Sensing low concentrations of CO using flame-spray-made Pt/SnO2 nanoparticles
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Tin dioxide nanoparticles of different sizes and platinum doping contents were synthesized in one step using the flame spray pyrolysis (FSP) technique. The particles were used to fabricate semiconducting gas sensors for low level CO detection, i.e. with a CO gas concentration as low as 5 ppm in the absence and presence of water. Post treatment of the SnO2 nanoparticles was not needed enabling the investigation of the metal oxide particle size effect. Gas sensors based on tin dioxide with a primary particle size of 10 nm showed signals one order of magnitude higher than the ones corresponding to the primary particle size of 330 nm. In situ platinum functionalization of the SnO2 during FSP synthesis resulted in higher sensor responses for the 0.2 wt% Pt-content than for the 2.0 wt% Pt. The effect is mainly attributed to catalytic consumption of CO and to the associated reduced sensor response. Pure and functionalized tin dioxide nanoparticles have been characterized by Brunauer, Emmett and Teller (BET) surface area determination, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) while the platinum oxidation state and dispersion have been investigated by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). The sensors showed high stability (up to 20 days) and are suitable for low level CO detection: <10 ppm according to European and 50 ppm according to US legislation, respectively.
Key wordsgas sensor CO detection flame spray pyrolysis tin dioxide nanoparticles platinum functionalization XPS/EXAFS combustion
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We would like to thank Dr. Frank Krumeich for providing the HRTEM, STEM and EDX analyses and Dr. Stefan Mangold for assistance in using beam line ANKA-XAS and the fluorescence detection at the Synchrotron Radiation Facility ANKA of Forschungszentrum Karlsruhe. The EXAFS studies were supported within the project XAS_03_030 by the European Community-Research Infrastructure Action under the FP6: “Structuring the European Research Area”. (Integrating Activity on Synchrotron and Free Electron Laser Science (IA-SFS) RII3-CT-2004-506008).
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