TiO 2 Nanocomposite Ammonia Vapor Sensor - International ...

Sensors & Transducers
Volume 125, Issue 2,
February 2011
www.sensorsportal.com ISSN 1726-5479
Editors-in-Chief: professor Sergey Y. Yurish, tel.: +34 696067716, fax: +34 93 4011989, e-mail: editor@sensorsportal.com
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Sachenko, Anatoly, Ternopil State Economic University, Ukraine
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Sensors & Transducers Journal (ISSN 1726-5479) is a peer review international journal published monthly online by International Frequency Sensor Association (IFSA).
Available in electronic and on CD. Copyright © 2011 by International Frequency Sensor Association. All rights reserved.

Sensors & Transducers Journal
Contents
Volume 125
Issue 2
February 2011
www.sensorsportal.com ISSN 1726-5479
Research Articles
Microcantilever Sensors in Biological and Chemical Detections
Qing Zhu............................................................................................................................................. 1
Design of a Low Voltage 0.18 um CMOS Surface Acoustic Wave Gas Sensor
M. Moghavvemi and A. Attaran .......................................................................................................... 22
Glucose Monitoring System Based on Osmotic Pressure Measurements
Alexandra Leal, António Valente, Ana Ferreira, Salviano Soares, Vitor Ribeiro, Olga
Krushinitskaya, and Erik A. Johannessen .......................................................................................... 30
Chemical Vapor Identification by Plasma Treated Thick Film Tin Oxide Gas Sensor Array
and Pattern Recognition
J. K. Srivastava, Preeti Pandey, Sunil K. Jha, V. N. Mishra, R. Dwivedi ........................................... 42
A Preliminary Test for Skin Gas Assessment Using a Porphyrin Based Evanescent Wave
Optical Fiber Sensor
Roman Selyanchyn, Sergiy Korposh, Wataru Yasukochi and Seung-Woo Lee. ............................... 54
Optical Characterization and Humidity Sensing Properties of Praseodymium Oxide
B. C. Yadav, Monika Singh and C. D. Dwivedi................................................................................... 68
Nanocrystalline SnO 2 -Pt Thick Film Gas Sensor for Air Pollution Applications
M. H. Shahrokh Abadi, M. N. Hamidon, Abdul Halim Shaari, Norhafizah Abdullah,
Rahman Wagiran and Norhisam Misron. ........................................................................................... 76
Characterization of WO 3 -SnO 2 Nanocomposites and Application in Humidity Sensing
N. K. Pandey, Akash Roy, Alok Kumar. ............................................................................................. 89
Detections of Water Content Changes in a Nitrocellulose Membrane Based on Polarized
Reflection Spectroscopy
Hariyadi Soetedjo ............................................................................................................................... 100
Fabrication of Polyaniline/ TiO 2 Nanocomposite Ammonia Vapor Sensor
S. G. Pawar, S. L. Patil, M. A. Chougule, B. T. Raut, S. A.Pawar and V. B. Patil ............................. 107
Impact of Mineral Composition on the Distribution of Natural Radionuclides in Rigosol-
Anthrosol
Z P. Tomić, A. R. Djordjević, M. B. Rajković, I. Vukašinović, N. S. Nikolić, V. Pavlović
and Č. M. Lačnjevac........................................................................................................................... 115
Design of Photoreactor and Study of Modeling Parameters for Removal of Pesticides in
Water: a Case Study of Malathion
Amit K. Sharma, R. K. Tiwari and M. S. Gaur .................................................................................... 131
Studies on Gas Sensing Performance of Cr-doped Indium Oxide Thick Film Sensors
D. N. Chavan, G. E. Patil, D. D. Kajale, V. B. Gaikwad, G. H. Jain ................................................... 142
Preparation and Studies on Gas Sensing Performance of Pure and Modified Sn-TiO 2 Thick
Film Resistor
P. D. Hire, V. B. Gaikwad, N. U. Patil, R. L. Patil, R. M. Chaudhri, S. D. Shinde G. H. Jain ............. 156
Electrocoductivity Studies of Grafted Polymer Thin Film 168

Muhammed Mizher Radhi ..................................................................................................................
Ester Sensing with Poly (Aniline-co-m-aminobenzoic Acid) Deposited on Poly (Vinyl
Alcohol)
S. Adhikari, J. Singh, R. Banerjee and P. Banerji .............................................................................. 177
Fiber Bragg Grating Sensor for Detection of Nitrate Concentration in Water
A. S. Lalasangi, J. F. Akki, K.G. Manohar, T. Srinivas, P. Radhakrishnan, Sanjay Kher,
N. S. Mehla and U. S. Raikar ............................................................................................................. 187
Study on Gas Sensing Performance of In 2 O 3 Thick Film Resistors Prepared by Screen
Printing Technique
S. C. Kulkarni, R. Y. Borse ................................................................................................................. 194
Periodically Tapered LPFG for Ethanol Concentration Detection in Ethanol-Gasoline Blend
J. Linesh, T. M. Libish, M. C. Bobby, P. Radhakrishnan and V. P. N. Nampoori............................... 205
Chemically Deposited n-CuInSe 2 / Polyiodide Based PEC Solar Cells
R. H. Bari and L. A. Patil..................................................................................................................... 213
Sensitivity and Selectivity Studies on Polyaniline / Molybdenum Trioxide Composites to
Liquid Petroleum Gas
Aashis S. Roy, Machappa T, M. V. N. Ambika Prasad and Koppalkar R. Anilkumar ........................ 220
Long-term Biosensors for Metabolite Monitoring by using Carbon Nanotubes
Cristina Boero, Sandro Carrara, Giovanni De Micheli........................................................................ 229
Modeling of a Bio Sensor Based on Detection of Antigens Concentration Using an
Electrically Actuated Micro Cantilever
Hadi Madinei, Ali-Asghar Keyvani-Janbahan, Mehdi Atashparva, Rasool Shabani,
Ghader Rezazadeh ............................................................................................................................ 238
A SAW Delay Line Sensor Combined with Micro-hotplate for Bio-chemical Applications
Babak Vosoughi Lahijani, Habib Badri Ghavifekr............................................................................... 247
Bioelectrical Impedance Analysis Device: Measurement of Bioelectrical Tissue
Conductivity in Dengue Patients
Herlina Abdul Rahim, Mohd Nasir Taib, Fatimah Ibrahim and Ruzairi Abdul Rahim......................... 256
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International Frequency Sensor Association (IFSA).

Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
Sensors & Transducers
ISSN 1726-5479
© 2011 by IFSA
http://www.sensorsportal.com
Fabrication of Polyaniline/ TiO 2 Nanocomposite
Ammonia Vapor Sensor
S. G. Pawar, S. L. Patil, M. A. Chougule, B. T. Raut, S. A. Pawar and * V. B. Patil
Materials Research Laboratory, School of physical Sciences, Solapur University,
Solapur (MS), India
Tel.: +912172744771, fax: +912172744770
E-mail: drvbpatil@gmail.com
Received: 23 November 2010 /Accepted: 15 February 2011 /Published: 28 February 2011
Abstract: Polyaniline/Titanium dioxide (PANi/TiO 2 ) nanocomposite was fabricated from PANi,
prepared by oxidative chemical polymerization and TiO 2 , synthesized by sol gel method. The
PANi/TiO 2 thin film sensors were prepared by spin coating technique. PANi/TiO 2 nanocomposites
were characterized by XRD and SEM. The cross sensitivity of thin film sensor indicate that the sensor
exhibit selectivity to ammonia (NH 3 ). The gas sensing measurements were carried out for different
concentrations of NH 3 . The gas sensing study revealed that the response value increases with
increasing concentration of NH 3 . Moreover, as concentration of NH 3 increases, the response time
decreases while recovery time increases, which can be attributed to the varying adsorption and
desorption rates of an ambient gas with increasing concentration. Copyright © 2011 IFSA.
Keywords: PANi/TiO 2 nanocomposite, Response, Selectivity, Response time, Recovery time.
1. Introduction
In recent years, the demand for gas sensors for safety control requirements and environmental
monitoring has expanded enormously. Choice of suitable sensing material along with efficient
microelectronics for the detection system is the key step in such efforts [1]. The use of conducting
polymers as sensing elements in chemical sensors is attracting attention due to their high sensitivity in
change of the electrical and optical properties when exposed to different types of gases or liquids. The
ease in synthesis of these polymers and sensitivity at room temperature add to the sensor’s advantages.
This can be of importance particularly as ammonia sensors that are used in different applications such
as industrial process, fertilizers, food technology, clinical diagnosis, farms and environmental pollution
107

Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
monitoring [2]. Polyaniline is one of the most attractive materials among the variety of conducting
polymers due to its unique electrical properties, environmental stability, easy fabrication process and
intrinsic redox reaction [3-5]. Polyaniline has also been used in different applications such as light
emitting diodes [6], rechargeable batteries [7] and photovoltaic cells [8]. However, the problems with
these conducting polymers are their low processing ability, poor chemical stability and mechanical
strength [9]. There is a tremendous approach for the enhancement of the mechanical strength and
characteristics of sensors by combining the organic materials with inorganic counterparts to form
composites [10, 11]. Accordingly, organic inorganic nanocomposite sensors have been developed by
several research groups. Dhawale et al [12] fabricated polyaniline titanium dioxide heterostructure gas
sensor for LPG sensing, Tai et al [13] fabricated a polyaniline titanium dioxide nanocomposite for NH 3
and CO sensors and reported that the resistance of the composite increased with increasing
concentration of the gases. The PANi/SnO 2 hybrid material was prepared by a hydrothermal method
and studied for gas sensing of ethanol and acetone by L. Geng et al [14]. Parvatikar et al [15]
fabricated polyaniline/WO 3 composite based sensor and reported that the film conductivity increased
with increasing humidity. Among the inorganic materials, nanocrystalline TiO 2 is one of the most
attractive and extensively used materials for detection of H 2 , LPG, NO 2 and NH 3 gases [12].
In the present paper, we report fabrication of polyaniline/ TiO 2 nanocomposite thin film gas sensors
working at room temperature. The cross sensitivity of the sensor to various gases indicate the
selectivity of the sensor to ammonia. The nanocomposites were characterized by X-ray diffraction
(XRD) in 2θ range of 10–70 o using X-ray Diffractometer (Model: Philips PW3710). Morphological
study of PANi/TiO 2 (0 – 50 wt %) composite films was carried out using scanning electron microscopy
(SEM Model: JEOL JSM 6360) operating at 20 kV. The gas sensing measurements were made using
gas sensor set up at room temperature.
2. Experimental
2.1. Fabrication of PANi/TiO 2 Nanocomposite Sensor Films
The TiO 2 nanocomposites with PANi were prepared by adding TiO 2 in different weight percentage
(0 - 50 weight %) in smooth agate mortar and pestle. The nanocomposite powder was put in m-cresol
and stirred for 11 hrs to get casting solution. Thin films were prepared on glass substrates by spin
coating method at 3000 rpm for 40 s and dried on hot plate at 100 0 C for 10 min [16]. The silver paste
strips of 1 mm wide and 1 cm apart from each other were made on films for contacts.
3. Results and Discussion
3.1. X- ray Diffraction Studies
Fig. 1 denotes X-ray diffraction patterns of the PANi, TiO 2 and PANi/TiO 2 nanocomposites
(20-50 wt %) materials. The XRD pattern of PANi (Fig. 1a) shows a broad peak at 2θ= 25.30˚ which
corresponds to (110) plane of PANi [17]. The diffraction pattern of TiO 2 (Fig. 1b) show sharp and well
defined peaks, indicate the crystallinity of synthesized material. The intensities of diffraction peaks for
PANi/TiO 2 nanocomposites (Fig. 1 c) are lower than that for TiO 2 . The presence of amorphous PANi
reduces the mass volume percentage of TiO 2 and sequentially weakens diffraction peaks of TiO 2 . It has
also been observed that the crystallinity of PANi is improved by the addition of TiO 2 nanoparticles.
XRD diffractograms of PANi/TiO 2 nanocomposites have shown that all major diffraction peaks of
nanocrystalline TiO 2 and are in the same peak angle positions. The observed 2θ values are consistent
with the standard JCPDS values (JCPDS No. 78-1285 & 86) which enumerate the mixed anatase and
rutile tetragonal structure of TiO 2 .
108

Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
(a)
Pure PANi
(b)
101 A
TiO2
Intensity (a.u)
Intensity (a.u)
101 R
111 R
004 A
200 A
105 A
211 A
204 A
116 A
220 A
215A
110
10 20 30 40 50 60 70
2 (degree)
20 30 40 50 60 70 80
2 (degree)
(a)
(b)
(c)
101 A
PANi:TiO 2
Intensity (a.u.)
50 %
40 %
110 PANi
004 A
112 A
105 A
211 A
204 A
116 A
30 %
20 %
10 20 30 40 50 60 70
2 q (degree)
(c)
Fig. 1. X ray diffraction patterns of a) Pure PANi b) TiO 2 and C) PANi/TiO 2 (0 - 50 wt %).
3.2. Scanning Electron Microscopy
Fig. 2 a, b and c shows the scanning electron micrographs of PANi, TiO 2 and PANi/TiO 2 (50 wt %)
films at x 20,000 magnification, respectively. The SEM image of the polyaniline film (Fig. 2a) exhibits
a fibrous structure with many pores and gaps among the fibers. Fig. 2b shows the surface morphology
of the TiO 2 nanoparticles film, annealed at 700˚C for 1 h. The image shows that the nanoparticles are
fine with an average grain size of about 60 nm. The image of the nanocomposite (Fig. 2c) shows that
there is no agglomeration and uniform distribution of the TiO 2 particles in the PANi matrix. It was
considered that the nanostructured TiO 2 particles embedded within the netlike structure built by PANi
chains.
The morphology plays an important role in sensitivity of the gas sensing films. The grain sizes,
structural formation, surface to volume ratio and film thickness are important parameters for gas
sensing films. It can be seen that the PANi and PANi/TiO 2 films have a very porous structure,
interconnected network of fibers and high surface area. It has also been pointed out that such structure
contributes to a rapid diffusion of dopants into the film.
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Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
(a)
(b)
(c)
Fig. 2. Scanning electron micrographs of a) PANi; b) TiO 2 and c) PANi/TiO 2 (50 wt %) films.
3.3. Gas Sensing Measurements
In order to record response to different gases, contacts were made on the silver paste strips, 1mm wide
and 1cm apart from each other. The films deposited on the glass substrates were mounted in an airtight
SS housing of 250 cc and measured quantity of desired gas (from a standard canister of 1000 ppm
concentration) was injected through syringe so as to yield desired gas concentration in the housing.
The room temperature gas response to various concentrations of different oxidizing and reducing
(ammonia, ethanol, methanol, nitrogen dioxide and hydrogen sulfide) gases were measured by
recording the resistance of the film in air and in presence of any particular ambient. A Rigol 3062
(6 ½ digit) DMM was used to measure the resistance variation of the sensor films. The sensor response
(S) was defined as S = (Rg – Ra)/Ra, where Rg and Ra are the resistance of sensor film in a measuring
gas and in clean air respectively [13]. The gas sensing measurement set up used is as shown in Fig. 3.
An attempt was made to study selectivity of PANi/TiO 2 films for lower concentration of NH 3 (20 ppm)
as compared to the sensitivities for higher concentration of CH 3 -OH, C 2 H 5 -OH, NO 2 and H 2 S
(100 ppm). The bar chart for selectivity is as shown in Fig. 4. It is observed that PANi/TiO 2 thin films
can sense lower concentration of NH 3 with higher sensitivity value as compared to large concentration
of other gases. The plausible mechanism of selectivity for NH 3 may be traced to the characteristics of
vapor adsorbed over the surface of PANi/TiO 2 nanocomposite.
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Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
Fig. 3. Gas sensing measurement set up.
20 pp m PANi/ Ti O2
10
8
Response %
6
4
2
0
100 pp m
100 pp m 100 pp m 100 pp m
NH3 CH3-OH C2H5-OH NO2 H2S
Gas
Fig. 4. Gas responses of PANi/TiO 2 sensor film to 20 ppm of NH 3 and 100 ppm
of CH 3 -OH, C 2 H 5 -OH, NO 2 and H 2 S.
Therefore the sensing capability of PANi/TiO 2 (50 wt %) nanocomposite sensor towards different
concentrations (20 -100 ppm) of ammonia vapour has been explored and compared with the results
obtained for PANi sensor film. Fig. 5 (a) shows electrical response of PANi to 100 ppm of NH 3 and
Fig. 5 (b) of PANi/TiO 2 to 20, 40, 60, 80 and 100 ppm of NH 3 . As seen for both the sensor films, the
resistance increases dramatically upon exposure to ammonia vapor, attains stable value and decreases
gradually after being transferred to clean air.
Moreover, the nanocomposite sensor exhibit high response to ammonia than pure PANi sensor. The
increase in resistance after exposure to NH 3 may be because of porous structure of PANi/TiO 2 films
leads to the predominance of surface phenomena over bulk material phenomena, which may again be
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Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
due to surface adsorption effect, and chemisorptions leads to the formation of ammonium. The
resistance attains stable value when dynamic equilibrium is attained [19]. In order to explain the higher
response and gas sensing mechanism of PANi/TiO 2 nanocomposite H. Tai et al [13] postulated that
PANi and TiO 2 may form a p-n junction and the observed increased response of the nanocomposite
material may be due to the creation of positively charged depletion layer on the surface of TiO 2 which
could be formed owing to inter –particle electron migration from TiO 2 to PANi at the heterojunction.
This would cause the reduction of the activation energy and enthalpy of physisorption for NH 3 gas.
(a)
Gas out
2.2
PANi
100ppm NH3
2.6
2.4
(b) PANi:TiO 2
100ppm
80ppm
60ppm
40ppm
20ppm
Resistance (x10 6 )/
2.1
2.0
1.9
Resistance (x10 5 )/
2.2
2.0
1.8
1.8
Gas in
0 100 200 300 400 500 600
Time/ s
1.6
100 200 300 400 500 600 700
Time/ s
(a)
(b)
Fig. 5. Gas responses of PANi/TiO 2 sensor film to 20 ppm of NH 3 and 100 ppm
of CH 3 -OH, C 2 H 5 -OH, NO 2 and H 2 S.
The response values of PANi/TiO 2 sensor film is plotted as a function of NH 3 concentration in Fig. 6. It
is observed that the response slows down at higher concentration; this may be due to less availability
of surface area with possible reaction sites on surface of the film.
50 PANi: TiO 2
45
40
35
Response%
30
25
20
15
10
20 40 60 80 100
NH 3
ppm
Fig. 6. Response of PANi/TiO 2 thin film sensor to NH 3 (20- 100 ppm).
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Sensors & Transducers Journal, Vol. 125, Issue 2, February 2011, pp. 107-114
The response/recovery time is an important parameter use for characterizing a sensor. The response
time and recovery time are defined as the times of 90% total resistance change [12]. Fig. 7 shows the
response and recovery times of PANi/TiO 2 for different concentrations of NH 3 . It is revealed that the
response time decreases from 72 s to 41 s, when NH 3 concentration increased from 20 ppm
to 100 ppm, this may be because of high surface area due to porous structure of exposed film which
facilitates rapid diffusion of gas molecules into the film. From the same graph, it is found that for
higher concentration of NH 3 , the recovery time was long. This may probably due to lower desorption
rate and reaction products are not leaving from the interface immediately after the reaction.
Response time /s
74
72
70
68
66
64
62
60
58
56
54
52
50
48
46
44
42
40
38
Response
Recovery
20 40 60 80 100
NH 3
Conc./ ppm
540
520
500
480
460
440
420
400
380
360
340
Recovery time /s
Fig. 7. Variation of response and recovery time of the PANi/TiO 2 thin film sensor
with NH 3 concentration.
4. Conclusions
The PANi/TiO 2 thin film sensor was fabricated by spin coating technique. The composites have poorer
crystallinity than TiO 2 , because of amorphous structure of PANi. But crystallinity of nanocomposites
has been improved with increasing percentage of TiO 2 nanoparticles. It can be seen that PANi/TiO 2
film has a very porous structure, interconnected network of fibers and high surface area, which
contributes to a rapid diffusion of dopants into the film. The cross sensitivity of thin film sensor
indicate that the sensor exhibit selectivity to ammonia (NH 3 ). The gas sensing measurements were
carried out for different concentrations of NH 3 at room temperature. It is observed that the response
slows down at higher concentration; this may be due less availability of surface area with possible
reaction sites on surface of the film. Moreover, as concentration of NH 3 increases, the response time
decreases while recovery time increases, which can be attributed to the varying adsorption and
desorption rates of an ambient gas with increasing concentration.
Acknowledgements
Authors (VBP) are grateful to the Department of Science and Technology, New Delhi for financial
support through the scheme no. SR/FTP/PS-09/2007. Thanks are also extended to Dr. Rashinkar,
Department of Chemistry, SUK for FTIR facility, Prof. Lonikar, School of chemical Sciences, SUS for
UV facility and Dr. P. S. Patil, Department of Physics, Shivaji University, Kolhapur for providing
SEM facility.
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