Elsevier

Sensors and Actuators B: Chemical

Volume 216, September 2015, Pages 33-40
Sensors and Actuators B: Chemical

Acetylene gas sensing properties of an Ag-loaded hierarchical ZnO nanostructure-decorated reduced graphene oxide hybrid

https://doi.org/10.1016/j.snb.2015.04.028Get rights and content

Highlights

  • Ag NPs-loaded hierarchical ZnO nanostructure-reduced graphene oxide hybrid was synthesized by photochemical method.

  • 5 wt% Ag-loaded hierarchical ZnO nanostructure-reduced graphene oxide hybrid enhanced the acetylene sensing performances.

  • Two dimensional graphene acted as a support catalyst.

  • The fabricated sensor showed good repeatability, fast response and very good selectivity.

  • The sensor response characteristics and response/recovery times in terms of humidity interface were also investigated and explained in details.

Abstract

Acetylene (C2H2) gas sensors were developed by synthesizing an Ag-loaded hierarchical (Hrc) ZnO nanostructure-reduced graphene oxide (Ag/ZnO Hrc-RGO) hybrid using a facile and rapid photochemical method. Morphological characterizations showed the formation of well-dispersed Ag nanoparticles-loaded hierarchical ZnO nanostructures onto the 3- to 5-layer thick RGO sheets. The hierarchical ZnO nanostructures were composed of numerous randomly oriented porous ZnO nanosheets with an average sheet thickness of 6 nm. It was also observed that Ag nanoparticles with an average diameter of 40 nm were closely affixed onto the ZnO nanosheets. Structural analysis revealed good agreement with the standard crystalline phases of ZnO, Ag and RGO. Gas-sensing characteristics of the synthesized materials were carried out in a temperature range of 25–300 °C at different C2H2 gas concentrations. At 200 °C, 5 wt% Ag/ZnO Hrc-RGO hybrid showed a preferable detection of C2H2 with high sensor response (12.3 toward 100 ppm), fast response time (57 s), a limit of detection (LOD) of 3 ppm, good linearity, with excellent reproducibility and selectivity. The fabricated sensor also showed less humidity effect in an open air environment.

Introduction

Increased concern about adverse impacts from the emission of various toxic and flammable pollutants on the environment and human health, increasingly promotes the development of accurate and low-power consuming gas sensors for reliable detection and monitoring of such pollutants. To meet the demand, during the last few decades, metal-oxide semiconductors (MOS)-based gas sensors have been the subject of extensive research and development [1]. With the continued development of various metal oxides, zinc oxide (ZnO) with different nanostructures (such as nanoparticles, nanowires, nanorods, nanofibers, microdisks, flowers, etc.) have become promising candidates for ultrasensitive sensors owing to their simplicity, low cost of preparation, and excellent chemical and thermal stability [2], [3], [4], [5], [6]. It is well established that the performance of such sensors is significantly influenced by the synthesis process and the architecture of the sensing materials. In recent years, great attention has been focused on the fabrication of low-dimensional building blocks into three-dimensional (3D) ordered hierarchical ZnO architectures at the nanoscale level. Such a unique and complex architecture not only provides more opportunities for exploring novel properties, but also promotes sensing behavior with superior performances owing to their ordered crystalline nanostructures, high surface-to-volume ratios, porosity, excellent gas molecule adsorption capabilities, and special physical and chemical properties [7]. However, many suffer from limitations, such as high operating temperature, slow response time, and poor selectivity and reproducibility, making them impractical monitors for area air quality and safety. Therefore, to overcome the sufferings, research attention has been focused on increasing the sensor performance at low temperatures, which is usually realized by the incorporation of noble metals or carbon materials on the surface of the base metal-oxide sensors [8], [9], [10].

It has been reported that the introduction of noble metals can produce some kind of synergistic effect, which influences the material's electronic and chemical distribution favorable to the adsorption of oxygen species, and results high performance in metal-oxide based sensors. Besides, two dimensional (2D) carbon material (graphene) as a support catalyst acts as a bridge inside the sensing materials, which greatly enhances the charge transfer among them. It can also act as an electron acceptor to increase the depletion layer of metal-oxide sensor and helps to boost the sensing performance [10].

Acetylene (C2H2) is an unsaturated, highly toxic and flammable hydrocarbon, widely used as fuel or raw material in many mechanical and chemical industries. In recent years, considerable interest has been focused on the development high-performance C2H2 sensors because of safety reasons. Numerous research results in the literature have reported significant improvements, but limitations like complex synthesis processes, high operating temperatures, detection limits, and selectivity are still the subjects of intensive research.

Recently, our group [11] reported a ZnO nanoparticles (NPs)-reduced graphene oxide (ZnO/RGO) based C2H2 sensor with a high response magnitude of 18.2 (100 ppm), a limit of detection (LOD) of 30 ppm at 250 °C, and a relatively slow response time (100 s). Wang et al. [12] synthesized a 5 at% Ni-doped ZnO nanofiber, and their device showed a maximum response of 17 (2000 ppm) at 250 °C. Tamaekong et al. [13] reported on Pt/ZnO thick films by using the flame spray pyrolysis method with a response of 43 (1000 ppm) and an LOD of 50 ppm at 300 °C. Zhang et al. [14] reported the most enhanced C2H2 sensing properties by synthesizing a hierarchical nanoparticles-decorated ZnO microdisk using a hydrothermal method. Their sensor showed a very high response magnitude of 52 (200 ppm), a large detection range of 1–4000 ppm, and a fast response time (15 s) at high temperature (420 °C). In addition, a few results for SnO2 NPs [15], Pd–SnO2 [16], Sm2O3–SnO2 [17], Au/MWCNT [18], Ag/Pd–SiO2 [19], Ag/ZnO [20], etc., have been reported in the literature with a few improvements. Most recently, our group [21] reported an Ag/ZnO NPs-decorated RGO hybrid synthesized via a chemical method. The fabricated sensor device showed excellent sensing performance, such as a high response of 21.2 (100 ppm), a fast response time (25 s), and excellent selectivity at 150 °C.

In the current work, we presented an Ag-loaded hierarchical (Hrc) ZnO nanostructure-decorated RGO hybrid, synthesized via a facile and rapid photochemical route. In our previous work [21], we investigated the sensing behaviors in a closed chamber, whereas in this work, we studied the sensing behaviors in an open air environment. We hope that our fabricated sensor device will open up additional opportunities to fabricate an efficient and practical C2H2 sensor in the near future.

Section snippets

Synthesis of materials and device fabrication

All the chemicals used in the synthesis process were of analytical grade purchased from Sigma–Aldrich Co. Inc., and were used without further purification.

Structural and morphological studies

Fig. 1 shows the XRD patterns of pure ZnO Hrc, Ag/ZnO Hrc and Ag/ZnO Hrc-RGO hybrid. The observed characteristic diffraction reflections for ZnO(1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2), (2 0 1), (0 0 4) and (2 0 2) are similar to bulk ZnO and corresponding to the wurtzite hexagonal phase of ZnO (JCPDS card No. 36-1451). The characteristic diffraction peaks appeared at 2θ = 36.9° and 44.32° corresponding to the cubic phase Ag(1 1 1) and (2 0 0) planes, respectively (JCPDS card No. 04-0783). An

Conclusions

In summary, an Ag NPs-loaded hierarchical ZnO nanostructures-decorated RGO hybrid was successfully synthesized via a facile, low cost, and rapid photochemical route. The synthesized hybrid was found to be more efficient and effective for the detection of C2H2, compared to the pure hierarchical ZnO nanostructures and Ag NPs-loaded hierarchical ZnO nanostructures at a moderate working temperature (200 °C). The fabricated sensor device showed a maximum sensor response of 32.4 for 1000 ppm (12.3 for

Acknowledgment

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded in 2014 by 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, and M.E. from the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea, in 2015. 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,

References (36)

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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, and M.E. from the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea, in 2015. 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 metal/metal oxide and graphene based nanosensors and flexible nanosensors.

Kwan-Woo Lee received his B.E. and M.E. Degrees in Electrical Engineering from the School of Electrical Engineering, University of Ulsan, Ulsan, South Korea, in 2013 and 2015, respectively. His research interests include Ag/hierarchical ZnO nanostructures-graphene based gas sensors.

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.

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