Highly efficient advanced oxidation processes (AOPs) based on pre-magnetization Fe0 for wastewater treatment

Accepted Manuscript Highly efficient advanced oxidation processes (AOPs) based on pre-magnetization Fe0 for wastewater treatment Xiang Li, Minghua Zhou, Yuwei Pan, Liting Xu, Zhuoxuan Tang PII: DOI: Reference:

S1383-5866(16)30613-X http://dx.doi.org/10.1016/j.seppur.2016.12.050 SEPPUR 13474

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Separation and Purification Technology

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2 June 2016 20 December 2016 21 December 2016

Please cite this article as: X. Li, M. Zhou, Y. Pan, L. Xu, Z. Tang, Highly efficient advanced oxidation processes (AOPs) based on pre-magnetization Fe0 for wastewater treatment, Separation and Purification Technology (2017), doi: http://dx.doi.org/10.1016/j.seppur.2016.12.050

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Highly efficient advanced oxidation processes (AOPs) based on pre-magnetization Fe0 for wastewater treatment Xiang Li,a,b Minghua Zhou, a

 ,a,b

Yuwei Pan, a,b Liting Xu,a,b Zhuoxuan Tang a,b

MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of

Environmental Science and Engineering, Nankai University, Tianjin 300350, China b

Tianjin Key Laboratory of Urban Ecology Environmental Remediation and Pollution Control,

College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China

ABSTRACT: Advanced oxidation processes (AOPs) has great potential for wastewater treatment, bust still limited in application due to their high cost for extensive reagent and energy demand, and restricted working conditions (e.g. narrow pH range). Here, AOPs based on pre-magnetization Fe0 (Pre-Fe0) were found to be highly efficient at wider pH conditions, partly solved the above problems. After pre-magnetization, Fe0 was supposed to be easier to be corroded, which remarkably improved processes (e.g., Pre-Fe0/H2O2, Pre-Fe0/K2S2O8) efficiency several to >100 folds and valid for many refractory contaminants (e.g. dyes, phenols, organic acids), compared with that conventional processes without pre-magnetization. Moreover, the process efficiency could be sustained by the recovery of magnetism of Pre-Fe0. Thus AOPs based on pre-Fe0 is more promising to take place of conventional Fe0 based AOPs since it more efficient but does not require any change of the present water and wastewater treatment process, and does not need an extra energy source, costly materials, and complex equipment. Keywords: AOPs; pre-magnetization Fe0; remarkable improvement; refractory contaminants * Corresponding author. E-mail address: [email protected] (M. Zhou).

1. Introduction Advanced oxidation processes (AOPs) have attracted more and more attention in wastewater treatment because they can degrade recalcitrant organic pollutants into less toxic products through the generation of highly powerful hydroxyl radical (·OH) or sulfate radicals (SO4-·) via Eq. (1) and Eq. (2) [1-3]. Fe2+ + H2O2 → Fe3+ + OH- + ·OH

(1)

Fe2+ + S2O82- → SO4-· + Fe3+ + SO42-

(2)

Among the transition metal ions which could be used as effective catalysts for radical generation, Fe2+ is advantageous since its high performance and simplicity (operated at room temperature and atmospheric pressure) for the oxidation of organics [4, 5] and its environmental friendly [6, 7]. As a reactive metal with standard redox potential (E0 = -0.44 V), Fe0 can generate Fe2+ under both aerobic and anaerobic conditions, especially under acidic environment (Eq. (3))[8] . Fe0+ 2H+ → Fe2+ + H2

(3)

Therefore, over the last decades, a large number of AOPs based on Fe0 have been reported to remove different organic and inorganic pollutants such as chlorinated organics [9], nitroaromatics [10], arsenic [11], nitrate [12], chromate [13], and selenite [14] from contaminated water, wastewater and groundwater. Particularly, Fe0/H2O2 producing ·OH and Fe0/K2S2O8 generating SO4-· via Eq. (4) and Eq. (5) are most extensively studied [15, 16]. H2O2 + Fe0 → 2·OH + Fe2+

(4)

2S2O82- + Fe0 → 2SO4-· + Fe2+ + 2SO42-

(5)

However, these AOPs have some drawbacks, such as low reactivity toward contaminants, reactivity decreased over time [17], the reactivity of Fe0 generally decreased significantly with increasing pH [18]. Though great efforts on process combination with the addition of electricity [19], UV light [20] and sound energy [21] and the use of different heterogeneous catalysts [22] or nanoscale Fe0 [23], have been paid to improve treatment efficiency, these enhancement would increase the costs of material, construction and operation. “Magnetic memory” defined as a period in which particles can sustain their magnetization properties of certain intensity [24]. Zero valent iron (ZVI) is ferromagnetic, and it becomes magnetized in an external magnetic field and remains magnetized even after the external field is removed. So in our work, Fe0 was pretreated after being exposed to a weak magnetic field for several minutes to obtain “Magnetic memory”. Meanwhile, the pre-magnetization Fe0 was used in AOPs to take place of conventional Fe0. Take pre-magnetization Fe0/H2O 2 (Pre-Fe0/H2O2) and pre-magnetization Fe0/PS (Pre-Fe0/PS) process as examples, it was verified that these AOPs based on Pre-Fe0 have miraculous improvement on organic pollutant degradation when comparing with conventional one, which would provide a more efficient alternative for wastewater treatment. The objects of this study were to (1) explore the suitability of the process for degrading various pollutant and advantages of AOPs system based on Pre-Fe0; (2) explore possible change of Fe0 characteristics after pre-magnetization; (3) the magnetic memory time of the Pre-Fe0. In order to study the feasibility of the process for refractory pollutants, such as dyes, pharmaceuticals, phenolic compounds, chlorine compounds and nitro-compounds, one or two typical pollutants of those various refractory contaminants were tested as examples, and compared performance with literature.

2. Experimental 2.1. Materials Tartrazine, Orange II, 2,4-DCP, p-nitrophenol, 4-CP, chlorobenzene, p-nitrochlorobenzene, phenol and acetylsalicylic acid were purchased from Aladdin chemistry Co., Ltd. (Tianjin, China). Potassium persulfate (K2S2O8), sulfuric acid (H2SO4) and sodium hydroxide (NaOH) were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Fe0 powder was obtained from Shanghai Jinshan smelter (Shanghai, China). H 2O2 was purchased from the Sinopharm Group Chemical Reagent Co., Ltd. (Shanghai, China). All solutions were prepared with deionized water and all chemicals used in this study were of analytical grade and were used as received without further purification. 2.2. Preparation of Pre-Fe0 The preparation of pre-magnetizated Fe0 was simple: suitable amount of Fe0 was mixed by a mechanical stirrer at 350 rpm for desired minutes in a breaker, under which two thin cylindrical neodymium-iron-boron permanent magnets were placed (see details in Supporting Information (Fig. S1)). 2.3 Experimental procedures The initial pH values were adjusted with NaOH (0.1 mM) and H 2SO4 (0.1 mM). The solution was mixed by a mechanical stirrer at 400 rpm. At the given intervals, the samples were sampled by plastic syringes and filtered through a 0.22 μm membrane filter. 2.4 Analytical methods The concentration of tartrazine and Orange II was monitored by spectrophotometer (VI-1501, Tianjin Gangdong Sci & Tech Development Co., LTD.) at 428 nm and 486 nm, respectively. The

concentration of 2,4-DCP, phenol, acetylsalicylic acid and p-nitrophenol was analyzed by a high performance liquid chromatograph (HPLC FL2200-2) on a Beckman ODS C18 column (5 μm,  4.6 × 250 mm) at a flow rate of 1.0 mL min-1. The mobile phase was methanol/water/acetic acid (v/v/v) at 60: 38: 2, methanol/water (v/v) at 60:40, methanol/monopotassium (v/v) at 40: 60 and methanol/water/acetic acid (v/v/v) at 35/65/0.5. The UV detector was set at 280 nm, 270 nm and 272 nm and 254 nm, respectively. Chlorobenzene and p-nitrochlorobenzene was determined by Gas chromatography (GC) under the following conditions: column temperature was 100°C and 145°C, gasification chamber and detector temperature was 200°C and 300°C. Cl- was quantified by ion chromatograph (Dionex ICS-900, USA) using an IonPac AS11-HC (Φ4 mm × 250 mm) column and DS5 conductivity detector. X-ray diffraction (XRD) analysis was analyzed by using a diffractometer (D-MAX 2200 VPC Japan) with radiation of Cu target (Ka, k = 1.54059 Å). Scanning Electron Microscopy (SEM) was analyzed by SHIMADZU SS-550. A pseudo first-order rate degradation was found well fitted the removal of contaminants (k1 and k2 were the rate constant of contaminant degradation by Pre-Fe0/PS or Pre-Fe0/H2O2 process and Fe0/PS or Fe0/H2O2 process, respectively). In order to evaluate the improvement of pre-magnetization process compared with traditional process, the f (k1/k2) was calculated by Eq. (6),

f 

k1 k2

(6)

Where k is the pseudo first-order rate constant of contaminants degradation, f is the multiple of k between pre-magnetization process and traditional process. The removal efficiency of 2,4-DCP (η/%), dechlorination efficiency (θ/%) was calculated by Eq. (7) and Eq. (8), respectively.

 /%

c0  ct 100 c0

(7)

 /%

bt 100 b0

(8)

Where c0 and ct were the concentration of 2,4-DCP at initial and given time t, respectively. b0 is the theoretical concentration of chloridion in solution and bt is the concentration of chloridion in solution at reaction time t. 3. Results and discussion To understand the change of Fe0 characteristics after magnetization, Fe0 was characterized by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD). As shown in the SEM image (Fig. 1A), Fe0 without pre-magnetization before reaction had a smooth surface. In contrast, after pre-magnetization, slight corrosion with many tiny particles on the surface was observed (Fig. 1B). These results suggested that the surface of Fe0 had significant variation, which might promote the corrosion of Fe0 (leaching Fe2+) which could promote peroxide or persulfate activation and then accelerate the degradation of pollutants. This fact met well with the BET tests, which showed that the specific surface area of pre-magnetization Fe0 (1.94 m2/g) was much larger than that of Fe0 (0.15 m2/g). Compared with the XRD patterns of Fe0 at different conditions (Fig. 1C), no new characteristic peaks occurred in the XRD pattern, indicating that the pre-magnetization did not change the composition of Fe0 on the surface. (Fig. 1) To check the effectiveness of the Pre-Fe0 based AOPs, the degradation of tartrazine, a model azo dye, was studied by individual Fe0, H2O2 oxidation, Fe0/H2O2 and Pre-Fe0/H2O2 process. As shown in Fig. 2, the pseudo-first-order degradation rates constant (k) was only 0.0002 min-1 by Fe0

alone, while for pre-magnetization Fe0 it significantly enhanced to 0.0008 min-1 at pH 4. However, tartrazine degradation by Fe0/H2O2 could be more rapid with the higher k value of 0.0082 min-1, which was 10 folds of that Fe0 alone, indicating there is a good synergy between Fe0 and H2O2 oxidation. Surprisingly, in the Pre-Fe0/H2O2 process, the k value was increased to 0.084 min-1. Therefore, such a synergistic effect would be more evident than that in the conventional Fe0/H2O2, indicating that Pre-Fe0/H2O2 process is more efficient and advantageous. Another main drawback of conventional Fe 0 based AOPs was the narrow effective pH ranges (2.5-3.5). To test whether this phenomenon was happened on the novel Pre-Fe0 based AOPs, the dependence of the degradation rate constant with initial pH was investigated in iron/hydrogen peroxide and persulfate system, respectively. As shown in Fig. 2B, at the same initial pH, the k for tartrazine degradation by Pre-Fe0/H2O2 process was 2.6–7.1 folds of those by Fe0/H2O2 process. As expected, the k decreased with the increase of initial pH in both two processes since iron dissolution hardly happened at high pH [6]. However, the enhancement ratio of pseudo-first-order rate constants (f) between Pre-magnetization Fe0 and Fe0 process did not decrease with the increase of pH, showing a good resistance to decline in Pre-Fe0/H2O2 process. This fact might be explained that pre-magnetization Fe0 could be corroded in a higher pH than that of conventional Fe0. Furthermore, the degradation rate constant of tartrazine by pre-magnetization Fe0/H2O2 process at pH 5 was higher than that by Fe0/H2O2 at pH 4, indicating the extension of suitable pH ranges. Similarly, in the Pre-Fe0/PS process, the k of Orange II was much higher than those of by the Fe0/PS (Fig. 2C). A faster degradation must be due to a faster and more SO4-· generation (shown in Eq.(2)) So, we evaluated the generation of Fe3+ at pH 7. As shown in Fig.S2, the generation of Fe3+ was 1.32 mmol/L at 30 min by Pre-Fe0/PS while only 0.11 mmol/L by Fe0/PS, indicating

extremely larger SO4•− generated in Pre-Fe0/PS process. The larger SO4•− generated induced the fast degradation of OG. Though the k value was sharply decreased with pH in Fe 0/PS process, it decreased slowly in Pre-Fe0/PS process and kept at relatively high value. Particularly, there was a whale of a difference on the removal of Orange II efficiency between Pre-Fe0/PS process and Fe0/PS process at pH 10 (Fig. S3), the f reached up to more than 100 at pH 10. The above results proved that Pre-Fe0 based AOPs could widen the working pH range, indicating a wider and more efficient application due to a less pH adjustment. (Fig. 2) This enhancement effect of Pre-Fe0/PS was also confirmed in dechlorination and denitrification. Fig. 3A and 3B show that not only the remove rate of 2,4-dichlorophenol (2,4-DCP) but also the dechlorination efficiency were accelerated. The k of 2,4-DCP decreased with the increase of initial pH in two processes, while the f value of 2,4-DCP by Pre-Fe0/PS process at pH 3-9 were 2.75-5.15 folds of those by Fe0/PS process. Consistent with the results of 2,4-DCP, the remove rate of nitrobenzene also was accelerated by Pre-Fe0/PS (Fig. 3C), and the f value by Pre-Fe0/PS process at pH 3-9 were respectively 5.6-10.9 folds of those by Fe0/PS process. At pH 3-7, the dechlorination efficiency was over 97% by Pre-Fe0/PS, but declined with the increasing pH to 9 and 10, which was 76.2% and 52.7%, respectively. However, in Fe0/PS system, the dechlorination efficiency reached maximum (86.4%) at pH 3, and it declined sharply when increasing pH to 10 (only 14.8%). Fe0 would be oxidized inevitably during preparation and store [25], and the oxides on the particles surface were dissolved rapidly at lower pH. Therefore, 2,4-DCP and nitrobenzene could be rapidly removed and the dechlorination efficiency reached a relatively high level in both systems. While at higher pH, zero-valent iron surface would form a

passive film which hindered further reaction [26], but in present Pre-Fe0, iron corrosion could be accelerated, so the removal of 2,4-DCP and nitrobenzene as well as the dechlorination efficiency were improved. (Fig. 3) These improvements were also observed on the removal of various refractory contaminants, such as dyes, phenols and pharmaceuticals. As shown in Fig. S4, the application of Pre-Fe0 process had remarkable improvement. The k of Orange II, 2,4-DCP, phenol and acetylsalicylic acid were improved greatly (Fig. S5), and the f of these contaminants was respectively 21.3, 9.2, 10.7 and 10.8 (Fig. S4A). Likewise, the removal efficiency of 4-CP, p-nitrophenol, chlorobenzene, phenol and p-nitrochlorobenzene was greatly improved by Pre-Fe0/PS process (Fig. S6), and the k of them was 5.18, 10.4, 3.1, 4.62 and 2.76 folds of this by Fe0/PS process, respectively (Fig. S4B). Therefore, Pre-Fe0 based AOPs could degrade a wide type of organic pollutants and accelerate the degradation of different pollutants. Moreover, the performance of Pre-Fe0 was compared other AOPs (e.g., photo-Fenton, Fenton and electrochemical oxidation) in literatures (Table 1), indicating that it was more efficient in improving the degradation rate constant 1-2 orders. One may argue how this magnetic memory can be sustained, and what’s the effect of external weak magnetic field on Fe0, which would be very important for the application of this material. Fig. 4A depicts the tartrazine removal at different intensities of magnetic fields (10 mT to 70 mT). When the intensity of magnetic field was 30 mT, the f reached maximum, which was 4.6 times that of Fe0/H2O2 system. Because, pre-magnetization could stimulate the breakdown of the passive film, so excessive high magnetic field could result in a negative effect of Fe0 due to large magnetic or improper characteristics eventually influencing the performance of Pre-Fe0 [27]. While a low

magnetic field could not stimulate Fe0 because Lorentz Force and a weak magnetic memory may hinder their growth activity, thus influencing the performance of systems[24]. Fig. 4B depicts the performance of Pre-Fe0/H2O2 process when using the Pre-Fe0 after different time periods, evaluated by the reaction rate constant k. The k was only 0.006 min-1 in Fe0/H2O2 process, while the k value after immediate magnetization was initially 0.031 min-1, and changed little during the first 12 h after Fe0 magnetization. After pre-magnetization 24 h, the k declined rapidly, and after 72 h it was only 0.009 min-1. Although the memory could last only 24 h, this lost “magnetic memory” after 24 h and 72 h was found to be effectively recovered when they experienced magnetization again (insert Fig. 4B). The k could be moved back to 0.031 min-1 and 0.030 min-1 respectively, indicating that the performance could be recovered even after 3 days after Fe0 pre-magnetization. This point was very important to maintain good performance for application and help to reuse the Pre-Fe0 even when it was not used on time and lost its “magnetic memory”. (Fig. 4) Table 1 compares the removal efficiency of different pollutants and reaction rate constant of this work with many literatures. Apparently, different reaction systems varied greatly on removal efficiency and reaction rate constant, and the present work showed a higher efficiency or a comparable result with less reagent addition, when comparing with other AOPs including nFe0/H2O2, UV/Fe2+/H2O2, electrochemical oxidation and nPd/Fe. Taking tartrazine (200 mg/L) as an example, it took 180 min for 100% removal efficiency in literature [29], but in the present work it was only 60 min with 1/35 H2O2 addition of that in literature and without UV input. Compared with the rate constant (0.0097 min-1) by electrochemical oxidation of 500 mg/L acetylsalicylic

acid [30], Pre-Fe0/H2O2 was more efficient with a rate constant was 0.018 min-1, at the same time, it did not need external energy consumption. For 25 mg/L phenol removal, the reaction rate in the present work in the presence of 4 mM Fe and 1 mM H 2O2 was 0.31 min-1, which was 20 times higher than that by US/nFe 0/H2O2 in the presence of 17.9 mM nFe0 and 17.9 mM H2O2 [31]. Similar enhancements on other pollutants (4-CP, 2,4-DCP, nitrobenzene, p-nitrophenol) were also observed by Pre-Fe0/PS or Pre-Fe0/H2O2 systems when comparing with other AOPs [32-36]. Therefore, the Pre-Fe0 would have widespread application prospects in environment pollution control. (Table 1) 4. Conclusions AOPs based on Pre-Fe0 not only could greatly enhance the organic pollutants removal rate, decreasing the dosage of reagent (e.g., Fe0) to reduce treatment cost, but also could extend a more wider applied scope (pH ranges). Above all, this Pre-Fe0 could be reused since its activity could be recovered by easily pre-magnetization again. This process was proved to achieve similar enhancement in performance on many kinds of organic pollutants, and thus AOPs based on Pre-Fe0 is more promising and efficient to take place of AOPs based on conventional Fe0 for a more efficient wastewater treatment.

Acknowledgments This work was supported by Natural Science Foundation of China (no. 21273120 and 51178225), Key Project of Natural Science Foundation of Tianjin (no. 16JCZDJC39300), National High Technology Research and Development Program of China (2013AA065901 and 2013AA06A205), National Key Research and Development Program (2016YFC0400706), National Special S&T Project on Water Pollution Control and Management (2015ZX07203-011),

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Figure captions Fig. 1 The SEM of Fe0 (A) and Pre-Fe0 (B); XRD patterns of Fe0 and Pre-Fe0 (C). Fig. 2 The synergistic effect between Fe0 and H2O2 (A) and Influence of tartrazine removal at different initial pH in Pre-Fe0/H2O2 and Fe0/H2O2 process (B) and Influence of Orange II removal at different initial pH in Pre-Fe0/PS and Fe0/PS process (C). Reaction conditions: (A) H2O2 2.0 mM, Fe0 4.0 mM, Tartrazine 200 mg/L; (B) H2O2 1.0 mM, Fe0 4.0 mM, Tartrazine 200 mg/L; (C) Orange II 200 mg/L, PS 1.0 mM, Fe0 4.0 mM, pH 7

Fig. 3 Pre-Fe0/H2O2 for 2,4-DCP degradation (A), dechlorination efficiency (B) and nitrobenzene removal (C). Reaction conditions: (A) 2,4-DCP 4.0 mg/L PS 1.0 mM, Fe0 1.0 mM, pH 7; (B) nitrobenzene 20mg/L, PS 2.0 mM, Fe 2.0 mM, pH 7 Fig. 4 Influence of different intensity of magnetic field on tartrazine removal by pre-Fe0/H2O2 (A) and the “memory” of pre-Fe0 (B). Reaction conditions: Fe0 4.0 mM, initial pH 4, Tartrazine 200 mg/L, H2O2 0.5 mM

No magnetization

C

1110

740

370

0

Pre-magnetization 1020

680

340

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

2θ

Fig. 1

A 84.25

-1

-3

k/min (10 )

90 88 86 84 82 80 78 76

8.2

8 6 4 2

1

0.8

0.26

0 Fe

0

Pre-Fe

0

0

0

H2O2

Pre-Fe /H2O2

Fe /H2O2

Different system

250

250

B

0

Fe /H2O2

238

0

Pre-Fe /H2O2 200

9

f

-1

-3

k/min (10 )

6

150 3

94

100

80

0 2

3

4

5

6

7

pH

59 50

15.6

16

6

0.73 5.2

0 2

3

4

5

6

7

-3

k(10 )/min

-1

pH

C

100

0

Fe /PS 0 Pre-Fe /PS

80

60

f

1200 1100 1000 900 800 700 600 500 400 300 200 100

40

437.49

20

239.71

184.82

182.63 51.16 pH 0

2

51.9

4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

3

4

5

6

7

8

9

10

11

3.88 2.8 1.9 0.848 3

4

5

6

7

8

pH

Fig. 2

9

10

11

12

13

500

6

A 460.7

0

Fe /PS 0 Pre-Fe /PS

5

400 f

4

3

271.8

-3

k (*10 )

300

2 2

3

4

5

6

7

8

9

10

11

pH

200

167.6

167.3

159.77

100

60.3

56.2

34.1 6.9

31 0 3

4

5

6

7

8

9

10

11

12

pH

Dechloridation efficiency(%)

100

B

0

Fe /PS 0 Pre-Fe /PS

80

60

40

20

0 3

4

5

6

7

8

9

10

pH

60

0

C

11

Fe /PS 0 Pre-Fe /PS

52.13

10

9

f

50

41.9

8

7

38.5

40

-1

-3

k/min (10 )

6

5 2

3

4

5

6

30

7

8

9

10

11

pH

21.91 20

10

17.07 9.2

6.67 3.83

2.01

1.6

0 3

4

5

6

7

pH

Fig. 3

8

9

10

11

12

A 4

f

3

2

1

0 0

10

20

30

40

50

60

70

Magnetic field /mT

50

B

30

45 25

20

-1

-3

k/min (10 )

40 35

15

5

-3

k/min (10 )

10

30

-1

20 15 10

No magnetization

25

0 0

24

72

t/h

5 0 0

0.5

2

6

12

t/h

Fig. 4

18

24

48

72

Table 1 Performance comparison with literatures. Time Pollutants

Reaction System

Removal

Reaction rate

Experimental conditions

References -1

(min)

efficiency (%)

constant (min )

60

53

0.0654

Orange II 105 mg/L, nFe0 10 mg/L, H2O2 200 mg/L nFe0/H2O2

[28]

(5.88 mM), pH 3.0, 30°C Orange II Orange II 200 mg/L, Fe 2.0 mM, H2O2 1.0 mM, 0

Present 45

Pre-Fe /PS

99.6

0.205

pH 3.0, 30°C

work

Tartrazine 200 mg/L, Fe2+ 1.0 mM, H2O2 1.75 ml/L UV/Fe2+/H2O2

180

100

-

60

100

0.238

[29]

(17.5 mM), UV 4W, pH 3.0, 25°C Tartrazine Tartrazine 200 mg/L, Fe 2.0 mM, H2O2 0.5 mM, Pre-Fe0/H2O2

Present

pH 3.0, 25°C Acetylsalicylic

Electrochemical

work

Acetylsalicylic acid 500 mg/L, Na2SO4 0.1 mM, 150

acid

oxidation

2

current density 50 mA/cm , 1%Ni-PbO2 electrode

77.2

0.0097

[30]

Acetylsalicylic acid 500 mg/L, Fe 4.0 mM, 0

Present 60

Pre-Fe /H2O2

78

0.018

H2O2 4.0 mM, pH 4.0

work

Phenol 25 mg/L, nFe0 17.9 mM, H2O2 30.0 mM, US/ nFe0/H2O2

60

75

0.014

[31]

pH 3.0, 20 kHz ultrasound irradiation Phenol Phenol 25 mg/L, Fe 4.0 mM, H2O2 1.0 mM, 0

Present 30

Pre-Fe /H2O2

90.5

0.31

pH 4.0

work

2,4-DCP 30 mg/L, nFe0 17.9 mM, PS 12.5 mM, nFe0/PS

180

98

0.071

[32]

pH 3.0, 25°C 2,4-DCP 30 mg/L, Fe0 1.0 mM, PS 1.0 mM, 0

Present 60

Pre-Fe /PS

75

0.083

pH 7.0, 25°C

2,4-DCP nPd/Fe

2,4-DCP 20 mg/L, nPd/Fe 6.0 g/L, pH 5.5, 30°C

work 300

100

0.051

2,4-DCP 20 mg/L, Fe0 1.0 mM, PS 1.0 mM, 0

Present 60

Pre-Fe /PS pH 7.0, 30°C

[33]

88

0.107 work

4-CP 20 mg/L, Fe0 3.6 mM, PS 0.78mM, Fe0/PS

60

88

0.036

[34]

25°C and no pH adjustment 4-CP 4-CP 20 mg/L, Fe0 1.0 mM, PS 1.0 mM, 0

Present 60

Pre-Fe /PS

90

0.112

pH 7.0, 25°C

work

Nitrobenzene 20 mg/L, pyrite 2 g/L, 300

Pyrite/H2O2

80

0.011

[35]

H2O2 250 mM, pH 3 Nitrobenzene Nitrobenzene 20 mg/L, Fe0 2.0 mM, 0

Present 60

Pre-Fe /PS

72.2

0.038

PS 2.0 mM, pH 7 UV/heat/PS

p-Nitrophenol 30 mg/L, PS 5.4 mM, 25°C, pH 4.5

work 120

89

0.034

p-Nitrophenol 30 mg/L, Fe0 2.0 mM, PS 2.0 Mm,

p-Nitrophenol 0

Present 90

Pre-Fe /PS pH 4.5, 25°C

[36]

89.3

0.039 work

Highlights 

AOPs based on pre-magnetization Fe0 could remarkably improve processes efficiency.



Pre-Fe0 process could save Fe0 dosages widen the working pH range.



The process efficiency could be sustained by the recovery of magnetism of Pre-Fe0