Synthesis and characterization of Pd-doped α-Fe2O3 H2S sensor with low power consumption

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Abstract

Pd-doped α-Fe2O3 nanoparticles were synthesized by chemical coprecipitation method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The gas sensing properties of undoped and Pd-doped α-Fe2O3 sensors were investigated. Compared with the undoped one, the doped sensors exhibited higher response, better selectivity, and faster response/recovery to H2S. The operating temperature of α-Fe2O3 to H2S is decreased after the addition of Pd, which result in the relative low power consumption in H2S detection. Among all the doped sensors, the sensor of 1.5 wt% Pd/α-Fe2O3 showed the largest response (128.3) to 100 ppm H2S at 160 °C.

Introduction

The increasing concern on environmental protection and human health has generated great interests in efficient gas detection [1], [2], [3]. α-Fe2O3 is an n-type metal oxide semiconductor, and has been used as gas sensing material since the 1980s of the last century [4], [5]. There have been many reports about good response and selectivity of α-Fe2O3 sensors to combustible gases and organic vapors in recent years, such as ethanol, acetone, gasoline and LPG, etc. [6], [7], while their gas sensing properties to H2S have been seldom reported until now. Recently, Zhang et al. found that α-Fe2O3 exhibited sensitivity to H2S based on the catalytic chemiluminescence at 360 °C [8]. Wang et al. reported the α-Fe2O3 sensors synthesized by microwave hydrolysis had a high sensitivity at 300 °C [9]. However, their application is limited by the high operating temperature. As a consequence, it is important to design new type of low power consumption H2S sensor.

Noble metal doping is an effective approach to improve the gas sensing properties of sensors. For instance, Kobayashi et al. developed CO sensor based on Au-doped α-Fe2O3 [10]. Shen et al. found that the response of α-Fe2O3 sensor to CO was greatly improved after it was doped with PdO [11]. In this paper, Pd-doped α-Fe2O3 nanoparticles were prepared by coprecipitation method. The gas sensing properties of the sensors were also investigated.

Section snippets

Experimental

All the reagents are of analytical grade and used as purchased.

Pd/α-Fe2O3 powders were prepared by a coprecipitation method [12]. A small quantity of polyglycol was added to an aqueous solution of PdCl2 (0.25, 0.5, 1.0, 1.5, 2.0 and 3.0 wt%) 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 diluted Na2CO3 aqueous solution in the reaction process. After stirring for 1 h, a solid

Material characterization

Fig. 3 shows the XRD pattern of α-Fe2O3 doped with 1.5 wt% Pd additions. The diffraction pattern of α-Fe2O3 (1.5 wt% Pd) matched perfectly with the standard α-Fe2O3 reflections (JCPDS No. 33-664). However, no obvious Pd peaks was observed, which may be due to high dispersion of Pd particles. The sharp peaks suggest that the crystal of α-Fe2O3 is perfect. The mean size of the crystals is around 40 nm, calculated by the Deby–Scherrer equation.

TEM image of 1.5 wt% Pd/α-Fe2O3 is shown in Fig. 4. It can

Conclusions

In summary, the Pd-doped α-Fe2O3 sensors have been prepared by chemical coprecipitation method. Compared with the undoped one, the doped sensors present much higher sensitivity, better selectivity and rather lower optimum operating temperature to H2S than the undoped one. The optimum doping amount is 1.5 wt% and the optimum operating temperature is 160 °C. The doped sensors also present long-term stability and short response/recovery time. Obtained results indicate that the Pd-doped α-Fe2O3

Acknowledgement

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

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