International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
Microwave –assisted Synthesis of Sb- doped ZnO
Nanostructures for Gas Sensor Application
Yogita S. Patil#1, F.C. Raghuvanshi*2, M. Ramzan#3 I. D. Patil*4
#
Department of Applied Science, Government College of Engineering, Jalgaon-425002, India.
2
3
4
Principal, Vidya Bharati Mahavidyalaya, Amravati, India.
Department of Mechanical Engineering, MMANTC College of Engg., Malegaon, India.
Professor& Head, Department of Biotechnology, SSBT’s College of Engg., Bambhori, Jalgaon, India.
Abstract-- ZnO and Sb-doped ZnO nanostructures were
size and shape has been strongly motivated and novel
applications can be investigated dependent on their
structural properties [7–10]. Among various
semiconductor
nanostructures,
variety
of
nanostructures of ZnO has been investigated
presenting it as richest family of nanostructures. It
crystallizes in a wurtzite structure and exhibits n-type
electrical conductivity [11]. ZnO nanomaterials with
one-dimensional structure, such as nanowires or
nanorods, are specifically attractive due to their
tunable electronic and opto-electronic properties, and
the potential applications in the nanoscale electronic
and optoelectronic devices [12]. Window layer [13],
varistor [14], gas sensor [15-17], etc., are the reported
Keywords- Sb-doped ZnO, microwave assisted synthesis,
applications. Researchers are now probing on this
nanostructures, thick films.
material as one of the alternative photoanode for dyesensitized solar cells [18-20]. Zinc oxide has proven
I.
INTRODUCTION:
Zinc Oxide (ZnO) is a wide-band gap semiconductor itself as one of the competitive and promising
metal oxide with wide range of optical and electronic candidates to replace expensive materials like CdS,
applications. It’s an n-type semiconductor of wurtzite TiO2, GaN, SnO2, and In2O3 for applications such as
structure with direct band gap of about 3.37eV at solar cells [21], photocatalysis [22], ultraviolet laser
room temperature. Polycrystalline ZnO has found [23, 24], transparent conductive oxides [25],
numerous applications such as related to surface spintronics [26], and gas sensors [27]. For gas sensor
acoustic wave devices, piezoelectric devices, varistors, application, SnO2 has been the most investigated
planar optical waveguides, transparent electrodes, UV material. However, ZnO is particularly applicable to
photo detectors, facial powders, gas sensors, etc. Out gas sensors because of its typical properties such as
of these applications of ZnO, gas sensor devices have resistivity control over the range 10−3 to 10−5 cm,
the sensitivity to various gases, high chemical stability, high electrochemical stability, absence of toxicity, and
and suitability for doping, non-toxicity and low cost [1, abundance in nature [28]. Zinc Oxide nanostructures
2]. ZnO films have attracted considerable attention could be synthesized by several techniques such as
due to its high electrical conductivity, high infrared vapour deposition, oxidation, sputtering, and pulse
reflectance and high visible transmittance. Low laser deposition. Several deposition methods have
resistive zinc oxide films have been achieved by been used to grow undoped and doped ZnO films such
doping with different group III elements like as Spray pyrolysis, evaporation, chemical vapour
aluminium, boron, indium, gallium or with group VII deposition, magnetron sputtering, pulsed laser
elements like fluorine(1). Due to the transparency in deposition, sol-gel technique, screen printing
the visible range, high electrical stability, direct band technique [29].
gap (3.37 eV), absence of toxicity, abundance in
nature, etc., ZnO is one of the versatile and
technologically important material [6]. Controlled
synthesis of semiconductor nanostructures in terms of
synthesized using microwave assisted precipitation method.
Thick films of prepared powders were fabricated using
screen printing method. The X-ray diffraction studies show
that the nanostructures are crystallized in the form of
hexagonal Wurzite crystalline phase and Sb-doping does not
change the structure of ZnO. The size of nanostructures
decreases with increasing the Sb+3-doping. Field emission
scanning electron microscope (FESEM ) images show the
change in morphology and size of nanostructures are
changing with change in doping percentage of Sb+3. The
UV- visible spectra shows the increase in band gap with
increasing the Sb +3-doping percentage. The gas sensitivity
of pure and Sb+3-doped ZnO nanostructures was studied.
The gas sensitivity of the films was improved with the doping
of 7% Sb+3 in ZnO.
ISSN: 2231-5381
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
II.
EXPERIMENTAL
2.1 Materials
Zinc acetate (Zn (CH3COO) 2, H2O), antimony
trichloride and sodium hydroxide from Loba Chemie
(India) Pvt. Ltd. were used as precursor to synthesize
ZnO nanostructure. The chemical reagents used were
analytical reagent grade without further purification.
All the glassware used in this experimental work was
acid washed. Deionized water was used for sample
preparation.
2.2 Synthesis of nanostructures:
The ZnO nanostructures were synthesized in
deionized water. In a typical experiment, 2g zinc
acetate (Zn (CH3COO) 2, H2O), was dissolved in 110
ml deionized water and stirred magnetically until a
homogeneous solution was obtained. Then 25 ml 2M
sodium hydroxide (NaOH) was added drop by drop to
above mixture. The stirring was continued for further
30 minutes after addition of 25 ml 2M NaOH to
confirm that a white voluminous precipitate appeared.
The solution was sonicated for 15 minutes in bath
sonicator at 300 C and 52 KHz frequency. The milky
suspension was irradiated in microwave for 2 minutes
followed by air cooling, filtering and multiple washing
with deionized water and absolute ethanol to remove
impurities. The product was dried in hot air oven at
700 C for 24 hours. In case of preparing 5,7 and 9 %
Sb+3-doped ZnO; an equivalent amount of antimony
trichloride was added to the zinc acetate and the above
procedure was repeated.
2.3 Thick Film Preparation
The thixotropic paste was screen printed on glass
substrate in desired patterns. Fluidity of the paste
depends up on extent of organic part, which goes in its
formulation i.e on solid to liquid ratio. Paste must
exhibit a certain degree of yield such that after flow
occurs under squeegee pressure, it should stiffen and
remain in position to have sharp line defined patterns
to be printed that should have thixotropic properties.
In present process, thixotropic paste was formulated
by mixing the synthesized ZnO powders with ethyl
cellulose a temporary binder in a mixture of organic
solvents such as butyl cellulose, butyl carbitol acetate
and turpineol. The ratio of ZnO to ethyl cellulose was
kept at 95:05. The ratio of inorganic to organic part
was kept as 75:25 in formulating the pastes. The
thixotropic pastes were screen printed on a glass
substrate in desired patterns. The films prepared were
fired at 500°C for 12 hr. Prepared thick films
were called as pure ZnO and Sb-doped ZnO thick
films.
ISSN: 2231-5381
2.4 Characterization
The X-ray diffraction (XRD) pattern of the powdered
sample was recorded using X-ray diffractometer at
room temperature. The crystallite size was estimated
using the Scherer equation from full width at half
maximum of the major XRD peak. The morphology,
size and composition of nanostructure were
determined by field emission scanning electron
microscope
(FESEM).
The
optical
transmission/absorption spectra of nanostructure were
recorded using UV-visible spectrophotometer.
III.
RESULTS AND DISCUSSION:
3.1 Morphological study
The morphologies of prepared powder were
investigated through field emission scanning electron
microscope (FESEM). Fig. 1 shows some typical
morphology of pure ZnO and ZnO doped with 5%, 7%
and 9% Sb+3 respectively. It is observed that pure ZnO
(Figure 1(a)), is in the form of flakes. ZnO flakes were
randomly distributed. As the 5%, 7% and 9% Sb+3 was
added to the reaction (Figure 1(b), 1(c), and 1(d)); the
flakes became smaller and darker. The composition of
the as-synthesized product was analysed by
FESEM/EDAX.
(a)
(c)
(b)
(d)
Fig. 1 FESEM images of (a) pure ZnO; (b) ZnO doped with 5%
Sb+3; (c) ZnO doped with 7% Sb+3; (d) ZnO doped with 9% Sb+3
3.2 Structural study
The crystallinity of grown nanoflakes was investigated
by XRD pattern. Fig. 2 shows XRD patterns of pure
and Sb+3-doped ZnO nanoflakes. Sharp intense peaks
are obtained for ZnO nanoflakes. The peaks at
scattering angles (2θ) of 31.4, 33.2, 35.1, 46.3, 55.4,
61.6 and 66.6 deg. corresponding to the reflection
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
from (100), (101), (002), (102), (110), (103),(112),
(201) crystal planes respectively are observed. These
are associated with the hexagonal wurtzite structure of
ZnO. As can be seen, pure ZnO has hexagonal
Wurtzite structure and no peaks attributable to
possible impuries are observed [30].The Sb+3-doped
ZnO nanostructures have similar XRD patterns to that
of pure ZnO and there are no characteristic peaks for
separate phases of ZnO and Sb2O3. The average
particle sizes, D were calculated by Debye Scherer’s
formula [31],
D=0.9λ/Bcosϴ
Where λ is the wavelength of radition, B is full-widthat half- maxima in radians and ϴ is characteristic Xray radition.The average particle sizes of the
nanostructures for pure, 5% Sb+3, 7% Sb+3, and 9%
Sb+3 are about 29, 18, 12, 6 nm respectively. The
particle size decreases with increasing the percentage
of Sb-doping.
Fig.3 UV-vis absorption spectra (a)Pure ZnO,(b)5% Sb +3doped,(c)7% Sb+3-doped,(d)9% Sb+3-doped
4. Gas Sensing Properties
4.1 Current-voltage characteristics of pure ZnO
Figure (a) shows I-V characteristics of pure ZnO thick
film which indicates ohmic contact.
I-V Characteristics of Pure ZnO
1.20E-05
1.00E-05
8.00E-06
6.00E-06
Current (pA)
4.00E-06
2.00E-06
0.00E+00
-30
-20
-10
0
10
20
-2.00E-06
-4.00E-06
-6.00E-06
-8.00E-06
Voltage (V)
Fig.2 XRD for (a)Pure ZnO,(b)5% Sb+3-doped,(c)7% Sb+3doped,(d)9% Sb+3doped
3.3 Optical property
To study the optical quality of nanoflakes; optical
absorption investigations were carried out. The pure
ZnO with absorption maxima 357nm shows a blue
shift relative to bulk ZnO with aborption peak of
384nm that can be due to the size effect of
nanocrystalline ZnO.
ISSN: 2231-5381
Fig.4(a) shows I-V characteristics of pure ZnO at room temperature.
4. 2 Gas respnce for pure and Sb+3 doped ZnO thick
films
The gas response of the sensor was defied as the ratio
of
the change in conductance of a sample upon exposure
to
the target gas to the original conductance in air.
Figure 4(b) shows the gas responses of ZnO thick
films to 300 ppm for LPG, NH3,CO2, H2, Cl2 gases.
Figure 4(b) also indicates that 7% Sb+3-doped ZnO
have maximum gas response (493) to 300 ppm NH 3,
whereas pure, 5% Sb+3 doped, 9% Sb+3-doped has
minimum gas response to NH3 gas. The higher
response of 7% Sb+3- doped ZnO nanostructure upon
exposure to NH3 may be attributed to the decrease in
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International Conference on Global Trends in Engineering, Technology and Management (ICGTETM-2016)
concentration of oxygen adsorbents ( Oad2- ) and a
resulting increase in concentration of electron. The
gas response was mainly dependent upon two factors.
The first was the amount of active sites for oxygen
and the reducing gases on the surface of the sensor
materials.
V.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
Fig. 4 (b) Gas responses of (a) Pure ZnO,(b) 5% Sb+3-doped,(c) 7%
Sb+3-doped,(d) 9% Sb+3-doped ZnO thick films.
[12]
[13]
IV.
CONCLUSION:
It can be concluded, from the above discussion, that
pure and Sb+3-doped nano ZnO can be successfully
synthesized by microwave assisted method. Surface
roughness and smoothness morphology was clearly
observed in FESEM which shows ZnO nanoflakes and
hexagonal wurtzite structure. The average particle
sizes of the nanostructures for pure, 5% Sb+3, 7% Sb+3,
and 9% Sb+3 are about 29, 18, 12, 6 nm respectively.
The particle size decreases with increasing the
percentage of Sb-doping. The thick films are
successfully prepared on glass substrate, The I-V
characteristics of pure ZnO thick film indicates ohmic
contact. The gas sensing characteristics are studied for
pure and Sb+3-doped ZnO, 7% sb+3- doped ZnO shows
gas response to NH3 gas for 300 ppm at 200 oC.
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
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