H2S sensing characteristics of Pt-doped α-Fe2O3 thick film sensors

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Abstract

α-Fe2O3 nanoparticles doped with different amounts of Pt were synthesized by chemical coprecipitation and characterized by X-ray diffraction (XRD), transmission electron micrograph (TEM) and X-ray photoelectron spectrometer (XPS). The gas sensing properties of the thick film sensors prepared by Pt-doped α-Fe2O3 nanoparticles were investigated and compared with those of undoped α-Fe2O3 sensors. Obtained results indicated that the Pt-doped α-Fe2O3 sensors presented much higher response, better selectivity and rather low optimum operating temperature to H2S than the undoped α-Fe2O3 sensors. The sensor of 2 wt% Pt/α-Fe2O3 still showed excellent response towards very low concentration H2S (10 ppm). The sensing mechanism of the Pt/α-Fe2O3 sensor to H2S was also discussed.

Introduction

Hydrogen sulfide (H2S) is a toxic and malodorous gas as main sources from gasoline, natural gases and city sewage. It is badly harmful to human body and the environment. According to the safety standards established by American Conference of Government Industrial Hygienists, the threshold limit value (TLV) defined for H2S is 10 ppm. Meanwhile, the type of oil or natural gas is correlative with the concentration of H2S. The oil or natural gases mines can be found depending on the concentration of H2S. Therefore, the detection and monitoring of H2S are of high importance for both resource exploitation and human health. In the recent researches, a number of semiconductor sensors have been found to be sensitive to H2S, including SnO2, WO3, In2O3, ZnO2, and a few perovskite-type materials like NdFeO3 and NiFeO4 [1], [2], [3], [4], [5], [6], [7], [8], [9]. Recently, Sun et al. have found that α-Fe2O3 exhibited is sensitive to H2S based on the catalytic chemiluminescence at 360 °C [10], [11]. However, the application of these sensors is limited by some disadvantages, for instance, poor selectivity, long response time, high operating temperature or the limited detection range. As a consequence, a new sort of H2S sensor, which can satisfy the requirement for application, must be searched.

α-Fe2O3 is an n-type semiconductor oxide and has been widely used as gas sensors. However, most of the researches on α-Fe2O3 sensors were focused on the sensing properties towards alcohol, and the sensing characteristics of Pt-doped α-Fe2O3 sensors to H2S have not been reported until now. In this paper, the crystallographic characteristics of undoped and Pt-doped α-Fe2O3 and their gas sensing performance to H2S are investigated. The sensing mechanism of them is also discussed.

Section snippets

Experimental

Pt/α-Fe2O3 powders were prepared by a coprecipitation method. A small quantity of polyglycol was added to the an aqueous solution of H2PtCl6·6H2O and Fe(NO3)3·9H2O. The aqueous mixture was then added dropwise to an aqueous solution of Na2CO3 under vigorous stirring at 80 °C. The pH of the solution was adjusted by a diluted Na2CO3 aqueous solution in the reaction process. After stirring for 1 h, a solid precipitate was formed and kept digesting overnight at room temperature. Then the precipitate

Structure characterization

Fig. 2 shows the XRD pattern of α-Fe2O3 doped with 2 wt% Pt additions. The diffraction pattern of α-Fe2O3 (2 wt% Pt) matched perfectly with the standard α-Fe2O3 reflections (JCPDS No. 33-664). However, no obvious Pt peaks were observed, which may be due to high dispersion of Pt particles. The sharp peaks suggest that the crystalline of α-Fe2O3 is perfect. The mean size of the crystalline is around 25 nm, calculated by the Deby–Scherrer equation.

TEM images of 2 wt% Pt/α-Fe2O3 are shown in Fig. 3.

Conclusions

In summary, Pt-doped α-Fe2O3 thick film sensors can be prepared by a chemical coprecipitation method. The dopant is highly dispersed on the surface of α-Fe2O3 nanoparticles in the form of PtO2. The Pt-dopping has led to a remarkable increase in response to H2S and a decrease in optimum operating temperature. Among all the tested sensors, the sensor based on 2 wt% Pt/α-Fe2O3 exhibits the largest response to H2S at 160 °C, and can detect low concentration H2S (10 ppm). A possible H2S gas sensing

Acknowledgement

We gratefully appreciate the financial support of the 973 program of China (No. 2005Cb623607).

Yan Wang is studying in Shihua Wu's group for her PhD degree in department of chemistry, Nankai University in China. Her research focuses on the synthesis, characterization and gas-sensing properties of metal oxide nanomaterials.

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Yan Wang is studying in Shihua Wu's group for her PhD degree in department of chemistry, Nankai University in China. Her research focuses on the synthesis, characterization and gas-sensing properties of metal oxide nanomaterials.

Shurong Wang is working at Nankai University. She received her MS degree in chemistry from Nankai University in 2004. Her research covers nanomaterials, catalysis and gas sensors.

Yingqiang Zhao received his Bachelor degree in chemistry from Tianjin Normal University in 2004. He is currently a postgraduate in the department of chemistry in Nankai University. His research is focused on the development and application of gas-sensitive materials.

Baolin Zhu received her PhD degree in chemistry from Nankai University in 2006. Now, she is working at Nankai University. Her research is focused on the preparation of nanomaterials.

Fanhong Kong is a graduate student in department of chemistry, Nankai University now. Her interest is devoted to the preparation and application of gas-sensitive materials.

Da Wang is an undergraduate student in department of chemistry, Nankai University now.

Shihua Wu received his degree in chemistry from Nankai University in 1970. At present, he is Professor of chemistry at the Department of Nankai University, where he has been working for many years in the field of preparation, characterization and catalytic and gas-sensing properties of metal oxides nanomaterials.

Weiping Huang is a professor of Chemistry Department at Nankai University. His researches are focused on the preparation and catalytic properties of nanomaterials.

Shoumin Zhang is an associate professor of chemistry in Nankai University. He received his PhD from Nankai University in 1999. His current research fields are inorganic chemistry and materials.

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