Detecting H 2 S oscillatory response using surface plasmon spectroscopy
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Detecting H2S oscillatory response using surface plasmon spectroscopy Enrico Della Gaspera1 and Alessandro Martucci*1 1 Università di Padova, Dipartimento di Ingegneria Industriale, Padova, Italy ABSTRACT The oscillatory change in the optical absorbance of NiO-TiO2 film containing Au nanoparticles in the presence of H2S gas are investigated. The oscillatory phenomena could be monitored by looking at the variation of the surface plasmon resonance peak of the Au nanoparticles embedded in the TiO2-NiO matrix. Au nanoparticles act as optical probes in the detection of H2S, while the oxide matrix is responsible for the catalytic oxidation of H2S. To the best of our knowledge, it is the first time that oscillatory phenomena are monitored by optical spectroscopy. INTRODUCTION Over the past few decades, there has been considerable interest in investigating oscillatory reactions occurring at gas/solid interfaces1,2,3,4. Among these, the oscillation in the oxidative reaction of CO on a SnO2-Pt surface are the most studied1,2,3. Oscillatory phenomena were observed for only a few gases (CO and H2) and they have never been monitored by optical spectroscopy. In previous papers we demonstrated the possibility to use surface plasmon resonance (SPR) based platforms to detect several different gases (H2, CO, H2S)5,6,7,8,9,10. In this paper, we report for the first time the use of surface plasmon spectroscopy to monitor oscillatory behavior of H2S oxidation on NiO-TiO2 film. EXPERIMENT The nanocomposite films were obtained by the sol-gel method: a detailed description of the synthetic route and of the characterization techniques adopted has been reported elsewhere6. Briefly, a solution of NiCl2·6H2O dissolved in Ethanol was mixed to a previously prepared solution of titanium(IV) butoxide in a mixture of ethanol and water, in the presence of 2,4pentanedione with a Ti:Ni molar ratio of 7:3 and let stir for 20 minutes. Before deposition, an ethanolic solution of HAuCl4·3H2O was added to the Ti-Ni solution in order to achieve a 5% molar Au content. All deposition were made by spin coating on SiO2 substrates at 4000 rpm for 30 seconds under nitrogen atmosphere. Samples were annealed directly at the 600 °C in air in a preheated muffle furnace. The films were characterized by XRD by using a Philips diffractometer equipped with glancing-incidence X-Ray optics. The surface structure of the nanocomposite films has been investigated with a Scanning Electron Microscope (SEM). High resolution, cross-sectional transmission electron microscopy (HR-TEM) measurements were taken with a field emission FEI TECNAI F20 SuperTwin FEG-(S)TEM microscope. Transmittance at normal incidence and ellipsometric quantities Ȍ and ǻ have been measured using a J.A. Woollam V-VASE Spectroscopic Ellipsometer. Film thicknesses and dispersion curves of refractive index and
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absorption coefficient have been evaluated from Ȍ, ǻ and transmittance data with the WVASE32 ellipsometric data analysis software. Optical sensor functionality was studied by conducting optical abs
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