Construction Of Silica Core-shell Structure And Inorganic Oxide Hollow Spheres

Recently, research of composite nanostructure aroused the interest of materials scientists, because of the novel properties of the composite structure compared to the single system, including the potential applications in optical, electricity, magnetism and biomedicine. Especially the core-shell structure has attactived increasing attention, due to the modification of the monomer when it is encapsulated one layer or more by other organic or inorganic template. Furthermore, nano/micro hollow spheres can be formed by etching the template in appropriate solvents or calcinations of core-shell particles. Hollow spheres are becoming one of the focuses of new materials research because of its low density,high specific surface areas and infiltration ability. In this dissertation, high monodispersed Co@SiO2 core shell nanoparticles were prepared by sol-gel method. In addition, mesorporous silica hollow spheres were fabricated by template, then the cores are removed by calcinations, the entire formation mechanism of silica hollow spheres was discussed. We also research the fabrication and characterization of inorganic hollow spheres including titanium dioxide and molybdenum trioxide. All the research contents and results are as follows:1. High dispersed Co@SiO2 core- shell nanoparticles were preparation in a weak acid condition at room temperature without oxygen. The diameters of core-shell structure nanoparticles regulated by the reaction time and the concentration of citric acid was discussed. The Co@SiO2 nanoparticles were stable after high temperature calcinations. The composition was confirmed by XPS. The magnetism was measured by SQUID.2. Mesoporous silica hollow spheres were fabricated by emulsion-templating method using triblock copolymer poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) (PEG-PPG-PEG) as a template. Sodium silicate or tertraethylorthosilicate (TEOS) was as precursor, benzyl alcohol was as cosolvents, the morphologies of silica hollow spheres were regulated from smooth to rough by changing the concentration of benzyl alcohol. The morphologies were also influenced by other reaction condition such as pH, temperature and reation time. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results revealed the surface morphologies and the thickness of hollow spheres. Brunauer-Emmett-Teller (BET) analysis confirmed that silica hollow microspheres were mesoporous structure.3. We adopt the similar method for fabrication of hollow silica microsphere using nonionic surfactant nonyl phenol ethoxylated decylether (NP-10) micelles as template, n-octadecane as core and sodium silicate as precursor of silica. The core materials were removed by ethanol during the reaction process. Hollow structure formed without calcinations. Hierarchical silica hollow microspheres were prepared by changing the concentration of the reactants and reaction time. Size of the core material was obtained from the temperature dependent dynamic light scattering (DLS) measurement. The morphologies and diameter of product were obtained by the images of scanning election microscopy (SEM) and transmission electron microscopy (TEM).4. TiO₂ hollow spheres were fabricated by template free method under hydrothermal condition using titanium potassium oxalate (TOP) as precursor. The formation mechanism was based on inside-out"Ostwald ripening". Phase transition from metastable phase to stable anatase TiO₂ hollow spheres were investigated by different reaction time. Morphologies from smooth solid particles to nanorod like TiO₂ hollow spheres are observed by scanning election microscopy (SEM), transmission electron microscopy (TEM) results confirmed that the mean diameter of hollow spheres was 1μm, selected area electron diffraction (SAED) revealed that the nanorod grew along [001]. Compared to commercial P25 powder, hollow spheres exhibited relatively higher photoactivities by degradation of RhB under UV light irradiation, the higher photoactivities of hollow spheres can be attributed to the large surface areas, the porous structure, and the high band-gap energy.5. Stable orthorhombic structured MoO₃ nanoribbons with the diameters of 100²00 nm and lengths up to several micrometers were successfully synthesized under the hydrothermal conditions without any template. Reaction time and pH play a key role in the surface morphologies. Based on the previous work, we discuss the transformation of crystal structure from monoclinic to orthorhombic. According to analysis of XRD and SAED, it is comfirmed thatα-MoO₃ nanoribbons grew along the [001] (c axis) direction. Furthermore, the as-preparedα-MoO₃ nanoribbons exhibited superior photocatalytic activity for the degradation of RhB than bulk MoO₃ and commercial P25.