Anal. Methods Environ. Chem. J. 5 (4) (2022) 87-95
Research Article, Issue 4
Analytical Methods in Environmental Chemi s try Journal
Journal home page: www.amecj.com/ir
AMECJ
Photocatalytic degradation of methyl orange using cerium
doped zinc oxide nanoparticles supported bentonite clay
Safoora Javana, Mohammad Reza Rezaei Kahkhab*, Fahimeh Moghaddamb,
Mohsen Faghihi-Zarandic, and Anahita Hejazid
a Departement of Environmental Health Engineering, Neyshabour University of Medical Sciences, Neyshabbur, Iran
b Department of Environmental Health Engineering, Zabol University of Medical Sciences, Zabol, Iran
c Foreign Language Department, Shahid Bahonar University of Kerman, Kerman, Iran
d Engineering Department of Occupational Health & Safety at Work, Kerman University of Medical Sciences, Kerman, Iran
ABS TRACT
Methyl orange (MO) is a common anionic azo dye that is a serious
harmful pollutant to the environmental aquatic sys tems, so it mus t
be treated before it can be discharged. Photocatalys ts are usually
semiconducting solid oxides that create an electron-hole pair by
absorbing photons. These electron holes can react with molecules on the
surface of the particles. Photocatalys ts are used in water purication,
self-cleaning glasses, the decomposition of organic molecules, etc.
Photocatalys ts are environmental cleaning materials that remove
pollution from surfaces and can des troy organic compounds when
exposed to sunlight or uorescence. The photocatalytic process
follows the following principles. Bentonite mineral is a natural
adsorbent material that has good adsorption capacity. In this work,
zinc oxide nanoparticles doped with cerium were prepared by the sol-
gel method (SGM) and deposited on bentonite clay to degrade methyl
orange (MO) dye. Important parameters that aected degradation
eciency such as contact time, amount of nanocatalys t, and initial dye
concentration were inves tigated and optimized. Results showed that
100% degradation eciency was obtained at 60 mg of nanocatalys t
and 50 mg L-1 of methyl orange in 120 minutes. The Kinetics of the
degradation process was consis tent with pseudo-second-order and
the adsorption isotherm of MO dye on nanocatalys t was tted with
the Langmuir isotherm model. The reusability of the synthesized
nanocatalys t showed that the nanocatalys t was applied successfully
seven times without a signicant change in degradation eciency.
Keywords:
Photocatalys t,
Degradation,
Clay,
Bentonite,
Methyl Orange,
Dye
ARTICLE INFO:
Received 3 Aug 2022
Revised form 20 Oct 2022
Accepted 17 Nov 2022
Available online 30 Dec 2022
*Corresponding Author: Mohammad Reza Rezaei Kahkha
Email: m.r.rezaei.k@gmail.com
https://doi.org/10.24200/amecj.v5.i04.216
1. Introduction
Photocatalys ts are one of the essential elements
for advanced oxidation processes (AOPs) [1, 2].
Zinc oxide (ZnO) is often the rs t choice due to
its cheapness, non-toxicity, chemical s tability,
and high photocatalytic activity. Photocatalys ts
absorb light radiation (ultraviolet or visible) by
the catalys t, and electrons are transferred from the
semiconductor’s valence band to the conduction
band. This transition creates a hole in the valence
band, and an electron is produced in the conduction
band (Schema 1).
The hole in the reaction with water molecules
produces active hydroxyl radicals[3, 4].
Moreover, the produced electron is transferred
to the dissolved oxygen and forms a superoxide
------------------------
88
radical. These radicals can remove pollutants in
aqueous media. Since the produced electron and
holes are uns table and can recombine and return
to their original s tate, doping elements were used
with ZnO to prevent these phenomena[5]. Cerium
is one of the elements of the lanthanide family
whose redox couple Ce (III)/Ce (IV) causes the
production of CeO2 and Ce2O3 oxides. Ce (IV)
traps the electron created in the conduction band,
which has los t its s table electron conguration,
tends to donate its electron and become s table,
which is possible by electron migration to oxygen
absorbed on the surface and the formation of
superoxide radicals. Therefore, the electron of
the conduction band enters a new cycle, which
reduces the possibility of its access to the hole[6,
7]. Despite the advantages of nanocatalys ts, their
use in water purication processes is limited due
to the small size of the particles. Problems such
as the separation of suspended particles, non-
recycling and secondary pollution are among the
limitations of this method. One proposed method
to solve this problem is xing nanocatalys ts
on suitable subs trates[8]. Many researchers
developed dierent types of subs trates such as
silica gel[9], activated carbon [10], s tainless s teel
[11], glass bers [12] and wood foam [13], has
been used. Recently, ZnO nanoparticles were
immobilized on cellulose paper [14], which was
used to treat textile was tewater in a photoreactor.
Natural clays such as bentonite, montmorillonite,
and perlite are used as catalys t subs trates due
to their high porosity, chemical inertness, non-
degradability, and high mechanical and thermal
resis tance compared to the other mentioned
subs trates[15]. In this work, ZnO-Ce nanoparticles
were rs t synthesized by the sol-gel method.
Then, nanoparticles were xed on bentonite. The
performance of the synthesized nanocatalys t as a
catalys t was inves tigated in the removal of methyl
orange in a batch photoreactor.
2. Material and methods
2.1. Reagents and ins trumental
All reagents and chemicals are analytical grade
and used as received. Zinc acetate dihydrate
Zn(CH3COO)2·2H2O; CAS Number: 5970-45-6),
cerium (CAS Number: 7440-45-1), nitrate (SRM
from NIS t: NaNO₃ in H₂O 1000 mgL-1 NO₃,
Sigma), hydrochloric acid (CAS Number: 7647-01-
0), sodium hydroxide (CAS Number: 1310-73-2),
absolute ethanol (CAS Number: 64-17-5) and MO
Anal. Methods Environ. Chem. J. 5 (4) (2022) 87-95
Schema 1. Photocatalytic process
89
dye (Content 85 %; CAS Number: 547-58-0; EC
Number: 208-925-3; Sigma) were obtained from
Sigma and Merck (Germany). Bentonite (CAS
Number: 1302-78-9) was purchased from Sigma
(Sigma, USA). The pH of the solutions was adjus ted
using a Metrohm (Metrohm, Switzerland) pH
meter. The color concentration was measured using
a double beam-Unico 4802 spectrophotometer at
its maximum wavelength (584 nm). FTIR spectrum
was recorded by Bruker Tensor 27 device.
2.2. Synthesis of ZnO-Ce nanoparticles
The sol-gel method was used to prepare ZnO-Ce
nanoparticles. Firs t, 8.5 mL of zinc acetate was
added to 40 mL of absolute ethanol and the solution
was placed in an ultrasonic bath for 30 minutes
(Solution A). Then 0.12 g of cerium nitrate was
dissolved in 20 mL of absolute ethanol and 3 mL
of deionized water and 2 mL of hydrochloric acid
were added to it. Then, the solution was placed
in an ultrasonic bath for 10 minutes (solution B).
Solution B was added drop by drop to solution
A while s tirring to form a gel. To evaporate the
ethanol, the gel was placed in an oven with a
temperature of 80°C for 12 hours and then calcined
for 3 hours in an oven at a temperature of 550°C.
2.3. Synthesize bentonite nanocatalys t
The immersion method was used to synthesize
bentonite nanocatalys ts coated with ZnO-Ce
nanoparticles. For this purpose, 0.1 g of ZnO-Ce
nanoparticles was added to one liter of ethanol and
water with a ratio of 3:1. For homogenization, the
slurry solution was placed in an ultrasonic bath (35
kHz, 40 W) for 30 minutes. Next, bentonite was
immersed in the solution for one minute. Then
the bentonite was rs t dried at room temperature
and then dried in an oven at 80°C for 2 hours. To
increase the adhesion of nanoparticles to the surface
of bentonite, the granular bentonite was heated in
an oven at a temperature of 550°C for 2 hours.
2.4. Removal procedure
Photocatalytic removal of MO by ZnO-Ce
nanoparticles was s tudied using a batch reactor,
equipped with a UVC lamp at room temperature
(25 °C). To enhance removal eciency, the reactor
was covered with aluminum sheets. The appropriate
dose of ZnO nanoparticle was mixed with dierent
amounts of MO dye. The solution was s tirred at
300 rpm for 30 minutes while the UV lamp at 3800
W irradiated the solution. After the experiment,
30 ml of the sample was taken and in order to
separate the zinc oxide nanoparticles, the sample
was centrifuged at 5000 rpm and ltered. Remind
concentration was measured by spectrophotometer
at 530 nm (Schematic 2) shows the diagram of
degradation of MO).
Photocatalytic degradation of MO by ZnO/Ce/bentonite clay Safoora Javan et al
Schema 2. Schematic diagram of degradation of MO
90
The removal percentage of MO dye (%removal)
was calculated as Equation 1.
(Eq.1)
Parameters aecting the removal of MO dye,
including the amount of the nanocomposite (10-
100 mg), initial concentration of MO dye ( 25
–150 mg L-1 ), and contact time (30-210 min), were
inves tigated.
3. Results and discussion
3.1. Characterization of nanocatalys t
3.1.1. XRD pattern of ZnO/Ce/ bentonite
Schematic 3 showed an XRD pattern of the
synthesized nanocomposite. It can be seen in
schema 3 that by doping cerium as an impurity, the
peaks related to the rutile phase are removed and
only the anatase phase is observed. In other words,
the presence of cerium as an impurity greatly
improves the growth of anatase phase crys tals and
prevents the transfer of the anatase phase to rutile.
3.1.2. SEM image of synthesized ZnO/Ce/
bentonite
Schematic 4 showed an SEM image of a synthesized
nanocatalys t. It can be concluded that the presence
of cerium in the ZnO s tructure reduces the size of
nanoparticles. Considering the s trong dependence
of the properties of nanoparticles on their size, we
can expect signicant changes in the properties of
ZnO/Ce/ bentonite nanoparticles.
Anal. Methods Environ. Chem. J. 5 (4) (2022) 87-95
Schema 3. XRD pattern of ZnO/Ce adsorbent
91
3.2. The optimized parameters for photocatalytic
removal of MO
3.2.1.Eect of amount of nanocatalys t
The amount of ZnO /Ce / bentonite nanocatalys t
impacts the adsorption of the MO dye. The removal
eciency and the adsorption capacity were
inves tigated. For this purpose, experiments were
conducted using an adsorbent dosage in the range
of 10 to 120 mg. As depicted in Figure 1, the uptake
of the MO dye was signicantly increased, up to
60 mg. Furthermore, by increasing the amount of
nanocatalys t, the removal eciency was increased.
3.2.2. Eect of initial concentration of MO dye
on removal eciency
The eect of the initial concentration of dye
on removal percentage by ZnO/Ce/Bentonite
nanocatalys t was inves tigated in the range of 20
to 150 mg L-1. The result is shown in Figure 2. In
the early s tages of adsorption, the results showed
a signicant increase. The maximum percent
removal was achieved at 50 mg L-1 of MO dye.
After this point, the saturation of active sites on the
nanocatalys t has occurred, resulting decrease in the
adsorbent’s ability to the sorbent.
Photocatalytic degradation of MO by ZnO/Ce/bentonite clay Safoora Javan et al
Schema 4. SEM image of synthesized adsorbent
Fig. 1. Eect of ZnO/Ce/Bentonite amount on degradation eciency
92
3.2.3. Eect of time on degradation eciency
The eect of contact time on the degradation eciency
of MO dye by ZnO/ Ce/ Bentonite nanocatalys t was
inves tigated. The results are depicted in Figure 3.
The removal percentages of MO dye increased
signicantly in the early s tages. After a while, the
percentage degradation will rise slightly until an
equilibrium is reached. The results showed that the
bes t dye removal percentage was obtained at 120
minutes. Hence, this time was selected for subsequent
experiments.
3.2.4. Kinetic s tudy
Adsorption kinetic s tudies of MO dye onto ZnO/
Ce/ Bentonite nanocatalys t were inves tigated
using pseudo-rs t-order and pseudo-second-order
kinetics. The results are shown in Figure 4 and at
summarized in Table 1. The kinetic model that bes t
ts the adsorption of MO dye on the nanocatalys t was
determined by R2 values. Considering the reported
R2 values, the adsorption of MO dye on ZnO/ Ce/
Bentonite nanocatalys t was followed by a pseudo-
second-order kinetics model.
Anal. Methods Environ. Chem. J. 5 (4) (2022) 87-95
Fig. 3. Eect of time on degradation eciency
Fig. 2. Eect of dye concentration on degradation eciency
93
Photocatalytic degradation of MO by ZnO/Ce/bentonite clay Safoora Javan et al
Fig. 4. Kinetic s tudies of the adsorption of MO dye on nanocatalys t.
a) Psuedo Firs t order b) Psuedo second order
Table 1. Kinetics parameters for MO dye
Firs t order kinetics Second order kinetics
MO dye R2K1 (min-1) R2K1 (g.mg-1min-1)
0.8344 -6.51X10-3 0.9992 1.88X10-2
3.2.5. Adsorption isotherms
For the evaluation of adsorption isotherms,
Langmuir and Freundlich’s isotherms were used
to illus trate the mechanism. The Langmuir and
Freundlich isotherms for MO dye on nanocatalys t
were depicted in Figure 5 and Table 2. It was
found that the adsorption of Mo dye on ZnO/Ce/
Bentonite nanocatalys t followed from Langmuir
isotherm.
3.2.6. Reusability of Nanocatalys t
Evaluating the reusability of ZnO/Ce/Bentonite
nanocatalys t on the degradation of MO dye
photocatalytic experiments in optimal conditions was
repeated several times. Afterward, the nanocatalys t
was washed, dried, and reused for the next run.
Results showed that degradation eciency was
decreased from 100 to 98.1 after 7 repeated
experiments that conrmed the reusability of
the nanocatalys t. Also, for the evaluation of the
94
sorption capacity of the nanocatalys t, a s tandard
solution containing 100 mgL−1 of MO was applied.
The initial and nal amounts of MO dye were
determined by spectrophotometer after adsorption
on ZnO/Ce/ Bentonite. The maximum adsorption
capacity was dened as the total amount of
adsorbed MO per gram of the nano catalys t. The
obtained capacity was found to be 115 mg g−1.
4. Conclusion
The degradation eciency of methyl orange using
ZnO/Ce/Bentonite nanocatalys t as photocatalys t and
adsorbent was inves tigated. The optimal conditions
for the degradation eciency of the dye were found at
a nanocatalys t dosage of 60 mg , a contact time of 120
min yellow. At optimum conditions, 100% of methyl
orange was removed by synthesized nanocomposite.
Also, the nanocatalys t was reused after 7 repeated
cycles, and adsorption capacity was obtained115 mg
g-1. The isotherm data of MO dye were tted with
the Langmuir model, while the kinetic data were
modeled by the pseudo-second-order, revealing that
the nature of the kinetic adsorption is chemical. The
present s tudy showed that the ZnO/ Ce/ Bentonite
nanocatalys t is an eective adsorbent for the
degradation of MO dye from aqueous solutions.
Fig. 5. a) Langmuir isotherm of MO dye onto nanocatalys t,
b) Freundlich isotherm of MO dye onto nanocatalys t
Table 2. Isotherms parameter of MO dye
Langmuir Freundlich
MO dye RLKLKFN
Results 0.9874 0.3989 0.03345 0.9513 11.9674 2.5713
Anal. Methods Environ. Chem. J. 5 (4) (2022) 87-95
95
5. Acknowledgements
Authors at this moment thank from health laboratory
of Zabol University for their cooperation to perform
experiments.
6. References
[1] A. Raq, M. Ikram, S. Ali, F. Niaz, M. Khan, Q.
Khan, M. Maqbool, Photocatalytic degradation
of dyes using semiconductor photocatalys ts
to clean indus trial water pollution, J. Ind.
Eng. Chem., 97 (2021) 111-128. https://doi.
org/10.1016/j.jiec.2021.02.017
[2] B. Viswanathan, Photocatalytic degradation of
dyes: an overview, Curr. Catal., 7 (2018) 99-
121. http://dx.doi.org/10.2174/22115447076661
71219161846
[3] J. Singh, Biogenic synthesis of copper oxide
nanoparticles using plant extract and its prodigious
potential for photocatalytic degradation of dyes,
Environ. Res., 177(2019) 108569. https://doi.
org/10.1016/j.envres.2019.108569
[4] S. Alkaykh, A. Mbarek, E.E. Ali-Shattle,
Photocatalytic degradation of methylene blue dye
in aqueous solution by MnTiO3 nanoparticles
under sunlight irradiation, Heliyon, 6 (2020)
e03663. https://doi.org/10.1016/j.heliyon.2020.
e03663
[5] L. Yang, Three-dimensional bacterial cellulose/
polydopamine/TiO2 nanocatalys t membrane
with enhanced adsorption and photocatalytic
degradation for dyes under ultraviolet-
visible irradiation, J. Colloid Interface Sci.,
562 (2020) 21-28. https://doi.org/ 10.1016/j.
jcis.2019.12.013
[6] H. Chaker, A s tatis tical modeling-optimization
approach for eciency photocatalytic
degradation of textile azo dye using cerium-
doped mesoporous ZnO: A central composite
design in response surface methodology, Chem.
Eng. Res. Des., 171 (2021) 198-212. https://doi.
org/10.1016/j.cherd.2021.05.008
[7] R. Jasrotia, Photocatalytic degradation of
environmental pollutant using nickel and cerium
ions subs tituted Co0. 6Zn0. 4Fe2O4 nanoferrites,
Earth Sys t. Environ., 5 (2021) 399-417. https://
doi.org/ 10.1007/s41748-021-00214-9
[8] A. Mohammad, Adsorption promoted visible-
light-induced photocatalytic degradation of
antibiotic tetracycline by tin oxide/cerium
oxide nanocatalys t, Appl. Surface Sci., 565
(2021) 150337. https://doi.org/10.1016/j.
apsusc.2021.150337
[9] M.R. AbuKhadra, Enhanced photocatalytic
degradation of acephate pes ticide over MCM-
41/Co3O4 nanocatalys t synthesized from rice
husk silica gel and Peach leaves, J. Hazard.
Mater., 389 (2020) 122129. https://doi.org/
10.1016/j.apsusc.2021.150337
[10] M.S. Nasrollahzadeh, Synthesis of ZnO
nanos tructure using activated carbon for
photocatalytic degradation of methyl orange
from aqueous solutions, Appl. Water Sci., 8
(2018) 1-12. https://doi.org/10.1007/s13201-
018-0750-6
[11] J. Singh, A. Dhaliwal, Electrochemical and
photocatalytic degradation of methylene blue by
using rGO/AgNWs nanocatalys t synthesized by
electroplating on s tainless s teel, J. Phys. Chem.
Solids, 160 (2020) 110358. https://doi.org/
10.1016/j.jpcs.2021.110358
[12] S. Fukugaichi, Fixation of titanium dioxide
nanoparticles on glass ber cloths for
photocatalytic degradation of organic dyes,
ACS omega, 4 (2019)15175-15180. https://doi.
org/10.1021/acsomega.9b02067
[13] Z. Wang, Ecient and sus tainable photocatalytic
degradation of dye in was tewater with porous and
recyclable wood foam@ V2O5 photocatalys ts,
J. Clean. Prod.. 332 (2022) 130054. https://doi.
org/10.1016/j.jclepro.2021.130054
[14] S. Li, Promoting eect of cellulose-based
carbon dots at dierent concentrations on
multifunctional photocatalytic degradation of
dyes by ZnO, Opt. Mater., 121(2021) 111591.
https://doi.org/10.1016/j.optmat.2021.111591
[15] A. Mishra, A. Mehta, S. Basu, Clay supported
TiO2 nanoparticles for photocatalytic
degradation of environmental pollutants: A
review, J. Environ. Chem. Eng, 6 (2018) 6088-
6107. https://doi.org/10.1016/j.jece.2018.09.029
Photocatalytic degradation of MO by ZnO/Ce/bentonite clay Safoora Javan et al
