Synthesis, Characterization, and Morphological Study of
ZnWO4 Nanoparticles By: JAWAHER KHDER ALZHRANI
Supervisor: Dr. Asma A. Alothman [email protected].
Chemistry Department, Collage of Science, King Saud University
Abstract
Results and Discussion
Conclusion
References
.
Materials and method
1. Fierro, J.L.G., Metal Oxides: Chemistry and Applications. 2005: CRC Press.
2. Cardarelli, F., Materials Handbook: A Concise Desktop Reference. 2018: Springer
International Publishing.
3. Trots, D.M., et al., Crystal structure of ZnWO 4 scintillator material in the range of
3–1423 K. Journal of Physics: Condensed Matter, 2009. 21(32): p. 325402.
4. The crystal structure of wolframite type tungstates at high pressure, in Zeitschrift
für Kristallographie - Crystalline Materials. 1993. p. 193.
5. Minh, N.V. and N.M. Hung, A Study of the Optical Properties in
ZnWO<sub>4</sub> Nanorods Synthesized by Hydrothermal Method %J
Materials Sciences and Applications. 2011. Vol.02No.08: p. 5
6. Bi, J., et al., A facile microwave solvothermal process to synthesize ZnWO4
nanoparticles. Journal of Alloys and Compounds, 2009. 480(2): p. 684-688.
7. Siriwong, P., et al., Hydrothermal synthesis, characterization, and optical properties
of wolframite ZnWO4 nanorods. CrystEngComm, 2011. 13(5): p. 1564-1569.
Figure 4 shows the energy dispersive X-ray (EDX) maps of oxygen, zinc,
and tungsten of ZnWO4 sample as function of time. According to the
analysis, neither N nor C signals were detected in the EDS spectrum for
sample after 24 hours, indicating that the product was pure and free of any
surfactant or impurity. The SEM mapping images of each zinc tungstate
samples confirmed that all NPs were homogeneously distributed over the
surface of the materials. Figure 5 shows 3D plot of the surface
compositions as a function of time (a), and the table in (b) which tabulated
the values. As seen as the reaction time increased, the surface become
more oxygen rich. The morphologies and sizes of ZnWO4 samples were
investigated by scanning electron microscopic (SEM) images (Figure 6).
SEM micrograph for the sample synthesized for 3 h was basically irregular.
Obviously, as longer the reaction goes as the particles became more well-
defined with rod-like structures. There is no significant difference in
particles shape for 6, 12 and 24 hours ZnWO4 samples (Figure 7).
Time (hour) D crystallite size
(nm)
3 11.63
6 13.52
12 13.83
24 14.42
Effect of reaction’s changing the solvent media on ZnWO4
morphologies:
Temperature (C) D crystallite size
(nm)
80 na
100 na
120 0.89
180 14.42
200 15.49
Solvent D crystallite size
(nm)
H2O 14.42
H2O/EtOH 13.40
H2O/EG 12.14
Figure 3. a. XRD patterns of ZnWO4 samples prepared hydrothermally at
180 C for 3, 6, 12, and 24 hours. b. The crystalline sizes of ZnWO4
samples prepared at 180 C for different selected period of time.
Figure 8. a. XRD patterns of ZnWO4 samples prepared hydrothermally at 80
, 100, 120, 180, and 200 C for 24 hours . b.The crystalline sizes of ZnWO4
samples prepared at different temperatures for 24 hours.
Introduction
Figure 1 represent the experimental flow chart for the synthesis of ZnWO4
nanoparticles. All materials were used as purchased without any furthers
purifications. Several experiments with the selected reactions parameters
as displayed in Table 1 were performed using CTAB as a surfactant of the
hydro/ solvothermal route to obtained ZnWO4 powders. The products were
characterized, and the influence of reactions parameters was illustrated.
Table 1. Selected temperature, time, and solvent reaction parameters,
with products yields.
Figure 9. I. SEM images with X 200,000 magnification of ZnWO4 samples
prepared at 80 (a), 100 (b), 120 (c), 180 (d), 200 (e) C for and 24 hours,
(f) represent the size of 5 nanotubes. II. 3D plot illustrates Zn, W, and O
surface compositions as a function of time.
Temperature (C) 80 100 120 180 200
Time (hours) 24 3 6 12 24 24 Solvent H2O H2O/EtOH H2O/EG H2O
Yield (%) 114
.7 130.5 135.6 94.9 85.9 79 100 80.4 80.3 100
200 210 220 230 240 250 260 270 280 290 300
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Ab
sorp
tio
n
Wavelength (nm)
3 hours
6 hours
12 hours
24 hours
4000 3500 3000 2500 2000 1500 1000 500
Tra
nsm
itta
nce
(A
rbit
ary U
nit
)
Wavenumber (cm-1)
3 hours
6 hours
12 hours
24 hours
Figure 2. a. UV-VIS spectra of the nanoparticulate solutions, and b. FTIR
spectra of ZnWO4 samples prepared hydrothermally at 180 C for 3, 6, 12,
and 24 hours
The UV–VIS spectra of as-prepared solution samples (Figure 2.a) show
wide absorption band with maximum 210 nm over the range of 200–300
nm could be assigned to the pure ZnWO4 which is in agreement with the
literature[5]
All XRD patterns in Figure 3 a. reveal that samples have diffraction peaks
of monoclinic wolframite ZnWO4 structure in accordance with the JCPDS
No. 15-0774 [6,7] ,corroborating to the results from FTIR analysis. The XRD
patterns also show the effect of increasing reaction times on increasing
the crystallinity of ZnWO4 samples. The crystalline sizes of the samples
were calculated and tabulated (Figure 3.b).
Effect of reaction’s time on ZnWO4 Nano-particles structures and
morphologies:
The FTIR spectra of ZnWO4 samples (Figure 2.b) show main absorption
bands between 500 and 1000 cm−1 which are attributed to the stretching
modes of W–O bonds and Zn–O–W bonds[6]Absorption bands at 1600 and
3400 cm-1 are related to the absorbed water.
These metal tungstates have two major structures, tetragonal scheelite
and monoclinic wolframite, depending on the sizes of divalent metals.
ZnWO4 particles have been synthesized by a traditional solid-state
reaction and by various wet methods such as: polymerized complex
method, microwave assisted technique, template-free hydrothermal, sol–
gel, electrodeposition and high direct voltage electrospinning process. The
use of solution chemistry can eliminate major problems such as long
diffusion paths, impurities and agglomeration which will result in products
with improved homogeneity, crystallinity, particle size distribution, and
morphology affecting the properties of ZnWO4 materials.
The objective of this study is to report the CTAB surfactant assisted
hydrothermal synthesis and characterization of ZnWO4 nanoparticles. In
addition, several experiments were conducted to study the effect of
reaction time, temperature, and different solvents on the morphology,
particle size, and crystal structure of ZnWO4 nanoparticulate/particles
using ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared
spectroscopy (FT-IR), X-ray powder diffraction (XRD), energy dispersive
X-ray spectroscopy (EDS), and scanning electron microscopy (SEM).
This study provides in-depth understanding on the morphology, particle
size, and crystal structure of ZnWO4 nanoparticulate. Monoclinic ZnWO4
nanoparticulate were prepared via a CTAB surfactant assisted
hydrothermal method. As-synthesized nanoparticulate were investigated
by ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared
spectroscopy (FT-IR), X-ray powder diffraction (XRD), energy dispersive
X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). The
effects of the reaction time and temperature on the above surface
properties were rationalized. Results show that the crystallinity was
enhanced with the increase of the reaction temperature and time. Besides,
performing the reaction using ethylene glycol/water mixture as a solvent
found to be effective in the enhancement of the surface morphology good
and the size distribution of the final product of ZnWO4 nanoparticles.
Figure 4. Energy dispersive X-ray (EDX) maps of oxygen, Zinc, and
tungsten of ZnWO4 sample as function of time.
Figure 6. SEM images with X 25,000 magnification of ZnWO4 samples
prepared at 180 C for 3(a), 6(b), 12(c), and 24 (d) hours.
Effect of reaction’s temperatures on ZnWO4 Nano-particles structures
and morphologies:
In similar manner to following the effect of reaction’s time, and as it
demonstrated, typical XRD peaks for the ZnWO4 nanoparticle samples
have been presented for all samples. These peaks become sharper and
strong with increasing synthesis temperature, indicating the increasing of
their crystallinity in Figure 8. The morphologies and microstructures of the
samples were then examined with SEM. The chemical composition and
purity of the as-synthesized ZnWO4 nanoparticles were investigated by
EDS analysis (Figure 9 I and II, respectively). As shown, the morphologies
and dimensions of the samples were strongly dependent on the reaction
temperature.
Figure 7. SEM images with X 200,000 magnification of ZnWO4 samples
prepared at 180 C for, 6(a), 12(b), and 24 (c) hours.
Figure 5. a. 3D plot illustrates Zn, W, and O surface compositions as a
function of time, b. surface compositions of ZnWO4 samples as a
function of time.
Figure 10. a. XRD patterns of ZnWO4 samples prepared hydrothermally at
180 C for 24 hours using H2O, H2O/EtOH, and H2O/EG solvents. b. The
crystalline sizes of ZnWO4 samples prepared at 180 C for 24 hours using
H2O, H2O/EtOH, and H2O/EG solvents
In the presence of H2O/ EtOH and H2O/EG mixtures as solvent (Figure 10,
11 and 12), the product showed smaller size than with CTAB as surfactant.
Based on the comparison, sample obtained from water and ethylene glycol
as solvent had smaller ZnWO4 nanoparticles because use of EG led to nano
particles with good size distribution .This limits the size of the nanoparticles
and protects them from further aggregation, and could also act as a capping
agent, playing an important role in the formation of nanoparticles.
Figure 11. SEM images with X 50,000 and X 100,000 magnification of ZnW
O4 samples prepared at 180 C for 24 hours, using H2O (a and d), H2O/
EtOH (b and e) and H2O/EG (c and f) solvents, respectively.
In conclusion, ZnWO4 nanorods were successfully synthesized by a CTAB
assisted hydrothermal route. The morphology and dimension of the
ZnWO4 crystallites were affected by synthesized time, temperature, and
solvent mixture. Using H2O/EG mixture as solvent produced pure ZnWO4
with smaller rode like structure particles, the effect of synthesized time and
temperature on the structure should be furthered investigated. The
formation of the material of the interest using different surfactants would
benefit drawing a clear vision on the mechanism of obtaining particles with
different shapes. Nevertheless, the optical properties in ZnWO4 should be
examined.
Figure 12. EDS analysis for ZnWO4 prepared at 180 C for 24 hours,
using H2O/EG as solvents.
a b a b
a b
I II