Novel method for fabrication of polyaniline–CdS sensor for H2S gas detection
Highlights
► Nanostructured PANi–CdS (0–50%) thin films fabricated by spin coating technique. ► PANi–CdS has a porous structure, interconnected network of fibers and high surface area. ► PANi–CdS sensor recognizes H2S at room temperature.
Introduction
Gas sensor devices commonly employ metal oxide semiconductors, the principle of which is based on the change in conductivity by interaction with gas molecules and this property is mostly dependent on the operating temperature. Thus metal oxide gas sensors require high operating temperature [1], [2]. Moreover such gas sensors have generally disadvantages of poor selectivity and low sensitivity to the very low concentration of gases. Therefore several different approaches have been explored in order to overcome these issues.
Recently, conducting polymers find place as gas sensors because of easy synthesis and room temperature operating devices [3], [4], [5]. Among several polymers studied, polyaniline presents advantages for applications in electronic devices since its electrical properties can be changed by oxidation or protonation in the imines nitrogen backbone, and additionally it presents thermal and environmental stability. Polyaniline-based solid state devices are of low cost and useful in electronics, storage devices and sensors. Polyaniline and its nanocomposites have been fabricated in bulk form using electrochemical polymerization [6]. Poylaniline–SnO2 hybrid material has been prepared by a hydrothermal route [7]. Similarly polyaniline has been processed into thin film form using different methods including spinning, vacuum sublimation, Langmuir–Blodgett (LB) techniques [8]. These films have been used for the detection of H2S, SO2, NH3, methanol, acetone, etc. and in biosensors as well [7], [9], [10].
However, with the best of our knowledge, there are no reports on the use of nanocomposites of polyaniline–CdS for H2S, NO2, Cl2 and NH3 sensors. Being highly toxic gases H2S, NO2, Cl2 and NH3 is a serious problem. Consequently, there is a need for development of cost effective sensors to monitor H2S, NO2, Cl2, C2H5OH, CH3OH and NH3 of the lowest possible concentration operating at room temperature (300 K).
The present work, for the first time, describes a technique to form polyaniline–CdS nanocomposites for monitoring toxic gases. The polyaniline–CdS nanocomposites in thin film form have been fabricated using simple spin coating technique. Before fabricating the nanocomposites, the individual films were characterized by XRD and SEM techniques. The change in resistance at room temperature was recorded before and after exposure to H2S, NO2, Cl2, C2H5OH, CH3OH and NH3 at concentrations in the range of 10–100 ppm.
Section snippets
Materials
Aniline (99%), hydrochloric acid (35% AR), ammonium peroxidisulphate (99%), methanol (99.8%), m-cresol (99%), cadmium acetate (AR) and thiourea (AR) were purchased from Sd fine Chem Ltd. Double distilled water was employed as a medium for the polymerization of aniline.
Synthesis of polyaniline (EB)
Polyaniline was synthesized by polymerization of aniline in the presence of hydrochloric acid (acts as a catalyst) using ammonium peroxidisulphate (APS) (acts as an oxidizing agent) by chemical oxidative polymerization method. For
Structural analysis of PANi, CdS and PANi–CdS nanocomposites
Fig. 2 shows the XRD patterns of pure polyaniline in the emeraldine base form, cadmium sulfide (CdS) and PANi–CdS nanocomposites (10–50 wt%). The XRD pattern of PANi shows a broad peak at 2θ = 25.30° which corresponds to (1 1 0) plane of PANi [11], [12], [13], [14]. This broad peak in the XRD pattern of PANi shows that it has some crystallinity. The crystallinity of PANi can be ascribed to the repetition of benzenoid and quinoid rings in PANi chains [15]. The XRD patterns of nano CdS, PANi–CdS (10–50
Conclusion
Nanostructured PANi–CdS (0–50%) thin film sensor was fabricated by spin coating technique on glass substrate operating at room temperature. It is observed that PANi–CdS film has a very porous structure, interconnected network of fibers and high surface area which contributes to a rapid diffusion of dopant into the film. The response behavior observed of the PANi–CdS nanocomposite thin film reveled higher sensitivity values, faster response and recover rates to H2S than those of pure PANi and
Acknowledgment
Authors (VBP) are grateful to the Department of Science and Technology, New Delhi for financial support through the scheme no. SR/FTP/PS-09/2007.
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