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There are many hazardous gases (like H2S, SO2, CO2, NH3, NO2, NO, etc.) that are used and/or are byproducts in agricultural sector, chemical industries, medicinal fields, refrigeration systems etc. The detection of these gases in an environment is very important due to safety reasons. However, among these gases, due to toxic nature and pungent odor, ammonia not only contributes toward air pollution but also causes irritation effect to the human beings even at very lower concentrations (below 50 ppm level).
Therefore, the timely detection of ammonia is very important. In the past, the different materials (like semiconducting metal oxides, silicon devices, conducting polymer composites) have been used for development of ammonia gas sensors. However, semiconducting metal oxides based and silicon devices based ammonia gas sensors have disadvantages like complex fabrication steps, high power consumption, high temperature operation etc. few years, there has been an extensive research for exploring the use of conducting polymer composites for gas sensing applications because of their several advantages such as facile synthesis; tunable electrical, optoelectronic & dielectric properties; processing via solution route; good sensitivity of their thin film based sensor towards number of acidic/basic gasses; improved response, recovery & sensitivity and most importantly, room temperature operation1-4.
Among various conducting polymer, polyaniline (PANI) is considered as most promising material for gas sensing purpose, due to its low monomer cost, lab scale synthesis via chemical route and flexibility in tuning of electrical properties, particle morphology, environmental/thermal stability and processability via selection of dopant and adjustment of oxidation level .
In particular, its ability to undergo non-redox doping via protonic acid dopants and undoping by base in reversible manner, makes PANI an ideal candidate for sensing of number of toxic gases having acidic/basic character or electron donating/accepting nature .
The development of polyaniline composites based on CNTs and graphene has drawn a great deal of attention as a route to obtaining new materials with new structural and functional properties superior to those of the pure components. As a famous carbon material, graphene is a single-atom thick, two-dimensional sheet of sp2 bonded carbon for outstanding electronic applications [8,9]. Graphene consisting of one or more graphene layers has been recognized as a promising, cost effective and high quality material . The graphene has excellent electronic, thermal property, high surface-to-volume ratio, remarkable mechanical stiffness and excellent conductivity which have been studied by various workers [11,12]. The gas response of graphene sensor was investigated for various gase like H2, NO2, NH3, H2O and CO [13-15]. Both the graphene and the PANI have conjugated electrons . There is growing interest on synthesizing graphene nanosheets (graphene)/PANI composite in the scientific community. Zhou et al.  prepared graphene/PANI composite by polymerized ionic liquid. Yan et al.  synthesized graphene/PANI composite and studied the property of supercapacitor electrodes. Tung et al.  reported the graphene/PANI nanocomposite and discussed its structure. Murugan et al.  obtained graphene/PANI nanocomposite for energy storage.
There is an efficient approach for the enhancement of the mechanical strength , thermal stability , long term stability, high surface to volume ratio and characteristics of sensors by combining the organic materials with inorganic counterparts to form composites . The graphene as inorganic nanofiller with conjugated electrons is added into PANI (Synthesized by chemical oxidative polymerization) via Physical mixing , which may enhance the prosperities of the ammonia gas sensor based on graphene/PANI nanocomposite. Until now, to our knowledge, there are few reports related to the graphene/PANI nanocomposite for NH3 gas sensor. In the present work, we report the results of the graphene/PANI nanocomposite as a new material for sensing NH3 gas. The graphene/PANI is synthesized by chemical oxidative polymerization and respectively characterized by Fourier transform infrared spectroscopy (FTIR), brunauer emmett tellerand (BET), ultraviolet-visible spectroscopy (UV-vis), photoluminescence (PL), X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). The graphene/PANI nanocomposite thin films sensor is formed on interdigital electrodes by drop coating method for NH3 gas detection at room temperature. The graphene/PANI nanocomposite thin films sensor exhibited higher sensitivity than that of PANI and show approximate linearity over a wide range of concentrations from 1 to 6400 ppm. Owing to the high surface-to-volume ratio of the incorporated graphene nanosheets, the fabricated graphene/PANI sensor is higher sensitivity for NH3 gas than that of only PANI thin films gas sensor. The NH3 adsorption of graphene/PANI and PANI are measured by the quartz crystal oscillating microbalance (QCM) technique. The adsorption of QCM coated graphene/PANI film is larger than that of PANI. Meanwhile, the sensor has fast response and good reproducibility in this study.
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