Abstract
Metal oxide semiconductors (MOS) in pristine form and functionalized by noble metals are extensively researched for gas detection. There is a lack of fundamental understanding of the relations between materials composition and sensitivity to volatile organic compounds (VOC). In this work, we compared the sensitivities of different pristine metal oxides and Au-functionalized metal oxides to methanol and acetone. Nanostructured MOS of p-type (NiO, CuO, Co3O4) and n-type (In2O3, ZnO, SnO2, TiO2, and WO3) were synthesized by common aqueous deposition techniques. The oxides differ in metal-oxygen bond energy (EM-O) which was chosen as a parameter for the comparison of sensitivity to methanol and acetone vapors. Metal oxides were functionalized by Au nanoparticles via colloid adsorption, and the effect of gold on the sensitivity to VOC was investigated. Acid sites and surface oxygen sites at the materials surfaces were determined by temperature-programmed probe molecule techniques. The interaction routes of methanol and acetone with materials surfaces were examined by diffuse-reflectance infrared spectroscopy (DRIFT). It was found that with the increase of metal-oxygen bond energy the surface acidity of MOS strengthened, which favored the adsorption and improved the sensitivity to methanol. Oxidation of methanol and acetone to formate and acetate species on the materials surfaces was revealed, and the roles of active sites in these reactions were rationalized. An enhanced sensitivity to VOC was observed for Au-functionalized metal oxides, with the most prominence for TiO2/Au nanocomposite. It was rationalized as a combination of a proper TiO bond energy and the catalytic effect of gold.
Published Version
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