Preparation, Characterization and Oxygen Gas Sensitivity of Nanosolid Superacid SO42-/ LaCoFeO4
Metal oxides have been applied in gas sensor technology while suffering poor sensitivity and high working temperature. In this work, a novel method has been adopted to improve these problems of the sensors. A mixture of Fe3+, La3+, Co2+ (Fe3+: La3+: Co2+ =10:3:1) and dispersing agent in water solution was precipitated by adding NH4+(pH=9) under agitation. The precipitate was filtered, washed and drying, then immersed with 0.5M (NH4)2SO4 in 12hr. Superacid SO42-/ LaCoFeO4 was prepared after calcined at 673K for 1h. The thick film units for oxygen sensor were dintered at 673K for 3h.The structure of this catalyst has been characterized by means of powder X-ray diffraction (XRD), transmission electron microscope (TEM), IR, X-ray photoelectron spectroscopy (XPS) and specific surface area measurements. The result indicated that the SO42-/ LaCoFeO4 grain sizes (10nm) were smaller and the specific surface area (126M2/g ) was higher than the pure metal oxide LaCoFeO4. The acid strength was measured by the model reaction of ethyl acetate synthesis and attributed as superacid. In addition, the SO42- was combined with metal ions in a bidentate fashion. The binding energy of SO42-/ LaCoFeO4 was larger than that of LaCoFeO4. The sensitivity as well as the working temperature is improved by comparison with the pure LaCoFeO4 phase. The relationship between the oxygen sensing properties and structure has also been discussed.
D. J. Lin et al., "Preparation, Characterization and Oxygen Gas Sensitivity of Nanosolid Superacid SO42-/ LaCoFeO4", Materials Science Forum, Vol. 694, pp. 209-213, 2011