Nanocomposite Material for Sensing of Halogenated Methanes: A Model Based on Charge Transfer Interaction for Selectivity
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Nanocomposite Material for Sensing of Halogenated Methanes: A Model Based on Charge Transfer Interaction for Selectivity. Rajiv Sangoi1, L. Fuller2 and K.S.V. Santhanam1,3 1. Center for Materials Science and Engineering, 2. Microelectronic Engineering, 3. Department of Chemistry, Rochester Institute of Technology, Rochester, NY, 14623 ABSTRACT A unique nanocomposite of poly (3-methylthiophene) with functionalized multiwalled carbon nanotubes (MWNT) has been synthesized that shows selective sensing for halogenated methanes. The sensor has been found to give the highest response for chloroform and none for methane. A tentative model has been proposed for this selective sensing of halogenated methanes. INTRODUCTION A wide variety of chemical sensors have been developed in the last decade to detect and monitor gases which are currently finding a large number of practical applications [1-10] in environmental monitoring and quality control in food processing, beverage and perfume industry. The sensors are based on their response to the gases through altering of one of the physical or chemical properties of the sensing material. Some of these sensors (oxide based) are amenable for environmental monitoring even though they do not have high selectivity. The oxide based sensors operate at higher temperatures of bout 300-700oC and fail to work at ambient temperatures. Conducting polymers have been studied for their application in sensing chemical vapors [3]. More significant among these have been polymers like polyaniline [4, 5], polythiophene [2, 6, 7], and polypyrrole [5, 8]. The principle sensing mechanism of conducting polymers is based on the redox interaction of the polymer with the analyte molecules. This causes changes in the doping level, carrier density and mobility, leading to changes in the electrical conductivity [3-8]. These sensors have potentiality to function at ambient temperatures. However, the conducting polymers currently employed in sensor applications are sensitive to a wide variety of organic vapors and hence their selectivity is poor. Also, there have been problems of the environmental stability of these polymers. Over the last decade, there has been a great interest in exploring the use carbon nanotubes (CNTs) [10] for variety of applications. Recently, the gas sensing capabilities of this unique form of carbon have been demonstrated [11-13]. The large surface area of CNTs makes them particularly attractive for sensing applications. The sensing mechanism is based on the adsorption of the analyte molecule on the surface of the CNTs thereby resulting in change in measurable electrical properties. The sensors using CNTs would be capable of room temperature operation. Nanocomposites formed by incorporation of nano fillers in conducting polymers are being researched for their use in chemical sensors. However, there have been very few reports [14] of sensors using this new class of materials. As of today, there exist very little criteria that could be used for the selection of a material in sensor
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