Air quality prediction by using semiconducting gas sensor with newly fabricated SmFeO3 film
Introduction
The perovskite-type LnMO3 oxides having lanthanoids (Ln) and tri-valent cations (M) are one of the most applicable materials for catalysis [1], electrodes and solid electrolytes of fuel cells [2], [3], and gas sensors [4], [5], [6], [7], [8], [9], [10], [11], etc. Although the solid-state reaction of Ln2O3 and M2O3 single oxides is the most conventional method for the preparation of these heterometallic oxides, this method is very difficult to control the powder quality and particle size. The synthesis using chemical processing methods such as co-precipitation method, sol–gel method, and glycothermal method is performed at considerably lower temperatures than that through solid-state reaction methods, and finer perovskite-type products are obtainable [12]. As a new chemical method, we have been investigating the preparation of the perovskite-type oxides having homogeneous and finer particles in size by the thermal decomposition of the appropriate heteronuclear complexes containing Ln:M=1:1 ratio such as hexacyano and organic complexes [13], [14], [15], [16], [17], [18]. The perovskite-type materials have been applied for NO2 gas sensor, because a number of perovskite-type oxides prepared in air show p-type semiconducting properties, and their conductivity increases with the adsorption of oxidizing gases [19], [20], [21], [22]. In our previous studies, we reported that the SmFeO3 thick films prepared by the thermal decomposition of Sm[Fe(CN)6]·nH2O showed higher NO2 sensing property compared with that of the solid-state reaction method [23]. It was observed that SmFeO3 had the high gas sensitivity in LnFeO3 (Ln=La∼Yb) and similar tendencies were also reported by Sugiyama et al. [21]. The highest sensitivity for NO2 observed for SmFeO3 was mainly attributed to the divalency of Sm3+ in SmFeO3 and a higher surface coverage of Sm ion [24]. For a practical use, it should be examined the cross sensitivity of some volatile organic compounds (VOCs).
The contamination with oxidative gases and VOCs in air becomes serious problem for human life. Commercially available gas sensor basing SnO2 sensing materials with n-type semiconducting behavior is sensitive to NO2 and also VOCs. In this case, the conductance is increased with VOCs and decreased with NO2. Under the mixture of VOC and NO2, it suggests that the output signal shows the same levels of pure air quality, although the contaminated levels were different in the respect to the NO2 and VOC levels. Use of plural gas sensors, electronic nose sensor is useful to predict an air quality [25], [26], [27].
In this study, we examined the gas sensing characteristics of the developed SmFeO3-based gas sensor for an application to air quality interpretations.
Section snippets
Preparation of SmFeO3 sensor
The Sm[Fe(CN)6]·nH2O heteronuclear complexes were synthesized by mixing aqueous solutions of equimolar amounts of Sm(NO3)3·6H2O and K3Fe(CN)6 with continuous stirring. The resulting precipitate was washed with water, ethanol and diethyl ether, before drying in air at 323 K. The SmFeO3 oxide powders were prepared by the thermal decomposition of the complex at 1173 K for 1 h. An X-ray diffraction (XRD, Model Rint 2000, Rigaku Corporation, using a Cu Kα radiation) analysis was used to confirm the
Characterizations of SmFeO3 film with XRD and XPS
Powders prepared by the thermal decomposition of heteronuclear complexes at various temperatures in air were examined by XRD as shown in Fig. 1. A single phase of perovskite-type oxide was obtained by the heating at 973 K. Particle size of the products was increased with the heat treatment temperature, since the full-width-at-half-maximum (FWHM) of XRD peak decreases with an increase in the temperature. The gas sensing characteristics were examined at 573 and 623 K. To prevent the growth of the
Conclusions
The contamination with oxidative gases and VOCs in air becomes serious problem for human life. The conductance changes of SmFeO3-based sensor and TGS2600 with VOCs and NO2 in air were examined. The use of one semiconducting gas sensor at a certain working temperature is poor to detect a level of contaminated air’s quality. For TGS2600, distinction of the contaminated levels with VOCs becomes difficult when NO2 levels were changed and also vice versa. The sensitivity for VOCs of TGS2600 is
Munenobu Tomoda received his ME in Department of Materials Science and Engineering from Ehime University in 2003.
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2018, Sensors and Actuators, B: ChemicalCitation Excerpt :Research has also been carried out on perovskite-type oxides as gas sensor materials [12–17], due to the high thermal stability, catalytic activity and semiconducting behavior of the perovskite structure. Detection of NO2 using perovskite-type oxides has also been reported [18–23]. In particular, SmFeO3 has shown the highest NO2 sensing response among perovskite-structured LnFeO3 (Ln = La- Yb) compounds [24].
Munenobu Tomoda received his ME in Department of Materials Science and Engineering from Ehime University in 2003.
Satoshi Okano received his BE in Department of Materials Science and Engineering from Ehime University in 2003. He is an academic staff in Ehime University.
Yoshiteru Itagaki received his BE in Department of Applied Chemistry in 1993 and his ME in 1995 in Graduate School of Engineering, Hiroshima University. He obtained a Dr. Eng. from Hiroshima University in 1998. He was at Linköping University in Sweden as a post-doctor from 1998 to 2000. Then, he was assistant researcher in Hiroshima University from 2000 to 2002 and researcher in Kinki University in 2002. He is research associate in Ehime University since 2003. His main interests are functional materials and materials chemistry.
Hiromichi Aono received his BE in Industrial Chemistry from Ehime University in 1986. He was on the Faculty in the Department of Industrial Chemistry at Niihama National College of Technology from 1986 to 1996. He obtained a Dr. Eng. from Osaka University in 1994. He has been on the Faculty in Department of Materials Science and Engineering at Ehime University since 1996. He is associate professor since 2001. His main interests are the solid-state chemistry and its applications.
Yoshihiko Sadaoka received his ME in Industrial Chemistry from Ehime University in 1971. He has been on the Faculty of engineering at Ehime University since 1971. He obtained a Dr. Eng. from Kyusyu University in 1979. He is professor at Department of Materials Science and Engineering since 1996. His main interests are inorganic and organic functional materials for chemical sensor and green materials.