe₂O₃–persulfate system but immediately after that, PCA degradation was significantly slowed down. At the initial stage, the two-phase PCA degradation processes in the γ-Fe₂O₃–persulfate system are due to quick consumption of Fe²⁺. In contrast, persulfate-FeO_3−xH_3−2x/Fe⁰ demonstrated the fastest and nearly complete degradation of PCA, which is higher than other processes due to generation of more sulfate radicals. These results revealed that PCA degradation was due to the synergistic galvanic-cell like effect of FeO_3−xH_3−2x/Fe⁰.

Fig. 7 PCA degradation of with different catalyst in the presence of PS (1) γ-Fe₂O₃ (2) Fe³⁺ (3) α-FeOOH (4) ZVI (5) FeO_3−xH_3−2x/Fe⁰ catalyst (1 g L⁻¹), pH = 7.0.

3.4. Effect of pH on the degradation of PCA

The pH value of the reaction plays an important role in the degradation of contaminants in advanced oxidation processes. The initial pH values investigated were 3, 5, 7, 9 and 11 when the concentrations of PCA and PS were 0.05 mmol L⁻¹ and 2.5 mmol L⁻¹ respectively, and FeO_3−xH_3−2x/Fe⁰ dosage was 1 g L⁻¹. As shown in Fig. 8, the degradation rate of PCA increased with decreasing pH and reached the highest at pH 3. Sulfate radicals could be produced at catalyst surface by the decomposition of persulfate. Maximum degradation of 99% was obtained within 5 min at pH of 3 followed by slightly lower extents of degradation (92%) at an operating pH of 5 within 30 min whereas the extent of degradation was 98% at the neutral pH of 7 after 2 h. While 84% and 57% PCA degradation was observed at pH 9 and pH 11, respectively. According to the results, the catalyst showed highly catalytic activity for the degradation of PCA from acidic to alkaline conditions. Shih et al.³⁶ studied the 2,2,3,3-tetrafluoro-1-propane and found that the mineralization efficiency decreased with the increase of solution pH. Under acidic conditions, the generation of SO₄˙⁻ increased due to acid-catalyzation via following eqn.³⁷

S₂O₈²⁻ + H⁺ → HS₂O₈⁻ (4)

HS₂O₈⁻ → SO₄˙⁻ + SO₄²⁻ + H⁺ (5)

Fig. 8 Effect of pH on PCA degradation [PCA]₀ = 0.05 mM; [PS]₀ = 2.5 mM; [FeO_3−xH_3−2x/Fe⁰ ]₀ = 1 g L⁻¹.

At high pH 11, the iron species might precipitate to form iron hydroxide (Fe(OH)₃) or hydrous ferric oxide (Fe₂O₃·nH₂O).³⁸ These iron precipitates have low sulfate radical production efficiency by activating persulfate. Under strong alkaline conditions sulfate radicals can react with hydroxyl anion to generate ˙OH and reactivity of ˙OH was inhibited due to presence of various anions (SO₄²⁻). The degradation efficacy of PCA decreased because SO₄⁻˙ can be scavenged by ˙OH at high pH (eqn (5) and (6)).^39,40

SO₄˙⁻ + OH⁻ → SO₄²⁻ + OH˙ (6)

SO₄⁻˙ + ˙OH → HSO₄⁻ + 0.5O₂ (7)

3.5 Recycling of Fe²⁺/Fe³⁺ during degradation of PCA

The experiments were conducted to investigate the changes of iron concentration under air and deoxygenated conditions at pH 7. As shown in Fig. 9, under aerobic conditions the concentration of Fe²⁺ 0.08 mg L⁻¹ was observed, while ferric ion concentration was about 0.3 mg L⁻¹. In deoxygenated conditions the detection of ferrous ions was low, while 1.30 mg L⁻¹ of ferric ion concentration was observed. The results indicated that ferrous ions were converted to ferric ions. The results showed that the mechanism of electron transfer also occurred during degradation of PCA. The recycling of ferric iron on the catalyst surface through the electron transferring to Fe³⁺, which can keep suitable Fe²⁺ concentration in solution. The following equations showed the recycling of ferrous ion to ferric ions.⁴¹ Recycling of ferrous iron/ferric iron and also oxidation of ferrous iron to ferric iron results in the production of Fe₂O₃ and FeOOH which decrease the total iron concentration. The iron oxides were produced. The decreased concentration of iron ion may be ascribed to the presence of oxygen.

Fe⁰ + 2Fe³⁺ → 3Fe²⁺ (8)

S₂O₈²⁻ + Fe²⁺ → Fe³⁺ + SO₄²⁻ + SO₄˙⁻ (9)

Fig. 9 Iron ion concentration changes in persulfate-FeO_3−xH_3−2x/Fe⁰ process with the presence of air (1) Fe²⁺, (2) Fe³⁺ and without air (3) Fe²⁺, (4) Fe³⁺.

3.6 Identification of radicals

One of the most advantages of persulfate for the degradation of organic contaminants is the generation of sulfate and hydroxyl radicals. Sulfate radicals are more selective as compared to hydroxyl radicals. Hydroxyl radicals are known to undergo by hydrogen abstraction while sulfate radicals are more specific for electron transfer reactions.⁴² The batch experiments were conducted to indentify major oxidizing species in the system. The radicals quenching agents were utilized to evaluate the different radicals. In the present study, alcohols such as methanol (MA, 1 M) and t-butyl alcohol (TBA, 1 M) were used as radical quenching agents. The results revealed that with the presence of methanol and TBA, the degradation of PCA significantly decreased as compared to without radical scavenger. The degradation of PCA by addition of TBA is higher than that of methanol because TBA quenched only hydroxyl radicals. While in the presence of MA, PCA degradation was reduced to 80% (Fig. 10). The reason is that MA has α-hydrogen and rapidly quench SO₄˙⁻ and ˙OH (k HO˙ = 1.2–2.8 × 10⁹ M⁻¹ s⁻¹; k SO₄˙⁻ = 1.6–7.7 × 10⁷ M⁻¹ s⁻¹).⁶ In addition, TBA has no α-hydrogen and reacts rapidly with hydroxyl radical (k HO˙ = 3.8–7.6 × 10⁸ M⁻¹ s⁻¹), while TBA reaction with sulfate radical is slow (k SO₄˙⁻ = 4–9.1 × 10⁵ M⁻¹ s⁻¹).⁶ The difference in the degradation of PCA drop by radical scavengers indicated the presence of SO₄˙⁻ and ˙OH in the system. The results showed that PCA was not fully quenched suggesting the possibility of insufficient quenching agent and/or self-dissociation of persulfate through non radical pathway in the solution.⁷ For further verification, the concentration of methanol (2 M) was further increased and the degradation of PCA almost stopped. According to results, the sulfate radicals are dominant radicals for the degradation of PCA.

Fig. 10 Effect of different radicals scavengers on PCA degradation. [PCA]₀ = 0.05 mM, [FeO_3−xH_3−2x/Fe⁰]₀ = 1 g L⁻¹, [persulfate]₀ = 2.5 mM, pH = 7.0.

3.7 TOC removal

The purpose of any pollutant degradation is not only the degradation of pollutant but also to attain mineralization of pollutant. In order to observe the PCA mineralization efficiency in persulfate-FeO_3−xH_3−2x/Fe⁰ system, TOC removal efficiency was investigated with initial PCA concentration 0.05 mM, PS concentration 2.5 mM, initial pH 7.0 and FeO_3−xH_3−2x/Fe⁰ dosage 1 g L⁻¹. As shown in Fig. 11, although the degradation efficiency of PCA was 97% after 1 h reaction time, but the TOC removal efficiency was about only 28.5%. While TOC removal efficiency reached 68% when reaction time was extended to 5 h. It shows that compared to PCA degradation, a longer time is needed to attain a suitable TOC removal. The results prove sulfate radical efficiency for the degradation and mineralization of PCA. The results are in agreement with other studies.^43–45

Fig. 11 TOC Removal [PCA]₀ = 0.05 mM; [PS]₀ = 2.5 mM; [FeO_3−xH_3−2x/Fe⁰]₀ = 1 g L⁻¹; pH = 7.0.

3.8 Stability of FeO_3−xH_3−2x/Fe⁰ catalyst

Stability is an important property for effective catalyst. The sequential experiments were conducted to check the stability of the catalyst in the oxidation process. After the degradation experiment was finished in the first cycle, the FeO_3−xH_3−2x/Fe⁰ catalyst was separated from the reaction solution, then washed with distilled water, dried in a vacuum oven and stored at ambient temperature. The recycled FeO_3−xH_3−2x/Fe⁰ catalyst was used for the second cycle of degradation experiment in a fresh solution. These procedures were repeated for several cycles. As shown in Fig. 12, it can be found that the catalytic activity of FeO_3−xH_3−2x/Fe⁰ was still strong after five cycles. The degradation efficiency of PCA were 98%, 97%, 98%, 96% and 97% after 160 min for cycle 1–5, respectively. It shows that FeO_3−xH_3−2x/Fe⁰ catalyst has a good long-term stability. The small declined in the activity of the FeO_3−xH_3−2x/Fe⁰ may be due to the accumulation of the reaction products produced during reaction on the surface of FeO_3−xH_3−2x/Fe⁰, which blocked some reactive sites of FeO_3−xH_3−2x/Fe⁰.

Fig. 12 Recycling study of the degradation of PCA. Experimental conditions: [PCA]₀ = 0.05 mM; [PS]₀ = 2.5 mM; [FeO_3−xH_3−2x/Fe⁰]₀ = 1 g L⁻¹; pH = 7.0.

4 Conclusions

The oxidation system consisting of persulfate-FeO_3−xH_3−2x/Fe⁰ has been demonstrated to be more effective oxidant reagent to degrade PCA in aqueous solution. PCA was successfully degraded in persulfate-FeO_3−xH_3−2x/Fe⁰ system within 1 h under the following optimized reaction conditions: PCA concentration 0.05 mM, FeO_3−xH_3−2x/Fe⁰ 1 g L⁻¹, persulfate 2.5 mM and pH 7.0. The results showed that high acidic pH values e.g. 3.0 were more favorable than neutral and basic pH for complete degradation of PCA. The optimum pH for degradation of PCA was 3.0 at which 99% degradation efficiency was achieved after 5 min. Radicals scavengers such as MA and TBA demonstrated the responsibility of sulfate radicals as well as hydroxyl radicals in the degradation of PCA. This study indicates that the sulfate radicals base AOPs is an effective tool for the remediation of water contaminated with PCA.

Acknowledgements

This study was financially supported by the Fundamental Research Funds of Guangdong Provincial Key Laboratory of Atmospheric environment and Pollution Control (China) (2011A060901011), the Fundamental Research Funds of State Key Lab of Subtropical Building Science, South China University of Technology (2015ZB25), China Postdoctoral Science Foundation Funded Project (Project no. 2014M562185) and funded by the Fundamental Research Funds of State Key Laboratory of Pulp and Paper Engineering (China) (201477).

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