Anal. Methods Environ. Chem. J. 5 (3) (2022) 31-39
Research Article, Issue 3
Analytical Methods in Environmental Chemistry Journal
Journal home page: www.amecj.com/ir
AMECJ
Catalytic ozonation process using ZnO/Fe2O3 nanocomposite
for efcient removal of captopril from aqueous solution
Maryam Dolatabadi a, b, Ruhollah Akbarpour c, Saeid Ahmadzadeh d, e*
a Student Research Committee, Kerman University of Medical Sciences, Kerman, Iran.
b Environmental Science and Technology Research Center, Department of Environmental Health Engineering, School of
Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran.
c MSc student in Environmental Engineering, Islamic Azad University, Estahban branch, Estahban, Iran.
d Pharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran.
e Pharmaceutical Sciences and Cosmetic Products Research Center, Kerman University of Medical Sciences, Kerman, Iran
ABSTRACT
The presence of pharmaceutical compounds in aqueous media, even
in low concentrations, has caused adverse effects on human, animal,
and environmental health. Captopril is a widely used pharmaceutical
compound detected in the environment at different concentrations.
Because of the concern and problems caused by the presence of
captopril in water and the aquatic ecosystem, it appears necessary
to remove it from the environment. The current study investigated
captopril removal by a catalytic ozonation process using ZnO/Fe2O3
nanocomposite as a low-cost catalyst. The effects of variables such
as ZnO/Fe2O3 nanocomposite dosage (0.5-2.5 g L-1), solution pH (3-
11), initial captopril concentration (10-70 mg L-1), and ozone dosage
(0.2-1.5 mg min-1) on captopril removal were investigated. The
removal captopril of 99.4% was obtained in the optimum condition,
including ZnO/Fe2O3 nanocomposite dosage of 2.0 g L-1, solution pH
of 5.0, initial captopril concentration of 40 mg L-1, and ozone dosage
of 0.5 mg min-1. The ZnO/Fe2O3 nanocomposite as a catalyst was a
critical component in the catalytic ozonation process. According to
the obtained results, the catalytic ozonation process in the presence of
ZnO/Fe2O3 nanocomposite has high efciency in removing captopril
from water sources.
Keywords:
Captopril,
Catalytic ozonation,
ZnO/Fe2O3 nanocomposite,
Removal,
Aqueous solution
ARTICLE INFO:
Received 27 Apr 2022
Revised form 23 Jun 2022
Accepted 15 Jul 2022
Available online 28 Sep 2022
*Corresponding Author: Saeid Ahmadzadeh
Email: saeid.ahmadzadeh@kmu.ac.ir
https://doi.org/10.24200/amecj.v5.i03.197
1. Introduction
Recently, the attention of many researchers
working in the eld of water and wastewater
treatment has focused on the removal of
pharmaceutical compounds as a new group of
emerging pollutants [1]. After humans and animals
consume pharmaceutical compounds, part of
them in their unmetabolized and metabolized
form is excreted from the body and enters the
environment [2]. Captopril is a commonly used
pharmaceutical compound prescribed to reduce
high blood pressure, treat heart failure, protect
the heart and blood vessels against damage and
heart attack, and protect the kidneys in diabetic
patients [3, 4]. Captopril is a potent, competitive
inhibitor of the angiotensin-converting enzyme, the
enzyme responsible for converting angiotensin I to
angiotensin II. Angiotensin II is a potent mediator
that causes the narrowing of blood vessels and
retention of sodium and water in the body [5].
Captopril has been detected in various
environments such as water and soil). The captopril
concentration in the environment causes dizziness,
------------------------
32 Anal. Methods Environ. Chem. J. 5 (3) (2022) 31-39
cough, hyperkalemia, impotence, nocturnal
enuresis, nausea, vomiting, diarrhea, insomnia,
Stevens-Johnson syndrome, gynecomastia,
thrombocytopenia, and angioedema. Considering
the problems caused by the presence of captopril
in the environment, removing captopril from
the aquatic environment is essential [3, 4].
Although conventional processes in water and
wastewater treatment can remove a part of
pharmaceutical compounds during the treatment
process, conventional treatment processes cannot
thoroughly remove these compounds, so we nally
need advanced oxidation processes to treat these
pollutants [6].
Ozonation technique is one of the advanced
oxidation processes in water and wastewater
treatment. Ozonation is used in water and
wastewater treatment for several purposes such as
disinfection, removal and control of taste, odor, and
color, oxidation of iron and manganese and other
mineral contaminants, algae control, improving the
coagulation process, and oxidation of persistent
organic contaminants [7, 8].
As a strong oxidant, Ozone molecules break down
recalcitrant and hazardous organic compounds into
smaller molecules [9, 10]. The ozonation reaction
is accomplished through two pathways (direct and
indirect). In the direct method, the ozone molecule
appears as an electron acceptor and thus oxidizes
the organic pollutants. Nevertheless, in the indirect
method, the ozone molecule is converted into a
radical (•OH) during chain reactions, which has a
higher oxidation potential than ozone. The indirect
method decomposes pollutants with incredible
speed and power [11, 12]. Ozone presents a
high reactivity mainly attributed to its electronic
conguration. It is a selective molecule that attacks
electron-rich functional groups like double bonds,
amines, and activated aromatic rings [13, 14]. In
recent years, heterogeneous catalytic ozonation
has received much attention in water treatment
due to its high oxidation potential. In the current
work, the effect of main operational variables,
including solution pH, catalyst dosage (ZnO/Fe2O3
nanocomposite), initial captopril concentration,
and reaction time was evaluated during the catalytic
ozonation for removal of captopril from aqueous
solution.
2. Material and methods
2.1. Chemical
Captopril (C9H15NO3S, CAS N: 62571-86-2) was
purchased from Darou Pakhsh Pharmaceutical
Company. Sodium chloride (NaCl, CAS Number:
7647-14-5; Molecular Weight: 58.44), sodium
hydroxide (NaOH, CAS 1310-73-2. Molecular
Weight 40.00), hydrochloric acid (HCl, reagent,
37%; CAS Number: 7647-01-0; EC Number: 231-
595-7), sodium thiosulfate (Na2S2O3, CAS Number:
7772-98-7; Molecular Weight: 158.11), ferric chloride
(FeCl3, CAS 7705-08-0, EC Number 231-729-4), zinc
oxide (ZnO, CAS 1314-13-2, Molecular Weight
81.39), acetonitrile anhydrous (CAS Number: 75-
05-8, Molecular Weight: 41.05) , triuoroacetic
(TFA, CAS 76-05-1, Molecular Weight 114.02), and
potassium iodide (KI, CAS 7681-11-0, Molecular
Weight 166.00), were obtained from Sigma,
Germany. All chemicals were of analytical reagent
grade.
2.2. Instrumental
The determination of captopril concentration
was analyzed using high-performance liquid
chromatography (HPLC) system (HPLC 862
Bar, Knauer Smartline, Germany). This system
consisted of a photodiode array (PDA) detector,
set at 282 nm, and a C18 column (RP-C18, 5 µm
4.6 ×150 mm) kept at 30°C, with an injection ow
rate of 1.2 mL min-1. The mobile phase solution
was applied using 15% acetonitrile and 85%
triuoroacetic/water acid (2% v/v) [16]. Digital PH
meter (meterohom 827 pH lab, Switzerland) was
used.
2.3. Preparation of the ZnO/Fe2O3 nanocomposite
In a theoretical procedure, 19.4 mg FeCl3 and
200 mg ZnO particles were added to 50 mL of
deionized water, and the mixture was dispersed at
100 °C for 12.0 h (Fig.1). After cooling to 20 °C, the
nanoparticles were separated using centrifugation
33
Removal of Captopril by ZnO/Fe2O3 Nanocomposite Maryam Dolatabadi et al
Fig.2. SEM images of the ZnO/Fe2O3 nanocomposite
Fig.1. Procedure for Preparation of the ZnO/Fe2O3 nanocomposite
and washed several times with ethanol and deionized
water. The ZnO/Fe2O3 nanocomposite was dried at
100°C for 3.0 h and then was used as the catalyst
in the ozonation process for the degradation of
captopril [15]. FE-SEM of nanoparticles of ZnO/
Fe2O3 nanocomposite showed in Figure 2.
2.4. Catalytic ozonation experiments
The catalytic ozonation of captopril was
performed in a 500 mL Pyrex reactor with 8.0
cm diameter and 12 cm high and equipped with a
magnetic stirrer at room temperature. Ozone was
generated from the air using an ozone generator
(ARDA, Model MOG+10) with an input rate of
5 g h-1. The reactor included an input/output port
for the ozone gas stream. Ozone was introduced
through a porous fritted diffuser that can produce
reasonably ne bubbles. The excess ozone at
the outlet was adsorbed by a sequential 2%
potassium iodide solution. The solution pH was
adjusted using NaOH or HCl in the catalytic
ozonation process. After performing the reaction
in each experimental run, 5 mL of sample was
34 Anal. Methods Environ. Chem. J. 5 (3) (2022) 31-39
0
20
40
60
80
100
010 20 30 40 50 60
Removal Efficiency (%)
Reaction time (min)
pH=3
pH=5
pH=7
pH=9
pH=11
taken and ltered by PTFE lters to analyze
for degradation efciency of captopril using
the catalytic ozonation process. Mechanism of
removal of captopril based on the ZnO/Fe2O3
nanocomposite by the catalytic ozonation which
was presented in Figure 3.
3. Results and discussion
3.1. Effect of solution pH
The effect of solution pH is one of the critical
parameters in the catalytic ozonation process for
removing contaminants. Therefore, in the present
study, the effect of solution pH was investigated in
the range of 3.0 to 11.0 for removal of captopril
from aqueous solution, in the constant condition,
including initial captopril concentration of 30 mg
L-1, ZnO/Fe2O3 nanocomposite dosage of 1.0 g L-1,
and ozone dosage of 0.5 mg min-1. The obtained
results are shown in Figure 4. According to the
achieved results, it was found that the removal
Fig.3. Mechanism of removal of captopril based on the catalytic ozonation
and the ZnO/Fe2O3 nanocomposite
Fig. 4. Effect of solution pH and reaction time for removal captopril using catalytic ozonation. Experimental
conditions: initial captopril concentration of 30 mg L-1, ZnO/Fe2O3 nanocomposite dosage of 1.0 g L-1, ozone
dosage of 0.5 mg min-1.
35
Removal of Captopril by ZnO/Fe2O3 Nanocomposite Maryam Dolatabadi et al
0
20
40
60
80
100
010 20 30 40 50 60
Removal Efficiency (%)
Reaction time (min)
Dose= 0.5 g/L
Dose= 1.0 g/L
Dose= 1.5 g/L
Dose= 2.0 g/L
Dose= 2.5 g/L
efciency of captopril decreased with the increase
of pH solution. As the pH value increased from 3
to 11, the removal efciency of captopril decreased
from 85.8% to 51.2% after 60 min. The removal
efciency in the acid conditions is better than in
alkali conditions because high pH in the solution
leads to the creation of more free radical scavengers
derived from the mineralization of organic material,
resulting in a decrease in the concentration of •OH.
Generally, ozone oxidation pathways include direct
oxidation by ozone molecules and radical oxidation
by •OH. Direct oxidation is more selective and
dominates under acidic conditions. While radical
oxidation is less selective and predominates under
primary conditions [17, 18]. Since the removal
efciency at a solution pH of 5 (82.6%) is very
close to the removal efciency at a solution pH of
3 (85.8%), due to the destructive effects of acidic
conditions, a pH of 5 was chosen as the optimal
solution pH in the catalytic ozonation process for
removal of captopril.
3.2. Effect of ZnO/Fe2O3 nanocomposite dosage
The effect of catalyst dosage (ZnO/Fe2O3
nanocomposite) on captopril removal in the
catalytic ozonation process was investigated in the
range of 0.50–2.5 g L-1. In the constant condition,
including solution pH of 5, initial captopril
concentration of 30 mg L-1, and ozone dosage of
0.5 mg min-1. According to the obtained results,
the captopril removal efciency increased with
increasing ZnO/Fe2O3 nanocomposite dosage.
As seen in Figure 5, the removal efciency of
captopril increased to 72.3%, 82.6%, 88.6%,
95.6%, and 98.2% when the catalyst dosage (ZnO/
Fe2O3 nanocomposite) was increased to 0.50, 1.0,
1.5, 2.0, and 2.5 g L-1, respectively. Nevertheless,
the captopril removal efciency at the catalyst
(ZnO/Fe2O3 nanocomposite) dosage of 2.0 g L-1 is
very close to 2.5 g L-1 (less than 3%). Therefore,
a catalyst dosage of 2.0 g L-1 was chosen as the
optimum catalyst dosage. The obtained results
illustrate that ZnO/Fe2O3 nanocomposites show
high performance on catalytic oxidation removal
of captopril. During catalytic ozonation, catalysts
can promote the ozonation process and generate
active free radicals. Consequently, enhancing
the degradation and mineralization of organic
contaminants [10, 14].
3.3. Effect of the initial captopril concentration
The effect of the initial concentration of captopril on
the removal efciency using the catalytic ozonation
process was investigated in the range from 10 to 70
mg L-1. In the stable condition, including solution
pH of 5, ZnO/Fe2O3 nanocomposite dosage of 2.0 g
L-1, and ozone dosage of 0.5 mg min-1. The results
are displayed in Figure 6. The removal efciency of
Fig. 5. Effect of ZnO/Fe2O3 nanocomposite dosage and reaction time for removal captopril
using catalytic ozonation. Experimental conditions: initial captopril concentration of 30 mg
L-1, solution pH of 5.0, ozone dosage of 0.5 mg min-1.
36 Anal. Methods Environ. Chem. J. 5 (3) (2022) 31-39
captopril indeed decreased with the increase of the
initial concentration. After 60 min of reaction time,
when the initial concentration of captopril increased
to 10, 30, 40, 50, and 70 mg L-1 removal efciency
reached 100.0%, 95.6%, 92.1%, 88.4%, and
73.9%, respectively. This phenomenon can be due
to, at constant conditions, the ozone concentration
in the reactor being constant, so the amount of •OH
in the reactor would be constant under the same
conditions. The high concentration of captopril
would consume more •OH, so the removal
efciency is reduced with the increase of the initial
concentration of contaminants [19, 20]. Due to the
captopril removal efciency at a concentration of
40 mg L-1 being a good performance (above 90%),
a captopril concentration of 40 mg L-1 was selected
as the optimum concentration.
3.4. Effect of ozone dosage
Figure 7 shows the removal efciency of captopril
under different ozone dosages. Various levels of
ozone dosage were set by adjusting the inlet gas
0
20
40
60
80
100
010 20 30 40 50 60
Removal Efficiency (%)
Reaction time (min)
0.2 mg/min
0.5 mg/min
1.0 mg/min
1.5 mg/min
0
20
40
60
80
100
010 20 30 40 50 60
Removal Efficiency (%)
Reaction time (min)
10 mg/L
30 mg/L
40 mg/L
50 mg/L
70 mg/L
Fig. 6. Effect of initial captopril concentration and reaction time for removal captopril using
catalytic ozonation. Experimental conditions: solution pH of 5.0, ZnO/Fe2O3 nanocomposite
dosage of 1.0 g L-1, ozone dosage of 0.5 mg min-1.
Fig. 7. Effect of ozone dosage and reaction time for removal captopril using catalytic ozonation. Experimental conditions:
solution pH of 5.0, ZnO/Fe2O3 nanocomposite dosage of 2.0 g L-1, initial captopril concentration of 40 mg L-1.
37
Removal of Captopril by ZnO/Fe2O3 Nanocomposite Maryam Dolatabadi et al
concentration. The ozone dosage effect in the
range of 0.2 to 1.5 mg min-1 was investigated in
constant conditions, including solution pH of 5,
ZnO/Fe2O3 nanocomposite dosage of 1.0 g L-1,
and initial captopril concentration of 40 mg L-1.
The experimental results are presented in Figure
4. According the results, the captopril removal
efciency increased to 75.0%, 92.1%, 99.4%, and
99.6% when the ozone dosage was increased to
0.2, 0.5, 1.0, and 1.5 mg min-1, respectively. More
than 99.4% of captopril is removed within 45
minutes when the ozone dosage is 1.0 mg min-1.
Further increase of ozone dosage (≥1.0 mg min-
1) had no signicant effect on the captopril
removal efciency. This result is probably because
the ozone dosage of 1.0 mg min-1 reached the
maximum ozone utilization of the ZnO/Fe2O3
nanocomposite. Thus, the optimum ozone dosage
was selected as 1.0 mg min-1 [21, 22]. He et al.
removed the metoprolol and ibuprofen using
catalytic ozonation; their results showed that in
optimal conditions, the catalyst dosage was 0.1 g
L-1 [21].
Bai et al. removed the sulfamethazine using a
catalytic ozonation process (Ce0.1Fe0.9OOH as a
catalyst), their results indicated that under optimal
conditions including pH of 7.0, catalyst dosage
of 0.2 g L-1, ozone dosage of 15 mg min-1, and
sulfamethazine concentration of 20 mg L-1, TOC
removal efciency was obtained of 44% at during
120 min [23]. In addition, Qi et al. removed the
phenacetin using catalytic ozonation with CuFe2O4
and its precursor; their results showed that in
optimal conditions (pH of 7.72, catalyst dosage
of 2.0 g L-1; ozone dosage of 0.36 mg min-1, and
phenacetin concentration of 0.2 mM), the TOC
removal efciency was obtained of 90% at during
180 min [24]. Moreover, Zhao et al. removed the
phenol using catalytic ozonation with NiFe2O4
as a catalyst; their results showed that in optimal
conditions (pH of 6.5, catalyst dosage of 1.0 g
L-1; ozone dosage of 0.75 mg min-1, and phenol
concentration of 300 mg L-1), the phenol removal
efciency was obtained of 38.9% at during 60 min
[25].
4. Conclusion
This current study aims to evaluate the removal
efciency of captopril using ZnO/Fe2O3
nanocomposite as a low-cost catalyst by a catalytic
ozonation process. The maximum captopril
removal efciency was 99.4% under optimal
conditions. During catalytic ozonation, catalysts
can promote the ozonation process and generate
active free radicals. It enhanced the degradation
and mineralization of organic contaminants.
Solution pH and initial captopril concentration had
an inverse effect, and the catalyst and ozone dosage
directly affected the removal efciency of captopril.
The catalytic ozonation process is an eco-friendly
advanced oxidation process successfully applied to
remove captopril from polluted water.
5. Acknowledgements
The authors would like to express their appreciation
to the student research committee of Kerman
University of Medical Sciences [Grant number
401000072] for supporting the current work.
Funding: This work received a grant from the
Kerman University of Medical Sciences [Grant
number 401000072].
Conict of interest: The authors declare that they
have no conict of interest regarding the publication
of the current paper.
Ethical approval: The Ethics Committee of
Kerman University of Medical Sciences approved
the study (IR.KMU.REC.1401.099).
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