Sonochemically prepared tin-dioxide based composition for methane sensor
Nandini Das ⁎, Asim K. Halder, Jalaluddin Mondal A. Sen, H.S. Maiti
Electroceramics Division, Central Glass and Ceramic Research Institute, Kolkata 700 032, India
Abstract
Nanosized (3.5–14.0 nm) tin dioxide based powders containing antimony oxide and palladium have been prepared by sonication-assisted simultaneous precipitation. Thick film sensors made with these powders showed good sensitivity towards methane and their resistance values are
optimum for practical applications. This contrasts with the film made with the powders prepared without sonication, which showed higher
resistance in the ambient.
Keywords: Nanosize; SnO2; Sonochemical; Sensor; Methane sensitivity
1. Introduction
Metal oxide based sensors have been widely used for the detection of gases, which include toxic and pollutant gases like CO, H2S, CH4, H2, etc. [1]. Many metal oxides viz. ZnO, TiO2, SnO2, WO3, and Ga2O3 have been examined for gas sensing [2–4]. Amongst them, tin dioxide has been widely used for gas sensing applications. Incidentally, sensors made with nanosized powder showed low operating temperature and high sensitivity [5,6]. Nanosized SnO2 powders have been prepared by different routes [7–13] like vapour deposition, sputtering, sol–gel processing, coprecipitation, spray pyrolysis, etc. Currently, sonochemical technique has emerged as a cheap, simple and alternative route of fine powder preparation [14]. The chemical effects of ultrasound arise out of acoustic cavitation, which is the formation, growth and implosive collapse of bubbles in a liquid [15]. There are two regions of sonochemical reactivity, the inside zone of the collapsing bubble and the interface between the bubble and the liquid. The cavitation can generate a temperature of around 5000 K and a pressure over 1800 kPa [16], which enable many chemical reactions to occur. In this study, nanosized SnO2 based powders containing
antimony and palladium have been prepared by sonicationassisted simultaneous precipitation. The powder composition was selected [17] keeping in view the role of Pd as a catalyst and the role of Sb (an “n” type dopant which goes into solid solution [17] with SnO2) in lowering the sensor resistance within acceptable limit for real life applications. The gas (methane) sensing characteristics of the powders in thick film form were compared with those of the powders prepared without sonication under identical conditions. 2. Materials and methods Batches containing tin dioxide, 0.25% (with respect to tin dioxide) antimony oxide and 10 wt.% palladium were prepared by sonication-assisted simultaneous precipitation technique. In this technique, reagent grade SnCl2·2H2O, Sb2O3 and PdCl2 were used to prepare the composition. In a typical synthesis procedure, SnCl2, Sb2O3, PdCl2, solutions were prepared [17] and mixed in the calculated ratio, and the mixture was taken in a beaker. The solution was sonicated (Ultrasonic processor, model—VPL P2, Vibronics, India, 1.25 stainless steel horn, 25 kHz, 250 W) for 30 min. NH4OH solution was then added slowly to the reaction mixture under sonication. The pH of the solution was kept at around 9. The sonication was continued for 4 h and the warm solution was allowed to cool. At the end of the reaction, black precipitate was obtained. The precipitate was centrifuged, washed by distilled water and ethanol in a sequence. The precipitate was sonicated in ethanol for 10 min and finally the ethanol was evaporated by slow heating to obtain a dry product. The filtrate after centrifuging was checked for the presence of any dissolved salt by further adding NH4OH Materials Letters 60 (2006) 991–994 www.elsevier.com/locate/matlet
