International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 3 Issue: 8 51...
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 3 Issue: 8 51...
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 3 Issue: 8 51...
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 3 Issue: 8 51...
International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169
Volume: 3 Issue: 8 51...
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Nanocrystalline Manganese Substituted Nickel Ferrite Thick Films as PPM Level H2S Gas Sensors

Citation/Export MLA R. S. Pandav, A. S. Tapase, P. P. Hankare, G. B. Shelke, D. R. Patil, “Nanocrystalline Manganese Substituted Nickel Ferrite Thick Films as PPM Level H2S Gas Sensors”, August 15 Volume 3 Issue 8 , International Journal on Recent and Innovation Trends in Computing and Communication (IJRITCC), ISSN: 2321-8169, PP: 5152 - 5156 APA R. S. Pandav, A. S. Tapase, P. P. Hankare, G. B. Shelke, D. R. Patil, August 15 Volume 3 Issue 8, “Nanocrystalline Manganese Substituted Nickel Ferrite Thick Films as PPM Level H2S Gas Sensors”, International Journal on Recent and Innovation Trends in Computing and Communication (IJRITCC), ISSN: 2321-8169, PP: 5152 - 5156
Published on: Mar 3, 2016
Published in: Engineering      
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Transcripts - Nanocrystalline Manganese Substituted Nickel Ferrite Thick Films as PPM Level H2S Gas Sensors

  • 1. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 3 Issue: 8 5152 - 5156 _______________________________________________________________________________________________ 5152 IJRITCC | August 2015, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Nanocrystalline Manganese Substituted Nickel Ferrite Thick Films as PPM Level H2S Gas Sensors R. S. Pandav, A. S. Tapase, P. P. Hankare Department of Chemistry, Shivaji University, Kolhapur, MHS, 416 004, India E-mail: p_hankarep@rediffmail.com G. B. Shelke, D. R. Patil* Bulk and Nanomaterials Research Lab., Dept. of Physics, R. L. College, Parola, Dist. Jalgaon, MHS, India, 425111 *E-mail: prof_drpatil@yahoo.in Mob: +91 9860335029 Abstract- A simple sol-gel auto combustion technique is introduced for the synthesis of nanocrystalline manganese substituted nickel ferrite dry powders. These dry powders were mechano-chemically mixed with organic binders to prepare thixotropic pastes. Thixotropic pastes of as prepared ferrite powders were formulated and screen printed on glass substrates to form thick films, followed by firing at 450o C. The crystal structure, phase, surface morphology and topography of the samples were characterized by X-ray diffraction study, scanning electron microscopy, transmission electron microscopy, etc. The gas sensing behavior of the samples were characterized by exposing the films to various inflammable and toxic gases like LPG, NH3, CO2, ethanol, H2S and Cl2. It was found that the sensors made from the composition containing x=1.0, exhibits highly selective and most sensitive towards 20 ppm of H2S gas at 3500 C. The effect of operating temperature, gas concentration, type of gases, etc. on gas response were studied and discussed. Keywords: Sol-gel, Ferrites, H2S gas sensors, etc. __________________________________________________*****_________________________________________________ I. INTRODUCTION Various polluting, toxic and hazardous gases have been liberated by the industries, which can cause the disastrous and defective deformation of living beings, even at trace levels. This is attributed to explosive industrialization, modernization, globalization, urbanization, and what not? In past decades sensors were based on semiconductor metal oxides like SnO2, ZnO, WO3, etc. Spinel oxides (AB2O4) have been known for a long time for their interesting optical, electronic and magnetic properties and are thus suitable for various industrial applications, viz. magnetic cores, high-frequency devices, etc. Nowadays, spinel oxides show their characteristic response towards various gases [1- 10]. Many researchers synthesized ferrites and worked for the study of their gas sensing properties [11-12]. Also, H2S is highly toxic and hazardous in such a way that, the few minute exposure to 1000 ppm concentration in air can be fatal to human, high doses can produce unconsciousness and respiratory paralysis. Thus monitoring and control of H2S gas is today’s need. Semiconducting oxides, mixed oxides, spinel oxides, ZnO, CuO/SnO2 composites, chemically modified CdIn2O4 thick films, surface modified Cr2O3, WO3, etc. are studied for H2S gas sensor [13-19]. However selectivity remains the main challenge for such materials. Hence there always needs for improved H2S sensor in the industrial area, which has high gas response, high selectivity, low response time and low recovery time along with long term stability. It is known that the electrical resistivity of a semiconducting oxide can be modified by adsorption of gases [20]. This property has been used in semiconductor sensors for the detection of inflammable and toxic gases [21-23]. The semiconductor gas sensors offer good advantages with respect to other gas sensor devices due to their lowest cost, high applicability, high reliability, affordable to laymen, real-time control systems, etc. [24]. In recent years the ferrites have demonstrated to be good materials for gas sensing applications [25]. The efforts are made to synthesize the nanoscaled ferrite material by sol-gel technique, one of the most suitable, simple, easily available and low cost techniques for the synthesis of Mn substituted Nickel Ferrite. II. EXPERIMENTAL TECHNIQUES A. Synthesis of NiFe2.-xMnxO4 compositions High purity AR grade ferric nitrate, manganese nitrate, nickel nitrate and citric acid were used in the synthesis. The metal nitrate solutions were mixed in the required stiochiometric ratios in deionized water. The pH of the solution was adjusted in the range from 9.1 to 9.5 by adding ammonia solution, drop wise and slowly. The solution was allowed for slow heating around 373o K with constant stirring, to obtain floppy mass, which was further subjected to thermal analysis for phase temperature identification. Thus, powdered samples of NiFe2.-xMnxO4, (0.0 ≤ x ≤ 2.0) for various concentrations of Fe and Mn were synthesized by sol-gel auto-combustion method. Thick films of as prepared samples were fabricated by screen printing technique [26-27]. III. CHARACTERIZATION TECHNIQUES A. X-Ray Diffraction Studies (XRD) X-ray diffraction patterns of Mn-substituted nickel ferrites are shown in Fig.1. From Table 1, it is showed that, all the samples of system are cubic and the lattice constant increases with substitution of manganese content. The increase in lattice constant with increase in Mn content is due to the higher ionic radii of Mn3+ (0.65Å) ions as compared to Fe3+ (0.64Å) ions. Here Mn has strong site preference energy for octahedral site; it tends to occupy the B site rather than A-site. From the X-ray diffraction peaks,
  • 2. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 3 Issue: 8 5152 - 5156 _______________________________________________________________________________________________ 5153 IJRITCC | August 2015, Available @ http://www.ijritcc.org _______________________________________________________________________________________ average crystallite size can be estimated using Debye- Scherer’s formula. t = 0.9λ / β cosθ (1) The X-ray density (dx) was calculated using the following relation. dx = 8M/Na3 (2) Where, N = Avagadros number (6.023 x 1023 atom/mole) M = Molecular weight in gm a = Lattice constant The values of lattice constant (a), crystallite size (t) and X-ray density (dx) are summarized in Table.1. The values of interplanner spacing (d), hkl planes and lattice constant (a) were obtained from XRD data with an accuracy of +0.03Å. 20 30 40 50 60 70 x= 0.0 2 theta (degrees) x= 0.25 x= 0.50 Intensity(a.u) x= 0.75 x= 1.0 (222) (440) (511) (422) (400) (220) (311) Fig.1: XRD of NiFe2.-xMnxO4 system Dopant Concentration (x) Lattice Constant ‘a’ (Å) X-ray density (gm/cm3 ) Crystallite size (nm) 0.0 8.33 5.37 31 0.5 8.34 5.34 28 1.0 8.35 5.31 24 1.5 8.37 5.26 28 2.0 8.38 5.22 27 Table 1: Lattice constant, crystallite size and X-ray density for all compositions Fig.2: TGA-DTA traces for the sample for x = 1.0 B. Thermal Analysis (TGA and DTA) Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the precursor with x = 1.0 was carried out from room temperature to 1000o C to determine its decomposition behavior (Fig. 2). Sample powders of about 6 mg were placed in a platinum crucible, ignited alumina was used as the reference material with the heating rate of 10o C·min-1 . The thermal analyses were carried out in static air and some thermoanalytical curves were recorded [27]. TGA of the precursor shows about 50% weight loss during this heating which is due to liberation of CO2, H2O, NOx, etc. It was found that all the decomposition occurs at or below 400o C. Above which, the precursor exhibits a near about constant weight. C. Microstructural Studies (SEM and TEM) (a) x = 0.0 (b) x = 1.0 (C) x = 2.0 Fig. 3 SEM images of NiFe2.-xMnxO4 system
  • 3. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 3 Issue: 8 5152 - 5156 _______________________________________________________________________________________________ 5154 IJRITCC | August 2015, Available @ http://www.ijritcc.org _______________________________________________________________________________________ Fig. 4 TEM image of NiFe2.-xMnxO4 for x = 1.0 The SEM images of Mn substituted nickel ferrites are shown in Fig.3. It is observed that, the average grain size goes on increasing on substitution of Mn content. They show the presence of very large lumps and found to be agglomeration of small spherical particles. This can be attributed to the generation of large volume of gases during the combustion reaction which occurs in a very short time. The morphology and grain size of manganese substituted nickel ferrite powder (where x=1) was further studied by TEM (Fig. 4). In manganese substituted nickel ferrite, it is noted that all particles are uniform and the average grain size is ~50 nm. Selected area electron diffraction pattern (SAED) of the particles suggests the polycrystallinity of individual crystallite and also confirms the formation of spinel ferrites. D. Electrical behavior of the sample (Resistivity) The d.c. electrical resistivity measurements showed linear plots of log (ρ) vs 1000/To K up to 400°C without any break or inflexion. Silver paste is applied at both the ends of the films for proper contact and connections. The results of electrical measurements show the decrease in resistivity with increasing temperature (Fig. 5) proving the negative temperature coefficient of resistance for the samples to be studied. Increase in temperature of the sample will help the trapped charges to be liberated and participate in the conduction process, with the result of decrease in the resistivity. The electrical resistivity temperature behavior of the NiFe2.-xMnxO4 system was found to be obeying Wilson’s law [28]. Fig. 5 log ρ versus 1000 / To K for the sample NiFe2.-xMnxO4 IV. GAS SENSING Sensing parameters for gas sensors viz. gas response, selectivity, response time and recovery time, are defined elsewhere [28-36]. Various parameters affect the gas sensing behavior of the sensor. Their effects are discussed below. A. Effect of Operating Temperature Fig. 6 depicts the gas responses of NiFe2.-xMnxO4 compositions with different operating temperatures. The NiFe2.-xMnxO4 film for x = 1.0 was observed to be a most sensitive film and shows maximum response to 20 ppm H2S gas at 3500 C. The maximum response of this film is attributed to the fact that, it adsorbs more oxygen species on the surface at such a higher temperature (350o C). Upon exposure, the H2S gas gets oxidized with adsorbed oxygen species on the surface of the film, trapping behind the electrons in the conduction band, which results in increase in conductance of the sensor. Thus this sensor monitors H2S gas in the open environment. Fig. 6 Variation of gas response with op. temperature B. Effect of H2S Gas Concentration Fig. 7 Variation in gas response with gas concentration (ppm) Fig. 7 depicts the variation of gas response of sample with H2S gas concentration at 350o C operating temperature. The sensor was exposed to the varying concentrations of H2S gas at higher temperature (350o C). The gas response was observed to increase linearly with the gas concentration up to 20 ppm. The increasing rate of gas response was relatively larger upto 20 ppm, and smaller afterwards. The region below 10 ppm, is called as cutoff region. The region in between 10 to 20 ppm is called as active region and above Samples: X = 0.0 X = 0.5 X = 1.0 X = 1.5 X = 2.0
  • 4. International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 3 Issue: 8 5152 - 5156 _______________________________________________________________________________________________ 5155 IJRITCC | August 2015, Available @ http://www.ijritcc.org _______________________________________________________________________________________ 20 ppm, a saturation region. For the sensors to work proper, the sensor should work in the active region. C. Selective Nature of the Sensor Fig. 8 Selectivity to H2S gas among various gases The selective nature of the sensor to H2S gas at 350o C is depicted in Fig. 8. The sensor showed high selectivity to H2S against LPG, CO2, C2H5OH, NH3, and Cl2 gases even at higher gas concentrations (1000 ppm). V. DISCUSSION Fig. 9 Actual sensing mechanism to H2S gas Gas sensing (Fig. 9) is the surface phenomenon. However, the surface is the region where periodicity of the crystal is interrupted, which leads the formation of localized energy levels, in the forbidden gap. Such energy levels can either capture electrons or donate electrons. Such energy levels are completely ionized at higher temperature, causing the increase in conductance of the sensor. The selective response of this sensor to ppm level H2S gas at higher temperature could be attributed to the adsorption-desorption type of sensing mechanism. At higher temperature (~350o C), more oxygen species (O- ) are adsorbed on the surface of the sensor. Upon exposure, the H2S gas gets oxidized with the adsorbed oxygen species viz. (O2 -  2O-  O2- ). The oxygen adsorption on the surface of the sensor occurs at different temperature ranges [13] are as follows: During oxidation of the gas, the electrons are released soon and become free to carry the current. 2 H2S + 3O2 (350 o C) ( 6 O - )  2 SO2 + 2 H2O + 6 e- At lower temperature, the smaller amount of oxygen would be adsorbed causes least oxidation of target gas, resulting in smaller gas response. At higher temperature (> 3500 C), the target gas may be oxidized before reaching the surface. Therefore, the gas response decreases further with increasing temperature. This shows n-type conduction mechanism. Thus generated electrons contribute to sudden increase in conductance of the thick film. On exposure to the H2S containing atmosphere, the resistance was observed to decrease crucially. Thus, obtains good response to 20 ppm H2S gas. As SO2 and water vapors are released from the film surface, the sensor recovers back to its original chemical status which would result in fast recovery. VI. CONCLUSION Manganese substituted nickel ferrites of nanocrystalline nature were successfully synthesized by sol-gel auto- combustion method. All the synthesized ferrospinel samples are in nanocrystalline (~50nm) form. Sensor having equivalent amount of Fe and Mn ions (x=1) shows higher response and better selectivity to H2S gas. ACKNOWLEDGEMENTS Authors are grateful to Hon’ble Kakasaheb Vasantrao More, President and Prin. B. V. Patil, Rani Laxmibai Mahavidyalaya, Parola, Jalgaon, MHS, India for providing excellent laboratory facilities, at Bulk and Nanomaterials Research Laboratory. PPH thankful to UGC for BSR fellowship and RSP is very thankful to UGC, New Delhi for financial assistance through Rajiv Gandhi National Fellowship. REFERENCES [1]. K. K. Khun, A. Mahajan and R. K. Bedi, J. Appl. Phys. 106, (2009). [2]. Wen Zeng , Tianmo Liu and Zhongchang Wang, J. Mater. Chem., 22, (2012), 3544-3548. [3]. Young-Jin Choi, In-Sung Hwang, Jae-Gwan Park, Nanotechnology 19, (2008), 095508. [4]. Shudi Peng, Gaolin Wu, Wei Song, and Qian Wang, J. Nanomater. (2013), Article ID 135147. [5]. A. V. Zaytseva, V. B. Zaytsev M. N. Rumyantseva, A. M. Gaskov, A. A. Zhukova, J. Nanoelectronics and Optoelectronics, 7, (2012), 607-613. [6]. T. SicilianoA. Tepore, G. Micocci, A. Serra, D. Manno, E. Filippo, Sens. Actuators B 133, 1, (2008), 321–326 [7]. S. Piperno, M. Passacantando, S. Santucci, L. Lozzi, and S. La Rosa, J. Appl. Phys. 101, (2007) 124504. Samples: X = 0.0 X = 0.5 X = 1.0 X = 1.5 X = 2.0
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