Simple Synthesis of ZnCo2O4 Nanoparticles as Gas-sensing Materials

Sensors & Transducers Volume 134 Issue 11 November 2011

www.sensorsportal.com

ISSN 1726-5479

Editors-in-Chief: professor Sergey Y. Yurish, tel.: +34 696067716, e-mail: [email protected] Editors for Western Europe Meijer, Gerard C.M., Delft University of Technology, The Netherlands Ferrari, Vittorio, Universitá di Brescia, Italy Editor for Eastern Europe 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 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. 95-106

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

Simple Synthesis of ZnCo2O4 Nanoparticles as Gas-sensing Materials * *

S. V. Bangale,* S. M. Khetre ** D. R. Patil and * S. R. Bamane

Metal Oxide Research, Laboratory, Department of Chemistry, Dr. Patangrao Kadam Mahavidyalaya, Sangli 416416 (M.S.) India ** Bulk and Nano Materials Research Lab, Dept. of Physics, Rani Laxmibai College Parola, Dist – Jalgaon, 425111 Tel.: 0233-2535993, fax: 0233-2535993 E-mail: [email protected]

Received: 15 July 2011 /Accepted: 21 November 2011 /Published: 29 November 2011 Abstract: Semiconductive nanometer-size material ZnCo2O4 was synthesized by a solution combustion reaction of inorganic reagents of Zn(NO3)3. 6H2O, Co(NO3)3.6H2O and glycine as a fuel. The process was a convenient, environment friendly, inexpensive and efficient preparation method for the ZnCo2O4 nanomaterial. The synthesized materials were characterized by TG/DTA, XRD, EDX, SEM, and TEM. Conductance responses of the nanocrystalline ZnCo2O4 thick film were measured by exposing the film to reducing gases like Acetone, Ethanol, Ammonia (NH3), Hydrogen (H2), Hydrogen sulphide (H2S), Chlorine (Cl2) and Liquefied petroleum gas (LPG). It was found that the sensors exhibited various sensing responses to these gases at different operating temperature. Furthermore, the sensor exhibited a fast response and a good recovery. The results demonstrated that ZnCo2O4 can be used as a new type of gas-sensing material which has a high sensitivity and good selectivity to Liquefied petroleum gas (LPG) at 100 ppm. Copyright © 2011 IFSA. Keyword: Nanostructure ZnCo2O4, XRD, SEM, TEM, Gas sensor.

1. Introduction Among the various materials, ZnO is the most promising semiconductor [1] to detect the toxic and hazardous gases. In recent years, one dimensional (1D) nanostructures of semiconducting metal oxides with high surface to volume ratio and small grain size have received focused attention due to their 95

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potential applications in fabricating gas sensors [2, 5], humidity sensors [6, 7] and nanoelectronic circuits [9]. Cr2O3-activated ZnO was reported to be a humidity sensors [10], Cr2O3-modified ZnO thick film resistors was reported to be LPG sensors [11]. Liquefied petroleum gas (LPG) is utilized in almost every kitchen all over the world. It is therefore, referred as a town gas or cooking gas. It is utilized in large extent for industrial purposes and in laboratories as fuel. Cooking gas consists chiefly of butane [12], which is a colourless and odourless gas. It is usually mixed with compounds of sulphur (viz.methyl mercaptan and ethyl mercaptan) having foul smell, so that its leakage can be noticed easily. This gas is potentially hazardous because explosion accidents [13] might be caused, when it leaks out by mistake. It has been reported that, at the concentration up to noticeable leakage, it is very much more than the lower explosive limit (LEL) of the gas in air. Explosion accidents destroyed many industries, laboratories, kitchens and houses, building, societies and what not? Many researchers are working on LPG sensor, but could not meet the challenges up to the depth of demand by society. So there is a great demand from the society of detecting LPG for the purpose of safety application in domestic and industrial fields. Among p-type semiconducting metal oxide, Co3O4 is a promising material due to its application potential in many technological areas such as heterogeneous catalysis [14], anode material in lithium rechargeable batteries [15], sensors [16], Zinc cobaltite ZnCo2O4 is one of these compounds, which has long been used as a ceramic color pigment or dying material [17,18]. In the same way, solid soluctions of nominal composition ZnxCo3-xO4 exhibit improved adsorbent capabilities so they find application as selective catalysts for oxidation and hydrogenation reaction [19], as well as for the monitoring and removal of harmful species such as Cl2, NO2, CO2 and H2S among others [20]. ZnCo2O4 is a cobalt based spinel oxide, where divalent Zn ions occupy the tetrahedral site in the cubic spinel structure and the trivalent Co ions occupy the octahedral site [21]. Different methods such as typical co-precipitation [22], sol-gel route [23], hydrothermal synthesis [24], high-temperature calcinations of hydroxide or carbonate precursor mixtures [25] and combustion method have been proposed recently and developed which make it possible to obtain spinel oxides in the form of ultrafine or nanoparticles. Chen and Coworkers [26] prepared by MCo2O4 ( M = Ni, Cu, Zn) nanotubes by using template assisted method and investigated their gas sensing properties to Cl2, NO2, C2H2OH, SO2 and CO. Du et al [27] synthesized ZnM2O4 ( M = Fe, Co, Cr) by microemulsion method and studied the gas sensing properties to Cl2, NO2, C2H5OH, H2S and acetone. The aim of the present work is to develop LPG sensor by ZnCo2O4 thick films. This could be able to detect the trace amount of LPG. It was studied that the gas sensing performance of the material can be improved by incorporating few additives into the base material and/ or surface activation of thick films. Some well-known materials used for the fabrication of LPG sensor are SnO2 [28], Ru-SnO2 [29], modified-SnO2 [30], etc. In the paper, we report a LPG sensor with gas response and good selectivity using cubic nanostructure ZnCo2O4 as the sensing material for the first time. The nanostructure ZnCo2O4 was synthesized by combustion route first time using mixed precursor (consisting of zinc nitrate, magnesium nitrate and glycine) at 800 0C in air for 4 h. The mixed precursor was prepared through a low cost and simple combustion method.

2. Experimental 2.1. Powder Preparation In this study, the as-synthesized ZnCo2O4 powder were prepared using combustion synthesis different molar composition of fuel, subsequently, the molar composition was maintained constant, and process was carried out under varying synthesis temperatures. Zinc cobalt oxide (ZnCo2O4) was synthesized using the modified solution combustion technique, starting from solution of Zn(NO3)26H2O (7.43g), (Co (NO3)26H2O (7.27g), and glycine (6.05g). glycine possesses 96

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a high heat of combustion. It is an organic fuel and providing a platform for redox reactions during the course of combustion. Initially the Zinc nitrates, Cobalt nitrates and Glycine are taken in the 1:1:4 stoichiometric amount and dissolved in a 250 ml beaker and made in homogenous peste. Peste formed was evaporated on hot plate in temperature range of 70 0C to 80 0C resulting into a thick gel. The gel was kept on a hot plate for auto combustion and heated in the temperature range of 170 0C to 180 0C. The nanocrystalline ZnCo2O4 powder was formed within a five minute. And it was sintered at about 300, 500, 800 and 1000 0C for about 4 hours when we got a black color shining powder of nanocrystalline ZnCo2O4.

2.2. Thick Film Preparation Zinc cobalt oxide powder was ground in an agate pastel-moter to ensure sufficiently fine particle size. The fine powder was calcined at 800 0C for 24 h in air and re-ground. The thixotropic paste [31, 32] was formulated by mixing the resulting ZnCo2O4 fine powder with a soluction of ethyl cellulose (a temporary binder) in a mixture of organic solvents such as butyl carbitol acetate and turpineol. The ratio of inorganic and organic path was kept as 75:25 in formulating the paste. The paste was then used to prepare thick films. The thixotropic paste was screen printed on a glass substrate in desired patterns. The films prepared were fired at 500 0C for 24 h.

2.3. Characterization The as –prepared samples were characterized by TG/DTA thermal analyzer (SDT Q600 V 20.9 Build 20), XRD Philips Analytic X-ray B.V. (PW-3710 Based Model diffraction analysis using Cu-Kα radiation), scanning electron microscope (SEM, JEOL JED 2300) coupled with an energy dispersive spectrometer (EDS JEOL 6360 LA), A JEOL JEM–200 CX transmission electron microscope operating at 200 kV analysis.

3. Result and Discussion 3.1 TG-DTA 2C2NH3O2 + (9/2) O2 → N2 + CO2 + 5H2O

(1)

Zn (NO3)3 + Co (NO3)3 + 4C2H5NO2 → ZnCo2O4 + 8H2O + 10H2O + 5N2

(2)

TG-DTA analysis was performed at a heating rate of 10 K min-1 to investigate the thermal properties of ZnCo2O4. The TG spectrum and its 1st derivative in Fig. 1 show the thermal decomposition of ZnCo2O4 is the curve indicates that the slight weight loss of about 13.2 % at temperature up to 140 0C in ZnCo2O4 powder due to little loss of moisture, carbon dioxide and nitrogen gas. The DTA curve of ZnCo2O4 recorded in static air and in shown in Fig. 1. The curve shown that ZnCo2O4 did not decompose, but weight loss was due to dehydrogenation, decarboxylation and denitraction. Further weight loss of about 28 % between the temperature range 300 0C and continuous loss in weight about 48 % up to 600 0C is attributed to loss of organic materials and yield final product at 650 0C, this weight loss and weight gained was very negligible. This weight change was in the range of 650 0C these indicating that the synthesized powder was almost stable from the begging. The formation temperature in the present work is found to be comparatively similar than that reported for corresponding solid state reaction route [33].

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Fig. 1. TG-DTA curve of mixed precursorZnCo2O4.

3.2. XRD Results The X-ray diffraction pattern of sample at different temperatures of synthesis. Is shown in Fig. 2. The observed d values compared with standard d values and are in good agreement with standard d value JCPDS data. (Card number 82-1042). The structure possesses the cubic may be attributed to the different preparation method which may yield different structural defects. The crystalline size was determined from full width of half maximum (FWHM) of the most intense peak obtained by shown scanning of X-ray diffraction pattern. The crystallite size was calculated by using Scherrer equation [25-26] d = 0.9λ/ βcosθ, where, d is the crystalline size, λ is the X-ray wavelength of the Cu Kα source (λ=1.54056 A0), β is the FWHM of the most predominant peak at 100 % intensity, θ is the Braggs angle at which peak is recorded. In order to obtain pure nanocrystalline ZnCo2O4 particles and understand the thermal characterizations, the as prepared ZnCo2O4 powder is further calcined at 180, 300, 500, 800 and 10000C respectively (the calcined temperature assigned as TC). Fig. 2 presents XRD patterns for ZnCo2O4 oxide nanoparticles. The effects of the calcinations temperature on the crystallite size of ZnCo2O4 particles can be demonstrated. Traces of ZnCo2O4 crystallites phases (111), (220), (311), (222), (400),(311), (422) and (511) are detected in the XRD pattern for all calcined temperatures and then their intensities increase abruptly when the TC above 1000 0C .In general, the sharpness of the XRD peak (i.e. high crystallinity) is increased as the TC increases. According to the (222) diffraction pattern of ZnCo2O4 crystalline, the particle size of ZnCo2O4 can be calculated from the full width at haif-maximum using the Scherrer equation. Obviously, the particle size of ZnCo2O4 changes as the Tc controlled fewer than 180, 300, 500, 800 and 1000 0C, the order is 7, 8, 9, 12 and 37 nm, respectively.

3.3. Particle Size Analyzer Particle size distribution studies Fig. 3 have been carried out by using dynamic light scattering techniques (DLS) via Laser input energy of 632 nm). It was observed that zinc cobalt oxide nanoparticles particles have narrow size distribute within the range of about 25-30 nm. Which well matches are with calculated from Debye-Scherrer equation?

98

111

1000 C

511

422

O

400 331

Intensity (arbitary unit)

220 311 222

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O

800 C O

500 C O

300 C O

180 C

20

40

60

80

100

2

Fig. 2. XRD pattern of calcinied mixed precursorZnCo2O4 at 300 0C, 500 0C. 800 0C, 1000 0C in air for 4 h.

Fig. 3. Particle size Distribution of mixed precursor ZnCo2O4 at 800 0C in air for 4 h.

3.4. Energy dispersive X-ray microanalysis studies (EDX) Fig. 4 shows the energy dispersive X-ray spectrum of ZnCo2O4. This was carried out to understand the composition of zinc, cobalt and oxygen in the material. There was no unidentified peak observed in EDX. This confirms the purity and the composition of the ZnCo2O4 nanomaterial.

3.5. Scanning Electron Micrograph Study The microstructure of the 800 0C sintered samples can be visualized from scanning electron microscope (SEM) tool. Fig. 5. epicts SEM images of ZnCo2O4 powder. Shown the partical morphology of high resolution, the partical are most irregular in shape with a nanosize range 100-200 nm some particles are found as agglomerations containing very fine particles. It can be observed that ZnCo2O4 have uniformed size of about 5μm.It seems that surface are smooth, spongy pores are seen in the micrograph. 99

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Fig. 4. EDX pattern of mixed precursor ZnCo2O4 at 800 0C in air for 4 h.

(a)

(b)

Fig. 5. SEM images of mixed precursor ZnCo2O4 at 800 0C in air for 4 h (a) low resolution, and (b) high resolution.

3.6. Transmission Electron Microscopy (TEM) The TEM image of the mixed precursor calcined at 800 0C for 4 h are shown in Fig. 6(a, b).It indicates the presence of ZnCo2O4 nanoparticles with size 30-40 nm which form beed type of oriental aggregation throughout the region. The selected area electron diffraction (SAED) pattern Fig. 6 (c) shows the spot type pattern which is indicative of the presence of single crystalline particles. No evidence was found for more than one pattern, suggesting the single phage nature of the material.

3.7. Thickness Measurement The thicknesses of the films were observed to be in the range from 25-35 µm. The reproducibility of the film thickness was achieved by maintaining the proper rheology and thixotropy of the paste.

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(a)

(b)

(c) Fig. 6. TEM (a, b) images of nanostructured ZnCo2O4 (c) SAED pattern.

4. Electrical Properties of the Sensors 4.1 I-V Characteristics Fig. 7. depicts I-V characteristics of ZnCo2O4 films. It is clear from the symmetrical I-V characteristics that the silver contacts on the films were ohmic in nature.

4.2. Electrical Conductivity Fig. 8 shows the variation of log (conductivity) with temperature. The conductivity values of sample increase with operating temperature. The increase in conductivity with increasing temperature could be attributed to negative temperature coefficient of resistance and semiconducting nature of ZnCo2O4. It is observed from Fig. 8 that the electrical conductivities of the ZnCo2O4 films are nearly linear in the temperature range from 50- 400 0C in air ambient.

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Fig. 7. I-V characteristics of the sensor.

Fig. 8. Variation log (conductivity) with reciprocal operating temperature (K-1).

5. Sensing Performance of Sensor 5.1 Gas Response, Selectivity, Response and Recovery Time The relative response (S) to a target gas is defined as the ratio of the change in conductance of a sample upon exposure of the gas to the original conductance in air. The relation for S is given as S = Gg-Ga/Ga, where Ga is the conductance in air and Gg the conductance in a sample gas. Specificity or selectivity is defined as the ability of a sensor to respond to a certain gas in the presence of different gases. Response time (RST) is defined as the time neede for a sensor to attain 90 % of the maximum increases in conductance on exposure to the target gas. Recovery time (RCT) is the time taken to get back 90 % of the original conductance in air. 102

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5.2. Gas Response and Operating Temperature Fig. 9 depicts the variation of 100 ppm gas responses with operating temperature. The ZnCo2O4 sensor was observed to be a temperature dependents gas sensor. From Fig. 9, it is observed that the sensor better responds to LPG gas at 350 0C, H2S gas at 3000C, Ethanol gas at 300 0C Acetone gas at 300 0C, NH3 gas at 300 0C, CI2 gas at 300 0C, H2 gas at 350 0C, CO2 gas at 250 0C. The sensitivity towards such gas depends on temperature. The same sensors could be used to identify LPG, H2S, Ethanol, Acetone, NH3, Cl2, H2, and CO2 just by varying the operating temperature. This is the most desirable characteristic of this sensor.

Fig. 9. Variation of different gas responses with operating temperatures.

5.3. Gas Response and Gas Concentration It is observed from Fig. 10 that the response of ZnCo2O4 film was observed to increases continuously with increasing the gas concentration up to 100 ppm, and it attains the maximum and saturates above 100 ppm. Therefore, the active region of the sensor would be up to 100 ppm, as the rate of rise of response is larger during this region. At lower gas concentration, the unimolecular layer of gas molecules would be expected to form on the surface, which would interact with the surface more actively giving larger responses. There would be multilayers of gas molecules on the sensors surface at the higher gas concentration (> 100 ppm) resulting in saturation in gas response.

5.4. Selectivity Fig. 11 depicts the variation of gas responses of ZnCo2O4 samples to LPG among the mixture of gases. It is clear from the figure that the ZnCo2O4 sample shows the selective response to LPG at 350 0C among all other gases.

5.5. Response and Recovery of the Sensor The time taken for the sensor to attain 90 % of the maximum increases in conductance on exposure of the target gas is known as response time. The time taken by the sensor to get back 90 % of the maximum conductance when the flow of gas is switched off is known as recovery time. The response and recovery 103

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of the ZnCo2O4 thick film sensors was quick ( ˜ 20 s) while the recovery was fast ( ˜ 44 s). The negligible quantity of the surface reaction products and their high volatility explain the quick response to LPG and fast recovery to its chemical status.

Fig. 10. Variation of gas response with gas concentration.

Fig. 11. Selectivity factor of sensor for various gases.

6. Discussion Gas sensing mechanism is generally explained in terms of conductance either by adsorption of atmospheric oxygen on the surface and/or by direct reaction of lattice oxygen or interstitial oxygen with the test gases. In case of former, the atmospheric oxygen adsorbs on the surface by extracting an electron from conduction band, in the form of super-oxide or peroxides, which are mainly responsible for the detection of the test gases. At higher temperature, the adsorbed oxygen captures the electrons from conduction band as: O2(air) + 2e-(cond.band) → 2O- (film surface). 104

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It would result in decreasing conductivity of the film. When LPG reacts with the adsorbed oxygen on the surface of the film, it gets oxidized to CO2 and H2O by following series of intermediate stage. This liberates free electrons in the conduction band. The final reaction takes place as: C4H10(gas) + 13O-(filmsurface) → 4CO2(gas) + 5H2O(gas) + 13e- (cond.band) This shows n-type conduction mechanism. Thus generated electrons contribute to a sudden increase in conductance of the thick film. The ZnCo2O4 misfit regions dispersed on the surface would enhance the ability of base materials to absorb more oxygen species giving high resistance in air ambient. Therefore response was obtained to 100 ppm LPG.

7. Conclusions (I) Nanocrystalline ZnCo2O4 has been synthesized by self combustion route. This synthesis route may be used for the synthesis of other metal oxide. (II) Among all other additives tested, ZnCo2O4 is outstanding in promoting the LPG gas sensing mechanism. (III) ZnCo2O4 to be optimum and showed highest response to LPG gas at 3500C. (IV)The sensor showed very rapid response and recovery to LPG gas. (VI) Sensing mechanism of ZnCo2O4 was the substitution of lattice oxygen by LPG gas. Material gains electrons in this substitution. (VII) The sensor has good selectivity to LPG against H2S, Acetone, NH3, CI2, H2 and CO2.

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