Elsevier

Sensors and Actuators B: Chemical

Volume 209, 31 March 2015, Pages 889-897
Sensors and Actuators B: Chemical

Hydrothermal synthesis of ternary α-Fe2O3–ZnO–Au nanocomposites with high gas-sensing performance

https://doi.org/10.1016/j.snb.2014.12.065Get rights and content

Highlights

  • This study reports for the first time the synthesis of ternary α-Fe2O3–ZnO–Au nanocomposites.

  • The ternary nanocomposites showed better sensing performance than binary iron oxide composites.

  • This study proposes the possible mechanism for the of ternary α-Fe2O3–ZnO–Au nanocomposites.

Abstract

This study reports facile hydrothermal strategies for the synthesis of novel ternary α-Fe2O3–ZnO–Au nanocomposites under mild conditions, through further surface coating of ZnO and Au nanoparticles (NPs) on α-Fe2O3 nanorods. The ternary α-Fe2O3–ZnO–Au nanocomposites are found to show (1) higher sensitivity/responses (S) of 113 and 57 toward 100-ppm n-butanol and acetone, respectively compared to single α-Fe2O3 (S = 11.7, 9.1 for n-butanol, acetone) and binary α-Fe2O3-ZnO (S = 54.4, 28 for n-butanol, acetone) sensing materials, and (2) lower optimum operating temperature, i.e., 225 °C. The enhanced sensitivity could be attributed to the chemical sensitization effect induced by the Au NPs, and the existence of conjugated depletion layers in the nanocomposites which promote a greater drop in resistance upon exposure to the gas. These results will be useful for future design of iron oxide-based ternary nanocomposites as gas-sensing materials with high sensitivity, selectivity and stability.

Introduction

Semiconductor gas sensors have found many applications in the monitoring of toxic and flammable gases, because of their unique physicochemical properties and high stability [1]. Numerous efforts have been carried out to overcome the limitations of metal oxide gas sensors by improving the ‘3S’: sensitivity (response), selectivity, and stability. The “3S” properties of metal oxides are heavily dependent on shape, size, structure and surface area to volume ratio [2]. To improve the “3S”, the combination of two or more metal oxides to form nanocomposite(s) by integrating physicochemical properties of individual one into a single system is necessary [3].

Among the semiconductors, hematite (α-Fe2O3), as an n-type semiconductor with a narrow band-gap (Eg) of 2.2 eV has been widely studied due to their potential applications in gas sensors [4], [5], [6], [7], batteries [8], [9], catalysis [10], [11], and environmental remediation [12], [13]. They exhibit several unique features which may be beneficial in gas-sensing applications such as low cost, high thermal/chemical stability, high-temperature corrosion resistance and easily controlled morphology [14]. However, pure iron oxide sensors usually suffer from limitations of showing either low responses or high optimum operating temperatures (>250 °C) [15], [16]. To solve these problems, a number of α-Fe2O3-based nanocomposites have been investigated, such as α-Fe2O3@ZnO [3], α-Fe2O3@SnO2 [17], α-Fe2O3-TiO2 [18], [19], α-Fe2O3@SnO2 [20] and α-Fe2O3-CeO2 [21]. Alternatively, noble metals (Ag [22], Au [23], and Pt [14]) have also been used to decorate the surface of pure iron oxides or their binary oxides to achieve high gas-sensing performance. Despite some efforts, there have been very few reports on the synthesis of iron oxide-based ternary nanocomposites for gas sensing, along with limitation in understanding of their sensing mechanisms.

In this study, we report facile and efficient strategies for the preparation of novel ternary α-Fe2O3–ZnO–Au nanocomposites by using α-Fe2O3 nanorods as the starting materials. The morphology and composition of the ternary nanocomposites will be characterized. The gas-sensing performance of such ternary nanocomposites toward two volatile organic gases, i.e., acetone and n-butanol, will be tested and compared with pure α-Fe2O3 and binary α-Fe2O3-ZnO and α-Fe2O3-Au nanocomposites will also be evaluated. Finally, the gas sensing mechanisms of the as-prepared α-Fe2O3–ZnO–Au nanocomposites will be discussed. The results are expected to be useful for design and construction of more ternary nanostructures with desired functional properties or applications.

Section snippets

Chemicals

Ferric chloride hexahydrate (FeCl3·6H2O, 97%), zinc sulphate heptahydrate (ZnSO4·7H2O, 99.9%), gold(III) chloride trihydrate (HAuCl4·3H2O, 98%), sodium borohydride (NaBH4, 99%), urea (CO(NH2)2, 99%), ethanol (C2H6O, 95%), acetone (C3H6O, 99%), n-butanol (C4H10, 99%) were purchased from Sigma–Aldrich and used as received without further purification. Ultra-pure water was used in all the synthesis processes.

Synthesis of α-Fe2O3–ZnO–Au nanocomposites

Porous α-Fe2O3 nanorods and ZnO modified α-Fe2O3 nanorods were synthesized using a

Morphology and composition

The ternary α-Fe2O3–ZnO–Au nanocomposites were achieved using a three-step method as schematically shown in Fig. 1. Porous α-Fe2O3 nanorods achieved by the calcination of β-FeOOH nanorods were used as a template to deposit ZnO NPs by using a solvothermal method. Finally, an in situ reduction of HAuCl4 was carried out to decorate Au NPs on the surfaces of the deposited ZnO NPs as well as on the inner and outer parts of the α-Fe2O3 nanorods. Fig. 2 displays the XRD patterns of the as-prepared α-Fe

Conclusions

This work has demonstrated the development of novel ternary α-Fe2O3–ZnO–Au nanocomposites through a facile and effective hydrothermal method under mild conditions for achieving high gas-sensing performance. The proposed method is advantageous because of its relatively simple procedures and the lack of need for high-temperature calcination to achieve pure α-Fe2O3 and ZnO phases. The surface decorated Au NPs (2–5 nm) can highly enhance their performance in gas sensing. This is evidenced by the

Acknowledgements

We gratefully acknowledge the financial support of the Australian Research Council (ARC) projects. The authors also acknowledge access to the UNSW node of the Australian Microscopy and Microanalysis Research Facilities (AMMRF).

Dr. Yusuf Valentino Kaneti has obtained his PhD degree in 2014 from the University of New South Wales (UNSW), Australia. He is currently a postdoctoral fellow in the School of Materials Science & Engineering at UNSW, focusing on the synthesis and characterization of semiconductor metal oxide nanostructures for photocatalysts and gas sensors.

References (34)

  • M.E. Franke et al.

    Metal and metal oxide nanoparticles in chemiresistors: does the nanoscale matter?

    Small

    (2006)
  • C. Wang et al.

    Metal oxide gas sensors: sensitivity and influencing factors

    Sensors

    (2010)
  • J. Zhang et al.

    Synthesis and gas sensing properties of α-Fe2O3@ZnO core–shell nanospindles

    Nanotechnology

    (2011)
  • Z. Sun et al.

    A highly efficient chemical sensor material for H2S: α-Fe2O3 nanotubes fabricated using carbon nanotube templates

    Adv. Mater.

    (2005)
  • X. Hu et al.

    α-Fe2O3 nanorings prepared by a microwave-assisted hydrothermal process and their sensing properties

    Adv. Mater.

    (2007)
  • C. Wu et al.

    Synthesis of hematite (α-Fe2O3) nanorods: diameter-size and shape effects on their applications in magnetism, lithium ion battery, and gas sensors

    J. Phys. Chem. B

    (2006)
  • X. Xu et al.

    Spindle-like mesoporous α-Fe2O3 anode material prepared from MOF template for high-rate lithium batteries

    Nano Lett.

    (2012)
  • Cited by (0)

    Dr. Yusuf Valentino Kaneti has obtained his PhD degree in 2014 from the University of New South Wales (UNSW), Australia. He is currently a postdoctoral fellow in the School of Materials Science & Engineering at UNSW, focusing on the synthesis and characterization of semiconductor metal oxide nanostructures for photocatalysts and gas sensors.

    Mr. Julien Moriceau is an honors candidate studying materials science and engineering at the Institute National des Sciences Appliquées de Lyon. His research interest emphasizes on the fabrication of shape-controlled metal oxide nanostructures for gas-sensing applications.

    Mr. Minsu Liu is a PhD candidate studying materials science and engineering at the University of New South Wales (UNSW), Australia. His research interest is on the synthesis of metal oxide (especially for vanadium oxides) nanostructures for energy and environmental applications.

    Ms. Yuan Yuan is a PhD candidate studying materials science and engineering at the University of New South Wales (UNSW), Australia. Her research focuses on the synthesis of shape-controlled noble metal nanostructures for hydrogenation catalysis.

    Dr. Quadir Zakaria is a material research manager in the Electron Microscope Unit (EMU), Analytic Center, and also a lecturer in the school of materials science and engineering at UNSW at UNSW. He has been worked as a research fellow in ARC Center of Excellence for Design in Light Metals and University of Hong Kong. He has published over sixty five peer reviewed research articles in the field of electron microscopy, thermo-mechanical processing, alloy-design, and grain growth. His current H-index is 12 by Scopus.

    A/Prof. Jiang has fully devoted to the study on synthesis, self-assembly and functional applications of nanoparticles since the award of his PhD in 2001. His research focuses on developing new techniques for the synthesis of noble metals, metal oxides and their nanocomposites for energy, environmental and biomedical applications. He has published over 90 papers with SCI citations over 3500 times, leading him to H-index 28.

    Professor Yu specialized in process metallurgy, obtained PhD in 1990 from the University of Wollongong (Australia). Since 1992, he has been with the University of New South Wales. Currently he is a Scientia Professor. His research is mainly in particle science and technology, process and materials engineering. He has published over 700 papers in various international journals and conference proceedings. He is an elected Fellow of the Australian Academy of Technological Sciences and Engineering, and Australian Academy of Science.

    View full text