Surface structure design of metal oxide nanostructures for highly effective gas sensors and catalysts

Abstract

The nanoparticles have been employed for various applications, such as catalytic reactions, sensors, and drug delivery systems, due to their high surface area and highly active surface. For these applications, researchers have great interest in the design of morphology and surface structure of nanoparticles to gain large surface area, adoptable electronic conductance and surface energies. In chapter 2, a hierarchical assembly of the single crystalline $Co_3O_4$ nanoparticles was yield using ZnO spheres as sacrificial templates. This material exhibited remarkable sensing performance, including extremely high sensitivity with a detection limit of 5 ppb, good selectivity for formaldehyde among the various indoor environmental gases, and good long term stability for up to three days in air. These superior properties stemmed from the regular, hierarchically assembled structures with a small crystalline domain size under a critical size of a grain (20 nm), a thin hollow morphology with a large surface area, and a three-dimensional conductive network with a two particle-wide diameter. In chapter 3, we have fabricated two distinct yolk-shell nanostructures from the $NiPt@SiO_2$ core-shell nanoparticles by simple thermal treatments. The labile nickel components behaved as sacrificial spacers that generated vacancy between Pt cores and silica hollow shells. The $NiPt@SiO_2$ core-shell nanoparticles transformed to the Pt@silica yolk-shell nanostructure with branches of nickel phyllosilicate under a basic condition. Hydrochlo-ric acid selectively dissolved the nickel components and formed the Pt@silica yolk-shell nanospheres. Because of its high reactivity and affordable price, nickel can act as a versatile sacrificial component for the formation of complex hierarchical structures with expensive noble metals. In chapter 4, we have fabricated a $SiO_2@MgO@Ni$ nanocatalyst bearing tiny nickel nanoparticles embedded on the surface of $SiO_2@MgO$ core-shell sphere, by the red...