Low temperature acetylene gas sensor based on Ag nanoparticles-loaded ZnO-reduced graphene oxide hybrid
Introduction
Acetylene (C2H2) is a colorless, flammable unsaturated hydrocarbon gas with a distinctive odor, widely used as a fuel in oxyacetylene welding and cutting of metals, and as a raw material in various industrial and consumer products, such as acetaldehyde, synthetic rubber, paints, fabric and floor coverings, dry-cleaning solvents, and insecticide sprays. Generally, acetylene is not toxic, but when generated from calcium carbide, can contain toxic impurities such as traces of phosphine and arsine. Notable hazards are associated with its intrinsic instability, especially when it is liquefied, pressurized, heated or mixed with air. Consequently, the combustion of acetylene can produce a large amount of heat (its highest flame temperature is about 3300 °C), and it can explode with extreme violence if the absolute pressure of the gas exceeds 103 kPa (15 psi). Therefore, for environmental and safety purposes, the development of a highly effective C2H2 sensor has become increasingly important to meet the demands of accurate environmental monitoring, for early leakage warning and for avoiding incomplete combustion. However, information on C2H2 sensors is still very limited in the literature.
Most recently, Wang et al. [1] showed successful advancement in C2H2 sensing with a response of 17 (for 2000 ppm) at 250 °C by synthesizing nickel-doped zinc oxide (ZnO) nanofibers. Tamaekong et al. [2] reported a Pt/ZnO thick film-based C2H2 sensor at a working temperature of 300 °C with a sensor response of 43 (for 1000 ppm). Zhang et al. [3] hydrothermally synthesized a hierarchical nanoparticle (NP)-decorated ZnO microdisk-based C2H2 sensor with a large detection range (1–4000 ppm) and very high response (7.9 for 1 ppm) at 420 °C. Dong et al. [4] reported arc plasma-assisted Ag/ZnO composites for C2H2 sensing, which had a maximum response of 42–5000 ppm C2H2 at 120 °C. In addition, SnO2 NPs [5], Pd–SnO2 [6], Sm2O3–SnO2 [7], Au/MWCNT [8], Ag/Pd–SiO2 [9], etc, have been studied for C2H2 sensing. However, high working temperature, low sensitivity and synthesis-process complexity, are still a great challenge.
In the last few years, among widely investigated metal oxide groups, ZnO has attracted considerable interest in sensing applications to detect volatile and toxic gases due to its high conductive electron mobility and good adsorption characteristics under the working conditions of the sensors [10], [11], [12], [13], [14], [15]. However, drawbacks like low sensitivity, poor selectivity and high working temperature limit practical applications in the gas-sensing area (i.e., flammable and explosive environments). Therefore, to overcome the shortcomings and to enhance sensing characteristics, researchers have been focusing on metal oxide–metal oxide and metal–metal oxide compositions with numerous synthesis techniques [16], [17], [18], [19], [20].
Interestingly, inherent catalytic properties of metal aggregates, dispersed into a metal oxide matrix, modify the surface reactions and greatly enhance the charge carrier separation of the oxide matrix. This phenomenon helps to boost the sensing mechanism, and hence improve sensing performance [21]. Among numerous metals, Ag has attracted immense interest, due to its promising catalytic properties, in the development of photocatalysis [22], [23], catalytic oxidation [24], chemical and gas sensing [25], [26], etc. A number of Ag–ZnO nanostructure-based high-performance gas sensors have been reported [25], [27], [28], [29], [30]. Moreover, two-dimensional graphene has concerned much attention since its discovery due to its excellent electrical, chemical and optical properties. Most recently, Fowler et al. [31] discussed chemically derived graphene as a highly sensitive chemical sensor due to its extraordinary carrier mobility. Besides the synergistic interplay between graphene and metal–metal oxide composition, graphene as a template plays a vital role in enhancing the physical properties and sensing performance of the composite materials [19], [32], [33], [34].
In this context, this paper is focused on the fabrication of a C2H2 sensor based on an Ag-loaded ZnO-reduced graphene oxide (Gr) hybrid via a facile chemical route in order to enhance C2H2 sensing performance at low operating temperatures. To the best of our knowledge, an Ag-loaded ZnO–Gr hybrid nanostructure-based acetylene gas sensor has not yet been reported in the literature. The fabricated sensor was evaluated systematically in terms of response, response/recovery times and selectivity toward C2H2. The humidity effect on the fabricated sensor was also studied in this work. The main aim of this work is to fabricate an effective, high-performance C2H2 sensor that can operate at low temperature.
Section snippets
Synthesis and characterization
All the chemicals used in the experiment were of analytical grade and obtained from Sigma Aldrich, Dongwoo Fine-Chem., and Dae Jung Chem. & Inds. Co. Ltd. Graphene oxide (GO) was prepared according to the process provided by Hummers and Offeman, and Phan et al. [35], [36]. ZnO powder was prepared through a solvothermal method using 4 M of Zn(NO3)2·6H2O and 8 M of sodium hydroxide (NaOH) in ethanol, at 120 °C for 8 h and dried at 60 °C. The Ag-loaded ZnO–Gr hybrid was synthesized via a chemical
Crystal structure and morphology
The observed XRD patterns of pure ZnO, and 0–5 wt% Ag-loaded ZnO–Gr hybrids are displayed in Fig. 2. The characteristic diffraction peaks of the as-synthesized materials exhibited a well-structured crystalline nature and mixed phases of Gr and ZnO (Fig. 2(b)), and silver, Gr, and ZnO (Fig. 2(c–e)), respectively. Fig. 2a shows the diffraction peaks of pure ZnO. The diffraction peaks of ZnO (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), and (1 1 2) were endowed with a harmonious standard ZnO hexagonal
Conclusions
In summary, acetylene gas sensing characteristics of an Ag nanoparticle-embedded ZnO–Gr hybrid were studied. The characterizations of the as-synthesized sensing material indicated a homogeneously distributed and closely affixed Ag–ZnO mixer on the surface of reduced graphene oxide. At optimum conditions (150 °C, 3 wt% Ag-loaded ZnO–Gr), the as-synthesized hybrid had an enhanced C2H2 sensing property compared with individual counterparts. The hybrid showed a high response of 21.2 (100 ppm C2H2) at
Acknowledgments
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by 2014 the Ministry of Science, ICT and future Planning (NRF-2014R1A2A2A01002668).
A.S.M. Iftekhar Uddin received his B.Sc. Eng. from the Faculty of Engineering, International Islamic University Chittagong, Chittagong, Bangladesh, in 2005. He joined as lecturer in Sylhet International University, Sylhet, Bangladesh, in 2006 and promoted as Assistant professor in 2010. He is now working as a Ph.D. candidature in the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea. His research interests include ZnO and graphene based nanosensors and flexible
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A.S.M. Iftekhar Uddin received his B.Sc. Eng. from the Faculty of Engineering, International Islamic University Chittagong, Chittagong, Bangladesh, in 2005. He joined as lecturer in Sylhet International University, Sylhet, Bangladesh, in 2006 and promoted as Assistant professor in 2010. He is now working as a Ph.D. candidature in the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea. His research interests include ZnO and graphene based nanosensors and flexible nanosensors.
Duy-Thach Phan received his B.E. from the School of Electrical Engineering, Hochiminh University of Technology, Ho Chi Minh, Vietnam, in 2008, and M.E. from the School of Electrical Engineering, Ulsan University, Ulsan, South Korea, in 2010. He is now working as a Ph.D. candidate in the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea. His research interests include SiC, ZnO, AlN based on SAW sensors, graphene-based sensors, and FEM and atomistic scale modeling.
Gwiy-Sang Chung received his B.E. and M.E. Degrees in Electronic Engineering from Yeungman University, Kyongsan, South Korea, in 1983 and 1985, respectively, and his Ph.D. Degree from Toyohashi University of Technology, Toyohashi, Japan, in 1992. He joined the Electronics and Telecommunications Research Institute (ETRI), Daejon, South Korea, in 1992, where he worked on Si-on-insulator materials and devices. Moreover, he also worked as a visiting scholar at UC Berkeley and Stanford University, CA, USA, in 2004 and 2009, respectively. He is now a professor in the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea. His research interests include Si, SiC, ZnO, AlN-M/NEMS, flexible self-powered wireless sensors nodes, energy harvesting, and graphene-based composites. He is the author or co-author of more than 125 scientific and technical SCI international journal papers.