Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
http://www.ijehse.com/content/12/1/1
JOURNAL OF
ENVIRONMENTAL HEALTH
SCIENCE & ENGINEERING
RESEARCH ARTICLE
Open Access
Response surface analysis of photocatalytic
degradation of methyl tert-butyl ether by
core/shell Fe3O4/ZnO nanoparticles
Mojtaba Safari1, Mohammad Hossein Rostami1*, Mehriana Alizadeh1, Atefeh Alizadehbirjandi2,
Seyyed Ali Akbar Nakhli2 and Reza Aminzadeh1
Abstract
The degradation of methyl tert-butyl ether (MTBE) was investigated in the aqueous solution of coated ZnO onto
magnetite nanoparticale based on an advanced photocatalytic oxidation process. The photocatalysts were synthesized
by coating of ZnO onto magnetite using precipitation method. The sample was characterized by X-ray diffraction
(XRD), scanning electron microscopy (SEM), and vibration sample magnetometer (VSM). Besides, specific surface area
was also determined by BET method. The four effective factors including pH of the reaction mixture, Fe3O4/ZnO
magnetic nanoparticles concentration, initial MTBE concentration and molar ratio of [H2O2]/ [MTBE] were optimized
using response surface modeling (RSM). Using the four-factor-three-level Box–Behnken design, 29 runs were designed
considering the effective ranges of the influential factors. The optimized values for the operational parameters under
the respective constraints were obtained at PH of 7.2, Fe3O4/ZnO concentration of 1.78 g/L, initial MTBE concentration
of 89.14 mg/L and [H2O2]/ [MTBE] molar ratio of 2.33. Moreover, kinetics of MTBE degradation was determined under
optimum condition. The study about core/shell magnetic nanoparticles (MNPs) recycling were also carried out and
after about four times, the percentage of the photocatalytic degradation was about 70%.
Keywords: Fe3O4/ZnO nanoparticles, Photocatalytic degradation, MTBE, Response surface modeling
Introduction
Methyl tert-butyl ether (MTBE) is commercially used
as an octane enhancer for gasoline. It can reach underground water resources in different ways such as leaking
underground fuel tanks, leaking pipelines, tank overfilling,
faulty construction at gas stations, spillage from vehicle
accidents and home owner releases may result in contamination of ground and surface water resources [1,2]. The
admissible limit of MTBE in drinking water is 20–40 ppb
[3,4] which has resulted in the prevention of this material
to be used as a gasoline additive since May 2006 [5].
The toxicity of MTBE to animals and humans is well
documented. It is well known that MTBE is carcinogenic
to animals, which is due to diverse properties such as the
existence of ether bond and long sub-branches (more than
one carbon) in its structure. MTBE is known as a very
* Correspondence: mhossein.rostami@gmail.com
1
Department Of Chemical Engineering, Amirkabir University Of Technology,
Tehran, Iran
Full list of author information is available at the end of the article
resistant substance to natural degradation [6,7]. In recent
decades, many technologies have been devoted to MTBE
degradation in water. Some of these technologies included adsorption on granular activated carbon (GAC),
air stripping, advance oxidation processes (AOPs) and
biodegradation [8]. Over the past three decades, AOPs
were efficient methods for degradation of organic contaminants. An AOP is a photocatalysis process, which
mineralizes and degrades the organic contaminants,
accordingly [9]. Many researchers have studied the
photocatalytic degradation of MTBE using TiO2 and
metal-doped TiO2 in either powder or thin film form
[9-11]. However, most of these studies have followed
the classical method of optimizing one factor at a time
(OFAT), which is a time consuming and laborious task.
This method, also, does not consider the interactions
among the operational factors. However, Response surface
methodology (RSM) can combine mathematics and
statistics to analyze the relative significance of various
operating parameters even in complicated systems
© 2014 Safari et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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[12]. Hence, this method can be applied to determine
the optimum conditions of various reactions in a more
convenient way resulting in saving time, labor, and cost.
Many types of photocatalytic reactors have been proposed according to respective application demands; among
them, however, a slurry type reactor has proved to be
most attractive for degrading organic contaminants which
dissolve in water namely in terms of reaction surface area
per unit volume of the reactor [13]. Nonetheless, one of
the main problems of the suspended photocatalyst system
is that it requires a separation step to recover photocatalyst particles. In this case, a suitable technique such as
centrifugation or filtration step is required to reuse fine
photocatalyst particles [14].
In this work Fe3O4/ZnO core/shell composite catalyst
was synthesized and then characterized by XRD, SEM
and VSM. The magnetic core enhancing the separation
properties of suspended particles from solution and the
photocatalytic properties of the outer shell zinc oxide
are used to destroy organic contaminants in wastewater
[15]. The four effective parameters, optimized using RSM,
were (i) pH, (ii) coating of ZnO onto magnetite concentration, (iii) MTBE initial, and (iv) molar ratio of
[H2O2]o/[MTBE]o. In the end, kinetics of MTBE degradation was determined in optimum condition.
Materials and methods
Materials
Methyl tert-butyl ether (99.9%), ferric chloride (FeCl3_6H2O),
hydrogen peroxide (35% w/w), ferrous sulfate (FeSO4_7H2O),
zinc acetate (ZnAC2_2H2O), aqueous ammonia (NH3_H2O)
HNO3 and NaOH were purchased from Merk. ammonium carbonate ((NH4)2CO3) purchased from Dae jung.
Instruments
The instruments used for studying synthesized nanoparticles were XRD (Equinox 3000, Inel france), SEM (AIS2100,
seron technology), BET (Autosorb-1, Quantachrome), 2
lamps (UVa 11W, Philips, Netherland), gas choromatography (GC) equipped with a helium ionization detector
(HID) (Model GC-Acme 6100, Korea), vibration sample
magnetometer (VSM, Meghnatis Daghigh Kavir Co., Iran),
magnetic stirrer (Dalahan Labtech, LMS-1003) and digital
pH meter (Elmetron, Cpc-501).
Preparation of the photocatalyst
A co-precipitation method was used to synthesize the
Fe3O4 magnetic nanoparticles (MNPs). Co-precipitation is
a facile and convenient way to synthesize MNPs from
aqueous salt solutions. This is accomplished by addition of
ammonia to mixture of ferric chloride (0.5 M) and ferrous
sulfate (0.5 M) with molar ratio of 1.75:1 under inert argon
protection until pH value reached to 9. After 30 min
stirring, the precipitate collected using a magnet and
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washed with deionized water until pH reached to 7. The
modification process has been carried out via sonication
of 4 g Fe3O4 and 200 ml sodium citrate (0.5 M) mixture
for 20 min, which was then stirred for 12 h at 60°C under
Ar protection. Afterwards, the precipitate collected and
rinsed with acetone. The Fe3O4/ZnO core/shell MNPs
were obtained by coating the modified Fe3O4 MNPs with
direct precipitation using zinc acetate and ammonium
carbonate. The modified Fe3O4 added to 100 ml of
deionized water and sonicated for 20 min to make a
stable ferrofluid. Then, 30 ml of this ferrofluid was
added into a flask to form Fe3O4/ZnO composite. Two
solutions were made by adding 12.16 g ZnAC2_2H2O and
7.6 g (NH4)2CO3 respectively into 100 ml of deionized
water, and then, these two solutions were dropped slowly
into the flask. Then the precipitate was collected and
washed with water, aqueous ammonia (pH 9) and ethanol.
Thereafter, the precipitate was dried under vacuum in
12 h and calcined according to desired calcination
temperature and time [16].
Experimental set up
Photocatalytic degradation of MTBE was performed in
a slurry batch reactor which was configured with a
cylindrical glass with one liter in volume. In order to
control the temperature of the reactions, the reactor
was provided with a jacket for water circulation. Two
lamps (11w, Philips, Netherland), which were immersed in
the solution, were applied to supply the UV radiation in
the reactor. The reactor was tightly sealed and in order
to ensure well-mixing during irradiation, the nanoparticles
were dispersed in the solution under magnetic stir. Besides, the air was injected into the reactor to supply the
required amount of oxygen for the photocatalysis.
Experimental design by RSM method
Initially, preliminary experiments by following single factor
study method were performed in order to find the most
effective experimental parameters and their ranges affecting the photocatalytic degradation of MTBE. The selected
parameters were catalytic dose, initial concentration of
MTBE, initial concentration of H2O2 and pH.
The four selected experimental parameters were optimized using RSM considering them as independent variables and removal percentages of MTBE as response
variables. By applying Box-Behnken design experiments,
the required number of experiments were designed. This
method was used because it is very efficient and does not
contain any point at the vertices of the cubic region
formed by the upper and lower limits of the variables.
Such design along with RSM is widely applied for
optimization of various physical, chemical and biological
processes [17,18].
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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As expressed in equation 1, the results were fitted to an
empirical quadratic polynomial model for the aforesaid
parameters using RSM.
Y ¼ β0 þ β1 A þ β2 B þ β3 C þ β4 D þ β11 A2
þβ22 B2 þ β33 C2 þ β44 D2 þ β12 AB þ β23 BC
þβ31 CA þ β41 DA þ β42 BD þ β34 CD
ð1Þ
where Y denotes the response variable, β0 the intercept,
β1,β2,β3,β4 the coefficients of the independent variables,
β11,β22,β33,β44 the quadratic coefficients, β12,β23,β31,β41,β42,β34
the interaction coefficients and A, B, C, D are the independent variables. Multivariate regression analysis and
optimization process were performed by means of RSM
and using Design Expert software (version 6.0.8, Stat
Ease Inc., USA). The obtained values from analysis of
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variance (ANOVA) were found significant at p < 0.05.
The optimum values for the independent variables were
found using three-dimensional response surface analysis
of the independent and dependent variables. The designed
experiments plus the experimental and predicted values of
the response are presented in Table 1. Also, the variations
are shown in Figure 1.
Results and discussion
Characterization of MNPs
The X-ray diffraction pattern of modified Fe3O4 sample
and Fe3O4/ZnO core/shell is presented in Figure 2. The
average crystallite size was calculated using the Debye–
Scherrer equation d= Kλ/(βcosθ) were about 13.9 nm
(a), 11.2 nm (b) for modified Fe3O4 and Fe3O4, respectively. According to Figure 2b it is shown that after coating
Table 1 Box–Behnken experiments along with actual and predicted values of responses
Std
Run
B, initial MTBE concentration (ppm)
A, catalytic dose (g/L)
C, pH
D, initial H2O2 (ppm)
Y, COD MTBE removal (%)
Actual
Predicted
7
1
100
1
7
10
59.1
59.19
11
2
50
2.5
7
10
92.5
92.28
3
3
50
2.5
9
5
90.1
90.27
24
4
100
2.5
9
10
59.5
60.25
9
5
50
2.5
7
0
94.5
94.75
6
6
100
4
7
0
58.4
58.97
2
7
150
2.5
5
5
55.3
55.78
23
8
100
2.5
5
10
63.5
62.95
29
9
100
2.5
7
5
77.8
76.78
12
10
150
2.5
7
10
56
55.5
22
11
100
2.5
9
0
62
62.12
10
12
150
2.5
7
0
57
56.97
28
13
100
2.5
7
5
76.8
76.78
13
14
100
1
5
5
58.5
58.12
5
15
100
1
7
0
60.2
60.45
15
16
100
4
5
5
57.5
56.84
4
17
150
2.5
9
5
53
52.38
17
18
50
1
7
5
89.3
88.07
27
19
100
2.5
7
5
75.8
76.78
20
20
150
4
7
5
47.8
48.6
1
21
50
2.5
5
5
91.2
92.47
14
22
100
1
9
5
55.8
56.22
26
23
100
2.5
7
5
77.3
76.78
19
24
50
4
7
5
87.2
86.94
16
25
100
4
9
5
55
54.13
21
26
100
2.5
5
0
66.2
65.02
8
27
100
4
7
10
55.9
56.3
25
28
100
2.5
7
5
76.2
76.78
18
29
150
1
7
5
52
51.84
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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Figure 1 Plot of the actual and predicted values for %MTBE removal.
some enhances in peak intensity was caused by overlapping of Fe3O4 peaks.
In addition, Figure 3 represents SEM images of the
samples. The SEM photographs of Fe3O4 MNPs before
and after treating with sodium citrate are shown in
Figure 3a and b respectively. It is shown that the dispersion of modified iron oxide is better than unmodified
one. Figure 3c represents Fe3O4/ZnO core/shell particles
which their average particle size was obtained about 60 nm.
The magnetic properties of MNPs are illustrated in
Figure 4. It demonstrates that the coating process did
not change the superparamagnetism of MNPs.
BET surface areas were determined using 3-points method
for Fe3O4/ZnO nanoparticles which was 65 m2/gr.
Statistical analysis
To acquire a desirable model, The results are summarized
in a common ANOVA table. The ANOVA table for removal
percentage of MTBE response is exhibited in Table 2. The
R-square is found to be 0.99, which is close to 1, which
implies that about 99% of changes in the data can be
explained by the model. The lack-of-fit P value of 0.3855
shows that the lack-of-fit is not significant relative to net
error. For a predictive model the value of Lack of Fit
should be not significant.
Following the experimental design (Table 2), empirical
second order polynomial equations are developed for the
removal percentage of MTBE in terms of the three independent variables as is expressed in equation 2.
Figure 2 XRD pattern of (a): modified Fe3O4 and (b): Fe3O4/ZnO core/shell.
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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Figure 3 SEM images of (a): Fe3O4 (b): modified Fe3O4 (c) Fe3O4/ZnO core/shell.
%MTBE removal¼‐4:7400‐0:6688MTBE þ28:1254pH
þ26:8259TiO2 þ2:1927 H2O2 þ0:0016 MTBE 2 ‐2:0423pH 2
‐5:3474TiO22 ‐0:2408H2O22 ‐0:0030MTBE pH þ0:0010
MTBE H2O2 þ0:0167 pH TiO2 þ0:0050pH H2O2
‐0:0467 TiO2H2O2
ð2Þ
The ANOVA of the second order quadratic polynomial
model (F = 487.4, p < 0.0001) indicates that the model
is significant, i.e. there is only a chance of 0.01% for
occurrence of the model’s F-value due to the noise. The
ANOVA regarding the regression models’s coefficient of
Figure 4 Magnetic hysteresis curves of (1): modified Fe3O4 (2): Fe3O4/ZnO core/shell.
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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Table 2 ANOVA for response surface reduced quadratic model- analysis of variance
Source
Sum of squares
Degrees of freedom
Mean square
F value
p-value prob > F
Model
5867.65
14
419.12
487.39
<0.001
Significant
Residual
12.04
14
0.86
Lack of fit
9.43
10
0.94
1.45
0.3855
Not significant
0.65
R-squared
0.9980
Adj R-squared
0.9959
Adeq precision
69.192
Pure error
2.61
4
Cor total
5879.69
28
the removal percentage of MTBE is presented in Table 3
as an extra tool to check the final model’s adequacy. The
normal probability plot (scatter diagram) for the studentized residuals is illustrated in Figure 5. The points on this
plot lie reasonably close to a straight line, confirming that
the errors have a normal distribution with a zero mean
and a constant. The curvature P-value < 0.0001 indicates
that there is a significant curvature (as measured by the
difference between the mean center points and the mean
factorial points) in the design space. As a result, a linear
model along with the interaction terms giving a twisted
plane was not adequate to explain the response. Besides,
plots of the residuals in Figure 6 reveal that they have no
obvious pattern, and their structure is rather abnormal.
Moreover, they indicate equal scatter above and below
the x-axis, implying the proposed model’s adequacy, so
there is no reason to suspect any violation. The optimum
conditions for the maximum degradation of MTBE, that is
selected with regard to proximity to the natural pH and
using lowest catalyst loading, shown in Table 4 and the
effect of the independents variable on the desirability
shown in Figure 7.
Effect of Initial pH
pH is one of the most crucial parameters in photocatalytic degradation of organic contaminants. Figure 7b and
c show the percent of degradation efficiency for several
initial pH conditions. The degradation efficiency increases
as the pH value is incremented from 5 to 7 and then
adversely decreases with the increased value of pH
from 7 to 9. The pH of the solution has complex effects
on the photocatalytic oxidation reaction. However, in
general, the pH effect depends on the type of pollutant
and zero point charge (ZPC) of semiconductor (catalyst)
in the oxidation process. Because, the pH of the solution
affects the electrostatic force between the catalyst surface
and the pollutant. Interactions among the semiconductor
surface, solvent molecules, substrate and charged radicals
formed during the reaction, the interpretation of the effect
of pH on obtained results from photocatalytic degradation
Table 3 ANOVA results for the coefficients of quadratic model for %MTBE removal
Factor
Coefficient estimate
Degree of freedom
Standard error
95% confidence
interval low
95% confidence
interval high
F-value
p-value
Intercept
76.780
1
0.41
75.89
77.67
-
-
A-MTBE
−18.642
1
0.27
−19.22
−18.07
4849.47
< 0.0001
B-pH
−1.400
1
0.27
−1.97
−0.83
27.35
0.0001
C-Catalyst
−1.092
1
0.27
−1.67
−0.52
16.63
0.0011
D-H2O2
−0.983
1
0.27
−1.56
−0.41
13.49
0.0025
A2
4.118
1
0.36
3.34
4.90
127.94
< 0.0001
B2
−8.169
1
0.36
−8.95
−7.39
503.39
< 0.0001
C2
−12.032
1
0.36
−12.81
−11.25
1091.95
< 0.0001
D2
−6.019
1
0.36
−6.80
−5.24
273.29
< 0.0001
AB
−0.300
1
0.46
−1.29
0.69
0.42
0.5281
AC
−0.525
1
0.46
−1.52
0.47
1.28
0.2765
AD
0.250
1
0.46
−0.74
1.24
0.29
0.5982
BC
0.050
1
0.46
−0.94
1.04
0.01
0.9157
BD
0.050
1
0.46
−0.94
1.04
0.01
0.9157
CD
−0.350
1
0.46
−1.34
0.64
0.57
0.4628
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Figure 5 Normal probability plot of residual for %MTBE removal.
cannot be expressed as a whole and this phenomenon
should be tested in the laboratory for each type of pollutant or should be found through available references
at desired operating conditions [19].
The phenomenon can be explained in terms of the
zero point charge location (isoelectric point) of the
Fe3O4/ZnO. In acidic pH, MTBE will be protonized to
Figure 6 Plot of residual vs. predicted response for %MTBE removal.
carry the positive charge while the surface of Fe3O4/ZnO
is electropositive. Therefore, the acidic pH does not favor
the adsorption of MTBE on the Fe3O4/ZnO particles.
When pH is alkaline, MTBE is neutral, but the surface
of Fe3O4/ZnO is electronegative. Hence, adsorption of
MTBE on the Fe3O4/ZnO particles in alkaline pH was
less than that in neutral pH. According to results
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
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Table 4 The optimum conditions selected for the maximum possible the percentage of MTBE removal
Solutions
Number
A, initial MTBE
concentration (g/L)
B, catalytic
dose (g/L)
C, pH
D, initial H2O2 (ppm)
MTBE removal (%)
Desirability
8
55.02
7.09
2.31
2.16
95.407
1
obtained from Figure 7b and c, natural pH was the best
pH value for degradation of MTBE in this study [10].
Effect of Fe3O4/ZnO MNPs concentration
The percentage of degradation efficiency against catalyst
loading is shown in Figure 7a for several initial Fe3O4/ZnO
nanoparticles’ concentrations. The percentage of degradation efficiency increases along the increase in the
catalyst loading from 1 to 2.5 g/L. However, by an increase
in excess of 2.5 g/L, this percentage declines. It should
be noted that, these results are highly contingent on
the maintained experimental condition. As the amount
of catalyst increases, the number of adsorbed photons
and molecules increases as well due to an increase in the
number of Fe3O4/ZnO nanoparticles. As a consequence,
the particle density within the illumination area increases.
This behavior can be attributed to the increase in opacity,
which gives rise to a reduction in the radiation passage
through the reactor [20]. It may also lead to Fe3O4/ZnO
aggregation, reducing the active points on its surface to
Selected
adsorb organic compounds and UV, thereby reducing the
quantity of e-h+ and OH free radicals and affecting the
degradation, accordingly [21]. After reusing of magnetic
particles, a small decrease in the photocatalytic activity
observed. After 4 times, the removal percentage decreased
to about 70 percent. This decrease can be due to fouling
of light-insensitive materials on active pores or loss of
particles (Figure 8).
Effect of initial MTBE concentration
Increase of initial MTBE concentration reduces its degradation as shown in Figure 7a and c. Similar results have
been reported on the photocatalytic oxidation of other
organic compounds interface [6-21]. At low MTBE concentrations, a larger number of water molecules will be
adsorbed onto the available Fe3O4/ZnO nanoparticles,
producing hydroxyl radicals and leading to a rapid oxidation process. On the other hand, at high MTBE concentration, there is a smaller portion of water molecules to
free active sites, since the number of active sites remains
Figure 7 Effect of catalyst loading, Initial MTBE concentration, H2O2 concentration and pH on %MTBE removal. (a): pH=7, H2O2
concentration= 5 mg/L; (b): Initial MTBE concentration= 100 mg/L, Catalyst loading= 2.5 g/L; (C): Catalyst loading= 2.5 g/L, H2O2 concentration=
5 mg/L.
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donor or an acceptor to the system. Usually, molecular
oxygen and hydrogen peroxide are used as electron acceptors in heterogeneous photocatalyzed reactions [23].
H2O2 can generate hydroxyl radicals through two ways
as follows:
Figure 8 MTBE concentration variation with time (at optimum
condition).
the same. Consequently, the competition between the
MTBE concentration and water molecules on adsorption
increases and leading to a decline in the degradation rate.
H2 O2 þ hv →2OH
ð5Þ
H2 O2 þ e → OH þ OH ‐
ð6Þ
The results are presented in Figure 7b show that the
degradation rate had a maximum of the [H2O2]/[MTBE]
molar ratio of 5. However, higher concentration of H2O2
can have a negative effect. This may be due to the formation of HOo2, a species that is significantly less reactive
than HOo [24]. As shown in equations 7 and 8, the excess
H2O2 molecules on the catalyst surface may also act as
powerful scavengers of radicals [25,26].
OH o þ H2 O2 → H2 O þ HOo2
ð7Þ
2 HOo2 → H2 O2 þ Oo2
ð8Þ
Kinetics of MTBE degradation
The Langmuir-Hinshelwood rate expression has been used
to describe the relationship between the heterogeneous
photocatalytic degradation rate and the initial pollutant
concentration [22].
Experimental results in optimum condition (Figure 8)
Indicated that the photodegradation rate of MTBE with
UV/Fe3O4/ZnO/H2O2 fitted the Langmuir-Hinshelwood
(L-H) kinetics model as follows:
−
dC
K r K eC
¼
dt
1 þ K eC
ð3Þ
It is assumed that the photodegradation of MTBE follows
a first-order reaction; therefore the above equation can be
simplified to an apparent first-order equation:
−
dC
K r K eC
¼
¼ KC
dt
1 þ K eC
ð4Þ
where Kr is the reaction rate constant (mg/l.min), Ke is
the adsorption coefficient of the MTBE (l/mg) and Kapp
is the apparent pseudo-first-order constant that is the
multiplication product of the adsorption constant and
the reaction constant. In this study, a reasonable agreement
(R2 = 0.96) was obtained between the experimental results
and the linear form of the L-H expression. Furthermore,
this expression used values of 0.033(1/min) for Kapp.
Conclusions
In this study, Fe3O4/ZnO nanoparticles were successfully
synthesized with average crystal size of 11.2 mm by precipitation method. Synthesized nanoparticles then utilized
as a catalyst for the photocatalytic degradation of MTBE.
The optimum levels of the operational parameters under
the related constraint conditions were found at pH of 7.02,
Fe3O4/ZnO MNPs concentration of 1.78 g/L, initial MTBE
concentration of 89.14 mg/L, and [H2O2]/[MTBE] molar
ratio of 2.33. In addition, according to the LangmuirHinshelwood kinetic model, the apparent pseudo-firstorder constant was 0.033 (1/min) for experimental results
under optimum conditions. Also the recycling and reuse
of MNPs was significantly successful.
Abbreviations
XRD: X-ray diffraction; SEM: Scanning electron microscopy; VSM: Vibration sample
magnetometer; RSM: Response surface modeling; MNP’s: Magnetic nanoparticles;
GAC: Granular activated carbon; OFAT: Optimizing one factor at a time; GC: Gas
chromatography; HID: Helium ionization detector; AVOVA: Analysis of variance;
ZPC: Zero point charge; AOP’s: Advanced oxidation processes.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
MS and MHR designed and performed experiments, analyzed data and
wrote the paper; MA designed and performed experiments; AA and SAAN
performed the experiments and prepared the final manuscript; RA designed
the kinetic model, revised and edited the manuscript. All authors read and
approved the final manuscript.
Effect of hydroxyl peroxide addition
Electron–hole recombination is the main energy-wasting
step in the photocatalytic reaction. The prevention of this
recombination is achieved by adding a proper electron
Acknowledgments
We would like to express our deep gratitude to Professor Manouchehr
Nikazar our research supervisor, for his patient guidance, enthusiastic
encouragement and useful critiques of this research work.
Safari et al. Journal of Environmental Health Sciences & Engineering 2014, 12:1
http://www.ijehse.com/content/12/1/1
Author details
1
Department Of Chemical Engineering, Amirkabir University Of Technology,
Tehran, Iran. 2Department Of Chemical And Petroleum Engineering, Sharif
University Of Technology, Tehran, Iran.
Received: 19 December 2012 Accepted: 29 September 2013
Published: 6 January 2014
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doi:10.1186/2052-336X-12-1
Cite this article as: Safari et al.: Response surface analysis of
photocatalytic degradation of methyl tert-butyl ether by core/shell Fe3O4/
ZnO nanoparticles. Journal of Environmental Health Sciences & Engineering
2014 12:1.
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