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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: [email protected] (Bo Lai), [email protected] (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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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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