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KARPAGAM JOURNAL OF ENGINEERING RESEARCH (KJER)
Volume No.: II, Special Issue on IEEE Sponsored International Conference on Intelligent Systems and Control (ISCO’15)
Synthesis Of Al/ZnO-PANI Nanocomposites For Gas Sensing
Application
R.Archana1, B.Divya Priya2, M.Monisha3, T.Vinoth4, P.Raji1*, R.Krishna sharma2*
1,2,3,4
Centre for Nanoscience and technology Mepco Schlenk engineering college
Sivakasi,India
[email protected]
*1,*2
Department of physics
Mepco schlenk engineering college
Sivakasi,India
[email protected]
*Corresponding Author
Abstract
Aluminum doped Zinc Oxide/Polyaniline (Al/ZnO-PANI) nanocomposite is prepared by a chemical
oxidation polymerization method and the sensor is fabricated using this nanocomposite material. Mixing
Al/ZnO with conducting polymer provides high active surface area for the gas sensing reaction and
enhances stability of the nanocomposite. Polyaniline-Al/ZnO nanocomposites were characterized for
their structural as well as surface morphologies and also for their conductivity studies. Characterization
includes XRD, SEM, EDAX, FTIR, UV, TG-analysis and electrical conductivity. The gas sensing
properties of ZnO-PANI nanocomposite are effectively improved by Al doping. It looks promising to use
the inexpensive Al/ZnO-PANI thin films in smart gas sensing devices that are able to recognize gas
species in low concentrations and are demanded for continuous monitoring.
Keywords: Chemical method, Al doped Zinc Oxide, Polyaniline, electrical conductivity
1. Introduction
Gas sensors based on metal oxides are commonly used in the monitoring of toxic pollutants and can
provide the necessary sensitivity, selectivity and stability required by such systems [1]. The need for a novel gas
sensor capable of providing reliable operation in harsh environments is now greater than ever. Such sensors find a
range of applications, including the monitoring of traffic pollutants or food quality with specially designed
electronic noses[2]. Gas sensing at room temperature is of great interest; most of the currently available sensors,
expect a few types of polymer-based gas sensor operate at elevated temperature [3, 4]. Thick film technology is
often used to fabricate such sensors and possesses many advantages; for example, low cost, simple construction,
small size and good sensing properties [5]. In addition, this approach provides reproducible films consisting of a
well- defined microstructure with grains and grain boundaries that can be studied easily [6].
Gas sensitivity, selectivity and durability are the most important sensor properties. In order to attain high
response and excellent selectivity, different approaches such as microstructure control, additives, physical or
chemical filters, operating temperature etc. have been adopted to modify the sensing properties of semiconductor
metal oxide gas sensors. It is well known that sensing mechanism is based on the surface reaction of the particles
with the exposed gas (adsorption and desorption of the test gas). Semiconductor metal oxide has attracted great
attention in the past few years[7,8]
Conductive polymers had been the topic of the large number of investigations during last decades because
of their unique properties such as mechanical strength, electrical conductivity, corrosion, stability and possibility of
both oxidative and electrochemical synthesis. Hence PANI is useful in wide area of application: such as solar energy
conversion, rechargeable batteries, electro chromic displays, electrochemical sensors, capacitors and active
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Volume No.: II, Special Issue on IEEE Sponsored International Conference on Intelligent Systems and Control (ISCO’15)
corrosion protector. Due to ease of synthesis, processing environmental stability and low synthetic cost, so
polyaniline is probably the most important industrial conducting polymer today. The type of dopant anion also
affects the stability of the conductivity in PANI at different atmospheres and at temperatures. Changing the nature of
the anion also has a significant influence on the kinetics and conversion in the electrochemical polymerization of
aniline[9]
ZnO is an n-type metal oxide semiconductor with wide band gap (3.37eV) and a large exciton binding
energy (60meV) having properties suitable for various applications such as ultraviolet optoelectronic devices,
transparent high power and high frequency electronic devices, piezoelectronic transducers and chemical gas sensors.
Applications are attractive because of low cost and lack of toxicity of ZnO. Recently researchers have studied ZnO
nanoparticles doped with metals (Al3+, In3+, Ga3+, etc.) can result in the formation of an n-type semiconductor and
can influence the optical and electrical properties significantly [10].
In the present work, we report the synthesis of Al doped ZnO nanoparticle and Al/ZnO nanoparticle doped
in Pani using Sol-gel method. The PANI provides high active surface area for the gas sensing reaction, and on the
other hand, Al/ZnO nanoparticles nucleated over polymer chains contribute to enhanced stability of the
nanocomposite by interlinking with the PANI polymer chains. The complementary properties of both components
generate a synergistic effect to enhance the gas sensing performance. The prepared Al/ZnO-Pani nanocomposites
was characterized by FT- IR,XRD,UV-Vis, TGA, and conductivity The gas sensing tests demonstrate that the
Al/ZnO-PANI nanocomposite is a promising candidate for the application of various gas sensor at room
temperature.
1.1. Operating Principle of Gas Sensor
The overall surface resistance of such films is generally influenced by chemisorptions (chemical
adsorption) of oxygen from air on the surface and at the grain boundaries. The chemisorbed oxygen traps conduction
electrons and remains as negatively charged species (O2 -, O- or O2- depending on temperature.) on the surface
[11]. The process results in an increase of surface resistance. In presence of reducing gases the trapped electrons are
released due to the reaction between the gas molecules and negatively charged chemisorbed oxygen species
resulting in decreasing in resistance of the materials. When the gas is removed from the sensor environment, the
resistance again increases and the material recovered to original resistance
2. Experimental Setup
2.1. Materials
Aniline, zinc acetate, aluminium nitrate, methanol, sodiumhydroxide and hydrated cupric sulphate
2.2. Preparation Of Al/ZnO
10.9g of zinc acetate dehydrate was dissolved in 80mL of methanol at room temperature. The sol was left
under stirring until clear sol is obtained. 0.187g of Al-nitrate was dissolved in 20mL of methanol and then added to
zinc acetate sol and left under stirring for few hours.3M/LNa(OH)aqueous solution was added dropwise to the sol to
get white precipitate. The pH value was adjusted to 11-12. The white colloid was left under stirring at room
temperature overnight. It was treated hydrothermally for 8h at 200ºC. The precipitate was then washed with water 34 times and then dried in air at 100ºC for 24 hours
2.3. Preparation Of Al/ZnO-PANI Nanocomposite
0.1g of as prepared Al/ZnO nanoparticle was mixed with 7ml of aniline solution (5ml methanol+2ml
aniline), the solution was magnetically stirred for 1hr. To this solution 25ml of aniline solution in methanol was
added again and mixed thoroughly on a magnetic stirrer for 30 min .Now 5ml of 0.5M aqueous CuSo 4 solution was
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added drop by drop with constant stirring, where a dark blackish green. colored precipitate was obtained .the
precipitate was allowed to settle overnight, filtered and dried in vacuum oven at 60˚C and annealed at different
temperatures 350 ˚C and 360 ˚C.
2.4. Sensor Fabrication
The Al/ZnO-PANI thin film is prepared by spin-coating method. Al/ZnO–PANI nanocomposite (100 mg)
is dissolved in 5 mL DMF. The solution is used as a precursor solution to cast the film at 500 rpm on a glass slide
which has to be dried on hot plate at 100oC for 10 min. The Aluminium contacts of thickness 200 nm were deposited
on the corners of the sensor by physical vapour deposition (PVD) techniques .
3. Results And Discussion
3.1. X-Ray Diffraction
The peaks appearing in the XRD pattern indicate good crystallinity of Al/ZnO-PANI nanocomposite, no
characteristics peaks of any other phase were observed. . The average crystal size is 69 nm which is calculated using
Debye–Scherrer formula. The Debye – Scherrer is given by,
Ʈ = K λ/ (β CosƟ)
where,
τ- It is the mean size of the ordered (crystalline) domains, which may be smaller or equal to the grain size.
λ- It is the wave length of the X – Ray used.
Β-It is is the line broadening at half the maximum intensity, after subtracting the instrumental line
oadening, in radians. This quantity is also sometimes denoted as Δ (2θ),
θ-It is the Bragg angle.
Fig:1 XRD image of Al/ZnO-PANI
3.2. Scanning Electron Microscope
The morphological studies of Aluminum doped zinc oxide nanoparticles were analyzed by scanning electron
microscopy. The image depicts the porous morphology of Al doped ZnO. These structures contribute to a rapid
diffusion of dopant. Pore size is found to be around 100nm to 300 nm.
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Volume No.: II, Special Issue on IEEE Sponsored International Conference on Intelligent Systems and Control (ISCO’15)
Fig:2 SEM image of Al/ZnO
The uniform distribution of the Al/ZnO nanoparticles in the PANI matrix is given in fig 3. It was
considered that the nanostructured Al/ZnO particles surrounded within the mesh like structure built by PANI chains.
The size of the nanocomposite were found to be in the range of 234nm
Fig:3 SEM image of Al/ZnO-PANI
3.3. UV-Vis Spectra Of Al/ZnO-PANI Nanocomposite
The absorption spectra of aluminum doped ZnO–Polyaniline measured between 350 and 650nm and the
maximum absorption (𝜆max) was found at 364nm and 467nm.The peak at 384nm is shifted to 364nm which is
attributed to π–π*. It indicates that insertion of Al/ZnO nanoparticles has the effect on the doping of conducting
polyaniline.
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Fig:4 UV Spectra of Al/ZnO-PANI
3.4. FTIR Spectra Of Al/ZnO-PANI Nanocomposite
Inorder to understand the chemical and structural nature, the synthesized material was examined by fourier
Transform Infrared spectroscopy (FTIR) The peak due to O-H stretching and bending vibration of hydroxyl group
is observed at 3258.25.15cm-1.The Peak at 1596.24cm-1 indicates the benzenoid ring stretching. C=C stretching
mode of benzenoid ring is observed at 1485.36 cm-1 Stretching of C=N=C is observed at 1163.50 cm-1 The peak at
1108.07 cm-1 shows the benzenoid ring deformation The peak at 1013.69 cm-1 shows the aromatic ring deformation
Quinoid ring deformation is observed at 954.55 cm-1 The Peak at 751.84cm-1 indicates the Al-O stretching bond.
The peak at 422.83cm-1 shows the Zn-O stretching bond.
Fig:5 FTIR image of Al/ZnO-PANI
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3.5. TG Analysis Of Al/ZnO-PANI Nanocomposite
Thermal degradation of Al doped ZnO-Polyaniline is shown in the Fig 5.11.The weight loss occurring
around 211ºC is due to the removal of dopant and the weight loss occurring around 300 ºC is due to the
decomposition of polymer, In Al/ZnO-PANI nanocomposites the reduction is reduced because of strong interaction
at the interace of Al/ZnO and PANI which supports that the presence of Al/ZnO can improve the properties of
conducting polymers.
Fig:6 TG of Al/ZnO-PANI
3.6. AFM Analysis Of Al/ZnO-PANI Film
0.1g of synthesized nanocomposite is dissolved in 5ml of DMF in a beaker. This solution is then sonicated
for 10minutes using Ultrasonicator.The dispersed solution is then coated over a glass slide. Thus the sample is
prepared for AFM analysis. Thin film of Al/ZnO-PANI nanocomposite was prepared on a glass slide by pouring the
nanocomposites solution over the glass slide. In non-contact mode of AFM the glass slide was analyzed and image
was captured. Using XEI software the 3D image processing was done and the film thickness was found to be
100nm.
Fig:7 AFM of Al/ZnO-PANI film
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3.7. Electrical Conductivity Of Al/ZnO-PANI Film
Electrical conductivity of pure PANI ranges from 10 -10 to 10-3 based on the dopants and fillers. Electrical
conductivity of Al doped ZnO/PANI nanocomposite is found to be around 1.33 S cm -1 .This result shows that the
electrical conductivity of PANI decayed on adding Al/ZnO .This can be attributed to adsorption of –NH of PANI
on the surface of Al/ZnO and bond formation in the structure. The conductivity of the polymer depends on the
nature of dopant and the inorganic material concentration ,which have an important role in conductivity off
nanocomposite[12].
4. Conclusion
Al/ZnO-PANI nanocomposites were synthesized successfully via chemical technique. The XRD, UV-VIS
and FTIR study suggests that PANI undergoes interfacial interactions with Al/ZnO crystallites. The crystallinity of
PANI-Al/ZnO nanocomposites thin film sensor fabricated by spin coating technique has been improved with
increasing percentage of Al/ZnO nanoparticles though the composites has poorer crystallinity than Al/ZnO, because
of amorphous structure of PANI. It can be seen that Al/ZnO nanoparticles has a very porous structure, high surface
area, which contributes to a rapid diffusion of dopants into the film. The electrical property of nanocomposites is a
function of the filler as well as the matrix. In the case of PANI-Al/ZnO composites, the electrical conductivity is
predominantly increased comparing with PANI due to addition of impurities as dopants which is Al/ZnO.
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