Flame spray synthesis of tin oxide nanoparticles for gas sensing
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Flame spray synthesis of tin oxide nanoparticles for gas sensing Thorsten Sahm1, Lutz Mädler2, Alexander Gurlo1, Nicolae Barsan1, Sotiris E. Pratsinis2 (speaker) and Udo Weimar1 1 Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany. 2 Particle Technology Laboratory, Swiss Federal Institute of Technology (ETH) Zurich, Sonneggstrasse 3, CH-8092 Zürich, Switzerland. ABSTRACT Tin oxide nanoparticles for gas sensing application have been synthesized with an aerosol method. The particles were manufactured with the versatile Flame spray Pyrolysis (FSP) method producing highly crystalline powders with closely controlled a primary particle and crystallite size of 10 nm and 17 nm. The single crystalline particles were only slightly aggregated and directly used for thick film sensor deposition by drop coating and screen printing. The flame made SnO2 nanoparticles showed high and rapid response to reducing gases such as propanal and CO. INTRODUCTION In recent years nano- and micrometer tin oxide particles for gas-sensing applications have been produced by different methods, e.g. by sol-gel, gas-phase condensation, decomposition of organometallic precursor, oxidation of metallic tin, hydrothermal treatment of colloidal solutions, laser ablation, and mechanochemical processing [1]. The importance of size control, the required large and easily accessible surface area (large pore size, no micropores), the desired high crystallinity, the ability of noble metal doping and competitive production rates put high demands on the method of nanoparticle production for sensor materials. Particle manufacture in the gas phase (aerosol route) such as flame synthesis and especially Flame Spray Pyrolysis (FSP) is a very promising technique for sensor material (e.g. metal oxide) fabrication [2] since its enables primary particle and crystal size control [3,4], which is important to tailor sensitivity [5,6]. It has been shown that due to the high external surface area and due to the absence of micropores of the FSP made particles the mass transfer rates in catalysis are higher compared to wet phase prepared materials in general [6]. Furthermore, FSP bears the advantage to manufacture the nanopowder in a single high temperature step without affecting the microstructure in a subsequent annealing process as is necessary in conventional spray pyrolysis or wet methods. EXPERIMENTAL Tin(II) 2-ethylhexanoic acid (Aldrich) was diluted in ethanol (propanal sensor) or toluene (CO sensor), respectively, to obtain a 0.5 M precursor solution. The precursor was fed into a flame spray pyrolysis (FSP) reactor by a syringe pump with a rate of x=5 or 8 ml/min and was dispersed by y=5 or 3 l/min of oxygen, respectively, into fine droplets by a gas-assist nozzle. The conditions will later be referred later as (EtOH or Toluene /x/y). Cooling of the reactor avoided any evaporation of the precursor within the liquid feed lines or overheating of the nozzle. The
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spray flame was maintaine
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