Synthesis and Characterization of Zinc-oxide
Nanoparticles
The Research Project submitted to the
Raja Mahendra Pratap Singh State University
for the Degree of
Master of Science
By
Shiv Kumar(2522023220018)
(Under the Supervision of Dr. Mohan Kumar)
Department of Chemistry
Shri Varshney College
Raja Mahendra Pratap Singh State University
Aligarh-202001, U.P.
India
1
Acknowledgment
It has been a glorious and often formidable experience while working on the
M.Sc. Research Project. I received immense support and encouragement from my
friends, colleagues, and my family members. I am indebted to all those people for giving
me an unforgettable experience. At the completion of this Research Project, I would like
to thank all those people who made this project possible.
I would like to express my gratitude to my supervisor, Dr. Mohan Kumar. This
work would not have been possible without his guidance, support, and encouragement. I
consider it a great opportunity to do my Research Project under his guidance and to learn
from his research expertise.
I would like to thank to Prof. Neerja Sharma, Head, Department of Chemistry,
Shri Varshney College, Aligarh, Raja Mahendra Pratap Singh State University, for
providing me with all the research facilities.
I would like to express my unfeigned thanks to all the faculty members of the
Department of Chemistry, Shri Varshney College, Aligarh for their insightful comments and
suggestions.
Lastly, I would like to thank all people who helped me directly or indirectly
during my Research Project. and I also feel very sorry for people whom I forget to
mention their names here. Above all, I bow to my head God Almighty for bestowing
upon me the courage to face the complexities of life, and for the ceaseless blessings to
fulfill my dreams successfully.
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List of Captions of Figures
Fig:1 Zinc Oxide Nanoparticles…………………………………………..........6
Fig:2 ZnO different crystalline structure………………………………………7
Fig:3 Hydrothermal Synthesis of ZnO nanoparticles…………………………9
Fig:4 XRD Pattern of ZnO nanoparticles……………………………………..10
Fig:5 SEM micrographs of ZnO nanoparticles of microemulsion…………..11
Fig:6 Prepared ZnO at Lab by co-precipitation method……………………13
Fig:7 SEM image of nanoparticles…………………………………………….14
Fig:8 UV-Visible spectrum of absorption spectrum………………………….15
Fig:9 SEM image of zinc oxide prepared using zinc sulphate as the starting
material………………………………………………………………………….19
Fig:10 Scanning electron microscopy………………………………………….20
Fig:11 Zinc nanoparticles as multitarget……………………………………...25
Fig:12 ZnO nanoparticles cytotoxicity in cell…………………………………27
Fig:13 Applications of NPs in dentistry……………………………………….29
Fig:14 Metal oxide use in NPs…………………………………………………30
Fig:15 Endodontics of tooth……………………………………………………32
Fig:16 Peridontics………………………………………………………………33
Fig:17 Orthodentist fixes crowed teeth……………………………………….34
Fig:18 ZnO NPs in food……………………………………………………….36
Fig:19 Zinc Oxide for functional textile………………………………………37
Fig:20 ZnO NPs in paint………………………………………………………38
Fig:21 Nanoparticles in monuments conservation…………………………..39
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Fig:22 XRD of ZnO Nanoparticles……………………………………………40
Fig:23 SEM of Nanoparticles………………………………………………….41
Fig:24 UV-Visible absorption spectrum of ZnO nanoparticles………………42
List of Abbreviations
XRD
X-ray Diffraction
SEM
Scanning Electron Microscope
NPs
Nanoparticles
TEM
Transmission Electron Microscopy
4
Abstract
The present investigation deals with facile polyol-mediated synthesis and
characterization of ZnO nanoparticles and their antimicrobial activities against
pathogenic microorganisms. The synthesis process was carried out by refluxing zinc
acetate precursor in diethylene glycol (DEG) and triethylene glycol(TEG) in the presence
and in the absence of sodium acetate for 2 h and 3 h. All synthesized ZnO nanoparticles
were characterized by X-ray diffraction (XRD), UV visible spectroscopy (UV),
thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), field
emission scanning electron microscopy (FESEM), transmission electron microscopy
(TEM) and energy dispersive X-ray spectroscopy (EDX) technique. All nanoparticles
showed different degrees of antibacterial and antibiofilm activity against Gram-positive
Staphylococcus aureus (NCIM 2654) and Gram-negative Proteus vulgaris (NCIM 2613).
The antibacterial and antibiofilm activity was inversely proportional to the size of the
synthesized ZnO nanoparticles. Among all prepared particles, ZnO nanoparticles with the
least size (~ 15 nm) prepared by refluxing zinc acetate dihydrate in diethylene glycol for
3 h exhibited remarkable antibacterial and antibiofilm activity which may serve as
potential alternatives in biomedical applications.
5
Introduction
1.1 Introduction
Zinc oxide nanoparticles are nanoparticles of zinc oxide (ZnO) that have
diameters less than 100 nanometers. They have a large surface area relative to their size
and high catalytic activity. The exact physical and chemical properties of zinc oxide
nanoparticles depend on the different ways they are synthesized. Some possible ways to
produce ZnO nano-particles are hydrothermal methods, electrochemical depositions, sol–
gel
method,
thermal
decomposition,
combustion
methods,
microwave-assisted
combustion methods, two-step mechanochemical–thermal synthesis, anodization, coprecipitation, electrophoretic deposition, and precipitation processes using solution
concentration, pH, and washing medium. ZnO is a wide-band gap semiconductor with an
energy gap of 3.37 eV at room temperature. ZnO as a wide band gap semiconductor has
received great attention in many research areas. This is due to the electrical, optical, and
structural properties of the ZnO. These properties make ZnO one of the major contenders
for many photonic applications. ZnO has distinguished electrical and optical properties.
ZnO is considered as a potential contender in optoelectronic applications such as solar
cells and ultraviolet (UV) emitters. The nanostructured ZnO material has many
applications in the area of nano based devices. The ZnO nanoparticle three dimentiona
structure shown in fig 1
Figure 1: Zinc-Oxide Nanoparticles
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1.2 ZnO Properties
ZnO is classified as a negative (n-type) semiconductor material as grown. ZnO is
one of group 2–4 semiconductor materials. ZnO has a band gap of 3.37 eV. ZnO also has
a high binding energy. The ZnO binding energy is about 60 meV [1]. The ZnO material
has a high exciton binding energy and high thermal stability [2]. It also has a high optical
gain [2]. These properties made ZnO as one of the most interesting materials for
electronic and optoelectronic based devices. On the other hand, the ZnO’s high binding
energy permits the fabrication of several photonic devices with a high optical efficiency
[3]. Also, the short wavelength optoelectronic devices are being made based on ZnO’s
wide band gap [3]. ZnO is a transparent optical material suitable for the visible
wavelength region [4]. ZnO is also one of the potential materials for optoelectronic
applications [5, 6, 7]. The ZnO’s characteristically properties were investigated by many
research groups. That leads to the improvement of the electrical and optical properties of
ZnO. Many other properties of ZnO allow a variety of applications. These applications
include photovoltaics, LEDs, photodetectors, and microelectromechanical systems
(MEMs) [8, 9, 10, 11, 12].
1.3 ZnO crystalline structure
It normally has a hexagonal structure. The Zinc atoms are tetrahedrally
coordinated with four oxygen atoms [13]. Moreover, there are two crystalline structures
of ZnO. These structures are the wurtzite and the Zinc-blende. These two structures of
ZnO lead to a perfect polar symmetry along the hexagonal axis of the ZnO’s crystalline
structure. The ZnO-based piezoelectricity and spontaneous polarization are due to these
crystalline structures. The two ZnO’s crystalline structures are shown in Figure.2
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Figure. 2: ZnO different crystalline structure
Preparation of Zinc oxide
2.1 ZnO nanoparticles by hydrothermal method
In order to synthesize the ZnO nanoparticles, stock solutions of Zn(CH 3COO)
2.2H2O (0.1 M) were prepared in 50ml methanol under stirring. To this stock solution
25ml of NaOH (varying from 0.2 M to 0.5 M) solution was prepared in
methanol was added under continuous stirring in order to get the pH value of reactants
between 8 and 11. These solutions was transferred into Teflon-lined sealed stainless steel
autoclaves and maintained at various temperature in the range of 10 -200 oC for 6 and 12
h under autogenous pressure. It was then allowed to cool naturally to room temperature.
After the reaction was complete, the resulting white solid products were washed with
methanol, filtered and then dried in air in a laboratory oven at 60 oC. The synthesized
samples were characterized for their structure by x-ray diffraction (Rigaku D max-C)
with Cu Kα radiation. Transmission electron microscopy (TEM) selected area electron
diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM)
were performed with a JEOL JEM-3100F transmission electron microscope operating at
200 kV. The sample for TEM was prepared by placing a drop of the ZnO suspension in
methanol onto a standard carbon-coated copper grid. The grids were dried before
recording the micrographs. The optical band gap Eg was estimated from the UV-Vis-NIR
diffuse reflectance spectroscopic (UV-Vis-NIR DRS) studies in a wavelength range from
8
190nm to 1200nm with JASCO V-570 spectrophotometer. The samples for this study
were used in the form of powder and pure BaSO4 was used as the reference. The
elemental composition of the ZnO nanoparticles was determined by using Thermo
Electron IRIS INTREPID II XSP DUO inductively coupled plasma atomic emission
spectrometer (ICP-AES). Room temperature photoluminescence (PL) of the samples was
measured on Horiba Jobin Yuon Fluoromax-3 spectrofluorimeter using Xe arc lamp as
the excitation source.
Figure 3: Hydrothermal Synthesis Of ZnO nanoparticles
2.2 ZnO nanoparticles by solvothermal method
Typically, the synthesis of ZnO was carried out by a solvothermal process at
80°C. Poly(vinyl pyrrolidone) PVP 30K was dissolved in absolute ethanol under
stirring at room temperature, then zinc acetate dihydrate was slowly added to the
solution. Consequently, the solid NaOH was put into the reaction mixture. The
resulting solution was stirred for several minutes. The solution was then transferred to
polypropylene vessel, then sealed and heated in temperature-controlled autoclave at
80°C for 24 h. After cooling to room temperature, the white powder was precipitated
and then washed with absolute ethanol several times to dissolve other impurities.
Finally, the powder was dried under vacuum at 60°C overnight and determined in
9
terms of their structural, morphology, and optical properties. The mixed solvent of
ethylene glycol and absolute ethanol without a polymer template was also investigated.
The crystalline structures of the products were characterized by X-ray diffraction
(XRD) analysis using a JEOL JDX-3530 diffractometer. Dry powder of samples which
were re-dispersed in ethanol and consequently deposited on a glass slide was used for
the structural measurement. The X-ray diffraction (XRD) patterns were recorded from
20°C to 80°C in 2θ with a scanning rate of 0.2°/s. The absorbance spectra were
recorded on a PerkinElmer Lambda 650 UV-vis spectrophotometer. The size and
morphology of the products were observed by transmission electron microscopy (TEM)
which was taken on a JEOL JEM-2010 electron microscopy using an accelerating
voltage of 200 kV in bright field and electron diffraction (ED) modes. A small drop of
the ZnO powder re-dispersed by ethanol was dropped on a carbon film-coated copper
grid. The sizes of ZnO were measured and averaged by several TEM images (n = 20).
Figure 4: XRD Pattern of ZnO nanoparticles.
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2.3 ZnO nanoparticles by oil microemulsion
The microemulsion system used for the present study consisted of cetyl trimethyl
ammonium bromide (CTAB, 99%; Fisher Scientific) as a surfactant; 1-butanol(99.8%;
Fisher Scientific) as co-surfactant; n-octane (reagent grade) as continuous oil phase and
an aqueous solution as the dispersed phase (Table 1). For the preparation of particles, a
microemulsion containing 0.1 M zinc nitrate (99.9% Aldrich) solution as the aqueous
phase was mixed with another microemulsion containing the precipitating agent,
ammonium carbonate as the aqueous phase. Continuous collision of these microdroplets
leads to their coalescence and subsequent formation of zinc carbonate precipitate in the
droplet. The surfactant monolayer inhibits the growth and coagulation of the carbonate
particles. A detailed schematic representation of this process has been illustrated earlier.
The zinc carbonate precipitate was separated by centrifuging. It was washed with a 1:1
mixture of methanol and chloroform to remove any oil or surfactant from the particles.
The precipitate was dried at 100°C to yield zinc carbonate precursor particles. To
ascertain the efficacy of this method we made a parallel study of the properties of ZnO
particles prepared by the bulk precipitation method and those from conventional powder.
The bulk precipitation was carried out by mixing together aqueous solutions of Zn(NO 3)2
and (NH4)2CO3, the molarity being the same as used for microemulsion synthesis. For the
conventional powder, ZnCO 3 (99.8%; Fischer Scientific) was calcined at 250°C to
obtain ZnO. For the varistor fabrication, dopants were added chemically by precipitation
onto the ZnO particles to obtain an overall base composition of 96.5 mol% ZnO; 0.5
mol% Bi2O3; 1.0 mol % Sb2O3; 0.5 mol% MnO; 1.0 mol% CoO and 0.5 mol% Cr 2O3.
11
Figure 5: SEM micrographs of ZnO nanoparticles of microemulsion
2.4 ZnO nanoparticles by co-precipitation method
Zinc nitrate, sodium hydroxide, and ethanol were purchased and used without
further purification of zinc oxide nanoparticles were synthesized by co-precipitation
method using zinc nitrate and sodium hydroxide precursors. In this experiment, a 0.1M
aqueous solution of zinc nitrate (Zn(NO3)2·6H2O) was kept under constant stirring using
a magnetic stirrer to completely dissolve the zinc nitrate for one hour, and 0.8M aqueous
solution of sodium hydroxide (NaOH) was also prepared in the same way with stirring of
one hour. After the complete dissolution of zinc nitrate, 0.8M NaOH aqueous solution
was added under high-speed constant stirring, drop by drop (slowly for 45 min) touching
the walls of the vessel. The reaction was allowed to proceed for 2 h after the complete
addition of sodium hydroxide. The beaker was sealed at this condition for 4 h. After the
completion of the reaction, the solution was allowed to settle overnight, and further, the
supernatant solution was separated carefully. The remaining solution was centrifuged for
10 min, and the precipitate was removed. Thus, precipitated ZnO NPs were cleaned three
times with deionized water and ethanol to remove the byproducts which were bound with
the nanoparticles and then dried in air atmosphere at about 60°C. During drying, Zn(OH)2
12
is completely converted into ZnO. The prepared ZnO nanoparticles were characterized
for their optical and nanostructured properties.
Figure 6: Prepared ZnO at Lab by co-precipitation method
2.5 ZnO nanoparticles by sol gel processing
The experiment sol-gel technique is used for the manufacturing of ZnO
nanoparticles. In this research the use of materials are Zinc acetate dihydrate, Sodium
Hydroxide, methanol and distilled water. Zinc acetate dihydrate is used as precursor and
methanol as a reagent. Distilled water is used a solvent. All chemical reagents in this
experiment were obtained from commercial sources as guaranteed-grade and were used
as received without further treatment. In this experiment sol-gel method is used for
synthesized ZnO nanoparticle. In this experiment , Zinc acetate dihydrate was used as
zinc precursor as zinc precursor. Mixing 0.2M zinc acetate dihydrate in methanol at room
temperature. After then mixing this solution ultrasonically at 25℃ for 120 min. then we
get clear and transparent sol with no precipitate and turbidity was obtained. Now 0.02 M
of NaOH was added to the sol and stirred ultrasonically for 60 min. keep the sol
undisturbed till white precipitates settle down at the bottom of the sol. After precipitation,
13
the precipitate were filtered and washed with excess methanol to remove starting
material. Precipitates were dried at 80℃ for 15 min on hot plate. After these precipitates
were annealed at 400 ℃ for 30 min.
Figure 7: SEM image of a nanoparticle
Characterization Techniques
3.1 UV-Visible spectroscopy
The as-synthesized ZnO nanoparticles were characterized by means of various
analytical techniques including powder X-ray diffraction (XRD), Fourier transform
infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM),
Energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM), and
Brunauer–Emmett–Teller and Barrett–Joyner Halenda (BET/BJH) analysis. The XRD
analysis was carried out on a Bruker D8 Focus powder diffractometer with Cu Ka
radiation wavelength of 0.15406 nm. The samples were scanned from 10°to 80°with a
step size of 0.025°. The mean crystalline size of the sample was calculated from the full
width at half maximum (FWHM) of the intense X-ray diffraction peaks using Scherrer’s
equation. The FT-IR spectrum was recorded in transmission mode with a thermoscientific
NICOLET 6700 apparatus in the region of 400–4,000 cm-1. The FESEM images for the
14
determination of surface morphology were performed on a Zeiss SUPRA 55 scanning
electron microscopes. The scanning electron micrographs were obtained at an operating
voltage of 3 kV. TEM images for the determination of the internal morphology were
performed on a Philips CM-12 instrument at an operating voltage of 100 kV. The
porosity and surface area of the sample was determined by nitrogen adsorption–
desorption analysis at 77 K using a Micromeritics ASAP 2010 instrument. The specific
surface area of the sample was assessed by BET method and the pore size and pore
volume distribution was determined by BJH method. The optical properties of the sample
were
studied
using
UV–Visible
and
photoluminescence
spectroscopy.
The
photoluminescence spectrum. Of the sample was taken in a FLSP920 Edinburgh
Instrument with 450 W Xenon lamp as the radiation source and an excitation wavelength
of 300 nm. The UV–Visible absorbance spectrum was recorded in a Perkin–Elmer
Lambda-35 (Varian Cary) spectrophotometer using water as the reference solvent.
Figure 8: UV-Visible spectrum of the absorption spectrum
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3.1.1 Experimental method
Zinc nitrate, sodium hydroxide, and ethanol were purchased and used without
further purification. Zinc oxide nanoparticles were synthesized by a wet chemical method
using zinc nitrate and sodium hydroxide precursors. In this experiment, a 0.5 M aqueous
ethanol solution of zinc nitrate (Zn(NO3)2·4H2O)was kept under constant stirring using
a magnetic stirrer to completely dissolve the zinc nitrate for one hour and 0.9 M aqueous
ethanol solution of sodium hydroxide (NaOH) was also prepared in the same way with
stirring of one hour. After the complete dissolution of zinc nitrate, 0.9 M NaOH aqueous
solution was added under high speed constant stirring, drop by drop (slowly for 45 min)
touching the walls of the vessel. The reaction was allowed to proceed for 2 hrs after the
complete addition of sodium hydroxide. The beaker was sealed at this condition for 2 h.
After the completion of the reaction, the solution was allowed to be for overnight and
further, the supernatant solution was separated carefully. The remaining solution was
centrifuged for 10 min, and the precipitate was removed. Thus, precipitated ZnO NPs
were cleaned three times with deionized water and ethanol to remove the byproducts
which were bound with the nanoparticles and then dried in air atmosphere at about 60◦C.
During drying, Zn(OH) 2 is completely converted in to ZnO. The prepared ZnO
nanoparticles were characterized for their optical and nanostructures properties. X-ray
diffraction pattern for the ZnO NPs was recorded using an X-ray diffractometer
(PANLYTICAL) using Cu Kα radiation of wavelength λ=0.1541nm in the scan range 2θ
= 20–90◦C. The morphology of the sample was investigated using a scanning electron
microscope (SEM with EDXA, Sirion) which also has been used for compositional
analysis of the prepared ZnO nanoparticles. The optical transmission/absorption spectra
of ZnO dispersed in water were recorded using a UV-VIS spectrophotometer (Hitachi, U3010). The photoluminescence (PL) spectrum of the ZnO nanoparticles dispersed in
water has been measured using a spectrofluorometer (F-2500 FL Spectrophotometer,
Hitachi).
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3.2 X-Ray Diffraction (XRD)
The XRD patterns of the synthesized ZnO nanoparticles. The X-ray diffraction
data were recorded by using Cu Kα radiation (1.5406 Angstrom). The intensity data were
collected over a 2θ range of 20–80°. The average grain size of the samples was estimated
with the help of the Scherrer equation, using the diffraction intensity of (101) peak. X-ray
diffraction studies confirmed that the synthesized materials were ZnO with wurtzite
phase and all the diffraction peaks agreed with the reported JCPDS data; no characteristic
peaks were observed other than ZnO. The mean grain size (D) of the particles was
determined from the XRD line broadening measurement using the Scherrer Equation (1):
D = 0.89λ/(βCosθ)
D = 0.89λ/(βCosθ)
Where λ is the wavelength (Cu Kα), β is the full width at the half-maximum
(FWHM) of the ZnO (101) line and θ is the diffraction angle. A definite line broadening
of the diffraction peaks is an indication that the synthesized materials are in the
nanometer range. The lattice parameters calculated were also in agreement with the
reported values. The reaction temperature greatly influences the particle morphology of
as-prepared ZnO powders.
3.3 Scanning Electron Microscopy (SEM)
For the preparation of zinc oxide nano-particles, two different precursors were
used. The first one is zinc sulfate heptahydrate (M=287.49g/mol, Sigma Aldrich), and
zinc acetate (M=219.5g/mol, Merk), PolyVinyl Alcohol (PVA) (Sigma Aldrich)was used
as the surface munificent, distilled water was used as the solvent To the aqueous solution
of zinc sulfate heptahydrate sodium hydroxide was added drop wise in a molar ratio of
1:2, under vigorous stirring, and the stirring action is continued for almost 18 hours and a
large amount of white precipitate was formed, this precipitate was filtered and washed
17
with distilled water and dried using a muffle furnace at a temperature of 100 C and it is
ground to fine powders and finally the powder obtained was calcined at different
temperatures such as 500°C, 700°C, 900°C. Here the particles are calcined at different
temperatures in order to obtain just an idea about the relation connecting yield and
temperature, as the calcination temperature increases the yield decreases. Initially, 1M
zinc acetate solution was stirred vigorously, and to this vigorously stirred zinc acetate,
2M sodium hydroxide solution was added dropwise, large amount of white slurry’s were
formed, and this white slurry were continuously stirred for 18 hours, a white precipitate
was formed, which was filtered and washed with distilled water and dried using muffle
furnace and it is ground to fine powders and finally calcined at 400 °C. If the temperature
is more than 400°C then the particles start to thermally degrade and We can observe a
noticeable colour change from white to a dark ash colour. To prepare zinc oxide
nanoparticles 0.01% PVA solution was prepared initially and 2ml PVA was added to 1M
zinc sulphate heptahydrate solution and 2M sodium hydroxide was added to it dropwise
very slowly the resulting solution is stirred for almost 18 hours. One thing should keep in
mind that if the concentration of PVA is high then it will leads to a situation in which
plenty of foam will form instead of the precipitate. After 18 hours large amount of white
precipitate was formed which was filtered and washed with distilled water and dried in a
muffle furnace at a temperature of 100°C for 2 hours then it was ground to fine powders
and finally calcined at 450°C.
Figure 9: SEM image of zinc oxide prepared using zinc sulphate as the starting material.
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Figure 9 shows the Scanning Electron Microscope (SEM) image of the zinc oxide
nanoparticles under lower magnification and it shows that the particles are agglomerated
and complete separation does not occur. The second figure shows its SEM image at
higher magnification and we can see that the particles are held together because weak of
physical forces. Here particles were formed with sizes in the micron range, we want
particles with sizes in the region of at least 100nm so it concludes that zinc oxide
prepared using zinc sulfate as the staring material does not produce particles with sizes in
the nanometer range and also the particle separation is not good and this method of
preparation was highly affected by particle agglomeration.
Figure 10: Scanning Electron Microscopy
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Material and Methods
In this experiment 0.1 M zinc acetate was dissolved in methanol stirring on a
magnetic stirrer with heating at 400C and 0.2 M Sodium hydroxide was dissolved in
methanol with stirring. Then Sodium hydroxide was added dropwise to the zinc
acetate solution with heating. A milky white solution was obtained and stirring
continued for 4hrs. The solution was aging for 24hrs then filtered with Whatman filter
paper. It washed with methanol several times to remove any impurities in this solution.
The sample was placed in oven at 700 C for 12hrs and then white powder was
collected in a ceramic crucible. The crucible was placed in the mafule furnace and
heat- treated at 4000C for 2hrs
Seeds
The mungbean seeds were purchased from market these seeds were kept in a dry place
in the dark under the room temperature before using.
Seedling Exposure
The seeds were checked for their viability by suspending them in double distilled water.
The seeds which are settled to the bottom were selected for further study. The seeds
were rinsed in double distilled water thrice and then surface sterilization of seeds was
done. The seeds were sonicated for 3hr in prepared nanoparticle suspensions (20, 40,
60, 80 and 100mg) using a sonicator instrument. The soaked seeds were put in prepared
pots. Observe of the growth is studied.
Seed germination test
This test was conducted on mungbean seeds. The seed germination rate (RSG) and
relative root growth (RRG) were calculated using the equation and
germination index
(GI).
Relative seed germination Rate = (SC \SS)×100 Relative root growth= (RS\RC)
20
×100 Germination index = (RSG\RRG) ×100
Where SS is the number of seed germinated in sample, SC is the number seed germinated
in control, RS is the average root length in sample and RC is the average root length in
control.
Root and shoot length
Root length was taken from the point below the hypocotyls to the end of the tip of the
root. Shoot length was measured from the base of the root-hypocotyl transission zone up
to the base of the cotyledons. The root and shoot length was measured with the help of a
thread and scale.
Seedling vigour index
The seedling vigor index was determined by using the formula given by Abdul
baki and Anderson (1973). Seedling vigor index= Average root length in cms + Average
shoot length in cms ×Germination percentage.
Fresh and Dry weight
The fresh weight of the root and shoot of seedlings was determined by the weight
of the root and shoot separately on electric balance. After the fresh weight was taken
then the seedlings were kept in a hot air oven at 60 ° C for 48 hrs then the weight of dry
matter was recorded.
Applications of Zno Nanoparticles
1. ZnO Nanoparticles for cancer treatment
Cancer is reported as the second leading cause of death in the US and accounts for
~25% of all deaths. Even more serious is the recent projection by the World Health
Organization, which anticipates total cancer cases will more than double by the year 2030
from the 12.4 million new cases seen in 2008. Despite the fact that scientific
understanding of the functioning of the human body at the molecular level has improved
tremendously, advances in therapeutic options for cancer have lagged by comparison.
21
Current anticancer chemotherapies based on alkylating agents, antimetabolites, biological
agents, and natural products frequently fail to produce a complete anti-cancer response
due to the development of drug resistance or their failure to effectively differentiate
between cancerous and normal cells. This indiscriminate action frequently leads to
systemic toxicity and debilitating adverse effects in normal body tissues including bone
marrow function suppression, neurotoxicity, and cardiomyopathy, which greatly limits
the maximal allowable dose of the chemotherapeutic drug. In this regard, recent studies
have shown that ZnO nanoparticles exhibit a high degree of cancer cell selectivity with
the ability to surpass the therapeutic indices of some commonly used chemotherapeutic
agents in similar ex vivo studies. In addition, the rapid elimination or widespread
dissemination of the anti-cancer drug across non-target tissues requires drug
administration in large quantities which can further complicate problems related to nonspecific toxicity. Thus, there is an urgent need to develop new classes of anticancer drugs
with new modes of action that better target cancer cells while sparing healthy tissues.
The use of nanomaterials as pharmaceutical carriers to enhance in vivo anti-tumor
efficacy has been considered for more than 30 years. The first studies on the clinical
potential of nano-drug carriers as liposomes occurred in the mid-1970 where treatment of
tumor-bearing mice with liposome-entrapped actinomycin D was shown to significantly
prolong survival. Today, the use of nanomaterials for the delivery of pharmaceutical and
diagnostics agents remains at the forefront of nanomedicine, where recent improvements
have been described by conjugating cell-specific ligands to the surface of nanoparticles
resulting in greater control of drug targeting at the tissue and cellular levels, and by
encapsulating drugs within nanoparticles to significantly improve drug release profiles
[9–11]. Numerous preclinical studies using nanoparticle-targeted therapies in oncology
are underway, although some ideas have already been brought to the clinic. The FDAapproved Abraxane®, an albumin-paclitaxel (Taxol®) nanoparticle treatment for
metastatic breast cancer has shown a promising overall response rate of 33%, compared
with 19% for Taxol® alone in a randomized, open-labeled trail of 454 patients. Overall
side effects were fewer with the nano-based drug even though it delivered a 50% higher
22
dose of the active Taxol® than the conventional formulation. An additional example is
Myocet®, a liposomal formulation of doxorubicin that has significantly improved the
therapeutic index, the ratio of the amount of an agent that causes the desired therapeutic
effect to that which causes unwanted cell death, compared with conventional
doxorubicin. The development of Myocet ® through nanotechnology has yielded a less
cardiotoxic, better tolerated, and equally efficacious doxorubicin capable of extending the
therapeutic options for the management of breast cancer.
In addition to nano-drug carriers, interest is growing regarding the ability of
certain nanomaterials to mediate anti-cancer effects on their own, including metal oxides.
One approach involves the successful use of TiO2 metal oxide nanoparticles to kill cancer
cells when UV irradiated. In these studies, HeLa cells were completely killed in the
presence of TiO2 and UV irradiation, and in vivo, tumor growth was arrested for up to 30
days, while no cancer cell killing was observed in the absence of TiO 2 nanoparticles and
UV light.
Although effective for the treatment of skin cancer, a limitation of this
photodynamic nanomedicine-based approach is the inability of UV light to penetrate
more than 1 mm through skin, unless fiber optics or surgery are used in conjunction.
Nanomedicine-based hyperthermia is another promising therapy for cancer treatment.
Infusing a tumor with magnetic or metal nanoparticles, and then exposing the patient to
an alternating magnetic field or shortwave radiofrequency energy produces heat that
warms areas immediately adjacent to the nanoparticles. When sufficient supernormal
temperatures are reached, the tumor cells are killed without harming surrounding healthy
tissue. Both photodynamic and hyperthermic nanoparticle-based cancer approaches share
the challenge of preferentially accumulating at tumor sites unless targeting strategies are
also employed. In addition to the above-described applications, emerging approaches
using zinc oxide nanoparticles are gaining interest in the development of new anti-cancer
therapeutics and are described below.
23
Figure 11: Zinc nanoparticles as multitarget
1.1 ZnO nanoparticles and cancer cell cytotoxicity
Several studies have suggested an increase in in vitro cytotoxicity with nanophase
ZnO compared to micron-sized ZnO for several types of cancers including glioma, breast,
bone, colon, and leukemias and lymphomas [19,20,21,22]. In most of these studies,
however, a systematic review of cancer cell cytotoxicity compared to relevant nonimmortalized cell types was not performed. Perhaps the most compelling evidence of
ZnO preferential toxicity comes from controlled studies comparing nanoparticle
susceptibility of cancerous cells to primary non-immortalized cells of identical lineage.
These studies showed that cancerous cells of lymphocytic lineage were ~28–35 times
more susceptible to ZnO nanoparticle- induced cytotoxicity compared to their normal
counterparts [23]. This high degree of selective cancer cell killing exceeds the ex vivo
therapeutic indices of ≤ 10 reported for commonly used chemotherapeutic drugs such as
doxorubicin and carboplatin against a variety of leukemias, lymphomas, and solid tumors
using similar biological assays. The preferential cytotoxicity was found to be dependent
upon on the proliferation status of cells, with rapidly dividing cells being the most
susceptible [23]. Based on a growing body of evidence, ROS production is proposed as a
24
key cytotoxic mechanism of ZnO nanoparticles [23] leading to cell death via an apoptotic
mechanism.
Based on the self-lighting photodynamic therapy concept, photoactivation of ZnO
nanoparticles is predicted to lead to greater levels of ROS release which, if effectively
targeted to cancer cells, will lead to their selective destruction. Recent supporting studies
have described the ability of ZnO nanoparticles conjugated to porphyrin to synergistically
induce cytotoxicity in ovarian cancer upon exposure to UV A light, while little
cytotoxicity was observed under dark conditions, or with UV exposure in the absence of
nanoparticles [24]. Similar studies have demonstrated that co-administration of ZnO
nanoparticles and the chemotherapeutic drug, daunorubicin, resulted in synergistic
cytotoxic effects on leukemic cancer cells, which was further enhanced by UV irradiation
[25]. Collectively, these reports indicate that photoactivation of ZnO nanoparticles
conjugated to tumor ligands may be useful for the targeted destruction of cancer cells.
Future efforts in this area of research are expected to investigate direct drug conjugation
or encapsulation within the ZnO nanocrystal structure to further improve anti-cancer
efficacy as discussed below.
Figure 12: ZnO nanoparticles cytotoxicity in cell
25
1.2 Metal Oxide Nanoparticles and Tumor Imaging and Early Cancer Detection
Interest is growing regarding the use of ZnO and other metal oxide nanomaterials
for use as biomarkers for cancer diagnosis, screening, and imaging. Recent studies have
shown that ZnO nanoparticle cores capped with polymethyl methacrylate are useful in the
detection of low abundant biomarkers [26]. These nanobeads work by facilitating surface
absorption of peptide/proteins from cell extracts enabling increased sensitivity and
accuracy of cancer biomarker detection using mass spectrometry. Using another
approach, a ZnO nanorod- based cancer biomarker assay has been developed for highthroughput detection of ultralow levels of the telomerase activity for cancer diagnosis and
screening [27].
In an additional approach, multiple reports have described the successful use of
iron oxide nanoparticles as contrast agents for cancer detection. Superparamagnetic oxide
nanoparticles coated with a cell resistant polymer have been shown to accumulate within
tumor sites via the EPR/enhanced permeation and retention effect in tumor xenograft
mice model using magnetic resonance imaging [28]. In another report, the surface of
nanoparticles composed of an iron oxide core and oleic acid coating were modified with
various pluronic and tetronic block copolymers and shown to provide superior in-vivo
tumor imaging properties compared to Feridex IV, a commonly used contrast agent [28].
These modified nanoparticles exhibited an extended systemic circulation half-life and
reduced clearance properties allowing them to diffuse throughout the tumor vasculature
to act as whole tumor contrast agents. While the superparamagnetic properties of iron
oxide nanoparticles offer an advantage for magnetic resonance imaging compared to
ZnO, ZnO composite nanomaterials may ultimately prove useful for tumor imaging in the
future.
2. ZnO nanoparticles in dentistry
Nanotechnology is the most widely accepted technologies in the 21st century.9
The term of “nano” is derived from the Greek word meaning “dwarf. Nanoparticles, as
26
novel dental materials, have unrivaled phys- icochemical and biological properties,
making them suitable to overcome complications associated with traditional dental
treatments through the therapeutic intervention.29-31 Preventive therapy, curative
therapy and tissues regenerative therapy are triple purposes in dental therapeutic
treatments. Nano- products are widely used in numerous dental applications in order to
improve the quality of products such as endodontic, periodontics, orthodontics,
restorative and adhesive dentistry, implant dentistry, acrylic resins, tissue engineering,
and oral cancer.[32-35] Nanoparticles are usually incorporated into dental materialsrelated restorative materials, cements/sealants, adhesives bonding, and prosthesis bases
systems. NPs used in dentistry can be made of silica, carbon-based NPs, different
polymers, solid lipids, hydroxyapatite, hydrogel, dendrimers and metal/metal-oxide. It
has been found that NPs are present in approximately 3500 dental materials. Over the
past decade, NPs applied in dentistry mostly include noble metals, such as platinum,
gold, silver and metal oxide NPs, including iron oxide, zinc oxide, titania, and zirconia
owing to their broad- spectrum bactericidal properties. For these reasons, many recent
studies have focused on the properties of NPs. Nano- particles can be divided into three
main categories of dentistry [35].
Figure 13: Applications of NPs in dentistry
27
2.1 Antibacterial nanoparticles
Nanoparticles can act as an efficient antibacterial agent and are widely accepted in
biomedicine [36-37] The superior bactericidal activity of NPs with antibacterial activities
is attributed to their electrostatic attraction between positively charged NPs and have the
potential to reduce or eliminate the evolution of more resistant bacteria, since their
mechanism of action is directly in contact with the bacterial cell wall and simultaneously
targets multiple biomolecules. The small size of NPs improves not only their
antimicrobial action with minimal adverse effects, including hypersensitivity and allergic
reactions, but also their mechanical properties. Many studies investigated the antibacterial effect of NPs combined with a wide range of dental materials. Fig. summarizes
the most common metal oxides NPs used in dentistry. These NPs are less toxic and have
a higher antibacterial activity in comparison to other metal oxide nanoparticles such as
AuO, AgO/AgO2, etc. The uses of AuO, AgO/AgO2 NPs in dentistry have been severely
limited and have not yet been fully studied because of the difficult
obtain or synthesize [37].
Figure 14: Metal oxide use in NPs
28
or expensive to
2.2 Antimicrobial in dentistry
ZnO NPs have been found to improve the mechanical and anti-bacterial properties
of dental restorative materials. According to a study by Wang et al., it was reported that
when ZnO NPs were incorporated in dental resin composites, there was inhibition in the
growth and adhesion of S. mutans, and in small amounts did not affect the mechanical
properties.[38-39] This is extremely beneficial in not only in the prevention of secondary
caries but also in the interception of bulk fracture of the material. Similarly, in a study
done by Teymoornezhad et al., it was reported that incorporation of 3% ZnO NPs on
flowable resin composite lowered the microleakage. A comparable outcome was reported
in the study by Hojati et al. (2013), on flowable resin composite. When 10% ZnO NPs
was added to resin-based dental composites, it showed anti-bacterial effectiveness against
S. Sobrinus. These NPs were also found to exhibit anti-bacterial activity against S.
mutans and Lactobacillus.[38] ZnO NPs when incorporated in Glass Ionomer Cement
(GIC) was also found to significantly improve the anti-bacterial properties against S.
mutans without altering the mechanical properties.
2.3 Endodontics
The applications of ZnO NPs in endodontics are diverse. In a study by Jowkar et
al., When incorporated in EDTA solution for irrigation, the fracture resistance of the
roots was enhanced. In a study done by Aguiar et al., it was reported that these NPs
promoted alkalinization and action against E. faecalis when used as an intracanal
medicament along with calcium hydroxide NPs and chlorhexidine.[39] ZnO NPs when
used as an sealer after endodontic therapy was found to exhibit excellent sealing efficacy
along with remineralization of the radicular dentin thereby strengthening the tooth. It was
also reported that ZnO NPs brought about a reduction in the apical microleakage when
used as a nano-sealer in endodontics. It also significantly improved the penetration depth
into the dentinal tubules. Pristine gutta-percha cones that were pre-treated argon plasma
treatment and coated with ZnO NPs were found to exhibit antibacterial activity against S.
29
aureus and E. fecalis which provides an excellent hermetic seal thereby reducing chances
of reinfection and subsequent endodontic failure [39-40].
Figure 15: Endodontics of tooth
2.4 Peridontics
In the field of periodontal regeneration using guided tissue regeneration, the
loading of ZnO NPs into composite membranes of polycaprolactone (PCL) and gelatin
(GEL) which were electrospun, brought about a reduction in the planktonic and the
biofilm growth of the S. aureus significantly [41] These local anti-bacterial properties
brought about enhancement in the clinical prognosis of treatments. Similarly, when ZnO
NPs were incorporated in electrospun membranes made of PCL and PCL/GEL, it showed
anti-bacterial activity against P. gingivalis and F. nucleatum species which in turn
brought about an enhanced and better predictable periodontal regeneration. ZnO NPs and
serum albumin microspheres containing minocycline when incorporated in a Carbopol
hydrogel exhibited enhancement of properties such as the anti-microbial spectrum, pHresponsiveness, sustained release, tissue-repairing, and adhesion, and also enhanced
controlled drug delivery that can increase the stability of the drug [41-43]
30
Figure 16: Periodontics
2.5 Orthodontics
Nanoparticles have been used in orthodontics to improve the quality of
orthodontic treatment either in the form of nano-coated archwires, orthodontic adhesives,
and orthodontic brackets. The zinc oxide nanoparticles coated orthodontic appliances
minimise bacterial adhesion and enamel demineralization due to its antimicrobial and
remineralization potential.[44] Even attempts are made to add ZNO NPs into both
orthodontic attachments and bonding materials since they provide a platform for bacterial
attachment. It was reported that coating of the NiTi wires with ZnO NPs brought about
reduction in the frictional forces by 21% and exhibited anti-bacterial activity against S.
mutans. It was also reported that ZnO NPs exhibited anti-corrosion effect that enhanced
the corrosion resistance properties in the orthodontic wires. When a mixture of 10%
weight each of ZnO NPs and chitosan NPs was incorporated into are resin-based dental
composite bonding agents for the placement of brackets, it exhibited anti-bacterial
activity against S. mutans, S. sanguis and L. acidophilus [45] This can significantly bring
about reduction in the incidence of white-spot lesions during orthodontic therapy.
Another study investigated that ZNO and CuO NPs coated orthodontic brackets showed
better antibacterial activity against S. mutans, thus reducing the incidence of dental
31
caries.[47] It has been reported that when both orthodontic wires and brackets were
coated with ZnO NPs the antibacterial potential against S. mutans was enhanced and
reduced the frictional forces of coated wires. Similarly, the stainless-steel wires and
orthodontic brackets coated with chitosan NPs or ZnO NPs reduced the friction between
orthodontic brackets and a Stainless-steel wire thus enhancing the anchorage control and
root resorption risk. Europium ions doped ZnO NPs were incorporated has orthodontic
nano adhesive to enhance the visibility of material for thorough removal of orthodontic
adhesive after completion of treatment. It has been reported that orthodontic adhesive
with less titanium dioxide, zinc oxide, and silver NPs causes bracket failure because the
combination reduces shear bond strength. The addition of ZnO to a light cure resin
modified GIC as an orthodontic bonding agent improved the original compound’s
antimicrobial, physical, and flexural properties. Hence ZnO NPs have the potential to be
widely used in orthodontic applications to improve treatment outcomes, including
increased strength of materials and reduced bacterial count around the orthodontic
appliance [47-48]
Figure 17: Orthodontist fixes crowded teeth
32
3. ZnO nanoparticles in food packaging
Although the FDA has deemed macro-sized ZnO safe, ZnO NPs are highly toxic
to humans and are a major concern that requires alternatives to overcome the toxicity
issue. However, emerging ZnO NPs with polymeric materials or other NPs could reduce
or eliminate its toxicity [49] To that end, gelatin and starch are biomaterials that are
commonly used to promote green food packaging films over petroleum-based films.
Embedding ZnO NPs in the gelatin matrix of food packaging film has been found to
provide better mechanical strength as well as protect food for a long time. The
incorporation of ZnO NPs in gelatin films has been found to successfully inhibit the
growth of food-borne bacteria, such as P. aeruginosa, S. aureus, and E. coli. Meanwhile,
chitosan NPs loaded with ZnO NPs have also been used as food packaging to reduce the
release of excessive Zn2+ ions into food. Fruits and vegetables such as oranges, apples,
carrots, and broccoli are commonly required good food packaging to prevent the growth
of bacteria and mould that could deteriorate the freshness of these foods. According to
previous literature the food (carrot) was preserved for five days due to effective
interactions between the ZnO NPs and the hydroxyl (-OH) and amino (-NH2) groups in
the chitosan as well as the presence of the bio-active components of azadirachtin in the
neem oil.[49-51] Apart from food packaging, ZnO NPs are also useful in the textile
industry, especially for biomedical applications, as they could potentially control
antimicrobial activities and protect the surface of textiles from microorganisms. The
application and functionality of ZnO NPs in the textile industry is discussed in the next
subtopic.
Figure 18: ZnO NPs in food
33
4. Zno NPs in textile for biomedical
The use of ZnO NPs in the textile industry is increasing due to its unique
properties such as hydrophobicity, UV protection, self-cleaning, and antimicrobial
activity [49], which could prevent the transmission and spread of harmful microbials. The
advantages of ZnO NP coatings in the textiles industry have contributed to its wider
application such as medical equipment, home curtains, beddings, and car seats to name a
few. For instance, face masks and personal protection equipment (PPE) will perform
better with these coatings as they provide an extra barrier for microbial organisms to
overcome. Furthermore, cotton and wound dressings coated with ZnO NPs exhibit
significant antimicrobial activity against E. coli . Furthermore, reducing or killing
bacteria on these textiles may reduce odour as well as help them last longer by preventing
the formation of mould. Cotton is generally used in daily life due to its softness and
affinity to skin. As cotton fabrics comprise threaded textures that are rich in OH − groups,
they are easily stained by liquids that eventually lead to bacterial growth. Recently, ZnO
NPs have been reported to create superhydrophobic surfaces on cotton fabrics via the
Lotus effect. Wound dressings have also been innovated by adopting nanotechnologies
such as the addition of NPs, including ZnO NPs, that could improve their antimicrobial
activity [50] The antiviral potential of ZnO NPs can be used to make cotton-based face
masks, especially to prevent SARS-CoV-2 infection. This is an important discovery as
face masks are one of the new norms implemented to prevent SARS-CoV-2 from
spreading [51]
.
Figure 19: Zinc Oxide for functional textile
34
5. ZnO nanoparticles in the paint industry
Furniture, decorations, and walls are familiar surfaces in homes that could harbor
and support the growth of microorganisms such as fungi, viruses, and bacteria, especially
in moist environments. Wood such as maple and rubber wood are popular choices of
materials for furniture and decorations in homes. However, they are easily exposed to the
formation of fungi and bacteria. Therefore, the addition of ZnO NPs into resin coatings
such as varnish could improve the quality of wood surfaces as ZnO NPs are less
pigmented, hydrophobic, and self-cleaning, which is favoured in painting applications as
the coating needs to be transparent, restrict moisture penetration as well as require only a
few cleanings [51-54] Paints containing ZnO NPs have been found to possess effective
antifungal, antimicrobial, anticorrosive, antidiatom, and self-cleaning properties.
However, the current antimicrobial coatings available in the industry contain a nonnatural chemical that may be harmful to the environment. Therefore, green alternatives
that use plants and bio-based materials for coatings can overcome this issue as well as the
shortage of nonrenewable resources such as petroleum. Figure shows that a few items
that use commercial paints such as PU, enamel, and acrylic, with ZnO NPs, perform
better as coatings [55] Furthermore, ZnO NPs are also compatible with resins due to their
good blending ability as well as their ability to maintain its viscosity and consistency. As
wood is commonly used in the marine industry to construct boats and jetties, paints that
contain ZnO NPs have good antimicrobial properties that can be used to support
antifouling activity. This will be elaborated upon in the next subtopic [56]
Figure 20: ZnO NPs in paint
35
6. Preservation work
The preservation of old manuscripts and buildings are necessary to restore culture
heritage sites. As such, ZnO NPs are widely used in the preservation industry due to their
resistance to microorganisms and its self-cleaning ability. As seen in Figures, a ZnO NPs
coating can be used to maintain the aesthetics of an old manuscript.[57] Furthermore, the
antimicrobial properties of these NPs can protect the surface of the paper from
destructive microorganisms such as C. albicans (white mould), fungus, and dirt as well as
provide a UV protective barrier. Protective coatings such as paper varnish could also be
blended with ZnO NPs to preserve coloured oil paintings in museums for a longer period
of time. Additionally, ZnO NPs are also used as reinforcing fillers in steel surface
coatings as it is cheap, convenient, biocompatible, anticorrosive, antibacterial, and
antifungal as well as possess good mechanical properties and is nontoxic. Moreover, the
addition of consolidates or water-repellent materials blended with ZnO NPs can reduce
the formation of A. niger (black mould) on stone monuments by tenfold [57,60,78] As
seen in Figures varnishes containing ZnO NPs (C1 and C2) improved the properties of
the surface in terms of mold formation and colour compared to uncoated surfaces (A1
and A2) and varnishes without ZnO NPs (B1 and B2) after 40 days. Therefore, ZnO NPs
are suitable for use in the preservation of old manuscripts and buildings [90]
Figure 21: Nanoparticles in monuments conservation
36
Result And Discussion
XRD analysis showed that all obtained samples are of the wurtzite structure
[98-102]. The XRD pattern of a typical product is shown in Fig. The diffraction
peaks agree with the JCPDS card No 36-1451 which corresponds to the hexagonal
wurtzite structure of ZnO. As revealed, there are no noticeable differences between
the spectra of the bulk and nanosized ZnO. An exception is the E (LO) mode located
at 583 cm−1 [105] From the presence of the E2 (high) in both Raman spectra, we
deduce that the synthesized nanocrystals exhibit features of the wurtzite phase. No
appreciable shift exists between bulk and nanostructures ZnO indicating the absence
of confining effects on phonon frequencies [107,108,110]]
Figure 22: XRD of ZnO Nanoparticles
Scanning Electron Microscopy
A scanning electron microscope is a kind of electron microscope that images a
sample by scanning it using a high-energy electron beam. The electrons interact with the
atoms making up the sample, thus producing signals which reveal information about the
composition, surface topography and other properties such as electrical conductivity
[67,97,112].
37
Thus the surface morphology and size of the silver nanoparticles were analyzed
by Scanning Electron Microscope. SEM image had shown individual ZnO nanoparticles
as well as number of aggregates.[70] Figiure illustrates the particles are predominantly
spherical in shape and aggregates into larger particles with no well-defined morphology
[75,99,101] The SEM image shows the size of the ZnO nanoparticles ranging from 23-25
nm. This size is better compared to previously reported ZnO nps synthesized by Aloe
Vera extract which is 40nm.[106]
Figure 23: SEM of Nanoparticles
UV visible spectroscopy
The size of the nanoparticles plays an important role in changing the entire
properties of materials. Thus, the size evolution of semiconducting nanoparticles
becomes very essential to explore the properties of the materials.[115] UV-visible
absorption spectroscopy is a widely being used technique to examine the optical
properties of nanosized particles. The absorption spectrum of ZnO nano powder is shown
in Figure It exhibits a strong absorption band at about 355 nm [115-119].
38
Figure 24: UV-Visible absorption spectrum of ZnO nanoparticles
Conclusion
The chemical precipitation process at room temperature was used to create
ZnO nanoparticles. Due to the uniform spherical shape and full conversion of
hydorzincite to ZnO at this temperature, 550°C was determined to be the ideal
calcination temperature after investigating the effects of calcination temperature on
the morphology of ZnO nanoparticles. Using electron microscopy, it was determined
that the particles annealed at 550 °C were spherical and ranged in size from 25 to 40
nm. Synthesised ZnO particles were extremely crystalline and were of the hexagonal
wurtzite phase, according to the X-128 ray diffraction pattern. Additionally, the
electronic spectra of synthetic ZnO had a distinctive peak at 360 nm.
Zinc oxide is a material with numerous useful features, including piezo- and
pyroelectricity, a broad UV absorption spectrum, strong photostability, biocompatibility,
and biodegradability. ZnO may be produced with a variety of particle configurations,
which affects how it is used in new materials and how it might be used in various
technological domains. Therefore, both science and business are becoming more
interested in the development of a process for creating crystalline zinc oxide that can be
employed on an industrial scale.
The review of current research given here shows that nano- and micrometric zinc
39
oxide particles may be manufactured using a variety of techniques. These can be
separated into chemical and metallurgical processes. Zinc oxide is produced in
metallurgical operations by roasting a suitable zinc ore, either directly or indirectly. The
two categories of chemical techniques are condensation methods and dispersion
procedures. Zinc oxide is produced by grinding appropriate precursors in dispersion
(mechanochemical) processes. Particles of around 20 nm may be included in the final
product. A molecularly homogenous solution that has undergone a process of nucleation
is used in the condensation procedures (including controlled precipitation, the sol-gel
method, hydro- and solvothermal methods, formation in an emulsion or microemulsion
environment, and many more).
The necessity to restrict the amount of agglomeration and minimize the amount of
zinc oxide in particular materials has prompted the development of a number of ZnO
surface modification techniques.
According to several studies in the literature,
depending on how the systems created are to be employed, modification activities can be
carried out utilizing inorganic chemicals (oxides and hydroxides), organic substances
(alkoxysilanes, carboxylic acids), and specific polymer matrices. Crystalline oxide
powders provide opportunities to gain better chemical, mechanical, optical, or electrical
characteristics when mixed with other materials.
One of the scientific and technical fields that is now advancing the most quickly is
the study of oxide materials with nano- and micrometric dimensions. Among other
things, the usage of such materials can produce catalysts, transparent solar screens that
resist infrared and ultraviolet light, and ceramics that are more durable. Additionally,
these resources are beneficial for scientific research, illness detection, and therapy. They
can be utilized to safely deliver medications to sick cells while avoiding side effects.
According to the review of the research presented here, zinc oxide may be
categorized as a multifunctional material. This is made possible by characteristics
including a broad spectrum of radiation absorption, strong photostability, low electrical
constant, high electrochemical coupling index, and high chemical stability. It is
40
reasonable to anticipate that zinc oxide will continue to gain popularity and that this will
result in the creation of fresh opportunities for its use.
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