Journal of Crystal Growth 591 (2022) 126718
Contents lists available at ScienceDirect
Journal of Crystal Growth
journal homepage: www.elsevier.com/locate/jcrysgro
The impact of excessive ethanol on synthesis and characterization of Zinc
oxide nanoparticles
Asha Chauhan a, *, A.K. Shrivastav a, Anjali Oudhia b
a
b
Department of Physics, National Institute of Technology, Raipur, Chhattisgarh, 492010, India
Department of Physics, Nagarjuna P. G. Science College, Raipur, Chhattisgarh, 492010, India
A R T I C L E I N F O
A B S T R A C T
Communicated by K. Deppert
Zinc oxide (ZnO) nanostructures are one of the most prominent areas of research in the present scenario. In this
work, we have synthesized ZnO nanoparticles (NPs) using a simple sol–gel method with varying amounts of
ethanol, changes in the amount of ethanol led to some promising changes in the quality of ZnO. With an increase
in the amount of ethanol the size of ZnO, gets reduced since ethanol. UV–Visible (UV–Vis) spectroscopy and
photoluminescence (PL) analysis confirmed the existence and behavior of ZnO nanostructure. Photo­
luminescence emission spectra suggested that the ethanol can suppress the zinc and oxygen vacancy hence
improving the crystallinity of ZnO NPs. The X-ray diffraction (XRD), scanning electron microscopy (SEM), energy
dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR) established the formation
of ZnO NPs. This work explores the simple synthesis technique, bandgap tailoring, and impact of ethanol on ZnO
nanostructures.
Keywords:
A1. Nanostructure
B1. ZnO
A2. Sol-gel method
B1. Ethanol
1. Introduction
Zinc Oxide (ZnO) is one of the most prominent materials when it
comes to application-based research. It has properties that interest re­
searchers like a wide direct bandgap, high electron mobility, non-toxic
nature, ease to synthesize, and cost-effectiveness. The major areas of
applications of ZnO nanoparticles (NPs) are in solar cells, LEDs, super­
capacitors, gas sensors, biomedicine, etc. The most important advan­
tages of NPs over larger size particles are their high surface-to-volume
ratio, higher surface energy, and excellent electronic, magnetic, and
optical properties [1,2]. ZnO has advantages like being non-toxic,
viable, morphologically tunable, biologically acceptable, antibacterial
nature, and cost-effective [2,3]. Also, it is one of the most promising
materials for target drug delivery in cancer or tumor treatment [3]. In a
recently published article, applications of 0D ZnO nanostructures were
mentioned. Some theoretical studies also provided us with a platform to
discover the novel type of ZnO nanostructures, which can be used
further for experimental trials [4].
The sol–gel method is the widely used low-cost synthesis method of
ZnO NPs, due to its conventional and easy steps [5,6]. During the syn­
thesis of NPs like - ZnO NPs, the processing parameters like temperature,
the addition of cation solution, and stirring time are all kept under
consideration [7,8]. Inexpensive ethanol plays a very important role in
the synthesis process of NPs and nanostructures, which can reduce the
size of particles to nano-level, it can also be used as a solvent to nucleate
the nanocrystallite like ZnO, Co, and Ni particles [9-12]. The sol–gel,
wet-chemical, and precipitation method of synthesis, suggested that the
pH value and processing temperature of the final solution is the most
important part of the enhanced crystallization and morphology of ZnO
NPs [13,14,16,17,19].
Majorly semiconductor nanostructures are formed as colloidal solu­
tions. In this study, we have synthesized ZnO NPs with varying amounts
of ethanol using a simple sol–gel method [6,9]. This work verifies simple
manufacturing techniques of ZnO nanostructures and establishes a good
understanding of the quality of nanostructures synthesized by the
change in the amount of ethanol solution. We have morphologically and
optically certified our synthesized samples by XRD, SEM, UV–Vis, PL,
and FTIR spectroscopy in this work. The main concern of this work is to
study the impact of ethanol on the structure of ZnO nanomaterials.
* Corresponding author.
E-mail address: achauhan.phd2019.phy@nitrr.ac.in (A. Chauhan).
https://doi.org/10.1016/j.jcrysgro.2022.126718
Received 23 February 2022; Received in revised form 21 April 2022; Accepted 5 May 2022
Available online 11 May 2022
0022-0248/© 2022 Elsevier B.V. All rights reserved.
A. Chauhan et al.
Journal of Crystal Growth 591 (2022) 126718
Fig. 1. The schematic diagram of the prepared ZnO nanostructure solutions.
2.2. Synthesis of Zinc oxide solutions
Before the synthesis of the ZnO NPs, all the glassware was cleaned
twice with detergent water, acetone, and double-distilled water,
respectively. ZnO NPs were synthesized by the sol–gel method, and the
following method was adapted from the literature, given in this refer­
ence [6,7]. In the chemical synthesis method, the sol–gel method gives
better compositional control over the semiconducting materials. The
sol–gel method is preferred as it is a cost-effective method, consumes
less energy and time to synthesize nanomaterials [56,58]. For the syn­
thesis of ZnO NPs, 2 g of zinc acetate dihydrate and 8 g of sodium hy­
droxide were weighed and dissolved into 10 ml and 15 ml of distilled
water respectively, at room temperature [6,16]. Each solution was
vigorously stirred by a magnetic stirrer at a constant stirring speed for
five minutes at a temperature of 60 ◦ C. After that, the NaOH solution was
added dropwise into the zinc acetate solution, until got a crystal-clear
ZnO solution (as shown in Fig. 1). As previously reported, the pH
value of 11 in a solution of ZnO showed the enhanced crystallization and
morphology of ZnO NPs so, we added the NaOH solution until got a pH
of 11 in the final ZnO solution [17,19] as shown in the figure below.
Since we have synthesized the ZnO NPs by the sol–gel method the pH of
the sol is the most important factor which influenced the properties of
NPs. The morphological properties are affected by the pH of a sol since it
affects the hydrolysis and condensation of the final solution [18]. The
addition of ethanol (at raising temperature) into the ZnO solution
changed the pH of the final ZnO solution since both the parameters
temperature and pH have modulating impact on each other, as reported
in the previous study [51]. We have also recorded the pH value of the
various solutions by a digital pH meter during the synthesis process. The
digital pH meter was cleaned sequentially after taking each pH of the
ZnO solution. The reactions that take place in the synthesis process of
ZnO NPs are shown in the equations given below [13,15]:
Fig. 2. Schematic representation of ethoxy adsorption on Oxygen and
Zn2+ vacancy.
2. Synthesis method
2.1. Materials
Zinc acetate dihydrate (Zn(CH3COO)2⋅2H2O, 99.9%) (Sigma
Aldrich), sodium hydroxide pellets (NaOH ≥ 98%) (Sigma Aldrich),
ethanol (CH2COOH) (Loba Chemicals), and distilled water. Zinc acetate
dihydrate, sodium hydroxide, ethanol (C2H5OH), and distilled water
were used as precursor, reducing-reagent, and solvent, respectively. All
the chemicals were of analytical grade with extra purity and were used
without any further purifications.
2
Zn(CH3COO)2 + NaOH → Zn(CH3COO) (OH) + NaCH3COO
(1)
Zn(CH3COO) (OH) + NaOH → ZnO + NaCH3COO + H2O
(2)
A. Chauhan et al.
Journal of Crystal Growth 591 (2022) 126718
Fig. 3. (a) absorption spectra (b), (c), (d), (e), and (f) bandgap calculation by Tauc’s plot for various amounts of ethanol (Pristine, 25 ml, 50 ml, 75 ml, and 100 ml)
(g) absorption spectra of ZnO nanopowders.
After stirring for five minutes the mixed ZnO solution (Zn(CH3COO)2
+ NaOH), different amounts of ethanol (25 ml, 50 ml, 75 ml, and 100
ml) were poured into the final ZnO solution with different stirring times
and temperatures (30 min, 35 min, 40 min, and 45 min; 65 ◦ C, 70 ◦ C,
75 ◦ C, and 80 ◦ C, respectively) [9-11]. With the addition of ethanol into
the ZnO solution at various stirring temperatures and times, the color of
the solutions got changed from a clear transparent solution to the darker
color of laguna, yellow, amber, and red, respectively, as shown in Fig. 1.
The addition of ethanol into the base material may change the structure
of ZnO in the solution and the color changes due to adsorption and
dissociation of ethanol and making the complex ZnO solution [31]. Also,
the absorbed ethanol dissociated into ethoxy and hydrogen, and the
dissociated ethoxy molecularly adsorbed on oxygen or Zn2+ ions site
hence reduction of Zn2+ to ZnO, as reported in previous studies [33].
However, this process of adsorption of ethanol may increase the
complexity of the pristine ZnO solution (without the addition of ethanol)
and turn the darker red color of the mixture solution, G.D. Jeyaleela
et al. obtained similar experimental results with the addition of a
reducing agent isolated flavonoid quercetin into ZnO base solution [32].
The schematic picture of all the prepared ZnO solutions with various
amounts of ethanol is shown in Fig. 1.
the residual present in the prepared ZnO samples. After that, the residual
free precipitate was dried at 100 ◦ C for 30 min, followed by calcination
at 450 ◦ C for five hours, and then cooled naturally. Finally, we have
obtained the synthesized different colors of ZnO nanopowder by the
method shown in the above diagram [6,7]. All the synthesized nano­
powder with various amounts of ethanol were obtained in different
colors from pristine ZnO after calcination. The images of ZnO nano­
powders are shown in Fig. 6 (g). After the annealing process, color
variations from white color as the color of solutions of ZnO were
observed in the final ZnO nanopowder [9,12]. Although the colors of the
final ZnO nanopowder are changed since ethanol, XRD, EDAX, and FTIR
spectra confirmed the existence of ZnO nanostructure [20]. ZnO nano­
powder synthesis process is a green-wet chemical and environmentfriendly method since all the chemical used in the synthesis process is
inorganic chemicals, which can be processed in outdoor conditions.
3. Results and discussion
3.1. Sample characterization
All the synthesized samples of ZnO were characterized in the range
from 190 to 1100 nm by UV–Visible (UV–Vis) spectroscopy (UV-3600,
Shimadzu); photoluminescence (PL) spectroscopy was recorded in the
range from 280 to 800 nm (PL spectrophotometer, Shimadzu); and the
crystal structure of ZnO NPs was characterized by XRD with CuKα ra­
diation of wavelength 1.5404 Å (XRD-3 KW PAN-alytical, Xpert powder
diffractometer by Bruker) at room temperature, to study the
2.3. Synthesis of Zinc oxide nanopowder
During the synthesis of ZnO NPs, after the formation of white pre­
cipitate, the ZnO solution was filtered by Whatman’s filter paper and
then cleaned two times with deionized water, which helped to remove
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Journal of Crystal Growth 591 (2022) 126718
Fig. 3. (continued).
morphological and optical properties of ZnO NPs along with their var­
iations. A digital pH meter was used to measure the pH value of the
prepared solutions, which was calibrated first by a buffer solution of pH
measurements 4.0 and 6.86 at room temperature. The gold coating with
a thickness of 7 nm was deposited on each sample by a sputtering
(Quorum-SC7620). The scanning electron micrographs (SEM) and
energy-dispersive X-ray analysis (EDAX) of synthesized ZnO nano­
structures were recorded by an electron microscope (Thermo Scientific
Phenom Desktop SEM). The compositional analysis of the prepared ZnO
samples was characterized by Fourier-transform infrared spectroscopy
(FTIR) in the range from 400 to 4000 cm− 1 (Shimadzu Corpn. Japan, IRPrestige 21).
kept in a transparent quartz cuvette of 1 cm path length then obtained
the absorbance property of all ZnO NP solutions. If we dilute the ZnO
nanopowder with ethanol again then the properties of ZnO NPs may be
further changed so, the UV–Vis measurements were taken for all ZnO
liquid solutions.
The absorption peak of the pristine ZnO solution was observed at
378 nm. The blue shift of absorbance peaks was observed, attributed to
the size reduction of nanostructure as compared to the pristine ZnO
solution [6,9,10,20]. Fig. 3 (b, c, d, e, and f) shows the bandgap of the
ZnO nanostructure solution. The bandgap of the prepared samples was
obtained by the tangent of Tauc’s plot of equation (3) [21].
3.2. Optical analysis
Where h = Planck’s constant; hυ = photon energy; Eg = bandgap
energy; k = proportionality constant; α = absorption coefficient.
The relation between the photon energy and wavelength can be
written as:
(αhυ)2 = k(hυ − Eg )
UV–Vis spectroscopy is a technique that is used to measure the
amount of light energy absorbed by a chemical substance. In our study,
to observe the influence of ethanol on the absorbance properties of the
prepared ZnO solutions was measured by UV–Vis spectroscopy as a
function of wavelength from the range of 200 to 900 nm as shown in
Fig. 3 (a). During the synthesis process, the formation of a clear trans­
parent solution (without the addition of ethanol) was the indication of
the formation of ZnO NPs before the addition of ethanol. With the
indication of the formation of ZnO NPs into the prepared solution, the
UV–Vis absorbance spectra were taken while the ZnO was in the liquid
solution. Similarly, we obtained the UV–Vis spectra of all remaining
laguna, yellow, amber, and red liquid solutions. The ZnO solutions were
hυ =
hc 1240
=
eV
λ
λ
[since hc = 1240 eV].
Further, equation (3) can be modified as:
(
)
(
)2
1240
1240
2.303*absorbance*
− Eg
=k
λ
λ
(3)
(4)
(5)
The obtained bandgap at room temperature for pristine ZnO solution
from equation (3) is ~ 3.28 eV while the bandgap increased to 3.45 eV,
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Journal of Crystal Growth 591 (2022) 126718
Fig. 4. (a) PL spectra; (b), (c), (d), (e), and (f) Gaussian deconvoluted PL spectra for various amounts of ethanol (Pristine, 25 ml, 50 ml, 75 ml, and 100 ml) (g) PL
spectra of ZnO nanopowders.
3.47 eV, 3.50 eV, 3.53 eV for 25 ml, 50 ml, 75 ml, 100 ml of ethanol,
respectively processed at various temperatures (65 ◦ C, 70 ◦ C, 75 ◦ C, and
80 ◦ C), attribute to the formation of ZnO nanostructure and quantum
confinement effect of low dimensional crystallites [6,9-12]. It is re­
ported that in the semiconducting material the bandgap increases due to
the reduction in the size of nanomaterials and it is a very important
characteristic of materials affecting their electrical, chemical, and lightabsorbing properties [22]. The reduction in the size of ZnO NPs leads to
an increase in the surface area of nanomaterials which helped to
chemically absorb more easily on the absorbing body [60,61]. After
collecting ZnO powders from each liquid solution UV–Vis absorption
spectra have been obtained by redispersing the ZnO powder into
ethanol, to confirm the ethoxy adsorption on the ZnO surface. The
UV–Vis absorption spectra of ZnO powders are shown in Fig. 3 (g). The
absorption spectra of ZnO in liquid and solid forms significantly match
indicating the ethoxy adsorption on the surface of ZnO [31]. However, a
very slight change in the absorption peak of pristine ZnO compared to
UV–Vis of liquid samples of pristine ZnO was observed due to evapo­
ration of liquid and size reduction when annealing the samples at a
temperature of 450 ◦ C [6,7,9,12]. The experimental results were also
compared and validated with the previously reported articles [20].
The PL emission establishes due to the defect, vacancies, and
recombination of electron-hole pairs in semiconducting materials [23].
Fig. 4 (a) showed a sharp PL emission of pristine ZnO solution at 380 nm
in the ultraviolet region due to the bandgap ~ 3.28 eV and recombi­
nation of electrons from the conduction band with the holes in the
valence band [24,27]. The addition of ethanol blue-shifted the PL
emission in the ultraviolet region attributed to the smaller size of ZnO
nanoparticles with the addition of ethanol in the ZnO solution [20,34].
The PL emission in the UV region is the characteristic signature of
wurtzite ZnO, and our study established the enhancement of UV emis­
sion with higher intensity, suggesting the improvement of crystallinity
of the nanoparticles [36,38]. The ZnO with 100 ml of ethanol showed
the dominant behavior in the UV region in our study. As we moved to­
wards the visible range in the PL spectra the broad PL emission centered
at 550 nm in the range of 400 to 660 nm originated from oxygen or Zn2+
vacancies of ZnO NPs [24,25] as shown in Fig. 4 (a). This weak and
broad range of PL emission is the combination of two green and blue
regions, due to Zn2+ and oxygen vacancies, respectively [26-29].
However, the addition of ethanol decreases the intensity of visible
luminescence with the peak still centered around 550 nm, until the
ethanol is 50 ml. However, the peak intensity in the visible region was
suppressed and blue-shifted as compared to the pristine ZnO for ethanol
100 ml (seeFig. 5).
We observed the shift in PL emission towards the blue region as the
amount of ethanol varied after 50 ml. The ZnO has a wurtzite hexagonal
crystal structure which is composed of negatively charged ions surface
on (0001)-O with other positively charged ions surface on (0001)-Zn,
establishing the oxygen and Zn2+ vacancy level in ZnO materials, due to
these vacancy level ZnO is highly chemically reactive material as re­
ported [47]. During the synthesis process at a given temperature, the
added ethanol into the ZnO solution molecularly adsorbs on the surface
of ZnO and dissociated into two parts as equation (6) ethoxy (C2H5O)
and hydrogen (H), and the dissociated ethoxy adsorbed on the oxygen
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Journal of Crystal Growth 591 (2022) 126718
Fig. 4. (continued).
(0001)-O negative surface or Zn2+ vacancy (0001)-Zn positive surface
while hydrogen adsorbed on the oxygen lattice [33,48]. Ethoxy is an
organic compound that is chemically reactive and has a bonding nature
with semiconducting materials [31]. The schematic diagram of ethoxy
adsorption on ZnO vacancy is shown in Fig. 2. Although the visible
luminescence intensity was deceased with ethanol addition, however 50
ml of ethanol was not sufficient to suppress the oxygen and Zn vacancy
level. Although the oxygen and Zn vacancy was not completely
quenched in the visible region, we were able to minimize these va­
cancies by an extremely easy method. It is also reported that the
adsorbed ethanol was also desorbed at various annealing temperatures
during the calcination process of ZnO NPs [31].
Gaussian deconvoluted spectra with the constituent peak of all PL
emission spectra. The term Vo is related to the donor level while VZn and
OZn are related to vacancy or acceptor between the conduction energy
band and valence energy band [45,46]. Further, we have also classified
the donor and acceptor levels by relating the element peaks of Gaussian
deconvoluted spectra. We found that the peak at ~ 480 nm is related to
donor energy level and ~ 460 nm and 520 nm, related to acceptor en­
ergy level lies in between the bandgap of ZnO materials. The peak > 540
nm is related to the interstitial defect. These results demonstrated that
we have synthesized the ZnO NPs with enhanced optical properties
which may be a potential semiconductor for photovoltaic and opto­
electronic applications like PSCs and LEDs [1,2,7]. The solutions other
than pristine ones showed less intense luminescence peaks in the visible
region due to the size reduction of ZnO nanostructure [30]. However, a
similar pattern of PL emission was observed for all ZnO solutions
showing that the addition of ethanol does not change the fundamental
structure of ZnO [20]. The PL emission of ZnO nanopowder by redis­
persing it into ethanol has been obtained and no obvious change in the
PL spectra of ZnO compared to PL emissions of liquid samples was
observed as shown in Fig. 4 (g) which indicates the ethoxy adsorption on
the surface of ZnO which can suppress the vacancy level present in the
synthesized ZnO nanostructures [31]. ZnO NPs are not hazardous to the
environment and it is very easy to synthesize; with various types of
doping, we can achieve the desired one and can use them in outdoor
conditions without any harmful impact [9-11].
C2H5OH(Ethanol) C2H5O (Ethoxy) + H (Hydrogen) [Dissociation of ethanol]
(6)
Further, the broad PL emissions in the visible range were Gaussian
deconvoluted to resolve constituent peaks present in the PL emission
spectra of prepared ZnO. The deconvoluted peak at ~ 2.7 eV (460 nm) is
related to Zn vacancy (VZn) [38,39]. The PL peak positioned at ~ 2.53 eV
(480 nm) and ~ 2.38 eV (520 nm) are the most controversial and related
to Vo [34,35,40,41] and OZn, [37,42,43] respectively. The peak related
to yellow and orange emission at > 540 nm is related to Oi [44]. In the
PL spectra, luminescence at wavelength > 700 nm is the resultant of the
secondary UV diffraction [34]. Fig. 4 (b, c, d, e, and f) shows the
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Journal of Crystal Growth 591 (2022) 126718
Fig. 5. (a) bandgap (b) pH (c) comparison of crystallite size for various amounts of ethanol (Pristine, 25 ml, 50 ml, 75 ml, and 100 ml).
3.3. X-ray diffraction analysis
D=
To confirm the hexagonal crystal phase of ZnO NPs we have analyzed
the samples by XRD analysis, shown in Fig. 6 (a). The XRD spectra were
plotted with position 2θ (degree) from 10◦ to 70◦ along X-axis and in­
tensity (a.u.) along Y-axis. All the crystallographic planes (1 0 0), (0 0 2),
(1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2), and (2 0 1) were obtained at
positions 31.73◦ , 34.50◦ , 36.24◦ , 47.58◦ , 56.57◦ , 62.95◦ , 66.42◦ , 67.93◦ ,
and 69.18◦ , respectively, for all the synthesized ZnO nanopowder
[57,59]. The XRD pattern depicted the Wurtzite crystal structure and
rotation along the c-axis of all the prepared nanostructure [6]. Corre­
sponding to the XRD peak (1 0 1) assigned at 36.24◦ , the crystallite size
of the prepared pristine ZnO nanopowder was 22.23 nm determined
using the Scherrer equation as mentioned in equation (7) [49]. How­
ever, the crystallite size decreased from 22.23 to 12.36 nm as the
amount of ethanol was increased to 100 ml. The decrease in the crys­
tallite size suggested a decrease in the size of ZnO NPs and improve the
Wurtzite signature of ZnO NPs since ethanol [50]. These XRD charac­
terizations confirmed the synthesis of ZnO NPs, which can be used for
future optoelectronic-based applications [3,6,7,9].
kλ
βcosθ
(7)
Where D = size of the crystallite diameter; k = Scherrer constant; λ =
wavelength of X-ray; β = breadth of the peak.
To evaluate the average crystallite size and lattice strain induced on
the ZnO samples may be due to the crystal imperfection we have also
used the Williamson-Hall (W-H) equation [66]:
βcosθ =
kλ
+ 4εsinθ
D
(8)
Where ε = strain induced on the particles.
Plots shown in Fig. 6 (b, c, d, e, and f) are drawn with 4sinθ along the
x-axis and βcosθ along the y-axis for high intense peaks and thus the
crystallite size of ZnO NPs can be obtained. The deviation was observed
in the crystallite size of ZnO NPs calculated by Scherrer or W-H data as
shown in Table 1. It is expected that the Scherrer method does not
include the variation due to strain in the calculation of particle size. On
the other hand, the strain is calculated theoretically in the W-H method
[66,67]. A similar type of variation in the crystallite size of ZnO NPs has
been observed by Scherrer, W-H, and SEM results, Gosh et al. reported
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Journal of Crystal Growth 591 (2022) 126718
Fig. 6. (a) XRD spectra, (b-f) W-H plot, and (g) images of ZnO nanopowder with various amounts of ethanol (Pristine, 25 ml, 50 ml, 75 ml, and 100 ml).
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Journal of Crystal Growth 591 (2022) 126718
Fig. 6. (continued).
Table 1
Crystallite size and strain calculation of ZnO NPs.
Samples
Intercept
Slope
Average particle size from SEM
analysis (nm)
Crystallite size by Scherrer
method (nm)
Crystallite size by W-H
method (nm)
ε (lattice
ZnO
ZnO@25 ml
Ethanol
ZnO@50 ml
Ethanol
ZnO@75 ml
Ethanol
ZnO@100 ml
Ethanol
0.00294
0.00394
0.00087075
0.00087079
30
28
22.23
20.02
48
36
5.81E-3
4.31E-3
0.00524
0.00087081
25
17.52
27
2.75E-3
0.00604
0.00087087
23
15.02
24
2.67E-3
0.00706
0.00087088
21
12.36
21
1.22E-3
9
strain)
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Journal of Crystal Growth 591 (2022) 126718
Fig. 7. The FTIR spectra of ZnO nanopowder with various amounts of ethanol (Pristine, 25 ml, 50 ml, 75 ml, and 100 ml).
similar results with ZnO semiconducting material. The deviation in
crystallite size calculated from the Scherrer and W-H method is mainly
due to the inclusion of lattice strain in synthesized materials [67].
However, the possible estimation of the range of error in the crystallite
size of ZnO NPs is ± 0.38%. The observation in Table 1 showed that the
calculated strain on ZnO samples is very small. Hence the W-H method
can be considered an additional and promising tool to evaluate the strain
and crystallite size of the synthesized materials.
additive ethanol in the ZnO solution, the size of the ZnO nanostructure
reduced and became compact and denser [9]. From the SEM images, it is
seen that with the varying amount of ethanol the size of synthesized ZnO
nanostructure got reduced compared to zero and 25 ml of ethanol
[9,10]. The sizes 30 nm, 28 nm, 25 nm, 23 nm, and 21 nm have been
depicted by the micrographs of ZnO. With zero and 25 ml of ethanol in
ZnO solution, the almost uniform and spherical shapes of ZnO nano­
structures were obtained. However, the excessive amount of ethanol
transformed the ZnO into agglomerated and nonuniform small-size
particles [20]. It is reported that with doping and at the lower size of
the particles the agglomeration started since they are closely arranged
[56,63–65]. The average agglomeration size of particles of ZnO
increased with the lower size of ZnO NPs [62]. Even though a clear
boundary between them is observed which can distinguish the particles.
Ilyas and Rao et al. reported a similar type of observation with ZnO
nanomaterials. These obtained results significantly match the crystallite
size calculated in section 3.3. The enhanced quality (small in size, high
crystallinity, and lower bandgap) of ZnO nanostructure was achieved by
the addition of 100 ml of ethanol processed at a temperature of 80 ◦ C.
Fig. 9 shows the compositional analysis of the prepared ZnO nano­
structure with varying amounts of ethanol. The presence of various el­
ements of semiconductor ZnO like Zn, and O confirmed the existence of
ZnO structure [52]. The pristine ZnO showed a very less intensity of
carbon (C). However, the magnitude of carbon significantly increased
with amounts of ethanol in the ZnO solution, which is due to the
adsorption of ethoxy on the surface of ZnO. The below figures showed
that the intensity of Zinc (Zn) slightly increased and the intensity of
Oxygen decreased with varying amounts of ethanol in the ZnO solution.
No other impurity elements were present in the synthesized ZnO sam­
ples. The results showed that ethanol has a significant impact on the ZnO
nanostructure. The weight and atomic percentage of all synthesized ZnO
nanostructures are enclosed in Table 2. Hence this study demonstrated
that ethanol has a positive impact on the optical, structural, and
morphological properties of ZnO semiconducting materials.
3.4. FTIR analysis
FTIR measurements have been carried out, to get more insight into
the interaction of ethanol with ZnO NPs. Fig. 7 shows the FTIR spectra of
prepared ZnO nanopowder with various amounts of ethanol. The FTIR
spectra depicted the presence of various functional groups in the syn­
thesized ZnO nanopowder. A significant vibration band ranging from
400 to 600 cm− 1 is assigned to the characteristic stretching mode of the
Zn–O bond [53,59]. In the case of ZnO with various amounts of ethanol,
the intensity of the Zn-O bond remains similar to the pristine ZnO, which
indicated that the characteristic properties of ZnO were not changed
with the addition of ethanol to pristine ZnO [31]. In FTIR spectra of ZnO
with ethanol, the C-H bending vibration peaks assigned at 952 cm− 1 and
1407 cm− 1 attributed to the ethoxy adsorption on the surface of ZnO
– O stretching
[54]. A broad peak at 1632 cm− 1 is attributed to the C–
vibration [55]. The O–H stretching vibration assigned at 3434 cm− 1
indicates the presence of hydroxyl residue which is due to atmospheric
moisture present in the ZnO samples [53].
3.5. Morphological analysis
Fig. 8 shows the SEM micrographs of prepared ZnO nanostructure
synthesized at different temperatures and various amounts of ethanol.
Before taking the micrographs of all the samples the gold coating of a
thickness of 7 nm on each of the prepared samples was coated by a
sputter. As expected, with an increase in the excessive amount of
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Journal of Crystal Growth 591 (2022) 126718
Fig. 8. SEM images of ZnO nanostructure (a) Pristine ZnO, (b) ZnO@25 ml ethanol, (c) ZnO@50 ml ethanol, (d) ZnO@75 ml ethanol, and (f) ZnO@100 ml ethanol.
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Journal of Crystal Growth 591 (2022) 126718
Fig. 9. EDAX spectra of prepared ZnO nanoparticles.
4. Conclusion
nanostructure obtained by our synthesis method. This work of ZnO
nanostructure shows the further scope of optoelectronic applicationbased research with the possibilities of bandgap engineering.
This work verified a simple, green, wet-chemical, cost-effective, and
fast method for the synthesis of ZnO nanostructure with zero wastage of
the materials. With the variation in the quantity of ethanol, the physical
and chemical nature of the ZnO nanostructure was changed. The
changes were observed in the color of solutions, PL peak positions,
UV–Vis curve, and band gap value. The excessive amount of ethanol in
the ZnO solution can tune the band of the prepared samples from 3.28 to
3.53 eV. The PL study showed the vacancies of ZnO were suppressed
with the addition of ethanol to the ZnO solutions. The XRD, SEM, FTIR,
EDAX analysis also confirmed the uniform shape of the ZnO
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
12
A. Chauhan et al.
Journal of Crystal Growth 591 (2022) 126718
Fig. 9. (continued).
support and lab access for this work.
Data Availability All relevant data and materials have been already
mentioned in the manuscript.
Compliance with Ethical Standards.
Author’s Contribution A. C. carried out the experiments. The re­
sults of the experiments were analyzed by all authors. The manuscript
was written by A. C. and A. O. All authors have contributed to this work
and agreed to the publication.
Table 2
The compositional elements present in the synthesized ZnO nanostructure.
Samples
Element
Weight %
Atomic %
Pristine ZnO
O
Zn
C
O
Zn
C
O
Zn
C
O
Zn
C
O
Zn
C
34.08
61.6
4.32
36.92
56.95
6.13
39.73
55.0
7.27
40.12
52.01
7.87
41.7
49.13
9.17
70.61
26.2
3.19
72.6
23.29
4.11
73.21
21.65
5.14
74.19
20.1
5.71
75.5
18.5
6.03
ZnO@25 ml Ethanol
ZnO@50 ml Ethanol
ZnO@75 ml Ethanol
ZnO@100 ml Ethanol
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Acknowledgement
The authors would like to thank Icon Analytical Lab Pvt. Ltd. Navi
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Central Instrumentation Facility (CIF) at Birla Institute of Technology
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