Fabrication of Polyaniline-ZnO Nanocomposite Gas Sensor

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Nov 29, 2011 - Pamidighanta, Sayanu, Bharat Electronics Limited (BEL), India ..... stainless steel housing of 250 cc and fixed amount of chosen gas (from a standard canister of .... This is because in the initial stage PANi-ZnO sensor may undergo ... S. A. Chen, K. R. Chuang, C. I. Chao, H. T. Lee, White light emission from ...
Sensors & Transducers Volume 134 Issue 11 November 2011

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ISSN 1726-5479

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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 134 Issue 11 November 2011

www.sensorsportal.com

ISSN 1726-5479

Research Articles Nanomaterials and Chemical Sensors Sukumar Basu and Palash Kumar Basu ............................................................................................

1

Fabrication of Phenyl-Hydrazine Chemical Sensor Based on Al- doped ZnO Nanoparticles Mohammed M. Rahman, Sher Bahadar Khan, A. Jamal, M. Faisal, Abdullah M. Asiri .....................

32

Nanostructured Ferrite Based Electronic nose Sensitive to Ammonia at room temperature U. B. Gawas, V. M. S. Verenkar, D. R. Patil.......................................................................................

45

A Humidity Sensor Based on Nb-doped Nanoporous TiO2 Thin Film Mansoor Anbia, S. E. Moosavi Fard...................................................................................................

56

A Resistive Humidity Sensor Based on Nanostructured WO3-ZnO Composites Karunesh Tiwari, Anupam Tripathi, N. K. Pandey ..............................................................................

65

Highly Sensitive Cadmium Concentration Sensor Using Long Period Grating A. S. Lalasangi, J. F. Akki, K. G. Manohar, T. Srinivas, Prasad Raikar, Sanjay Kher and U. S. Raikar .................................................................................................................................

76

MEMS Based Ethanol Sensor Using ZnO Nanoblocks, Nanocombs and Nanoflakes as Sensing Layer H. J. Pandya, Sudhir Chandra and A. L. Vyas ...................................................................................

85

Simple Synthesis of ZnCo2O4 Nanoparticles as Gas-sensing Materials S. V. Bangale,S. M. Khetre D. R. Patil and S. R. Bamane.................................................................

95

Nanostructured Spinel ZnFe2O4 for the Detection of Chlorine Gas S. V. Bangale, D. R. Patil and S. R. Bamane.....................................................................................

107

Fabrication of Polyaniline-ZnO Nanocomposite Gas Sensor S. L. Patil, M. A. Chougule, S. G. Pawar, Shashwati Sen, A. V. Moholkar, J. H. Kim and V. B. Patil

120

Synthesis and Characterization of Nano-Crystalline Cu and Pb0.5-Cu0.5- ferrites by Mechanochemical Method and Their Electrical and Gas Sensing Properties V. B. Gaikwad ,S. S. Gaikwad, A. V. Borhade and R. D. Nikam........................................................

132

Surface Modification of MWCNTs: Preparation, Characterization and Electrical Percolation Studies of MWCNTs/PVP Composite Films for Realization of Ammonia Gas Sensor Operable at Room Temperature Sakshi Sharma, K. Sengupta, S. S. Islam..........................................................................................

143

An Investigation of Structural and Electrical Properties of Nano Crystalline SnO2: Cu Thin Films Deposited by Spray Pyrolysis J. Podder and S. S. Roy .....................................................................................................................

155

Nanocrystalline Cobalt-doped SnO2 Thin Film: A Sensitive Cigarette Smoke Sensor Patil Shriram B., More Mahendra A., Patil Arun V..............................................................................

163

Effect of Annealing on the Structural and Optical Properties of Nano Fiber ZnO Films Deposited by Spray Pyrolysis M. R. Islam, J. Podder, S. F. U. Farhad and D. K. Saha....................................................................

170

Amperometric Acetylcholinesterase Biosensor Based on Multilayer Multiwall Carbon Nanotubes-chitosan Composite Xia Sun, Chen Zhai, Xiangyou Wang.................................................................................................

177

Fabrication of Biosensors Based on Nanostructured Conducting Polyaniline (NSPANI) Deepshikha Saini, Ruchika Chauhan and Tinku Basu.......................................................................

187

Authors are encouraged to submit article in MS Word (doc) and Acrobat (pdf) formats by e-mail: [email protected] Please visit journal’s webpage with preparation instructions: http://www.sensorsportal.com/HTML/DIGEST/Submition.htm International Frequency Sensor Association (IFSA).

Sensors & Transducers Journal, Vol. 134, Issue 11, November 2011, pp. 120-131

Sensors & Transducers ISSN 1726-5479 © 2011 by IFSA http://www.sensorsportal.com

Fabrication of Polyaniline-ZnO Nanocomposite Gas Sensor a

S. L. PATIL, a M. A. CHOUGULE, a S. G. PAWAR, b Shashwati SEN, c A. V. MOHOLKAR, d J. H. KIM and a* V. B. PATIL a*

Materials Research Laboratory, School of Physical Sciences, Solapur University, Solapur -413255, (MS), India b Crystal Technology Section, Technical Physics Division, BARC, Mumbai, India c Department of Physics, Shivaji University, Kolhapur, M.S., India d Department of Materials Science and Engineering, Chonnam National University, South Korea Tel.:-91-2172744770, fax: +91-2172744770 * E-mail: [email protected]

Received: 20 October 2011 /Accepted: 21 November 2011 /Published: 29 November 2011 Abstract: In the present investigation, we report on the performance of a room temperature ammonia gas sensor based on Polyaniline-ZnO nanocomposite. The nanocomposite film was fabricated using spin coating method on glass substrate. Polyaniline-ZnO nanocomposites were characterized for their structural as well as surface morphologies and ammonia response was studied. The structural (XRD) analysis showed formation of nanocrystalline ZnO while polyaniline exhibited amorphous nature. Morphological analysis using scanning electron microscopy (SEM) of the nanocomposite reveled uniform distribution of ZnO nanoparticles in the PANi matrix. The nanocomposite showed the maximum response of ~14 % upon expose to 100 ppm NH3 at room temperature. Copyright © 2011 IFSA. Keywords: PANi-ZnO thin films, NH3 sensor, Response, Selectivity, Response time, Recovery time.

1. Introduction The use of conducting polymers as sensing elements in chemical sensors is a center of attention due to their high sensitivity in change of the electrical and optical properties when exposed to different types of gases or liquids. The simplicity 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, 120

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farms and environmental pollution monitoring [1]. Polyaniline is one of the most prominent materials among the variety of conducting polymers due to its unique electrical properties, environmental stability, easy fabrication process and intrinsic redox reaction [2-4]. Polyaniline has also been used in different applications such as light emitting diodes [5], rechargeable batteries [6] and photovoltaic cells [7]. However, the problems with these conducting polymers are their low processing ability, poor chemical stability and mechanical strength [8]. There is a great approach for the improvement of the mechanical strength and characteristics of sensors by combining the organic materials with inorganic counterparts to form composites [9, 10]. Accordingly, organic inorganic nanocomposite sensors have been developed by several research groups. Dhawale et al [11] fabricated polyaniline titanium dioxide heterostructure gas sensor for LPG sensing, Tai et al [12] fabricated a polyaniline titanium dioxide nanocomposite for NH3 and CO sensors and reported that the resistance of the composite increased with increasing concentration of the gases. The PANi/SnO2 hybrid material was prepared by a hydrothermal method and studied for gas sensing of ethanol and acetone by L. Geng et al [13]. Parvatikar et al [14] fabricated polyaniline/WO3 composite based sensor and reported that the film conductivity increased with increasing humidity. Among the inorganic materials, nanocrystalline ZnO is one of the most attractive and extensively used materials for detection of H2, LPG, NO2 and NH3 gases [16, 17]. However, due to the long term instability at elevated temperature, it is desirable to develop sensors that operate at room temperature. In the present work, we report on a PANi-ZnO nanocomposite material in which the nanostructured ZnO particles were embedded within the netlike PANi. The netlike PANi provides high active surface area for the gas sensing reaction, and on the other hand, ZnO nanoparticles nucleated over polymer chains contribute to enhanced conductivity and stability of the nanocomposite material by interlinking the PANi polymer chains. The complementary properties of both components generate a synergistic effect to enhance the gas sensing performance. It is an aim of the present work to investigate PANiZnO composite as gas sensing materials with several analytical tools such as X-ray diffractometry, FT-infrared spectroscopy, scanning electron microscopy, UV-Vis spectroscopy and Four probe techniques. The gas sensing tests demonstrate that the PANi-ZnO composite is a promising material in the application of gas sensor at room temperature.

2. Experimental Details 2.1. Fabrication of PANi-ZnO Nanocomposite Sensor Film The PANi-ZnO nanocomposites were prepared by adding ZnO nanopowder in different weight percentage (0 - 50 %) into undoped polyaniline 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 technique at 3000 rpm for 40 s and dried on hot plate at 100oC for 10 min [15, 18]. The silver paste strips of 1 mm wide and 1 cm apart from each other were made on films for contacts. The thickness of the PANi (EB) film, ZnO film and PANi-ZnO film was measured by using Dektak profilometer and is found 0.21 µm, 0.29 µm and 0.32 µm respectively.

3. Results and Discussion 3.1. Structural Studies Fig. 1 shows X-ray diffraction patterns of the PANi (EB), ZnO and PANi-ZnO (10-50 wt %) nanocomposites. 121

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50 60 2  (degree)

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(c) Fig. 1. X ray diffraction patterns of (a) Pure PANi; (b) ZnO, and (c) PANi-ZnO (10 - 50 wt %).

The XRD pattern of PANi (EB) (Fig. 1a) shows a broad peak at 2θ= 24.38˚ which corresponds to (110) plane of PANi [18]. The diffraction pattern of ZnO (Fig. 1b) show sharp and well defined peaks, indicate the good crystallinity of synthesized material. The intensities of diffraction peaks for PANiZnO nanocomposites (Fig. 1 c) are lower than that for ZnO. The presence of amorphous PANi reduces the mass volume percentage of ZnO and sequentially weakens diffraction peaks of ZnO. It has also been observed that the crystallinity of PANi is improved by the addition of ZnO nanoparticles. XRD diffractograms of PANi-ZnO nanocomposites have shown that all major diffraction peaks of nanocrystalline ZnO and are in the same peak angle positions. The observed 2θ values are consistent with the standard JCPDS values (JCPDS No. 80-0075) which specify the wurtzite structure of ZnO [15]. 122

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3.2. Morphological Studies Fig. 2 (a), (b) and (c) shows the scanning electron micrographs of PANi (EB), ZnO and PANi-ZnO (10-50 wt %) films at x 10,000 magnification, respectively.

(a) PANi

(b) ZnO (700 C)

(c) 10 % ZnO

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(g) 50 % ZnO Fig. 2. Scanning electron micrographs of (a) PANi, (b) ZnO & (c-g) PANi-ZnO(10-50 wt%) nanocomposites.

The SEM image of the polyaniline film (Fig. 2a) exhibits a fibrous structure with many pores and spaces among the fibers. Fig. 2(b) shows the surface morphology of the ZnO nanoparticles film, annealed at 700 ˚C for 1 hour. The image shows that the nanoparticles are fine with an average grain size of about 72 nm [15]. 123

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The image of the nanocomposites (Fig. 2 c-g) shows that there is no agglomeration and uniform distribution of the ZnO nanoparticles in the PANi matrix. It was considered that the nanostructured ZnO particles surrounded within the mesh like structure built by PANi chains. In the gas sensing the morphology plays an important role in sensitivity of the gas sensing films. The grain sizes, structural formation,esurface to volume ratio and filmf thickness are important parameters for gas sensing films. It can be seen that the PANi (EB) and PANi-ZnO (10-50 %) 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.

3.3. Fourier Transform Infra-Red Spectroscopy (FTIR) Studies Fig. 3 shows the FTIR spectra of pure PANi (EB), ZnO and PANi–ZnO (10-50 wt %) nanocomposites. The characteristic absorption peaks of PANi (EB) at 1662cm−1, 1564 cm−1, 1462 cm−1, 1285 cm−1, 1103 cm−1 and 798 cm−1 corresponds to the C═N iminoquinone, C═C stretching mode of quinoid rings, the C═C stretching mode of the benzenoid rings, the stretching mode of C–N, the stretching mode of N ═Q═ N where Q represents the quinoid ring and C–H bonding mode of aromatic rings [20-23]. The PANi–ZnO (10-50 wt %) nanocomposites also show the same characteristic peaks. However, the corresponding peaks of pure PANi(EB) at 1564 cm−1shifted to 1580 cm−1, 1462 cm−1 shifted to 1480 cm−1, 1285 cm−1 shifted to 1294 cm−1, 1103 cm−1 shifted to 1120 cm−1 and 798 cm−1 shifted to 808 cm−1 wave numbers in PANi–ZnO (10-50 wt %) nanocomposites. The shift may be ascribed to the formation of hydrogen bonding between ZnO and the NH group of PANi (EB) on the surface of the ZnO particles. Such kind of interaction between PANi (EB) and ZnO particles is also observed by He et al. [20] and Paul et al. [24].

3.4. UV - Vis Spectroscopy Studies UV-Vis spectra of PANi (EB), ZnO nanoparticles and PANi-ZnO (10-50 wt %) nanocomposite are shown in Fig. 4. Fig. 4(a) shows that three distinctive peaks of polyaniline(EB) appear at about 336, 441 and 924 nm, which are attributed to the π–π*, polaron- π* and π- polaron transition, respectively and one distinctive peak of ZnO appear at about 337 nm which is attributed to the π–π* transition [20-23]. From Fig. 4, it can be noted that the characteristic peaks of ZnO nanoparticles and polyaniline all appear in PANi- ZnO nanocomposite (Fig. 4 c). Moreover, the peaks of pure PANi (EB) at 341 nm shifted to 334nm, 441nm shifted to 435 nm, and 924 nm shifted to 869 nm. It indicates that insertion of ZnO nanoparticles has the effect on the doping of conducting polyaniline, while this effect should owe to an interaction at the interface of polyaniline and ZnO nanoparticles [24].

3.5. Gas Sensing Measurements In order to record response to different gases, contacts were made on the silver paste strips, 1 mm wide and 1cm apart from each other after complete drying of paste. The films were mounted in an airtight stainless steel housing of 250 cc and fixed amount of chosen 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. To measure the change in resistance of the sensor films a Digital Multimeter Rigol 3062 (6 ½ digit) was used. 124

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ZnO

3416.92

2849.40

2920.92

2322.30

1599.28 1593.06 1742.33

1020.87 1117.28

3748.11

538.87 667.92 870.05

Transmittance(a.u)

2922.38

3240.90

1296 1462 1564 1662

798

PANi(EB)

1019 1105

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(a)

500 1000 1500 2000 2500 3000 3500 4000 -1 Wavenumber ( cm )

500 1000 1500 2000 2500 3000 3500 4000

(a)

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-1

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(c)

PANi-ZnO nanocomposites

3488

2849 2920

1480 1580

1294

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710 808

O n Z % 0 4 O n Z % 0 3 O n Z % 0 2

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O n Z % 0 5 O n Z % 0 1

500

1000

1500

2000

2500

3000

3500

4000

-1

Wavenumber(cm )

(c)

Fig. 3. FTIR of (a) PANi, (b) ZnO and (c) PANi-ZnO nanocomposite

334 nm

Absorption(a.u)

435 nm

200

337nm

(a) PANi (EB) (b) ZnO (c) PANi(EB)-ZnO(50%)

(c)

341 nm441 nm

869 nm

(b) 924 nm

(a )

300

400

500 600 700 Wavenumber(nm)

800

900

Fig. 4. UV-Vis spectra of (a) PANi(EB), (b) ZnO & (c) PANi-ZnO (50 %) nanocomposite. 125

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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. Fig. 5 shows the room temperature gas sensing set up used for measurement of gas sensing properties of PANi-ZnO nanocomposite films.

Fig. 5. Room temperature gas sensing measurement setup.

3.5.1. Selectivity of PANi-ZnO Sensor From structural, morphological, optical and electrical investigation of PANi-ZnO (10-50 wt %) nanocomposites, it is revealed that the PANi-ZnO (50 wt %) nanocomposites showed improved structural, morphological and optoelectronic properties [25]. The PANi-ZnO (50 %) nanocomposite gives the excellent gas response compared to the rest of composites also these films showed much improved stability, reproducibility and mechanical strength due to presence of ZnO in the PANi films. Therefore the present study aims at gas sensing properties of PANi-ZnO (50 wt %) nanocomposites. Therefore an attempt was made to study selectivity of PANi-ZnO (50 %) films for lower concentration of NH3 (20 ppm) as compared to the sensitivities for higher concentration of CH3-OH, C2H5-OH, NO2 and H2S (100 ppm). The bar chart for selectivity is as shown in Fig. 6. It is observed that PANi-ZnO thin films can sense lower concentration of NH3 with higher sensitivity value (~ 4.6) as compared to large concentration of other gases. The probable mechanism of selectivity for NH3 may be traced to the characteristics of vapor adsorbed over the surface of PANi-ZnO nanocomposite. 126

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PANi-ZnO 50%

Response,S %

4

3

2

1 100 ppm

100 ppm

100 ppm

100 ppm

0

NH 3

NO 2

H 2S

C 2H 5OH

CH 3OH

Gases

Fig. 6. Selectivity bar chart of PANi-ZnO (50 %) sensor film.

3.5.2. NH3 Sensing Properties of PANi-ZnO Sensor The gas sensing studies were carried out for NH3 at room temperature being selective to PANi-ZnO. Therefore the PANi-ZnO (50 wt %) nanocomposite sensor films were explored to different concentrations (20-100 ppm) of NH3. Fig. 7 shows variation of electrical resistance with time when films are exposed to NH3. As seen from figure, the resistance increases dramatically upon exposure to NH3 vapor, attains stable value and decreases gradually after being transferred to clean air.

235

(a)20 ppm (b)40 ppm (c)60 ppm (d)80 ppm (e)100 ppm

Resistance(M)

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225

(d)

220

(c)

215

(b)

210

(a)

205 0

100

200

300

400

500

600

Time(sec)

Fig. 7. Gas responses of PANi-ZnO film to NH3 (20-100 ppm).

3.5.3. Gas Response Transient of PANi-ZnO Sensor The gas response transient of PANi-ZnO thin film when exposed to NH3 (20-100 ppm) is as shown in Fig. 8. 127

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14 (e)

Response, S (%)

12 (d)

10

(a)20 ppm (b)40 ppm (c)60 ppm (d)80 ppm (e)100 ppm

(c)

8 6

(b)

4

(a)

2 0 0

100

200

300 400 Time (sec.)

500

600

Fig. 8. Dynamic responses of PANi-ZnO sensor to NH3 (20-100 ppm).

The increase in resistance after exposure to NH3 may be because of porous structure of PANi- ZnO films leads to the predominance of surface phenomena over bulk material phenomena, which may again be due to surface adsorption effect and chemisorptions leads to the formation of ammonium. The resistance attains stable value when dynamic equilibrium is attained [28]. In order to explain the higher response and gas sensing mechanism of PANi-ZnO nanocomposite, Tai et al [29] postulated that PANi and TiO2 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 TiO2 which could be formed owing to inter –particle electron migration from TiO2 to PANi at the heterojunction. This would cause the reduction of the activation energy and enthalpy of physisorption for NH3 gas. The response values of PANi-ZnO sensor film is plotted as a function of NH3 concentration in Fig. 9. 16 PANi:ZnO(50%)

14

Response,S (%)

12 10 8 6 4 2

20

40

60 80 NH3 gas (ppm)

100

Fig. 9. Response of PANi-ZnO thin film sensor to NH3 (20- 100 ppm).

The response values of PANi-ZnO sensor film is plotted as a function of NH3 concentration in Fig. 9. It is observed that the response value increase rapidly with increasing concentration of NH3 and the rate of increase of response value slows down at higher concentration. The relative response tends to 128

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increase initially with increasing concentrations possibly due to the availability of a large number of reactive species in the sensing layer; however the slowly increasing response at higher concentration may be due to less availability of surface area with possible reaction sites on surface of the film due to adsorption of gas molecules [30].

3.5.4. Response and Recovery Times of PANi-ZnO Sensor The response and recovery times were depicted from the electrical response curve (Fig. 7) of PANiZnO to various concentrations of NH3. The response time is defined as the time taken by the sensor to attain 90 % of the maximum increase in resistance on exposure of target gas and recovery time as the time to get back 90 % of the maximum resistance when exposed to clean air. The variation of response and recovery times with different concentration of NH3 at room temperature is represented in Fig. 10. It is observed that the response time and recovery time varies inversely with respect to concentration of NH3. The response time decreases from 153 s to 81 s while recovery time increases from 135 to 315 s with increasing NH3 concentration from 20 to 100 ppm. The decrease in response time may be due to large availability of vacant sites on thin films for gas adsorption as evident from SEM image; and increasing recovery time may be due to gas reaction species which left behind after gas interaction resulting in decrease in desorption rate [20]. From Fig. 10, it is found that for higher concentration of NH3 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. 340

170 160

300

150

280

140

260

130

240

120

220

110

200

100

180

90

160 140

80 70

Recovery time (sec)

Response time (sec)

320

Response time Recovery time

120 20

40

60

80

100

Fig. 10. Response and recovery curve of PANi-ZnO sensor for 100 ppm NH3.

3.5.5. Stability of PANi-ZnO Sensor In order to check the stability of PANi-ZnO sensor, the change in resistance is studied at room temperature upon exposure of fixed concentration (100ppm) of NH3 for 30 days at an interval of 5 days, after the first measurement and the results of gas response are shown in Fig. 11. Initially PANiZnO sensor showed relatively high response, however it dropped from 14 to 10 % and stable response obtained after 15 days. This is because in the initial stage PANi-ZnO sensor may undergo interface modification during operation and then reaches to steady state indicating the stability of the PANi-ZnO sensor operating at room temperature.

129

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Sensitivity (%)

14 13 12 11 10 9 8

0

5

10

15 20 Time(days)

25

30

Fig. 11. Stability curve of PANi-ZnO sensor operating at room temperature.

4. Conclusions The crystallinity of PANi-ZnO nanocomposites thin film sensor fabricated by spin coating technique has been improved with increasing percentage of ZnO nanoparticles though the composites have poorer crystallinity than ZnO, because of amorphous structure of PANi. It can be seen that PANi-ZnO 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 (NH3). The gas sensing measurements were carried out for different concentrations of NH3 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 NH3 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.

Acknowledgement Authors (VBP) are grateful to DAE-BRNS, for financial support through the scheme no.2010/37P/45/BRNS/1442.

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