Archives of

1. Introduction
upplying drinking water, energy, and food
are the major future challenges; more importantly,
water significantly influences the
quality and quantity of energy, environment,
and food [1]. Aromatic organic compounds,
like Terephthalic Acid (TPA), are produced in
high volume and are among the main sources of water
pollution in industrialized countries.
TPA is widely used in numerous industries for producing
polymers, such as Polyethylene Terephthalate (PET),
polybutylene terephthalate, polyester, and polyamide
[2]. Additionally, it is used for producing carriers in
paint, plasticizer, drug, metal-organic framework, filler
in some military smoke grenades, as well as deuterated
terephthalate and related polymer [3, 4]. Due to the very
large-scale production of this substance in the world,
there is always some of this substance in the environment.
Moreover, according to research, this substance
presents carcinogenic properties in rats [5] and reproductive
toxicity in male mice [6].
There exist numerous methods to remove pollutants
from water and wastewater, such as coagulation and
flocculation, filtration, biological purification by microorganisms,
reverse osmosis, Electro-Dialysis Reverse
(EDR), ion exchange resins, adsorption, evaporation,
and Advanced Oxidation Processes (AOP) [7-9]. Researchers
found that each of these methods has disadvantages
and advantages [7-9]. Implementing Advanced
Nanoparticles (NPs) in AOP provides special opportunities
for the recovery of wastewater. Specifications, such
as the elimination of trace, toxic contaminants, microbial
pathogens, resistant pollutants, the conversion of the
wide range of organic materials to carbon dioxide and
water, the low cost of equipment, the high rate of reactions,
less energy consumption, and less human toxicity
are benefits, i.e., likely to result from AOP [7, 10]. Additionally,
what has motivated the researchers to choose
the AOP method is the ability of photo-catalyst to integrate
the NPs with multifunction water purification systems.
Moreover, using NPs has been developed in the
field of water treatment [11].
Therefore, MnFe2O4 was applied as the main catalyst
to exploit its properties. The MnFe2O4 was immobilized
on a base to increase the specific surface area, raise the
strength of the catalyst, facilitate its separation on large
scale, reuse the catalyst, and reduce the cost of the operation
[11, 12]. Therefore, Willemite was selected as the
basis, because of its excellent chemical and thermal stability,
water resistance, and cost-effectiveness [13].
Statistical design techniques may be used to model
and optimize the process. In the statistical design experiments,
the factors involved in tests at their respective
levels were simultaneously varied. One of the most
widely used experimental design techniques is the full
factorial method; this approach simultaneously investigates
the effect of more than one factor in the response.
Two-level full factorial designs of experiments are the
most common patterns in which each factor is experimentally
tested for only two levels [14].
Therefore, in this research, the degradation of TPA, as
an aromatic pollutant was investigated by O3/MnFe2O4/
Willemite, as photo-catalytic ozonation under the UV Irradiation
process. The effects of pH, the initial concentration
of TPA, the amount of catalyst, and O3 dosage
for higher degradation of TPA were investigated using a
full factorial experimental design. Additionally, a kinetic
study was developed using the experimental results attained
in this investigation.
Numerous studies have been accomplished to eliminate
TPA (Table 1) by photo-catalysts, such as TiO2, Fe, ZnO,
and TiO2/AC [3, 15-21]. The process of removing contaminants
by these photo-catalysts is not only time-consuming
but also the mineralization of TPA and intermediates fail to
occur absolutely. Furthermore, catalyst separation is a difficult
task. The magnetic properties of MnFe2O4/Willemite
allow the photo-catalyst to be separated and retrieved.
It has certain characteristics, such as chemical stability,
low cost, and very low bandgap energy [12].
In this study, the TPA removal process was examined
by photo-catalytic methods (MnFe2O4/Willemite) in
a Circulating Fluidized Bed Reactor (CFBR) by one
UV-A lamp and ozone generator. To compare different
processes, the TPA degradation experiments were performed
by UV, UV-Cat., O3, UV-O3, Cat.-O3, and UVCat.-
O3, separately. Full factorial experimental design
with 4 factors was used for modeling and optimizing the
process. In the optimal conditions, the amounts of pH,
TPA, Cat., and O3 were obtained. The relevant results
suggested that the UV-Cat.-O3 process has higher efficiency.
Finally, the kinetic and reproducibility of photocatalytic
was considered in optimum conditions.
2. Materials and Methods
Most required chemical reagents were provided from Sigma
Aldrich and Merck Company. Agilent 8453 UV-visible
S
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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Summer 2021. Volume 10. Number 3
Table 1. Some studies to remove TPA by the kind of catalyst
Photo-catalyst Synthesis
Method Condition Degradation
Efficiency Ref.
UV–TiO2;
UV–H2O2;
UV–H2O2–Fe;
O3;
O3/Fe;
O3/TiO2;
UV-O3-H2O2-Fe;
UV-O3-H2O2-Fe-
TiO2
Commercial
Terephthalic acid (ppm): 50; H2O2 (mM): 3; Fe2(SO4)3 Conc.
(mg/L): 90; Cat. amount (mg/L): 1000; Particle size (nm): 20±5
nm; particles surface area (m2 g-1): 50±15; pH: 8; Temp.(oC):
ambient temperature; removal time (min): 600 in UV–TiO2 system,
to <10 by UV-H2O2-Fe-O3 system; kinetic model: pseudofirst
order; irradiation source: six quartz tube mercury vapor
(40W); irradiation intensity (μW/cm2): 144; wavelength (nm):
253.7; the amount of ozone (mg/h): 2.4
UV-TiO2<
UV-H2O2<
UV-H2O2-Fe(III)<
O3 <
O3-Fe(III)<
O3-TiO2<
UV-H2O2-Fe(III)-TiO2-
O3≤
UV-H2O2-Fe-O3
[3]
UV-H2O2-Fe -
Terephthalic acid (ppm): 28.450; H2O2 (mM): 20; FeSO4(g/L): 1;
pH: 9; removal time (min): 40; irradiation source: six UV light
(Phillips, tube mercury vapor lamps, 40 W); irradiation intensity
(μW/cm2): 144; wavelength (nm): 253.7
60
UV-O [15] 3-Fe
Terephthalic acid (ppm): 28.450; FeSO4(g/L): 1; removal time
(min): 10; irradiation source: six UV light (Phillips, tube mercury
vapor lamps, 40 W); irradiation intensity (μW/cm2): 144;
wavelength (nm): 253.7
95
UV-O3-H2O2-Fe
Terephthalic acid (ppm): 28.450; removal time (min): 30; irradiation
source: six UV light (Phillips, quartz tube mercury vapor
ultraviolet lamps, 40 W); irradiation intensity (μW/cm2): 144;
wavelength (nm): 253.7; the amount of ozone (g/hr): 2.4
-
SO4
2-/TiO2;
bare TiO2;
P25
Sol-gel
-
Commercial
The aqueous solution of phthalic acid (ppm): 38.2; Cat. amount
(%): 1.38; particle size (nm): 12, 25 (for SO4
2-/TiO2 & bare TiO2);
pH: 9; Temp.(oC): 25±2; removal time (min):120; kinetic model:
pseudo-first order; K (min-1): 0.072 (for initial [TA]: 38.2 ppm
& 3.79% SO4
2-/TiO2); irradiation source: UVP mercury lamp B-
100AP/R (100 W); irradiation intensity (μW/cm2): 18
SO4
2-/TiO2 ~
bare TiO2 ~
P25
[16]
O3;
O3-LEDs;
O3-ZnO;
O3-VxOy/ZnO;
O3-VxOy/ZnOLEDs
Terephthalic acid (mg/L): 30; Cat. amount (gr/L): 0.1; Particle
size (nm): 41; particles surface area (m2 g-1): 8.60; pH: without
pH; Temp.(oC): 25; removal time (min): 60; K (min-1):0.0512,
0.0565, 0.0523, 0.0656, 0.0644, 0.628 in ozone, O3-LEDs, O3-
ZnO , O3-VxOy/ZnO, O3-VxOy/ZnO-LEDs, respectively; irradiation
source: six UV light (Phillips, quartz tube mercury vapor
ultraviolet lamps, 40 W); irradiation intensity (μW/cm2): 144;
wavelength (nm): 253.7; the amount of ozone(g/hr): 2.4; rector:
double-vessel Pyrex semi-batch reactor (2 L)
32% (for O3);
40% (for O3-UVAs);
64% (for O3-ZnO);
74% (for O3-VxOy/
ZnO)
98% (for O3-VxOy/
ZnO-UVA)
[17]
TiO2;
ZnO Commercial
Terephthalic acid (ppm): 20-100; Cat. amount (gr/L): 2.5; particle
size (nm): 21 & 100 for TiO2 & ZnO; particles surface area
(m2 g-1): 50±15, 13.01 for TiO2 & ZnO; pH: 6 and 9 for TiO2 and
ZnO; H2O2 (mmol/L):5.4; Temp.(oC): 25-30; removal time (min):
30; kinetic model: pseudo-first order; K (min-1):0.124 & 0.1001
for TiO2 and ZnO; KLH (ppm/min):2.582 & 3.176 for TiO2 & ZnO;
irradiation source: eight quartz tube mercury vapor lamps; irradiation
intensity (μW/cm2): 21; wavelength (nm): 253.7; Reactor:
double-walled Pyrex batch cylindrical (1.5 L)
42% (for TiO2)
62% (for ZnO) [18]
TiO2/AC Sol-gel
Terephthalic acid (ppm): 6 g/L; Cat. amount (gr/L): 7 ; particle
size (nm): 17.6; particles surface area (m2 g-1): 887.11; Temp.
(oC): room temp.; Removal time (h): 8; irradiation source: UV
lamp (20 W); wavelength (nm): 253.7
64.3% [19]
Photolysis;
O3;
O3-VxOy/TiO2;
O3-VxOy/TiO2-LED
Impregnation
Terephthalic acid (g/L): 30; Cat. amount (gr/L): 0.1 ; Temp.
(oC): 25; removal time (min): 60; Kinetic model: pseudo-first
order; irradiation source: LEDs and UV lamp (4 W m−2); wavelength
(nm): 380–430 nm & 365–465 (for LED & UV lamp);
the amount of ozone(mg/L): 10; reactor: double-vessel Pyrex
semibatch cylindrical (2.0 L)
O3-VxOy/TiO2>
O3-VxOy/TiO2-LED>
O3 >
O3-VxOy/TiO2-UV>
O3- TiO2>
O3-TiO2-LED
[20]
TiO2
Hydrolysis
of TiCl4 in a
highly acidic
media
Terephthalic acid (ppm): 20; Cat. amount (g/L): 0.75; particle
size (nm): 6.8; pH: 3.7; Temp.(oC): 25; removal time (min):180;
kinetic model: pseudo-first order; K (min-1): 0.0336; irradiation
source: visible light; reactor: double-walled borosilicate cylindrical
batch reactor.
99 [21]
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Summer 2021. Volume 10. Number 3
spectrophotometer was employed to appoint the presence
of TPA in a sample and the percentage of degradation in
aqueous media. In the degradation pollutant process, one
UV-A lamp with a power of 15 W and ozone generator
was obtained from Philips and Nabbzist Company
(Iran), respectively. The decomposition of TPA was performed
in a Circulating Fluidized Bed Reactor (CFBR)
with rotary current and an effective volume of 1 liter. The
structure and chemical properties of TPA are illustrated
in Table 2.
The process of photocatalytic decomposition of TPA
was performed by Circulating Fluidized Bed Reactor
(CFBR) with rotary current and effective volume of 1
liter (Figure 1). One UV-A lamp with a power of 15 W
(Philips) was directly placed in the reactor so that the
liquid flow revolves around the lamp. This reactor was
continuous for ozone and batch for MnFe2O4/Willemite
and TPA. An ozone generator from Nabbzist Company
(Iran) was used in this process. A pressure capsule was
applied to produce the pure oxygen for passing in the
ozone generator. The photo-reactor was developed with
a water-flow jacket joined to a Thermo-Bath (ALB64
model, FINEPCR Korean Company) for controlling
the temperature at 25ºC in all experiments. The pH was
measured by pH meter F-71 HORIBA (Germany).
Catalyst preparation
The preparation of Willemite was performed according
to previous research [13, 22]. Therefore, 0.1 moles
of (ZnSO4.7H2O) was dissolved in 100 mL of deionized
water. NaOH solution (0.2 moles NaOH/100ml H2O)
was added drop-wise to zinc sulfate solution and stirred
at 80°C. The solution was gradually cooled to ambient
temperature. The precipitated Zn(OH)2 was separated
from the solution by centrifugation and dried at 100°C
for 12 h. Moreover, 2 moles of Zn(OH)2 and 1 mole of
silica high purity powder were added to 200 mL water
and stirred at 80°C for 4 h. Finally, the precipitate was
separated by centrifuge, dried at 80°C, and calcined at
1050°C (Figure 2).
Based on previous research [23, 24], 0.2 moles of
(Fe(NO3)3.9H2O) and 0.1 moles of (Mn(NO3)2.4H2O)
were completely dissolved in the 200 mL of distilled
water. Then, urea solution (0.4 moles of urea in 250 mL
water), as the precipitating agent, was added to the solution
containing iron nitrate and manganese nitrate, drop
Table 2. The structure and characteristics of TPA
Item Information
Pollutant Para-Terephthalic Acid (TPA)
Structure
λmax (nm) 240
Molecular weight (g.mol-1) 166.132
Figure 1. The experimental set-up
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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by drop. The total solution was refluxed at 85°C for 12 h.
After the gradual cooling of the contents, the precipitate
was separated by centrifuge and washed by water and
ethanol. Precipitates were dried in the oven at 80°C and
calcined in the furnace at 990°C. The main photo-catalyst
was synthesized by mixing MnFe2O4 and Willemite
(1:3 w/w %) in the presence of ethanol using agate pestle
and mortar. Next, this mixture was dried at 110°C in an
oven for 2 h and calcined at 1050°C in the furnace for
5 h. The precipitation was sieved applying a 100 mesh
standard sieve (Figure 2).
The experimental design was used to study the effects
of simultaneously changing the values of variables on the
removal of TPA from an aqueous solution. Additionally,
the main factor influencing the process, the interaction
manner of variables on each other, and the percentage
of removal of TPA were determined by the experimental
design method.
The designed experiment was created in Minitab 17 using
a full factorial design [14]. Operational factors, containing
an initial TPA concentration, ozone dosage, the
amount of photo-catalyst, and pH are presented in Table
3. Operation factors and factor levels being influential on
the response of the TPA degradation were confirmed by
primary experiments. Other parameters, such as temperature,
light wavelength, light intensity, and stirring rate
were constant in the process. Corresponding to Equation 1,
nineteenth runs (N) were designed based on 4 factors (k),
2 of factor levels, 3 of center points (C0), and without
replicates of the corner points (r).
(1) N=r×(level)k+C0
The randomization technique was selected to balance the
effect of irrelevant or uncontrollable conditions and estimate
the intrinsic variation. Besides, DOE was performed
by coding factors corresponding to the design matrix.
Based on experimental data, there were significant relationships
between the response (TPA degradation) and
4 input factors (Equation 2). New results will easily predict
based on mathematical Equation 2.
(2) Y=β0+β1A+β2B+β3C+β4D+β12AB+β13AC+β14AD+
β23BC+β24BD+β34CD+β123ABX+β124ABD+β134ACD+β2
34BCD+β1234ABCD+ԑ
Where ß0 is overall mean, ß1, ß2, ß3, and ß4 are linear
coefficients, ß12, ß13, ß14, ß23, ß24, ß34, ß123, ß123, ß124, ß134,
ß234, and ß1234 are interactions coefficients, and ɛ is random
error or noise. The Analysis of Variance (ANOVA)
was performed by the consideration of P-value related
to the Adjusted Mean Square (Adj. MS) of the main factors,
the Adj. MS of interacting factors, total Adj. MS,
error Adj. MS, model Adj. MS, and the inspection of the
standard deviation of the residuals (S), R Square (R2),
Adjusted R Square (Adj. R2) and Predicted R Square
(Pred. R2) values.
A regression analysis model was simplified by eliminating
insignificant terms at P≤0.05. The adequacy of the
model was inspected by examining residuals distribution
and its independence. The main effect plot and interaction
plot were employed to predict possible interactions. Finally,
the response optimizer was applied to recognize the
factor settings that optimize a TPA degradation percentage,
cost, the sensitivity of factors, and desirability. Even-
Figure 2. The process of catalysts synthesis
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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Summer 2021. Volume 10. Number 3
tually, the efficiency of MnFe2O4/Willemite, MnFe2O4,
and Willemite was compared under optimal conditions.
At any run, the TPA solution to a specific concentration,
a particular pH, and a known amount of MnFe2O4/
Willemite photo-catalyst was mixed in the tank. This
solution was circulated in the reactor for 30 min in the
absence of UV-A radiation to reach equilibrium. After
homogenization, the radiation was started, and simultaneously,
O3 gas, created by an ozone generator, was
injected from the bottom of the reactor by a spongy diffuser.
The concentration of ozone in the gas phase was
determined by the iodometric method, using 2% neutral
buffered potassium iodide and sodium thiosulfate as a
titrant [25]. The required samples were obtained at specified
intervals, and the TPA concentration was measured
by spectroscopy at 240 nm. The acidity was adjusted at
the beginning of the experiments with dilute sodium hydroxide
and sulfuric acid (about 0.1 M). Total Organic
Carbon (TOC) was measured with a QBD1200 TOC
laboratory analyzer (Hach Company). The TPA removal
percentage was calculated by Equation 3 and recorded
under experimental response. Where [TPA]0 is the initial
concentrations of TPA at the beginning of the photo-catalytic
ozonation, and [TPA]t is the concentration of the
TPA at the time t after the start of the process.
(3) Removal of TPA(%)=(
[TPA]0-[TPA]t
[TPA]0
)×100
3. Results
In the process of the mechanism of photo-degradation
of TPA, MnFe2O4 semiconductor supported the Willemite
absorbs photons from light (Figure 3). The photons
which have energy equal (or more than) the photocatalyst
band gaps, transfer electrons from the Valence
Band (VB) to the Conduction Band CB). In this manner,
holes and electrons are created in valance and conductive
bonds, respectively. Then, the generated electrons
Table 3. Factors and levels
Levels
Factors Symbols
-1 +1
pH A 5 9
Initial TPA conc. (ppm) B 20 50
Catalyst amount (g L-1) C 0.5 1.5
Ozone dosage (mg/h) D 0.34 2.17
Figure 3. The mechanism of the photo-degradation of TPA in the experimental set-up
Terephthalic acid+O3+UV-A
CO2+H2O+Inorganic compounds
MnFe2O4/ Willemite
in CFBR reactor
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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Summer 2021. Volume 10. Number 3
and holes migrate to other parts and the following the
occurrence of reactions (Reactions 1-5).
(1) MnFe2O4/Willemite+hϑ MnFe2O4/
Willemite+(h++e−)
(2) O3+e- → O3• -
(3) h+o+ H2O → H+o+ •OH
(4) O3• -+H+ → HO3•-
(5) HO3•- → •OH+O2
Furthermore, hydroxyl radicals are created by the radiation
of UV on ozone and hydrogen peroxide in solution
(Reaction 6 and 7).
(6) O3+H2O+hν → H2O2+O2
(7) H2O2+hν →2OH•
Finally, Hydroxyl radicals and ozone, attack organic
matter. Subsequently, organic matter is oxidized and decomposed
(Reactions 8-10) [26].
(8) O3 +R → Rox
(9) O3+OH− → OH•+(O2• ↔ HO2•)
Table 4. The full factorial design matrix
Coded Variables Response
Run
O Cat. TPA pH Experimental Predicted 3
1 1 -1 -1 1 92.0010 91.8603
2 -1 -1 1 1 61.9110 62.0031
3 0 0 0 0 68.2000 68.0974
4 -1 -1 1 -1 39.2000 39.3266
5 1 1 -1 1 98.0930 98.2695
6 -1 1 -1 1 92.7000 93.3318
7 -1 -1 -1 -1 50.0100 50.4590
8 1 -1 1 -1 50.6000 50.2859
9 1 1 -1 -1 53.7430 53.4195
10 1 1 1 1 86.9414 86.8101
11 -1 1 1 1 79.3420 79.2857
12 -1 1 -1 -1 65.7000 65.2868
13 1 1 1 -1 58.8000 59.1499
14 -1 -1 -1 1 79.1000 78.5040
15 0 0 0 0 68.1755 68.0974
16 1 -1 1 1 77.7789 77.9460
17 0 0 0 0 68.2030 68.0974
18 -1 1 1 -1 56.7000 56.6092
19 1 -1 -1 -1 46.6510 47.0103
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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(10) OH•+R• → Rox
The percentages of TPA degradation for 19 sequential
experiments regarding the influence of factors, the levels,
and the combination of factors were applied for the execution
of full factorial design (Table 4). The comparison of
P-value of the main factors and interaction factors, choosing
α-level of 0.05 indicated that TPA, pH, O3, Cat., pH×TPA,
pH×O3, TPA×Cat., TPA×O3, Cat.× O3, and pH×TPA×O3
were statistically significant. In other words, the mentioned
terms were effective with %95 probability. Moreover,
the P-value of the lack of Fits (0.071) was more than
the selected α-value (0.05), reflecting that the model accurately
fitted the data (Table 5).
The R2 value emphasized that the model can explain
99.97% of the variance in TPA degradation yield. The adjusted
R2 was measured as 99.92 %. Both values signify that
the model fitted the data well. R2 prediction was computed
as 99.68% for the new observations. The standard deviation
of the residuals (S) was equal to 0.46656. This value reflected
the standard distance of data from the regression line.
The regression coefficients were obtained by Equation 4
based on un-coded data. In this pattern, Deg% is the percentage
of TPA degradation yield or response; pH, Cat.,
TPA, and O3 are factors; Equation 4 represents the relationship
between the percentage of TPA degradation and
predictor variables. In this equation, the overall mean
score was equal to 68.097, and the absolute value of the
coefficient expresses the relative strength of each factor:
(4) Deg%=68.097+15.404pH-
4.170TPA+5.923Cat.+2.97O3-2820pH×TPA+2.724p
Table 5. ANOVA data after removing insignificant factors
Source df Adj. SS Adj. MS F P
Model 10 5165.75 516.57 2373.11 0.0001
Linear 4 4735.80 1183.95 5438.99 0.0001
pH 1 3796.51 3796.51 17440.91 0.0001
TPA 1 278.26 278.26 1278.31 0.0001
Cat. 1 561.30 561.30 2578.60 0.0001
O3 1 99.73 99.73 458.14 0.0001
2-way interactions 5 395.1 79.00 362.93 0.0001
pH×TPA 1 127.22 127.22 584.44 0.0001
pH×O3 1 118.69 118.69 545.24 0.0001
TPA×Cat. 1 6.03 6.03 27.68 0.001
TPA×O3 1 72.20 72.20 331.70 0.0001
Cat.×O3 1 70.87 70.87 325.59 0.0001
3-way interactions 1 34.94 34.94 160.49 0.0001
pH×TPA×O3 1 34.94 34.94 160.49 0.0001
Error 8 1.74 0.22 -
Lack-of-Fit 6 1.74 0.29 1274.97 0.071
Pure error 2 0.0001 0.0001
Total 18 5167.49
df=Degree of Freedom; Adj.SS=Adjusted sum of square; Adj.MS=Adjusted mean of square; F=value on the F distribution P=probability
value
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H×O3+0.614TPA×Cat.+2.124TPA×O3-2.105Cat.×O3-
1.478pH×TPA.×O3
The normal plot of the standardized effects (Figure
4A) shows that all the main effects were significant. Besides,
AB (pH by TPA conc.) and AD (pH by O3), as
the interaction effects, presented the largest effect on the
response, and BC (TPA by O3) provided the slightest effect
on response. Furthermore, the normal plot proves
that A, C, D, AD, BC, and BD positively impacted the
response. In other words, the TPA degradation yields increase
when the mentioned effects are altered from the
low-level to the high levels.
Pareto chart of the standardized effects (Figure 4B)
displays the ranking of effects; there exist 10 significant
effects on the TPA elimination processes.
Residual plots were considered to check the assumptions
of normality, constant variance, and randomness
in the final model (Figure 5). The normal probability
plot (Figure 5A) illustrates that the data were normally
distributed, and outliers did not exist in the data. Ad-
Figure 4. The normal plot of the standardized effects
A: Normal plot of the standardized effects; B: Pareto chart of the standardized effects.
Figure 5. Residual plots for the percentage of degradation
A: The normal probability plot of residuals; B: Residuals versus fitted values; C: The histogram of the residuals; D: Residuals versus
the order of the data.
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ditionally, residuals versus fitted values (Figure 5B) established
no outlets, and the normality assumption of
residuals was valid. In the histogram (Figure 5C), there
was no distance between bars; thus, it signifies that outliers
did not exist in the data. Residuals versus the order of
the data (Figure 5D), specified no systematic effects in
the data due to the time or order of data collection. The
structure of Figure 5D acknowledges no correlation between
the residuals. Thus, all mentioned interpretations
confirmed that the ANOVA data (Table 5) were reliable
and the model can predict TPA degradation yield within
+/- 0.4665 with a 95% confidence level.
90
75
60
90
75
60
-1 1
90
75
60
-1 1 -1 1
pH * TPA
pH * Cat. TPA * Cat.
pH * O3
pH
TPA * O3
TPA
Cat. * O3
Cat.
-11
TPA
-11
Cat.
-11
O3
Mean of Deg%
(b) interaction plot for Deg%
Fitted Means
-1 1
80
70
60
50
-1 1 -1 1 -1 1
pH
Mean of Deg%
TPA Cat. O3
(a) main effects plot for Deg%
Fitted Means
All displayed terms are in the model.
Figure 6. The magnitude of the main effect for pH
A: Main effects plot; and B: Interaction plot for percent of TPA degradation.
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
Figure 7. The percentage of TPA removal under different process
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Summer 2021. Volume 10. Number 3
The settings that maximize degradation of TPA were
determined by target parameters (goal=100 i.e., target,
lower boundary=39.2, & upper boundary=100) in response
optimizer for each response. The best-operating
conditions which maximized the sensitivity of factors
and desirability were obtained equal to 9, 20 ppm, 1.5
g/L, and 2.17 mg/h for pH, TPA, Cat., and O3, in sequence.
The predicted value for photo-catalyst efficiency
and desirability, based on the best factor levels, equaled
98.2695% and 0.97168, respectively.
The magnitude of the main effect for pH indicated the
greater effect of it, compared to the other variables. Besides,
the main effects plot proves that pH, Cat., and O3
positively affected the response. Furthermore, TPA adversely
impacted the response (Figure 6A). The interaction
plot for the percentage of TPA degradation (Figure
6B) manifested several interactions, as lines are not parallel
to each other.
The plot indicated the increase in the degradation of
TPA (Deg%) while the amount of TPA changes from 50
ppm to 20 ppm depending on the extent of ozone. While
ozone is low (dashed line), the change in degradation is
more than the time when ozone is high (straight line).
Additionally, enhanced degradation of TPA (Deg%),
as moving from the low to the high level of catalyst, is
greater while the ozone is lower than (straight line) the
time when it is high (dashed line).
Moreover, the interaction plot indicates that the increase
in the degradation of TPA (Deg%) when the pH
changes from low to high depending on the amount of
TPA and ozone. When the amount of TPA is high, the
alternation in degradation is less than low TPA. Moreover,
when O3 dosage is high, the change in degradation
is more than low O3 conditions.
To compare different processes, the TPA degradation
experiments were performed by UV, UV-Cat., O3, UVO
3, Cat.-O3, and UV-Cat.-O3, separately. The relevant
results suggested that the UV-Cat.-O3 process presented
a higher efficiency (Figure 7). The percentage of TPA
removal in the UV-Cat.-O3 process indicated that Mn-
Fe2O4/Willemite contributes to ozone decomposition
and radicals generation.
To investigate the kinetics of TPA degradation, the
experiments were performed by synthesized photo-catalysts
in optimum conditions. Then, experimental data
were fitted with Equation 5. Where A0 and A are the
maximum absorptions at maximum absorption wavelength
before light exposure and the maximum absorption
at time t, respectively. Moreover, k represents the
rate constant.
(5) Ln =
A0
A kt
The kinetic equations (Table 6) reveal that the TPA
photo-degradation reactions by MnFe2O4/Willemite and
MnFe2O4 catalyst approximately are the pseudo-first-order
kinetics. Comparing apparent speed constants (Kapp) of kinetic
equations clarified that MnFe2O4/Willemite presented
the most efficiency in the TPA photo-catalytic degradation
processes. The increase in the efficiency of catalyst
can be due to fixing MnFe2O4 on Willemite. The effective
surface of the catalyst and the number of active sites was
increased by fixing MnFe2O4 on the surface of Willemite.
To gather more evidence, a modified Langmuir-Hinshelwood
(L-H) equation was applied (Equation 6).
Where kadd, kLH, and k are the apparent Langmuir adsorption
constant, the apparent maximum photo-catalytic
degradation rate, and the pseudo-first-order kinetic
constant (derived from Equation 4), respectively. C0
Table 6. The kinetic equations of TPA degradation in optimum conditions
Nanoparticles Kinetic Equations R2 Kapp (min-1)
Apparent Speed Constants
MnFe2O4/Willemite Y=0.2707x-0.3723 0.997 0.2707
MnFe2O4 Y=0.0976x-0.1063 0.9933 0.0976
Table 7. The Langmuir-Hinshelwood kinetic of TPA degradation in optimum conditions
Nanoparticles Kinetic Equations R2 KLH (ppm min-1) Kadd (ppm-1)
MnFe2O4/Willemite Y= 0.2681x-5.3821 0.985 3.729 0.051
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
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Summer 2021. Volume 10. Number 3
represents the initial concentration of TPA. L-H kinetic
parameters were obtained corresponding to Table 7.
(6) 1 = 1 + C0
kaddkLH kLH k
After performing 5 successive experiments under optimal
conditions with depreciated NPs of MnFe2O4/Willemite,
comparing the degradation percentage of those
experiments revealed that the catalyst provided desirable
efficiency and repeatability (Deg% 98.02, 97.5, 97.04,
96.78, 96.53).
4. Discussion
The contamination of water by aromatic compounds,
like TPA, is among the greatest problems. Therefore, in
this research, an applied, affordable, and efficient method
was presented for the degradation of TPA. The high
yield of the TPA photo-degradation process applying O3/
MnFe2O4/Willemite as photo-catalytic ozonation under
UV irradiation process corroborated the high efficiency
of the employed method.
The study data disclosed that DOE, using full factorial
design, is the best technique to ascertain the efficiency
of O3/MnFe2O4/Willemite, to define influential factors,
to minimize response variability, and to affect the uncontrollable
variables, to reduce reaction time and total
cost; consequently, to optimize response. In this regard,
the TPA degradation process was successfully modeled
employing a full factorial methodology. of the obtained
ANOVA data were reliable; thus, the model can predict
TPA degradation yield within +/-0.46656 and a 95%
confidence level. The model with R2 of 99.97%, Adj. R2
of99.92%
and Pred. R2 of 99.68% fitted the data well.
Additionally, according to optimized results, the best
level for operation factors of pH, TPA, Cat., and O3 was
obtained equal to 9, 20 ppm, 1.5 g/L, and 2.17 mg/h, in
sequence. According to optimal conditions, the results of
testing the catalyst indicated that the model is suitable
and the photo-catalyst is efficient. In addition, the operation
factors provided the highest sensitivity due to the
efficiency of 98.2695% and the desirability of 0.97168.
5. Conclusion
TPA decomposition kinetics was determined pseudofirst-
order. Furthermore, the repeatability of the results
of the 5 tests of TPA degradation using the depreciated
photo-catalyst of MnFe2O4/Willemite and its constant
value indicated that the photo-catalyst is considerably reusable
and economic. Therefore, based on the evidence,
implementing this catalyst is recommended to TPA producer
companies. Moreover, developing studies and using
MnFe2O4/Willemite photo-catalyst in the removal of
other aromatic pollutants are recommended.
Ethical Considerations
Compliance with ethical guidelines
This article is a meta-analysis with no human or animal
sample.
Funding
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-profit sectors.
Authors' contributions
All authors equally contributed to preparing this article.
Conflict of interest
The authors declared no conflicts of interest.
Acknowledgments
The authors gratefully appreciate Islamic Azad University,
Arak branch for supporting the researchers.
References
[1] Damerau K, Patt AG, van Vliet OPR. Water saving potentials
and possible trade-offs for future food and energy
supply. Global Environmental Change. 2016; 39:15-25.
[DOI:10.1016/j.gloenvcha.2016.03.014]
[2] Díaz A, Katsarava R, Puiggalí J. Synthesis, properties and
applications of biodegradable polymers derived from diols
and dicarboxylic acids: From polyesters to poly(ester amide)s.
International Journal of Molecular Sciences. 2014; 15(5):7064-123.
[DOI:10.3390/ijms15057064]
[3] Thiruvenkatachari R, Kwon TO, Jun JC, Balaji S,
Matheswaran M, Moon IS. Application of several advanced
oxidation processes for the destruction of Terephthalic Acid
(TPA). Journal of hazardous materials. 2007; 142(1-2):308-14.
[DOI:10.1016/j.jhazmat.2006.08.023]
[4] Kricheldorf HR, Schmidt B. New polymer syntheses. 69. Polyamides
derived from deuterated terephthalic acid or phenoxyterephthalic
acid. Macromolecules. 1992; 25(23):6090-4.
[DOI:10.1021/ma00049a002]
[5] Cui L, Shi Y, Dai G, Pan H, Chen J, Song L, et al. Modification
of N-Methyl-N-Nitrosourea initiated bladder carcinogenesis
in Wistar rats by terephthalic acid. Toxicology and
Applied Pharmacology. 2006; 210(1-2):24-31. [DOI:10.1016/j.
taap.2005.06.008]
[6] Zhang XX, Sun SL, Zhang Y, Wu B, Zhang ZY, Liu B, et al.
Toxicity of purified terephthalic acid manufacturing wastewater
on reproductive system of male mice (Mus muscu-
Mahanpoor K, & Sharifnezhad Z. Photo-catalytic Ozonation for Degrading Terephthalic Acid in Water. Arch Hyg Sci. 2021; 10(3):201-214.
213
Summer 2021. Volume 10. Number 3
lus). Journal of Hazardous Materials. 2010; 176(1-3):300-5.
[DOI:10.1016/j.jhazmat.2009.11.028]
[7] Prasse C, Stalter D, Schulte-Oehlmann U, Oehlmann J,
Ternes TA. Spoilt for choice: A critical review on the chemical
and biological assessment of current wastewater treatment
technologies. Water Research. 2015; 87:237-70. [DOI:10.1016/j.
watres.2015.09.023]
[8] Mehta D, Mazumdar S, Singh SK. Magnetic adsorbents
for the treatment of water/wastewater-a review. Journal of
Water Process Engineering. 2015; 7:244-65. [DOI:10.1016/j.
jwpe.2015.07.001]
[9] Rajasulochana P, Preethy V. Comparison on efficiency of
various techniques in treatment of waste and sewage watera
comprehensive review. Resource-Efficient Technologies.
2016; 2(4):175-84. [DOI:10.1016/j.reffit.2016.09.004]
[10] Qu X, Alvarez PJJ, Li Q. Applications of nanotechnology
in water and wastewater treatment. Water Research. 2013;
47(12):3931-46. [DOI:10.1016/j.watres.2012.09.058]
[11] Kunduru KR, Nazarkovsky M, Farah Sh, Pawar RP, Basu
A, Domb AJ. Nanotechnology for water purification: Applications
of nanotechnology methods in wastewater treatment. In:
Grumezescu AM, editor. Water Purification. London: Academic
Press; 2017. pp. 33-74 [DOI:10.1016/B978-0-12-804300-4.00002-2]
[12] Cushing BL, Kolesnichenko VL, O’Connor CJ. Recent advances
in the liquid-phase syntheses of inorganic nanoparticles.
Chemical Reviews. 2004; 104(9):3893-946. [DOI:10.1021/
cr030027b]
[13] Takesue M, Hayashi H, Smith Jr RL. Thermal and chemical
methods for producing zinc silicate (willemite): A review.
Progress in Crystal Growth and Characterization of Materials.
2009; 55(3-4):98-124 [DOI:10.1016/j.pcrysgrow.2009.09.001]
[14] Myers RH, Montgomery DC, Vining GG, Borror CM, Kowalski
SM. Response surface methodology: A retrospective and literature
survey. Journal of Quality Technology. 2004; 36(1):53-77.
[DOI:10.1080/00224065.2004.11980252]
[15] Thiruvenkatachari R, Ouk Kwon T, Shik Moon I. Degradation
of phthalic acids and benzoic acid from terephthalic acid
wastewater by advanced oxidation processes. Journal of Environmental
Science and Health, Part A. 2006; 41(8):1685-97.
[DOI:10.1080/10934520600754136]
[16] Lin XH, Lee SN, Zhang W, Li SFY. Photocatalytic degradation
of terephthalic acid on sulfated titania particles and identification
of fluorescent intermediates. Journal of Hazardous Materials.
2016; 303:64-75. [DOI:10.1016/j.jhazmat.2015.10.025]
[17] Fuentes I, Rodriguez JL, Tiznado H, Romo-Herrera JM,
Chairez I, Poznyak T. Terephthalic acid decomposition by photocatalytic
ozonation with VxOy/ZnO under different UV-A LEDs
distributions. Chemical Engineering Communications. 2020;
207(2):263-77. [DOI:10.1080/00986445.2019.1581617]
[18] Shafaei A, Nikazar M, Arami M. Photocatalytic degradation
of terephthalic acid using titania and zinc oxide photocatalysts:
Comparative study. Desalination. 2010; 252(1-3):8-16.
[DOI:10.1016/j.desal.2009.11.008]
[19] Yuefeng Ch, Hui W, Mingjuan H, Guofeng G. Photocatalytic
degradation of organic pollutants in purified terephthalic acid
wastewater with activated carbon supported titanium dioxide.
Paper presented at: 2009 International Conference on Energy and
Environment Technology. 16-18 October 2009; Guilin, China.
[DOI:10.1109/ICEET.2009.397]
[20] Fuentes I, Rodríguez JL, Poznyak T, Chairez I. Photocatalytic
ozonation of terephthalic acid: A by-product-oriented decomposition
study. Environmental Science and Pollution Research.
2014; 21(21):12241-8. [DOI:10.1007/s11356-014-3176-1]
[21] Yener HB, Helvacı ŞŞ. Visible light photocatalytic activity of
rutile TiO2 fiber clusters in the degradation of terephthalic acid.
Applied Physics A. 2015; 120(3):967-76. [DOI:10.1007/s00339-
015-9263-4]
[22] Zaitseva NA, Onufrieva TA, Barykina JA, Krasnenko TI, Zabolotskaya
EV, Samigullina RF. Magnetic properties and oxidation
states of manganese ions in doped phosphor Zn2SiO4: Mn. Materials
Chemistry and Physics. 2018; 209:107-11. [DOI:10.1016/j.
matchemphys.2018.01.071]
[23] Bharathi S, Nataraj D, Mangalaraj D, Masuda Y, Senthil K,
Yong K. Highly mesoporous α-Fe2O3 nanostructures: Preparation,
characterization and improved photocatalytic performance
towards Rhodamine B (RhB). Journal of Physics D: Applied Physics.
2009; 43(1):015501. [DOI:10.1088/0022-3727/43/1/015501]
[24] Amighian J, Mozaffari M, Nasr B. Preparation of nano-sized
manganese ferrite (MnFe2O4) via coprecipitation method. Physica
Status Solidic. 2006; 3(9):3188-92. [DOI:10.1002/pssc.200567054]
[25] Rakness K, Gordon G, Langlais B, Masschelein W, Matsumoto
N, Richard Y, et al. Guideline for measurement of
ozone concentration in the process gas from an ozone generator.
Ozone: Science & Engineering. 1996; 18(3):209-29.
[DOI:10.1080/01919519608547327]
[26] Wang JL, Xu LJ. Advanced oxidation processes for wastewater
treatment: Formation of hydroxyl radical and application. Critical
Reviews in Environmental Science and Technology. 2012;
42(3):251-325. [DOI:10.1080/10643389.2010.507698]