Synthesis And Property Of Several Metal Oxide Spherical Core-Shell Structures

Recently, core-shell structures were considered to the hot issue compared to single composite materials because of their great improvement on chemical and physical propriety. In this dissertation, using carbon and silica spheres as sacrificial template, hydrothermal, reflux and sol-gel etc methods were used to synthesize several metal oxide core-shell spheres. A series of parameters such as template, the reaction time and temperature of hydrothermal process and the temperature and velocity of calcinations have been investigated on how they affect the morphology and propriety of ultimate products. The main results can be summarized as follows:1. Anew kind of Au@Y₂O₃:Eu³⁺ hollow spheres with moveable gold nanoparticle core and Y₂O₃:Eu³⁺ as shell have been successfully fabricated via a two-step coating process. The thickness of shell was controlled from 30 to 60nm. The size of Au core was about 10-40nm. The diameter of hollow spheres was controlled from 100-1000nm according to the size of silica template. The Au@Y₂O₃:Eu³⁺ hollow spheres with moveable Au nanoparticle core showed red light emission intensity at 613 nm as that for the Y₂O₃:Eu³⁺ hollow spheres, but are of blue-shifted absorption peak at 526 nm compared with pure Au nanoparticles and Au@SiO₂ core-shell spheres. These new core-shell structures with moveable gold particles have the optical properties of both Au nanoparticles and Y₂O₃:Eu³⁺ phosphor materials, which might have potential applications such as biologic detectors.2. Novel hollow nanospheres of moveable Au particle core/nanoporous titanium oxide particles shell structure have been successfully fabricated via two-step coating processes. The thickness of shell can be controlled in the range of 30 to 80nm. The size of Au core was about 10-40nm. The diameter of hollow spheres can be controlled in the range of 100-800nm according to the size of carbon spheres. This new structure shows excellent photocatalytic properties compared with that of pure TiO₂ hollow spheres and P-25 titanium powders. During three minutes, the degradation rate of methylene blue solution loaded with Au particle core/nanoporous titanium oxide shell structure was about 40%, whereas the other contrasted samples were lower than 20%. Therefore it might provide an efficient way to improve the photocatalytic property of TiO₂.3. Pt nanoparticles embedded silica hollow spheres with moveable Au core have been successfully fabricated via simply templating against Au@carbon spheres. The shell thickness can be controlled from 30 to 120nm. The size of Au core was about 10-40nm. The size of Pt core was about 5-60nm. The diameter of hollow spheres was controlled from 100-800nm according to the size of carbon spheres. Such novel materials shows excellent electrocatalytic properties compared with both typical hollow spheres and pure Pt nanoparticles. This might provide an efficient way to improve the electrocatalytic property of a bulk Pt/GC electrode. In addition, these hollow spheres loaded with noble metal nanoparticels will also find application in the molecule level nanoreactors by taking advantage of their unique hollow structures.