Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
Research Article, Issue 4
Analytical Methods in Environmental Chemi s try Journal
Journal home page: www.amecj.com/ir
AMECJ
ZnO nano s tructure synthesis for the photocatalytic
degradation of azo dye methyl orange from aqueous
solutions utilizing activated carbon
Ahmed Jaber Ibrahim a,*
a Scientic Research Center, Al-Ayen University, ThiQar 64011, Iraq
ABS TRACT
In this s tudy, zinc acetate (as a precursor) and activated carbon
carboxylic acid derivative were used to create the nano s tructure of
zinc oxide (ZnO) as a matrix. The carboxylic acid derivative was
produced by modifying the oxidized activated carbon with nitric
acid (AC-COOH). The modied activated carbon’s surface was then
impregnated with zinc to load it. By using BET, XRD, and SEM to
characterize the ZnO nano s tructure, it was discovered that it was
composed of nanoparticles with a surface area capacity of 17.78
m2 g-1 and a size range of 21–31 nm. The photocatalytic hydrolysis
of the dye methyl orange in an aqueous medium served as a te s t
case for the cataly s t’s performance. The primary variables were
considered, including pH, cataly s t dose, s tirring eect, and s tarting
dye concentration. Measurements of activity below UV light revealed
satisfactory outcomes for photocatalytic hydrolysis of the methyl
orange (MO). In addition, the eciency of the methyl orange (MO)
photolysis cataly s t prepared with unmodied activated carbon was
also evaluated. The outcomes proved that zinc oxide (ZnO), made
using a derivative carboxylic acid of activated carbon molecules by
a matrix, had more good photocatalytic action than zinc oxide (ZnO)
made by the real activated carbon matrix.
Keywords:
Degradation,
Zinc oxide,
Nano s tructure,
Methyl orange,
Photocatalytic
ARTICLE INFO:
Received 3 Sep 2022
Revised form 29 Oct 2022
Accepted 18 Nov 2022
Available online 29 Dec 2022
*Corresponding Author: Ahmed Jaber Ibrahim
Email: ahmed.jibrahim@alayen.edu.iq
https://doi.org/10.24200/amecj.v5.i04.200
1. Introduction
Reactive dye-containing euents from various
sectors frequently generate environmental issues [1].
The ecosy s tem of the receiving surface waterways
is severely harmed by this pollution [2]. Many
researchers’ eorts have focused on removing
pollutants and toxins from wa s tewater from dierent
sectors [3]. A variety of chemical and physical
procedures, such as membranes [4], adsorption
methods [5], and photolysis, have been employed
to remove dyes [6] presently. Several researchers
have recently used photolysis as one of the advanced
oxidation processes (AOPs) to get rid of dyes from
wa s tewater [7]. Without altering the sub s trate,
the photocatalytic reaction is catalyzed by light
and can proceed more quickly [8]. Under the right
circum s tances, semiconductors function as cataly s ts
due to the down breaking energy between the
capacitance and conduction bands [9]. The process
of photocatalysis requires two levels of dierent,
equal energy. The movement of the electrons caused
by the absorption of this energy leads to a hole (h+)
and a pair of electrons(e-). Both the oxidation of
the electron donor species and the reduction of the
electron acceptor species might include electrons
[10]. To degrade pollutants, many materials are
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6Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
utilized as photocataly s ts, including TiO2, ZnO,
ZrO2, CdS, MoS2, and WO3 [11]. TiO2 is one of
these materials frequently used as a photocataly s t
and has seen the mo s t application to date. TiO2 has
benets like environmental safety, non-toxicities,
chemical con s tancy, and the capacity for re s toration
and reuse. However, TiO2 has drawbacks, including
a high price tag and a UV absorption band. The
importance of ZnO as a suitable TiO2 alternative in
photocatalysis has lately increased [12]. One riche s t
s tructures, zinc oxide, has a variety of advantages.
As a result, ZnO has several uses in various scientic
projects [13]. ZnO has been produced using a variety
of techniques, including the soft chemical method
[14], the sol-gel method [15], the vapor-phase
growth [16], the vapor-liquid-solid process [17],
electrophoretic deposition [18], thermal evaporation
[19], homogeneous precipitation [20], chemical
vapor deposition [21], chemical bath deposition
[22], etc. In the aforementioned inve s tigations, ZnO
nanoparticles were only occasionally generated
through the activated carbon layer and by an auxiliary
matrix approach, as recommended by Park et al. [23].
In this s tudy, the photocatalytic activity of the
generated ZnO was used to break down the azo dye
methyl orange. Additionally, ZnO was produced
using modied activated carbon (containing
carboxyl functional groups).
2. Materials and Methods
2.1. Reagents
All chemical sub s tances were obtained with a high
degree of purity, including cau s tic soda (NaOH,
CAS Number: 1310-73-2, Sigma), hydrochloric acid
(HCl, CAS Number: 7647-01-0, Sigma, Germany),
activated carbon (AC, CAS Number: 7440-44-0,
Sigma), zinc acetate dihydrate (Zn(CH3CO2)2.2H2O,
CAS Number: 5970-45-6, Sigma), nitric acid (HNO3,
CAS Number: 7697-37-2, Sigma, Germany), and azo
dye methyl orange (C14H14N3O3SNa, CAS Number:
547-58-0, Sigma). Methyl orange was dissolved in
100 mL of deionized water (DI), 0.010 g at a time,
to create a s tock solution (100 g mL-1). All working
solutions were made at the necessary concentration
using di s tilled water to dilute the s tock solution.
2.2. Equipment
An ultraviolet-visible spectrophotometer (model
2600) to record Rayleigh UV–Vis spectra. A
Metrohm pH meter (model 744) to adju s t the
working solution’s pH to the desired values. Field
emission-scanning electron microscope (FE-SEM)
(model SU5000) to know the characterization
of the sample’s surface and shape morphology.
X-ray diraction in s trument (XRD) (model B8
ADVANCE) to record patterns via BRUKER. The
transformer coupled plasma (TCP) (model VIS tA-
PRO) to measure the presence of zinc in the samples.
Spectrophotometer (IR-470 Shimadzu) to record the
Infrared (IR) spectrum of samples. At the analytical
chemi s try laboratory of the college of education
(Ibn Al-Haitham) at the University of Baghdad,
experiments in the photocatalytic bleaching and
degradation of dye MO were carried out at a
photoreactor framework prepared there for it.
2.3. Synthesizing Zinc Oxide nanoparticles by
modied activated carbon particles
2.3.1. Activated carbon surface modication
According to Chang et al. [24], adding carboxyl
functional groups to the surface of activated carbon
caused the carbon particles to become activated.
To eliminate metal ions and other impurities, a
hydrochloric solution (10% v/v) solution was
r s t used to clean the activated carbon powder
for 24 hours. Following that, 300 ml of a 32.5
% (v/v) HNO3 solution was s tirred with 10 g of
pure activated carbon added, and the mixture was
heated at 60 °C for ve hours. The heterogeneous
mixture had ltered and neutralized with DI water
(deionized water) by wash and then dried below
decreased pressure for eight hours at 80 °C. the
carboxylic derivative of activated carbon makes up
the nal product (AC-COOH).
2.3.2. Synthesizing nanoparticles of zinc oxide
As a precursor for manufacturing ZnO nanoparticles,
100 mL of zinc acetate solution was mixed with 2
g of carboxylate-activated carbon (AC-COOH) in
dierent concentrations for 12 hours. The solution
was ltered, dried for 18 hours at 80 °C, and then
7
Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
calcined for 4 hours at 500 °C in an electric oven.
Dierent concentrations of zinc acetate dihydrate
were explored to create zinc nanoparticles by
examining the impact of the concentration of zinc
acetate precursor on the description of zinc oxide
(particle size, percentage values, photocatalytic
capabilities, etc.). To do this, ZnO nanoparticles were
created using solutions containing concentrations
of 0.09, 0.02, and 0.01 M(Molarity) zinc acetate
dehydrate, respectively. XRD spectra of three
samples were taken to verify the production of ZnO
nanoparticle forms. The XRD bandwidth pattern
and Scherrer’s Equation 1 [25, 26] were used to
measure the cry s tal size of three samples.
D = K (ƛ ⁄ ß cosø ) (Eq.1)
Where D represents the size of cry s talline particle
in units of a nanometer (nm), The coecient is K
(that equals 0.89), λ represents the wavelength of
the X-ray radiation in a unit of a nanometer (nm), β
means FWHM (full width at half maximum) is an
experimental value in radians (rad) and diraction
angle expressed in degrees had represented θ.
2.3.3. Synthesis of Zinc Oxide nanoparticles
utilizing unmodied activated carbon
2.0 g of activated carbon had put in 200 mL of
hydrochloric solution (10% v/v) to eliminate
impurities for twenty-four hours to s tudy the surface
modication phase of activated carbon particles in
the formation of Zinc Oxide(ZnO). After that, the
product was added to a concentration of 0.09 M
zinc acetate dihydrate solution for 12 hours, and the
resulting combination was then ltered. The nished
product was dried at 80 °C for 18 hours before being
calcined in an electric oven for 4 hours at 500 °C. To
determine the sample’s cry s tal size using Scherer’s
equation, XRD spectra were taken on a sample made
with unmodied activated carbon.
2.4. Procedure of methyl orange decomposition
in photocatalytic experiments
Initially, a 250 mL beaker was lled with 100 mL
of methyl orange(MO) solution with a concentration
of 10 mg L-1 and a pH of 6. The solution was then
supplemented with 20 mg of Zinc Oxide (ZnO)
photocataly s t. Methyl orange was adsorbed onto
Zinc Oxide(ZnO) nanoparticles after being combined
with the solution utilizing a magnetic s tirring device
in a dark environment for half hour (30 min).
Afterward conrming the balance of adsorption,
0.2 mL of the solution was placed into a te s t tube
and then centrifuged for ve minutes at 3000 rpm
to collect the photocataly s t deposition particles.
A spectrophotometer captured the solution’s
adsorption spectra in the 200–600 nm range.
After the absorption spectrum was recorded, the
combination was put into a photoreactor, and a UV
light was turned on. Twenty minutes after exposure
to UV light, ten samples were collected at intervals
of one, and their absorption spectra were recorded.
The control solution’s adsorption spectrum was
recorded similarly without including a photocataly s t.
2.5. Procedure of batch adsorption
To nd the be s t circum s tances for bleaching and
degrading MO (methyl orange) in the exi s tence of
Zinc Oxide (ZnO) photocataly s ts, batch experiments
were carried out. It was thoroughly explored how
relevant factors including methyl orange(MO)
concentration, pH, solution s tirring, photocataly s t
dose, and solution oxygen aected the outcomes.
One variable at a time optimization was utilized to
improve factors that aected the reaction. With this
procedure, s tudies were carried out in a batch setting
with 100 mL of dye solution (10 mg L-1) placed into
a beaker (250 ml). The magnetic s tirrer was used to
mix the suspensions for 30 minutes in the dark before
centrifuging them for 5 minutes at 3000 rpm. A UV-
Vis spectrophotometer was used to evaluate the clear
supernatant. Equation (2) was used to determine the
rate of bleaching and dye degradation [27].
R= (C0 - Ct ÷ C0) × 100 (Eq. 2)
Where R (percentage) represents the dye removal
eectiveness, C0 represents the dye’s s tarting
concentration (mg L-1), and Ct represents the dye’s
concentration at time t following adsorption (mg L-1).
8
3. Results and Discussion
3.1. S tudy of Nanoparticles’ characteris tics
3.1.1. X-Ray Diraction (XRD) examination
The XRD spectra of three produced zinc oxide
(ZnO) samples are shown in Figure 1 to illu s trate
that the nanoparticles formed appropriately.
Figures 1 show that the sample’s hexagonal zinc
oxide cry s tallization has been veried. Table 1
compares the XRD pattern characteri s tics for
three produced samples and the reference sample
[22]. It can be seen from the XRD spectrum in
Figure 1 and the data in Table 1 that as zinc acetate
dihydrate concentration increased, ZnO peak
density too increased, and spectral noise intensity
Table 1. Compares the s tandard sample with the XRD samples (a), (b), and (c),
as well as a sample made with unmodied carbon
Fig. 1. XRD spectra of synthetic ZnO nanoparticles at various concentrations
of zinc acetate dehydrate (a:0.01 M; b: 0.02 M; c: 0.09 M)
Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
9
decreased. This data may result from increased
ZnO nano s tructure production with rising zinc
acetate concentration. This data may be the result
of increased ZnO nano s tructure production with
rising zinc acetate concentration. According to Liu
et al. [20], the intensity of peak 005 in XRD spectra
is associated with carbon impurities that became
less intense as zinc acetate dihydrate concentration
was raised. Figure 2 displays the XRD spectrum of
the carbon-free synthetic sample. The production
of hexagonal ZnO has been conrmed based on
Table 1 and the dierentiation of the XRD data of
the produced samples (unmodied activated carbon
and the s tandard sample). Three samples that were
created using both modied and unmodied carbon
are shown in Table 2 by their cry s tal sizes.
Table 2. Scherrer’s equation-derived e s timated particle size
Fig. 2. XRD spectra sample using unmodied carbon and 0.09 M
of zinc acetate dihydrate.
Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
10
3.1.2. S tudy analysis using TCP, BET, and SEM
The ZnO percent (%) in samples was calculated
using TCP analysis. ZnO content was 9.94, 10.74,
and 31.81 % in samples a, b, and c, respectively.
according to TCP analysis. These ndings sugge s t
that raising the zinc acetate concentration leads
to an increase in the samples’ ZnO content. ZnO
percent was 19.8% for unmodied carbon in the
TCP measurement, demon s trating that ZnO % is
decreased in the absence of surface modication
of activated carbon. The specic surface area of
produced ZnO nanoparticles was measured using
BET analysis (only for sample c). The specic
surface area of this material is higher than the
specic surface area of traditional ZnO particles
(4.49 m2 g-1), according to the results of the BET
s tudy, which also revealed a total pore volume of 0.1
cm3g-1 and average pore width of 51.6 nm [28]. The
inclusion of activated carbon in the produced ZnO
accounts for this elevated amount. ZnO, activated
carbon, and AC-ZnO surface morphology and
textural characterization are signicant criteria that
could improve the eciency of the photocatalytic
activity [29]. SEM images of samples a, b, and c
as shown in Figure 3, were taken to evaluate the
morphology feature of produced ZnO nanoparticles.
It is evident that when the concentration of zinc
acetate rises, ZnO particles ll the pores of the
activated carbon, achieving uniform coverage on a
large portion of the activated carbons. Even though
the large holes in the activated carbon were lled
with ZnO particles, which prevent the porosity of
the carbon surface, sample C nevertheless displays
a porous nature with a sizable amount of surface
area and pore volume [30].
3.2. S tudy Ultraviolet-Visible (UV-Vis)
spectroscopic examination
Two adsorption bands at wavelengths of 464 and
272 nm can be seen in the methyl orange adsorption
spectra. While the breakdown of the azo link, which
results in bleaching, causes the absorption band
at 464 nm to drop, the methyl orange absorption
band decreases at 272 nm due to the phenyl rings
degrading and completing mineralization. As seen
in Figure 4, decolorization rates are very low, and
there is no total degradation or mineralization when
ZnO photocataly s t is not present. In contra s t to
what is depicted in Figure 5, complete bleaching
and degradation take place when ZnO nanoparticles
are present as a cataly s t. For additional research,
Figure 6 shows the absorption trend over time at
wavelengths of 464 nm and 272 nm under three
dierent circum s tances: Ultraviolet radiation, dark
medium, and ultraviolet radiation with the cataly s t
present.
The following gure demon s trates that dye methyl
orange completely bleaches and degrades in the
presence of a ZnO cataly s t within 200 minutes; s till,
these processes were nonexi s tent in the absence of
Fig. 3. SEM characterization for three samples (a, b, and c)
Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
11
a photocataly s t. After swirling the dye and cataly s t
combination in the dark for 20 minutes, data analysis
revealed that no simple degradation occurred and
that the adsorption of dye methyl orange onto the
surface cataly s t was s table. As a result, dye and
cataly s t mixtures were swirled for 30 minutes in
complete darkness in each experiment to guarantee
that adsorption equilibrium was reached.
Fig. 4. Shows the reaction sy s tem’s adsorption spectrum without a ZnO photocataly s t,
with 10 mg L-1 of methyl orange as the cataly s t.
Fig. 5. Shows the reaction sy s tem’s adsorption spectrum at pH 6, 200 mg L-1
of ZnO photocataly s t, and 10 mg L-1 of methyl orange.
Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
12
3.3. pH eect
The pH signicantly aects the adsorption
capacity of the adsorbent and removal eciency
by changing the adsorption chemi s try of the
adsorbent-adsorbate [31]. The appropriate contact
time was used to dissolve 20 mg of photocataly s t
into 100 mL of MO solution (10 mg L-1) for the
pH-related experiments. To change the pH of the
solution, 0.1 M HCl and 0.1 M NaOH solution
were utilized. Figure 7 shows how the pH of the
solution aects how quickly MO is bleached and
degraded by AC-ZnO. It is clear that pH six results
in the fa s te s t bleaching and dye degradation of
methyl orange (MO). Therefore, pH six was chosen
for additional research. Changes in the electro s tatic
attraction between the dye MO and the ZnO surface
can explain this removal process’s pH-dependent
behavior. In comparison to acidic circum s tances
(where the driving force is higher), the pollutant
adheres to the adsorbent particles more eectively
under optimal electro s tatic attraction [32]. ZnO’s
surface charge is positive at low pH 9 [33]. As a
result, anions are more likely to bind to ZnO in an
aqueous environment at a low pH of 9. However,
the pKa for methyl orange has been reported to
be 3.8 ±0.02 [34]. As a result, at pH values higher
than pKa, the concentration of methyl orange in its
anionic form is greater than in its cationic form. The
amount of methyl orange that could be adsorbed
onto ZnO increased as the solution pH was raised
to 6. The rate of bleaching and dye degradation was
shown to decrease at increasing pH values above 6,
because the hydroxyl radical’s oxidation potential
decreases with the rising pH of the solution [35].
Additionally, the anionic form of methyl orange
competes with OH ions in the solution due to the
greater OH content, which lowers the capacity of
methyl orange to bind to ZnO [36].
Fig. 6. The light absorption at wavelengths of 272 and 464 nm changes over time under the conditions
at pH 6, 200 mg L-1 of photocataly s t, and 10 mg L-1 of methyl orange.
Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
13
3.4. Photocatalys t dosage eects
To inve s tigate the eects of photocataly s t dose on
the bleaching and degradation of MO, a solution
with a primary methyl orange concentration of
10 mg L-1 and a reaction duration of 180 min
was added to a range of photocataly s t doses from
100 to 500 mg L-1. Figure 8 depicts the ndings
of these analyses. The result demon s trated that
bleaching and degradation increased when the
cataly s t concentration was raised to 200 mg L-1.
When the cataly s t concentration was increased
to 400 mg L-1, bleaching and degradation did
not change noticeably, but when the cataly s t
concentration was increased to 500 mg L-1,
bleaching and degradation decreased. As cataly s t
concentration grew, more surface active sites
were available. As a result, there is an increase
in the generation of hydroxyl radicals, which
increases ZnO’s photocatalytic activity. UV
light cannot penetrate the cataly s t’s surface
when the milky solution is in excess. As a result,
these occurrences can reduce the generation of
hydroxyl radicals, reducing the eectiveness
of dye deterioration and solution discoloration
[33,37]. For subsequent research, a dose of 200
mg L-1 photocataly s ts was used.
Fig. 7. The pH eects of methyl orange under the conditions of 200 mg L-1 photocataly s ts, and 10 mg L-1
methyl orange on; (a) the rate of bleaching, (b)the rate of dye degradation
Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
14
3.5. MO concentration eects
Several methyl orange (MO) concentrations
(5-20 mg L-1) at a reaction duration of 180 min
and a primary pH of 6 were s tudied to ascertain
the impact of primary MO concentration on the
method’s eectiveness. Figure 9 displays the
outcomes of these analyses. The ndings showed
that raising the initial dye concentration reduced
bleaching and degradation. This might be brought
on by a decline in the number of active surface
sites. As a result, the generation of hydroxyl
radicals declines, which may result in decreased
photocatalytic activity. Furthermore, as the dye
concentration increases, the di s tance of a photon
into a dye solution shortens. To conduct additional
research, MO at a concentration of 10 mg L-1 was
chosen because, at higher dye concentrations, the
dye molecules may absorb more sunlight than
the cataly s t, which could reduce the cataly s t’s
eectiveness [38, 39].
Fig. 8. Eect of cataly s t amount of methyl orange under the conditions of pH 6, 180 minutes,
and 10 mg L-1 of methyl orange on; (a) the rate of bleaching (b)the rate of dye degradation
Anal. Methods Environ. Chem. J. 5 (4) (2022) 5-19
15
3.6. Eects of s tirring the mixture
To find out how s tirring the solution affected
the bleaching and degradation of MO, specific
te s ts were conducted at reaction periods of
180 minutes, pH levels of 6, primary MO
concentrations of 10 mg L-1, and cataly s t doses
of 200 mg L-1. Figure 10 percent (%) the findings
of these analyses. The results show that swirling
the solution exacerbated the bleaching and
deterioration. Fir s t, agitation causes turbulence
in the solution, which promotes the solution’s
absorption of oxygen. In the synthesis of
hydroxyl radicals, soluble oxygen is crucial.
Second, s tirring the solution shortens the time
needed for equilibrium by accelerating MO
transfer and surface diffusion [40].
Fig. 9. Eect of primary concentration of MO under the conditions
of pH 6, and 200 mg L-1 photocataly s ts on; (a) the rate of bleaching (b)the rate of dye degradation
Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
16
4. Conclusion
In the current work, methyl orange from aqueous
solutions was subjected to a dye degradation process
employing ZnO as a photocataly s t. The results
showed that the AC-ZnO sy s tem successfully
de s troyed the MO dye. When ZnO was present,
the rate of deterioration was high, but when ZnO
wasn’t there, the degradation rate decreased. The
be s t dye degradation conditions were found at a pH
of 6.0 with 200 mg L-1 of photocataly s t for 10 mg
L-1 of MO based on agitating the dye solution in an
air environment. The outcomes also demon s trated
that synthetic photocataly s ts in the actual world
had much high ecacy and that recovering and
reusing photocataly s ts hurt the degradation rate
and bleaching. The current s tudy oered a novel,
co s t-eective adsorbent with great promise for
treating wa s tewater contaminated with dyes.
5. Conicts of intere s t
There are no conicts to declare
6. Acknowledgements
This research is supported by the Physical
Chemi s try Lab., Chemi s t Department, College
of Education for pure science (ibn-al Haitham),
University of Baghdad.
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Photocatalytic Degradation of Azo Dye Methyl Orange by ZnO Ahmed Jaber Ibrahim
