Studies on tin oxide-intercalated polyaniline nanocomposite for ammonia gas sensing applications
Introduction
Metal oxide thin-film gas sensors are widely used for detecting gas species by measuring changes in their physical properties on exposure to specific gas, in particular making use of reversible redox reactions in presence or absence of the specific gas media. Usually, the small change in chemical state of the film material may reflect as measurable change in some physical properties, such as electrical conductivity, which can be monitored by external electrical circuits. Pure tin oxide, SnO2 is a remarkable n-type semiconductor material having wide band gap (∼3.6 eV), and by making use of small quantity of dopant into it's matrix, thin films of this material find use in several devices such as flat panel displays, gas sensors [1], [2], etc. to name a few. However, the sensors incorporating tin oxide require an elevated temperature (≥200 °C) for their optimum operation. This calls for a separate temperature controlled heater assembly to operate the device, and requiring extra power for heating. In addition, the sensor operation at elevated temperature in itself causes gradual changes in the tin oxide film properties, which in turn deviate gas sensing properties of the device with time. Therefore, it is highly desirable to have sensors, which can operate at room temperature, but having comparable properties with that of tin oxide for gas sensing.
Conducting polymers (CPs) are in use as an alternative to metal oxide materials for gas sensing applications. Among the CPs, polyaniline (PANI) has become one of the technologically important CPs, because of it's relatively easier synthesis, and for having excellent electronic and electro-chromic properties. It has been used in making organic solar cell, as well as gas sensor applications [3], [4], [5], [6]. However, PANI is not as sensitive as metal oxides towards gas species, and its poor solubility in organic solvents limits its applications. In spite of these problems with PANI, efforts are being made to improve its solubility by involving protonation with organic acids or preparing it using emulsion polymerization in presence of surfactants [7]. There have been several reports on improving PANI's sensitivity and selectivity by making use of new methods, such as its synthesis in nano-structured forms [8], [9], or by addition of metal catalysts [10], [11], and by combination with other polymers [12].
Recently a new class of materials emerged, known as composites, prepared by mixing suitably the organic and inorganic base materials in proper form. The composite materials have special properties, but as seen in some of the cases, they can also have few desirable properties from both the parent organic and inorganic class of materials. As a consequence, there are growing interests in combining both organic and inorganic materials for applications in electronics, optics, magnetism, etc. [13], [14], [15]. In literature, there are some reports concerning PANI/inorganic nanocomposite sensors [16], [17], [18]. However, very few researchers have studied the composite SnO2/PANI for sensor application [19], [20].
We fabricated nanocomposites thin films of SnO2/PANI by incorporating SnO2 particles in the form of colloidal suspensions in PANI through solution route technique. The as-grown composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical absorbance studies. The as-grown films were exposed to NH3 gas at room temperature and the electrical response was noted. For a comparison, thin films of tin oxide, and PANI were also prepared separately, and evaluated along with the tin oxide/PANI composite films for sensing ammonia gas at room temperature. We report our findings in this paper and discuss a plausible mechanism for the formation and electronic behaviour of such nanocomposites.
Section snippets
Synthesis
We employed solution-route technique, to synthesize tin oxide/polyaniline nanocomposites. In this technique, formation of nanocomposites proceeds through an inorganic/organic interface reaction. Tin chloride (SnCl4·5H2O), hydrogen peroxide (H2O2), aniline, ammonium peroxydisulphate (APS) [(NH4)2S2O8] and hydrochloric acid (HCl) (all chemicals having AR grade), were purchased from M/s Loba Chemie, Mumbai (India). Aniline monomer was distilled under reduced pressure. Initially, SnCl4·5H2O, was
Reaction mechanism
Variation in pH and temperature of reaction bath with respect to time for both cases, i.e., for bath containing tin oxide nanoparticles suspension and without it, is shown in Fig. 1a and b. It may be seen that during the induction period (starting time of about 2–3 min), small change in bath temperature noticed, but subsequently a pronounced increase in bath temperature follows, indicating a faster film growth rate, and mainly due to the exothermic nature of aniline polymerization.
A simple
Conclusions
We synthesized tin oxide-intercalated polyaniline nanocomposites (SnO2/PANI) in thin film form, and compared the properties of the composite films with that of the thin films made from the constituent base materials. XRD studies were used to find particulate size, while FTIR study showed presence of both SnO2 and PANI molecules. SEM micrograph of these nanocomposite films revealed that the constituent composite particles have irregular shape and size, and encapsulated by fibrous PANI matrix. It
Acknowledgments
We are thankful to BRNS-DAE Project No. 2005/34/1/BRNS/380 for financial assistance to carry out the research work. We are also thankful to Head, Department of Physics, Dr. B.A.M. University, Aurangabad for providing the lab facilities. In addition, we highly acknowledge the help rendered by Dr. R.S. Devan and Prof. Y. Ma, Department of Physics, National Dong Hwa University, Taiwan for doing SEM characterization of our samples as well as helpful discussions. Authors especially, N.G. Deshpande
Mr. N.G. Deshpande is currently working for his PhD degree (from 2008) in Department of Physics, Hanyang University, Seoul, South Korea under the supervision of Prof. YoungPak Lee. Current interest of research work is 1D and 2D magnetic photonic crystals and their applications. Earlier worked as Senior Research Fellow (SRF) in BRNS-DAE project related to oxides, polymers and hybrid materials for gas sensor application (2005–2008). He published nearly 18 international research papers and
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Mr. N.G. Deshpande is currently working for his PhD degree (from 2008) in Department of Physics, Hanyang University, Seoul, South Korea under the supervision of Prof. YoungPak Lee. Current interest of research work is 1D and 2D magnetic photonic crystals and their applications. Earlier worked as Senior Research Fellow (SRF) in BRNS-DAE project related to oxides, polymers and hybrid materials for gas sensor application (2005–2008). He published nearly 18 international research papers and attended/presented (research work) at various international/national conferences.
Mr Y.G. Gudage is currently working for his PhD degree (from 2006) in Department of Physics, Dr. B.A. Marathwada Univeristy, Aurangabad (M.S.), India under the supervision of Dr. Ramphal Sharma. Current research interest is photoelectrochemical solar cells. He worked as Senior Research Fellow (SRF) in BRNS-DAE project on gas sensor applications. He has published nearly 12 international research papers and attended various conferences.
Dr. Ramphal Sharma received his PhD in 1991 from Rajasthan University, Jaipur, India. Currently, he is Associate Professor at Department of Physics, Dr. B.A.M. University, Aurangabad (M.S.), India. Currently, he is a Brain Pool Fellow in Department of Chemistry, Hanyang University, Seoul, Korea. He has more than 15 years of experience in teaching field; while 20 years of experience in research, i.e., in thin film technology. He has published more than 80 international and national papers in reputed journals. His main interest of research is gas sensor, photosensor and solar cells. He was visiting fellow of ICTP, Trieste, Italy in 1999–2001.
Dr. J.C. Vyas postgraduated in Physics from University of Rajasthan, Jaipur, and received PhD from Bombay University, Mumbai. He joined BARC in 1980, and over years worked in several different fields of technical interests, such as fabrication of space quality Si solar cells, growth and characterization of non-linear optical single crystals, oriented thin films growth using MBE and their characterization, high-temperature superconducting thin films based weak links for device applications, and thin film based gas sensors. He is a member of Indian Thermal Analysis Society, Material Research Society of India, etc.
Mr. JinBae Kim received his BS and MS degrees in Department of Physics of Sunmoon University, Korea, in 2000 and 2002, respectively. He has been a PhD candidate in Department of Physics from Hanyang University from 2002. He is currently focused on the physics and applications of magnetic nanostructures and magnetic photonic crystals. He has published nearly 20 papers in international journals and attended/presented his work at various reputed international/national conferences.
Prof. YoungPak Lee is currently Director of Quantum Photonic Science Research Center and Distinguished Professor in Department of Physics, Hanyang University, Seoul, Korea. He received his PhD degree in Condensed-Matter Physics, Iowa State University, Ames, Iowa, U.S.A. (1987). Besides this he has worked at various reputed posts and has been awarded many honors from Ministry of Science and Technology, Korea and others. His research interest is magnetic photonic crystals, meta-materials, nanomagnetism.