Synthesis, Characterization, and Morphological Study of

ZnWO4 Nanoparticles By: JAWAHER KHDER ALZHRANI

Supervisor: Dr. Asma A. Alothman jawaheralzhrani177@gmail.com.

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