Supporting Information for

Degradation of p-nitrophenol by Fe0/H2O2/persulfate system:

Optimization, performance and mechanisms

Jun Li a, Qingqing Ji a, Bo Lai a,*, Donghai Yuan b,

a Department of Environmental Science and Engineering, School of Architecture and Environment, Sichuan

University, Chengdu 610065, Chinab Key Laboratory of Urban Stormwater System and Water Environment, Ministry of Education, Beijing Climate

Change Response Research and Education Center, Beijing University of Civil Engineering and Architecture,

Beijing, P. R. China

Submitted to

Journal of the Taiwan Institute of Chemical Engineers

Summary:

Page 3-4: Materials and methods

Page 4-8: Parameters optimization (single-factor experiments)

Page 8-10: Parameters optimization (response surface methodology (RSM))

Page 10-12: Interactive relationship of Fe0, H2O2 and persulfate

Page 12-14: Proposed reaction pathway for the destruction of PNP

Page 15-18: Reference

Corresponding authors. Tel./fax: +86 18682752302E-mail address: laibo@scu.edu.cn (Bo Lai), yuandonghai@aliyun.com (Donghai Yuan)

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Page19: Table S1

Page 20: Table S2

Page 21: Table S3

Page 22: Fig. S1

Page 23: Fig. S2

Page 24: Fig. S4

Page 25: Fig. S5

Page 26: Fig. S6

Page 27: Fig. S7

Page 28: Fig. S8

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1. Materials and methods

1.1. Reagent

p-Nitrophenol (PNP, 99%), zero valent iron (ZVI or Fe0) powders, sodium

persulfate (Na2S2O8, 98%), hydrogen peroxide (H2O2, 30% v/v) and ferrous sulfate

heptahydrate (FeSO4·7H2O) from Chengdu Kelong chemical reagent factory were

used in the experiment. The zero valent iron powders have a mean particle size of

approximately 120 um, and their iron content was above 98%. Other chemicals used

in the experiment were of analytical grade. Deionized water was used throughout the

whole experiment process.

1.2. Analytical methodsThe surface morphologies of reacted Fe0 particles in Fe0/H2O2/persulfate system

were observed by JSM-7500F field emission scanning electron microscopy (FE-SEM,

JEOL Ltd., Japan). Besides, the surface elementary compositions of Fe0 particles were

analyzed by energy dispersive spectrometer (EDS). EDS analysis was carried out by a

permanent thin film window link (Oxford Instrument) detector and WinEDS software

in a JSM-7500F field emission scanning electron microscopy (FE-SEM). This

instrument was operated at 25kV and emission current of 60-70 μm subsequently. The

concentration of PNP, p-aminophenol (PAP), fumaric acid, maleic acid and p-

benzoquinone (p-BQ) in the samples was achieved by reversed-phase HPLC

chromatography (Agilent USA) equipped with the Eclipse XDB C-18 (5 μm, 4.6 ×

250 mm). The binary phase were water with 0.1% H3PO4 (A) and acetonitrile (B), and

the eluent was A and B (5:5, v/v) with a flow rate of 1.0 mL/min for PNP. Detection

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was performed by a G1365MWD UV detector set at 317 nm for PNP. For the

measurement of PAP, maleic acid, fumaric acid and p-BQ concentration, water with

0.1% H3PO4 (A) and acetonitrile (B) were used as the mobile phase for the gradient

elution. Water with 0.1% H3PO4 (A) and acetonitrile (B) were used as the mobile

phase for the gradient elution. The gradient was firstly as linearly from 95% to 10% of

A in 10 min, and remain unchanged for 5 min. The total Fe concentration of the

treatment effluent was detected by an atomic absorption spectroscopy (AA-6300,

Shimadzu, Japan). The residual S2O82− concentrations in the presence of iron were

determined based on the methods of Liang et al. (1). The measurement method in

detail was as follows: (i) Various volume of sodium persulfate stock solution (0.007

M), NaHCO3 (0.2 g) and 4 g KI were added into 40 mL RO water in 50 mL beakers.

(ii) The resulting solutions were hand shaken and allowed to equilibrate for 15 min.

(iii) The resulting solutions were analyzed an absorbance at 352 nm by a UV-Vis

spectrophotometer. The solution pH was measured by a PHS-25 meter (Rex, China).

The H2O2 concentration was determined using a UV-Vis spectrophotometer (2).

2 Results and discussion

2.1. Parameters optimization (single-factor experiments)

2.1.1. Effects of Fe0 dosage

Effects of Fe0 dosage (0-4.0 g/L) on PNP removal were evaluated thoroughly. Fig.

S1(a) shows that PNP removal rapidly increased to 92.2% when the Fe0 dosage

increased from 0 to 2.0 g/L after 6 min treatment. The above results can be explained

from the following aspects: (i) More active sites on the surface of Fe0 obtained with

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the increasing of Fe0 dosage; (ii) More corrosion products (e.g., Fe2+, Fe3+, Fe2O3,

Fe3O4 and FeOOH) associated with the augment of Fe0 dosage, which could activate

persulfate and H2O2 to produce more radicals (e.g., SO4•- and HO•) (Eqs. (1)-(3))(3-8);

(iii) Essential Fe0 was needed to form the Fenton-like reaction in the presence of

dissolved oxygen (DO) (Eqs. (4)-(6))(9). The outcome is in agreement with the

previous report that the increasing of Fe0 dosage improve the amount of released Fe2+

and efficiency of the degradation(10). However, PNP removal decreased gradually to

86.5% when Fe0 dosage further increased to 4.0 g/L. The outcome can be explained

that the generated radicals can be scavenged by the excess iron corrosion products

(e.g., Eqs. (7)-(8)). Therefore, the optimal Fe0 dosage of 2.0 g/L was selected in the

subsequent experiments.

Fe0 → Fe2+ + 2e- (1)

Fe0 + S2O82- → Fe2+ + 2SO4

2- (2)

Fe2+ + S2O82- → Fe3+ + SO4

•- + SO42- (3)

Fe0 + O2 + 2H+ → Fe2+ + H2O2 (4)

Fe0 + H2O2 + 2H+ → Fe2+ + 2H2O (5)

Fe2+ + H2O2 → Fe3+ + HO• + OH- (6)

HO•+ Fe2+ → Fe3+ + OH- (7)

Fe2+ + SO4•- → Fe3+ + SO4

2- (8)

2.1.2. Effects of H2O2 dosage

Effects of H2O2 dosage (0-30.0 mM) on PNP removal were evaluated. Fig. S1(b)

shows that the increasing of H2O2 dosage from 0 to 20.0 mM led to an enhancement in

the PNP removal from 0 to 92.2%, and then it only maintained a slight growth to

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92.9% when H2O2 dosage further grew to 30.0 mM. The results can be explained as

follows: (i) The increasing of H2O2 dosage can be activated effectively by Fe0 and its

corrosion products (e.g., Fe2+, Fe3+, Fe2O3, Fe3O4 and FeOOH) to generate more

radicals (e.g., HO•)(11); (ii) As shown in Eqs. (9) and (10), H2O2 can react with

persulfate to form the radicals (e.g., SO4•-, HO• and O2

•-)(12, 13); (iii) The further

increase of H2O2 dosage did not markedly increase the PNP removal markedly due to

the reaction of radicals with H2O2 to produce less reactive radicals (Eq. (11)). Thus,

the optimal H2O2 dosage was selected as 20.0 mM in the following experiments.

S2O82-+H2O2→2SO4

•-+2HO• (9)

S2O82-+2H2O2→2SO4

2-+2O2•-+4H+ (10)

HO•+H2O2→H2O +HO2• (11)

2.1.3. Effects of persulfate dosage

Persulfate is a critical parameter as the source of SO4•- in Fe0/H2O2/persulfate

process. Fig. S1(c) shows the effects of persulfate dosage (0-25.0 mM) on the PNP

removal. In particular, PNP removal significantly increased to 96.3% when persulfate

dosage increased to 7.5 mM. However, the continuous increase of persulfate dosage

(from 7.5 to 25.0 mM) could only improve PNP removal from 96.3% to 98.5%. In the

initial phase (persulfate dosage of 0-25.0 mM), the increased persulfate could react

with Fe0 and its corrosion products to generate more SO4•-, which could improve PNP

degradation. Meanwhile, the increased persulfate could also facilitate the reaction

between persulfate and H2O2 to generate more radicals (e.g., SO4•- and HO•)(14). In a

word, the increase of persulfate could significantly enhance the yield of the radicals

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when persulfate dosage was below 7.5 mM. Nevertheless, the excess persulfate not

only was activated to generate SO4•-, but also reacted with Fe0 to produce excess Fe2+

that could consume the radicals in solution(15). In addition, SO4•- recombination and

reaction with persulfate could occur when excess persulfate was added in the reaction

process (Eqs. (12) and (13))(14). Therefore, the optimal persulfate dosage of 7.5 mM

was selected in the following experiments.

SO4•- + SO4

•-→S2O82- (12)

SO4•- + S2O8

2-→SO42-+ S2O8

•- (13)

2.1.4. Effects of initial pH

Fenton-like process is intensely dependent on the solution pH mainly due to iron

and H2O2 factors. Effects of initial pH value (3.0-13.0) on PNP removal were

investigated thoroughly. Fig. S1(d) shows that PNP removal sharply increased to

99.0% when the initial pH decreased from 13.0 to 5.0. Then, the obtained PNP

removal decreased a little to 97.6% when initial pH further decreased from 5.0 to 3.0.

The results suggest that the lower initial pH was favorable for the PNP degradation by

Fe0/H2O2/persulfate system. The results can be explained as follows: (i) The higher pH

(> 6.0) would cause the formation of inactive iron oxohydroxides and ferric hydroxide

precipitate(16), which would inhibit the generation of radicals. Meanwhile, auto-

decomposition of H2O2 is accelerated at higher pH(17). For example, the optimum pH

for Fenton reaction was about 3.0, regardless of the pollutant substrate(18); (ii)

However, the too low pH (< 3.0) would result in the excess H+ present in the solution

that can deplete the HO• and then limit the removal of pollutants (Eq. (14))(19).

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Furthermore, iron complex species [Fe(H2O)6]2+ would be formed at pH of around 2.0,

which reacts more slowly with H2O2 than other species(20). In addition, the H2O2 gets

solvated in the presence of high concentration of H+ ions to form stable oxonium ions

[H3O2]+, which make H2O2 more stable and reduce its reactivity with ferrous ions(18).

In this study, however, the maximum PNP removal of 99.0% was obtained at initial

pH 5.0 because of the extra H+ from the decomposition of persulfate (Eqs. (15)-(16))

(21). Since the pH (5.3) of 500 mg/L PNP aqueous solution without adding acid was

close to the optimal pH (5.0), the initial pH of 500 mg/L PNP aqueous solution was

not adjusted in the following experiments.

H+ + HO• + e- →H2O (14)

H2O + S2O82- →2HSO4

- + 1/2O2 (15)

HSO4- →SO4

2- + H+ (16)

2.2. Parameters optimization (response surface methodology (RSM))

On the basis of the above optimal parameters (i.e., Fe0 dosage of 2.0 g/L, H2O2

dosage of 20.0 mM, persulfate dosage of 7.5 mM, initial pH of 5.3) obtained from the

single-factor experiments, the interaction among the four independent parameters (Fe0

dosage, H2O2 dosage, persulfate dosage and initial pH) were investigated thoroughly

by RSM. The outcomes recommended by CCD models of RSM were analyzed by

software. Subsequently, analysis of variance (ANOVA), regression coefficients and

polynomial regression equation were obtained. Results of the experimental matrix of

corresponding CCD design are presented in Table S1. Consequently, A (Fe0 dosage),

B (H2O2 dosage), C (persulfate dosage), D (initial pH), AB, AC, AD, BC, BD, CD, A2,

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B2, C2, D2, ABC, ABD, BCD, A2B, A2C, A2D and A2B2 were considered as significant

parameters of PNP removal by Fe0/H2O2/persulfate system.

As presented in Table S2 obtained from the Design-Expert 8.0.6, the “Model F-

value” of 308.06 and the value of “Prob > F” for the quartic model indicated that the

model was significant and there was only 0.01% chance that the “Model F-value”

could have been occurred as the result of noise. The value of “Prob > F” for the

model, being less than 0.05 (< 0.0001), implied that the model was statistically

significant. It should be noted that the “Lack of Fit p-value” was 0.98, which

suggested that the lack of fit was not significant and the model had a good

predictability. Besides, “Adeq Precision” reached 63.69, which indicated that the

signal to noise ratio was adequate (>4). Accuracy of experimental procedure is

acceptable if the ‘coefficient of variation’ (CV) is not greater than 10%. The CV value

of 2.55% demonstrates that a high reliability of experiments have been carried out.

Higher values for coefficients of determination R2 and Radj2 which are further

confirmation for fitness of the model were calculated as 0.9990 and 0.9957

respectively. The R2 of 0.9990 indicates that the regression model represented 99.90%

of the experimental results and only about 0.1% of the variability in the response was

not explained by this model(22). Thus, the model may be summarized as a

simultaneous function of Fe0 dosage (A), H2O2 dosage (B), persulfate dosage (C) and

initial pH (D) as follows:

PNP removal (%) = + 60.82 + 8.63A + 7.95B + 12.45C – 7.05D + 1.07AB + 4.73AC

+ 2.54AD – 1.31BC – 2.54BD – 4.56CD + 4.05A2 + 5.37B2 +

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2.97C2 – 3.30D2 – 1.62ABC + 1.99ABD – 0.74ACD + 1.44BCD –

4.94A2B – 6.66A2C – 10.34 A2D – 20.69 A2B2

Fig. S2 examines the correlation between the actual and predicted values of COD

removal. On the basis of Fig. S2, the developed quartic model wonderfully fit with the

experimental result. The distributed points relatively near to the straight line show a

good agreement between the predicted and actual values within the range of

experiment. Moreover, the result indicates a wonderful relationship between actual

and predicted values of the response in PNP removal obtained by Fe0/H2O2/persulfate

system. The results further proved that the RSM model excellently fit with the

experimental results.

According to the obtained RSM model, optimization of the four experimental

parameters could be conducted. An optimal condition of 1.3 g/L Fe0, 24.8 mM H2O2,

6.7 mM persulfate and initial pH 5.1 was predicted. In three parallel experiments

which were carried out under the optimal condition suggested by the software, the

average of PNP removal was 99.9%. Therefore, a good agreement between the model

prediction and the experimental data may demonstrate the validity of the model,

indicating that the optimization parameters proposed in the present work are reliable.

2.3. Interactive relationship of Fe0, H2O2 and persulfate

The 3D surface plots for the effect of parameters on PNP removal, which disclose

the mutual interaction between parameters and response, were constructed according

to the fitted models. Fig. S3 presents the plots with one variable kept at medium level

and the other two within the tested range. Fig. S3(a) illustrates the interactive

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relationship between Fe0 and H2O2. With the H2O2 dosage increasing in proportion, an

increase in the Fe0 dosage from 0.3 to 2.3 g/L led to a meager increase in the PNP

removal. Nevertheless, with the continual increasing of H2O2 dosage, PNP removal

would present a rising trend to the top point, and then decrease. In addition, for any

addition dosage of Fe0, an increase in the H2O2 dosage from 5.0 to 25.0 mM made the

PNP removal increase initially and decrease subsequently. The result confirms the

synergistic effect and interaction between Fe0 and H2O2. Zhou and his colleagues also

found similar effect between Fe0 and H2O2 when study the oxidation of 4-

chlorophenol by heterogeneous Fe0/H2O2(11).

Fig. S3(b) illustrates the interactive relationship between Fe0 and persulfate. The

lower dosage of Fe0 and persulfate has little effect on the PNP removal increasing.

However, at a persulfate dosage of 10.5 mM, the PNP removal would enhance with

the augment of Fe0 dosage appropriately and decline if Fe0 dosage exceeded the

optimum value. This could be attributed to the excessive Fe2+ in the solution would act

as the HO• and SO4•- scavenger(14). At a Fe0 dosage of 0.3 g/L, with increase of

persulfate dosage, there was a little increase observed in PNP removal. Since the

superfluous persulfate would react with SO4•- according to Eq. (13), the available SO4

•-

concentration in solution decreased. In summary, when the ratio of Fe0 and PS was

appropriate, a synergistic effect would exhibit in the Fe0-H2O2-PS system.

Fig. S3(c) evaluates the effect of pH and Fe0 dosage on the PNP removal. With the

increasing of pH, PNP removal decreased obviously. pH influences not only the

surface iron leaching process, but also iron speciation and reactivity in the induced

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homogeneous Fenton reactions. On one hand, Fe2+ in solution would change to

Fe(OH)+ and Fe(OH)2 as pH increases to 4.0(23). On the other hand, high pH

suppressed the iron corrosion, thus the radicals would decrease due to the less free

iron ions. And presence of relatively inactive iron oxohydroxides and formation of

ferric hydroxide precipitate made the activity of Fenton reagent reduce(18). Fig. S3(d)

shows the effect of persulfate and H2O2 dosage on the PNP removal. At a Fe0 dosage

of 1.3 g/L, increase of persulfate dosage (from 2.5 to 10.5 mM) or H2O2 dosage (from

5.0 to 25.0 mM) led to increase in PNP removal. That was because the addition of

persulfate and H2O2 accelerate the Fenton-like reaction, thus abundant radicals (e.g.,

SO4•-, HO•, HO2

•, O2•-). It is evident from Fig. S3(c) that the acid condition could favor

the corrosion of Fe0 and more free radicals would produce with a suitable Fe0 dosage.

Interaction between pH and H2O2 dosage in Fig. S3(e) reveals that under lower pH

condition, PNP removal was much higher than that at higher pH and increasing the

H2O2 dosage from 5.0 to 25.0 mM led to an obvious PNP removal growth. However,

at higher pH, increasing the H2O2 dosage had a slight increase in the PNP removal.

Yang et al.(24) and Xu et al.(25), from different research group, observed that organic

in wastewater could be treated effectively under acid condition, and the treatment

efficiency decreased obviously with an increase in pH. Finally, Fig. S3(f) shows that,

with the increase of PS dosage and the decrease of pH, a maximum PNP removal was

obtained. However, the initial pH had a little effect on the PNP removal for that the

addition of persulfate would make the solution acidic. A. Ghauch et al. also proved

that the decomposition of persulfate would release a plenty of H+ due to the formation

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of HSO4- responsible for the release of protons (Eqs. (15)-(16))(26). Thus, the acid

condition and addition of persulfate could not only promote the corrosion rate of Fe0,

bur also favor the generation of amounts of radicals (e.g., HO• and SO4•-).

2.4. Proposed reaction pathway for the destruction of PNP

In literature, the previous studies show that the benzene ring structure of p-

nitrophenol would be opened by oxidation process and generated the small molecular

organics (e.g., fumaric acid, maleic acid and acrylic acid) which would be further

degraded into CO2 and H2O(27). The degradation intermediates detected in this study

were p-aminophenol, p-benzoquinone, fumaric acid and maleic acid. The

concentration variation of each intermediate and the residual PNP during 20 min

treatment process by Fe0/H2O2/persulfate system is presented in Fig. 2. It can be seen

that PNP had been removed absolutely in the initial 6 min treatment process.

Meanwhile, the reduction product (i.e., p-aminophenol) rapidly increased to the

maximum (10.9 mg/L) at 100 s, and then it began to decrease gradually in the

following treatment process. In addition, the concentration of p-benzoquinone also

increased rapidly to the maximum (9.0 mg/L) at 40 s, and it was further removed in

following reaction time. Hydroquinone was not been detected by HPLC, which might

suggest hydroquinone was not produced in this system or was oxidized to p-

benzoquinone instantly in the catalytic oxidation(28). Furthermore, the concentration

of fumaric acid and maleic acid increased to the top point and decreased in a certain

extent as the reaction progress, which suggest that these intermediates could be

further decomposed and would not be accumulated largely in the treatment process.

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The concentrations of NO3- and NO2

- detected in the treatment effluent of

Fe0/H2O2/persulfate system reached 189.5 mg/L and 5.0 mg/L, respectively. It can be

calculated that the sum (i.e., 44.2 mg/L) of nitrate nitrogen (NO3--N) and nitrite

nitrogen (NO2--N) in the effluent was lower than the theoretical nitrogen

concentration (i.e., 50.4 mg/L) of 500 mg/L PNP aqueous solution. The results

present that the prime organic nitrogen of PNP was oxidized into NO2- and NO3

-, and

the other organic nitrogen might be transferred into N2, N2O or smaller molecular

organic nitrogen.

According to the measured intermediates, the main degradation pathway is

proposed in Fig. S5. In particular, two degradation pathways were proposed as

follows: (i) combined reduction and oxidation: According to the intermediates

detected by HPLC, it can be deduced that PNP is first reduced to p-nitrosophenol by

direct reduction of Fe0 or Fe2+ or indirect reduction of [H]abs, which is further reduced

to p-aminophenol. And then p-aminophenol is oxidized to hydroquinone or p-

benzoquinone by SO4•-, HO•, HO2

• and O2•- and so on. Moreover, their benzene rings

are opened and further oxidized to ring cleavage compounds (e.g., fumaric acid and

maleic acid). Finally, most of them are mineralized into CO2 and H2O. The

phenomenon was in accordance with the similar study reported in the literatures(28,

29). (ii) direct oxidation: PNP is oxidized directly to p-benzoquinone, and then they

are further transfered to fumaric acid and maleic acid. Finally, most of them are

mineralized completely. Therefore, a high PNP removal (99.0%) was obtained after 6

min treatment by Fe0/H2O2/persulfate system. The detected NO3- and NO2

- indicate

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that the main organic nitrogen of PNP was oxidized into NO2- and NO3

-, and the other

organic nitrogen might be transferred into N2, N2O or the smaller molecular organic

nitrogen.

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Reference

1. Liang C, Huang C-F, Mohanty N, Kurakalva RM. A rapid spectrophotometric

determination of persulfate anion in ISCO. Chemosphere. 2008;73(9):1540-3.

2. Sannino D, Vaiano V, Ciambelli P, Isupova LA. Mathematical modelling of the

heterogeneous photo-Fenton oxidation of acetic acid on structured catalysts. Chem

Eng J. 2013;224(0):53-8.

3. Xiong X, Sun B, Zhang J, Gao N, Shen J, Li J, et al. Activating persulfate by Fe 0

coupling with weak magnetic field: Performance and mechanism. Water Res.

2014;62:53-62.

4. Oh S-Y, Kang S-G, Chiu PC. Degradation of 2, 4-dinitrotoluene by persulfate

activated with zero-valent iron. Sci Total Environ. 2010;408(16):3464-8.

5. Tsitonaki A, Petri B, Crimi M, Mosbæk H, Siegrist RL, Bjerg PL. In situ

chemical oxidation of contaminated soil and groundwater using persulfate: a review.

Crit Rev Env Sci Tec. 2010;40(1):55-91.

6. Zhu L, Ai Z, Ho W, Zhang L. Core–shell Fe–Fe2O3 nanostructures as effective

persulfate activator for degradation of methyl orange. Sep Purif Technol.

2013;108:159-65.

7. Matzek LW, Carter KE. Activated persulfate for organic chemical degradation: A

review. Chemosphere. 2016;151:178-88.

8. Munoz M, de Pedro ZM, Casas JA, Rodriguez JJ. Preparation of magnetite-based

catalysts and their application in heterogeneous Fenton oxidation – A review. Applied

Catalysis B: Environmental. 2015;176–177:249-65.

9. Wang K-S, Lin C-L, Wei M-C, Liang H-H, Li H-C, Chang C-H, et al. Effects of

16 / 29

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309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

3334

dissolved oxygen on dye removal by zero-valent iron. J Hazard Mater. 2010;182(1–

3):886-95.

10. Kallel M, Belaid C, Mechichi T, Ksibi M, Elleuch B. Removal of organic load

and phenolic compounds from olive mill wastewater by Fenton oxidation with zero-

valent iron. Chem Eng J. 2009;150(2–3):391-5.

11. Zhou T, Li Y, Ji J, Wong F-S, Lu X. Oxidation of 4-chlorophenol in a

heterogeneous zero valent iron/H2O2 Fenton-like system: Kinetic, pathway and effect

factors. Separation and Purification Technology. 2008;62(3):551-8.

12. Crimi ML, Taylor J. Experimental evaluation of catalyzed hydrogen peroxide and

sodium persulfate for destruction of BTEX contaminants. Soil & Sediment

Contamination. 2007;16(1):29-45.

13. Tang J, Tang L, Feng H, Zeng G, Dong H, Zhang C, et al. pH-dependent

degradation of p-nitrophenol by sulfidated nanoscale zerovalent iron under aerobic or

anoxic conditions. J Hazard Mater.

14. Monteagudo JM, Durán A, González R, Expósito AJ. In situ chemical oxidation

of carbamazepine solutions using persulfate simultaneously activated by heat energy,

UV light, Fe2+ ions, and H2O2. Applied Catalysis B: Environmental. 2015;176–

177:120-9.

15. Ayoub G, Ghauch A. Assessment of bimetallic and trimetallic iron-based systems

for persulfate activation: Application to sulfamethoxazole degradation. Chem Eng J.

2014;256:280-92.

16. Parsons S. Advanced oxidation processes for water and wastewater treatment.

17 / 29

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

3536

Water Intelligence Online. 2005;4:9781780403076.

17. Szpyrkowicz L, Juzzolino C, Kaul SN. A comparative study on oxidation of

disperse dyes by electrochemical process, ozone, hypochlorite and Fenton reagent.

Water Res. 2001;35(9):2129-36.

18. Babuponnusami A, Muthukumar K. A review on Fenton and improvements to the

Fenton process for wastewater treatment. Journal of Environmental Chemical

Engineering. 2014;2(1):557-72.

19. Xu XR, Li XY, Li XZ, Li HB. Degradation of melatonin by UV, UV/H2O2,

Fe2+/H2O2 and UV/Fe2+/H2O2 processes. Separation & Purification Technology.

2009;68(68):261–6.

20. Xu X-R, Li X-Y, Li X-Z, Li H-B. Degradation of melatonin by UV, UV/H 2 O 2,

Fe 2+/H 2 O 2 and UV/Fe 2+/H 2 O 2 processes. Sep Purif Technol. 2009;68(2):261-

6.

21. Liang C, Lee IL, Hsu IY, Liang C-P, Lin Y-L. Persulfate oxidation of

trichloroethylene with and without iron activation in porous media. Chemosphere.

2008;70(3):426-35.

22. Toemen S, Bakar WAWA, Ali R. Investigation of Ru/Mn/Ce/Al2O3 catalyst for

carbon dioxide methanation: Catalytic optimization, physicochemical studies and

RSM. J Taiwan Inst Chem E. 2014;45(5):2370-8.

23. He J, Yang X, Men B, Wang D. Interfacial mechanisms of heterogeneous Fenton

reactions catalyzed by iron-based materials: A review. J Environ Sci. 2016;39:97-109.

24. Yang C, Wang D, Tang Q. The synthesis of NdFeB magnetic activated carbon and

18 / 29

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

3738

its application in degradation of azo dye methyl orange by Fenton-like process. J

Taiwan Inst Chem E. 2014;45(5):2584-9.

25. Xu H-Y, Liu W-C, Qi S-Y, Li Y, Zhao Y, Li J-W. Kinetics and optimization of the

decoloration of dyeing wastewater by a schorl-catalyzed Fenton-like reaction. Acta

Neurovegetativa. 2014;79(3):361-77.

26. Ghauch A, Ayoub G, Naim S. Degradation of sulfamethoxazole by persulfate

assisted micrometric Fe0 in aqueous solution. Chem Eng J. 2013;228:1168-81.

27. Martín-Hernández M, Carrera J, Suárez-Ojeda ME, Besson M, Descorme C.

Catalytic wet air oxidation of a high strength p-nitrophenol wastewater over Ru and Pt

catalysts: Influence of the reaction conditions on biodegradability enhancement. Appl

Catal B-environ. 2012;123–124(0):141-50.

28. Yuan S, Tian M, Cui Y, Lin L, Lu X. Treatment of nitrophenols by cathode

reduction and electro-Fenton methods. J Hazard Mater. 2006;137(1):573-80.

29. Lai B, Zhang YH, Chen ZY, Yang P, Zhou YX, Wang JL. Removal of p-

nitrophenol (PNP) in aqueous solution by the micron-scale iron-copper (Fe/Cu)

bimetallic particles. Appl Catal B-environ. 2014;144(0):816-30.

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Table S1 The CCD design and response of PNP removal by Fe0/H2O2/persulfate system.

Factorslevels and ranges

-α Low (-1) Middle (0) High (＋1) ＋α

A: Fe0 dosage (g/L) 0.3 0.8 1.3 1.8 2.3 B: H2O2 dosage (mM) 5.0 10.0 15.0 20.0 25.0

C: persulfate dosage (mM) 2.5 4.5 6.5 8.5 10.5

D: initial pH 4.0 5.3 6.6 7.9 9.2

Std RunA: Fe0

dosageB: H2O2

dosageC: persulfate

dosageD: pH

PNP Removal (%)

1 21 0.8 10.0 4.5 5.3 48.32 27 1.8 10.0 4.5 5.3 47.63 1 0.8 20.0 4.5 5.3 63.24 9 1.8 20.0 4.5 5.3 65.95 30 0.8 10.0 8.5 5.3 60.06 13 1.8 10.0 8.5 5.3 88.37 8 0.8 20.0 8.5 5.3 71.08 16 1.8 20.0 8.5 5.3 88.59 26 0.8 10.0 4.5 7.9 27.710 12 1.8 10.0 4.5 7.9 32.811 28 0.8 20.0 4.5 7.9 19.312 22 1.8 20.0 4.5 7.9 42.513 17 0.8 10.0 8.5 7.9 19.014 4 1.8 10.0 8.5 7.9 45.915 5 0.8 20.0 8.5 7.9 17.016 11 1.8 20.0 8.5 7.9 50.317 15 0.3 15.0 6.5 6.6 59.318 10 2.3 15.0 6.5 6.6 94.719 29 1.3 5.0 6.5 6.6 66.420 3 1.3 25.0 6.5 6.6 98.221 20 1.3 15.0 2.5 6.6 47.822 24 1.3 15.0 10.5 6.6 97.623 2 1.3 15.0 6.5 4 61.724 14 1.3 15.0 6.5 9.2 33.525 25 1.3 15.0 6.5 6.6 62.526 19 1.3 15.0 6.5 6.6 62.127 7 1.3 15.0 6.5 6.6 61.428 18 1.3 15.0 6.5 6.6 60.929 23 1.3 15.0 6.5 6.6 60.130 6 1.3 15.0 6.5 6.6 57.9

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Table S2 ANVOA (analysis of variance) for the optimized RSM model.

SourceSum of Squares

dfMean Square

F Valuep-value prob>F

Model 14352.49 22 652.39 308.06 < 0.0001 significantA-Fe0 1787.1 1 1787.1 843.87 < 0.0001

B-H2O2 505.62 1 505.62 238.75 < 0.0001C-

persulfate1240.02 1 1240.02 585.54 < 0.0001

D-initial pH

397.62 1 397.62 187.76 < 0.0001

AB 18.28 1 18.28 8.63 0.0218AC 358.16 1 358.16 169.12 < 0.0001AD 103.53 1 103.53 48.89 0.0002BC 27.3 1 27.3 12.89 0.0089BD 103.53 1 103.53 48.89 0.0002CD 332.15 1 332.15 156.84 < 0.0001A2 392.85 1 392.85 185.5 < 0.0001B2 692.3 1 692.3 326.91 < 0.0001C2 211.82 1 211.82 100.02 < 0.0001D2 262.02 1 262.02 123.73 < 0.0001

ABC 41.93 1 41.93 19.8 0.003ABD 63.6 1 63.6 30.03 0.0009ACD 8.85 1 8.85 4.18 0.0802BCD 33.35 1 33.35 15.75 0.0054A2B 130.35 1 130.35 61.55 0.0001A2C 236.3 1 236.3 111.58 < 0.0001A2D 570.63 1 570.63 269.45 < 0.0001A2B2 2283.9 1 2283.9 1078.46 < 0.0001

Residual 14.82 7 2.12Lack of Fit 0.98 2 0.49 0.18 0.8435 not significantPure Error 13.85 5 2.77Cor Total 14367.31 29Std.Dev. 1.46 R2 0.9990

Mean 57.05 RAdj2 0.9957

C.V.% 2.55 Adeq Precision 63.69

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Fig. S1. Effects of (a) Fe0 dosage, (b) H2O2 dosage, (c) persulfate dosage and (d) initial pH

value on the PNP removal in aqueous solution.

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Fig. S2. The actual values plotted against the predicted values derived from the model of

PNP removal (%) from the experimental design.

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Fig. S3. Interactive relationships between (a) Fe0 and H2O2, (b) Fe0 and persulfate, (c)Fe0 and

pH, (d) persulfate and H2O2, (e) H2O2 and pH and (f) persulfate and pH with the 3D response

surfaces for the PNP removal in aqueous solution in Fe0/H2O2/persulfate system.

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Fig. S4. Variations of PNP removal in different systems. ([Fe0]0 = 1.3 g/L, [H2O2]0 = 24.8 mM,

[Na2S2O8]0 = 6.7 mM and stirring speed = 350 rpm)

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Fig. S5. Proposed reaction pathway for the degradation of PNP in the Fe0/H2O2/persulfate

system.

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Fig. S6. XRD pattern of the fresh and reacted Fe0 particles in Fe0/H2O2/persulfate system.

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Fig. S7. Recyclability of Fe0 particle in Fe0/H2O2/persulfate system.

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Fig. S8. The effects of scavengers (EtOH and TBA) on the remoal of PNP in the

Fe0/H2O2/persulfate system.

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