High sensitive and selective flexible H2S gas sensors based on Cu nanoparticle decorated SWCNTs
Introduction
Recently, intense research efforts have been dedicated to the development of detectors and sensors for detecting ultra-low amounts of chemical agents with a relatively fast response time [1], [2]. H2S is a harmful gas to human that can cause death depending on the concentration and exposure time [3]. Hydrogen sulfide has serious erosion effects and is known to be the major source of acid rain. Hydrogen sulfide is generated in various industrial processes including natural gas processing and petroleum refining. Although several commercial devices have been developed for H2S monitoring, they suffer from high operating temperatures, high power consumption, and high cost [4], [5], [6]. Harmful effects of H2S, however, require the development of small, portable, fast, and sensitive gas sensors.
A single wall carbon nanotube (SWCNT) can be considered as a graphene sheet that has been rolled up into a seamless nano-cylinder [7]. CNTs are being used as building blocks of advanced functional materials due to their excellent electrical properties [8], [9], [10]. SWCNTs have been widely used as the channel materials for field effect transistors (FETs) [11], [12], [13], electrochemical sensors [14], [15], [16], [17], gas sensors [18], [19], [20], [21], [22], and biosensors [23], [24], [25]. The sensitivity of CNTs to the surface charge transfer is the key advantage of their applications as sensing elements [26]. Because of low level selectivity and sensitivity of pristine SWCNTs to chemical gases, various approaches have been used for functionalizing SWCNTs by polymers [27], enzymes [28] and metallic clusters [29].
In recent years, flexible sensors have been extensively used for direct attachment to the body skin for wearable smart and portable consumer device applications [30], [31]. Flexible sensors can be adopted for a wide range of applications due to their light weight, low cost, and mechanical flexibility [32], [33], [34]. Excellent mechanical properties of CNTs render them as prominent candidates for flexible devices. Recent studies show that CNTs can be easily assembled on flexible substrates using spray and plasma treatments [35]. Therefore, flexible sensors with CNTs are very promising for gas sensing application [36], [37], [38]. In this study, we present relatively fast and flexible sensors, employing SWCNTs decorated with Cu NPs for the detection of H2S. SWCNTs-based sensors are fabricated on a polyethylene terephthalate (PET) substrate which has a high degree of flexibility and transparency.
Section snippets
Materials and methods
SWCNTs (with outer diameters of ∼1–2 nm, lengths of ∼30 μm, purity 90%, supplied by Parsis Co. Iran) are used as building blocks of the sensitive film. SWCNTs sidewalls are functionalized by carboxyl groups using acid treatment process: 50 mg of pristine SWCNTs are dispersed in a solution of H2SO4:HNO3 (1:3) followed by sonication at 60 °C for 2 h. This process leads to the formation of active sites that are negatively charged which in turn facilitate chemical bonds. Functionalized SWCNTs (F-SWCNTs)
Structural study and EDS analysis
Fabricated devices on a PET substrate are shown in Fig. 2a. The photograph clearly shows that the substrate with Al electrodes can be easily bent. The electrode fingers have a height of 5000 μm and a gap size of 200 μm. Spin coated thin films of Cu-SWCNTs show strong adherence on the substrate. As shown in Fig. 2b pristine SWCNTs are dispersed as bare bundles and Fig. 2c illustrates that SWCNT bundles are successfully decorated with Cu NPs. The dense decoration of Cu NPs on the sidewalls of
Conclusion
We have successfully demonstrated that Cu-SWCNTs-based sensors exhibit enhanced response upon exposure to various concentrations of H2S gas from 5 ppm to 150 ppm. A fast response time and a recovery time of 10 s and 15 s, respectively, have been achieved for 5 ppm of the target gas. The fabricated sensors show a high selectivity for 20 ppm H2S, whereas the concentrations of interfering gases were set to 200 ppm. The flexible sensors exhibit fast, stable, and reproducible responses at room temperature
Acknowledgments
Authors acknowledge the technical discussion of the Prof. Mahdi Heidari Sani from Sharif University of Technology. Author would like to give special thanks to Mr. Hamed Farani from University of Tehran for Raman spectroscopy in preparing discussion section exhaustively.
Mohsen Asad is a PhD candidate and research assistant at Semiconductor Device Research Center, School of Electrical and Computer Engineering, Shiraz University, Iran. He has published over 17 articles in journals and conference papers and hold four patents in the field of chemical sensors. His research interests include fabrication of prototype devices based on quantum and semiconductor science considering functional materials (1D and 2D based systems) in chemical and biological sensors.
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Mohsen Asad is a PhD candidate and research assistant at Semiconductor Device Research Center, School of Electrical and Computer Engineering, Shiraz University, Iran. He has published over 17 articles in journals and conference papers and hold four patents in the field of chemical sensors. His research interests include fabrication of prototype devices based on quantum and semiconductor science considering functional materials (1D and 2D based systems) in chemical and biological sensors.
Mohammad Hossein Sheikhi received his BSc (1994) degree in electrical engineering from Shiraz University, Shiraz, Iran, the MSc (1996) degree from Sharif University of Technology, Tehran, Iran and the PhD degree in electrical engineering from Tarbiat Modarres University, Tehran in 2000. He was selected as the distinguished PhD student graduated from Tarbiat Modarres University in 2000. He joined Tohokou University, Sendai, Japan, as a Research Scientist in 2000. After joining Shiraz University in 2001, he focused on the optoelectronics, nanosensors, and nanotransistors. He is currently the Associate Professor and founder of Semiconductor Device Research Center, Shiraz University, Shiraz, Iran.
Mahdi Pourfath was born in Tehran, Iran, in 1978. He received the BS and MS degrees in electrical engineering from Sharif University of Technology, Tehran, in 2000 and 2002, respectively, and the PhD degree in Microelectronics from the Technische Universität Wien, Austria, in 2007. He has authored or co-authored over 100 scientific publications and presentations and authored one monograph. He is now an Assistant Professor in the School of Electrical and Computer Engineering, University of Tehran. He is also with the institute of Microelectronics, Technische Universität Wien, Austria. His scientific interests include novel nanoelectronic devices and materials.
Mahmood Moradi received his BSc degree (1977) in Physics from Isfahan University, the MSc (1981) from Shiraz University and the PhD (1989) in condensed matter Physics from Kent University in England. Now he is professor in Physics Department in Shiraz University and working on density functional theory, nanostructures, spintronics and liquid crystals. He has published more than 55 papers in international journals and held more than 100 presentations in national and international conferences.