Fe2O3/ZnO core–shell nanorods for gas sensors

https://doi.org/10.1016/j.snb.2005.11.050Get rights and content

Abstract

Fe2O3/ZnO core/shell nanorods were prepared by a solution phase controlled hydrolysis method, and were characterized by XRD, BET and TEM techniques. The surface area of these core/shell nanorods is higher than that of bulk ZnO sensor materials, and in our experiments, the resultant Fe2O3/ZnO gas sensor exhibited a high response, good stability and a short response/recovery time in the detection of low concentrations of various combustible gases. The response/recovery time was less than 20 s, and the response decreased slightly after 4 months.

Introduction

The increasing concern on the safety in laboratory and industrial activities has generated great interests in fast reliable gas detection. In recent years, zero-dimensional nanoparticles and one-dimensional nanoscale materials, for example, ZnO, SnO2, WO3 and MnO2 nanoparticles and nanorods, have been investigated to fabricate new semiconductor gas sensors [1], [2], [3], [4], due to their fine particle size and large surface area. The gas-sensing mechanism involves the chemisorption of oxygen on the surface of these oxides, followed by charge transfer during the reaction of oxygen with target gas molecules [5], which will cause a resistance change on the surface of the sensor.

Zinc oxide is an important oxide semiconductor for sensing applications to toxic and combustible gases [6], [7], [8], [9], [10], [11], [12]. Generally, ZnO sensors provide a wide variety of advantages, such as low cost, short response time, easy manufacturing, and small size, compared to the traditional analytical instruments. However, its working temperature is rather high, normally at 400–500 °C, and the selective response ability is fairly poor. In recent years, the study on ZnO gas-sensing materials has become one of the major research topics, and the research is focused on improving their preparation method and decreasing their working temperature [13], [14], [15]. In this paper, we report a solution phase controlled hydrolysis method to synthesize Fe2O3/ZnO core/shell nanorods. Compared to other sensor elements, these core/shell nanorods exhibit a high gas sensitivity, short response/recovery time and can work at relatively low temperatures.

Section snippets

Experimental

Fe2O3/ZnO core/shell nanorods were prepared through a hydrolysis process of Zn2+ in the presence of Fe2O3 nanorods. Uniform Fe2O3 nanorods were also prepared through a hydrolysis process of ferric chloride at 80 °C as literature described [16]. Hundred milligram of Fe2O3 nanoshuttles were dispersed in 200 mL deionized water by ultrasonication for more than 30 min. Then 20 mg Zn(Ac)2·6H2O was introduced to the solution, and the suspension was heated in an oil bath at 40 °C under vigorous stirring.

Result and discussion

The obtained core/shell Fe2O3/ZnO nanorods were 30–35 nm in width and 110–150 nm in length, as shown in Fig. 1a. For comparison, the morphology of the original Fe2O3 nanoshuttles is shown in Fig. 1b, which indicates that they were 25–32 nm in width and about 110–150 nm in length. This result indicates that the thickness of the ZnO shell coated on Fe2O3 is about 3 nm. The film thickness of the core/shell Fe2O3/ZnO nanorods coated on an Al2O3 ceremic tube observed by a light section microscope is

Conclusion

The thickness of the ZnO shell coated on the surface of Fe2O3 nanorods was estimated to be about 2–3 nm, which was smaller than that in conventional ZnO-based sensor devices. This Fe2O3/ZnO-based sensor showed higher responses to various combustible gases with a faster response/recovery time less than 20 s. In our experiments, the sensor also showed a good long-term stability. These favorable gas-sensing features make the present Fe2O3/ZnO core/shell nanorods to be particularly attractive as a

Acknowledgements

This work was supported by NSFC (50372030, 20025102, 20151001), the foundation for the author of National Excellent Doctoral Dissertation of PR China and the state key project of fundamental research for nanomaterials and nanostructures (2003CB716901).

S. Si received his Ph.D. degree in inorganic chemistry from Nankai University in 2002. His study focuses on the field of characterization of gas-sensing properties and catalysis of metal oxide materials.

References (19)

There are more references available in the full text version of this article.

Cited by (0)

S. Si received his Ph.D. degree in inorganic chemistry from Nankai University in 2002. His study focuses on the field of characterization of gas-sensing properties and catalysis of metal oxide materials.

C. Li is studying in Y. Li's group for his Ph.D. degree in department of chemistry, Tsinghua University in China since 2003. He has been working in the field of characterization and devices of functional materials.

X. Wang received his Ph.D. in chemistry from Tsinghua University in China in 2004. He has been working in the field of characterization and devices of transition metal oxides.

Q. Peng received his Ph.D. in chemistry from Tsinghua University in China in 2003. He has been working in the field of characterization and devices of transition metal oxides.

Y. Li received his Ph.D. degree in chemistry from Science and Technical University of China in 1998. He is one of leaders of National Center for Nanoscience and Nanotechnology and his researches are on semiconductor and devices of Inorganic materials. His present research interests include material science and surface science, focusing on catalysis and sensitivity of metal oxide deposits.

View full text