Synthesis, Structures And Luminescence Properties Of Silica-based Micro/Nano-structured Materials

This dissertation mainly focuses on the synthesis, morphology control and properties of micro-nano structured silica-based materials. On one hand, many efforts have been made to achieve the novel architecture of silica-based materials. On the other hand, valuable exploration has been carried out to realize high-brightness fluorescent emission. The obtained meaningful results have been listed as follows:1. the preparation and luminescence properties of silica-based nanoparticles1) The modified Stober process has been applied to successfully synthesize ethylenediamine-functionalized hybrid silica nanoparticles for the first time. Photoluminescence measurements are carried out and found that the product has a strong blue emission located at420nm. N-related defect pairs, such as NH3+/NH-, NH2+/N-, NH3+/N-and NH2+/NH-, generated in ethylenediamine groups, are proposed to interpret the origins of the blue emission.2) A one-step, reverse microemulsion process has been first applied to synthesize ethylenediamine functionalized polysilsesquioxane nanoparticles, using N-(3-trimethoxysilylethyl)ethylenediamine (TMSEEDA) as a sole precursor. The resultant organic-inorganic hybrid particles are characterized of abundant micropores, good thermal stability and strong blue-light emission, even maintaining high luminescence quantum yields under high temperature. N-related defects are proposed to be responsible for the blue emission centred at440nm.3) The Stober silica nanopricles with uniform particle size and monodispersity are found to have blue-light emission. The blue-light emission intensity was strongly enhanced through the heat treatment of the silica nanoparticles, which can get10times more than the uncalcined silica nanoparticles. We proposed that the blue emission probably origins from the oxygen-related defect. Heat treatments can directly increase the oxygen-related defect concentration in silica particles2. the preparation and luminescence properties of core-shell mesoporous silica-based nanoparticles1) An innovative preparation of core-shell nanoparticles with a solid silica core and a mesoporous silca shell has been denmostrated. The core-shell mesoporous silica nanoparticles are employed as host materials for encapsulation of guest substance. The organosilane molecules TMSEEDA, as guest materials, are covalently doped into the core-shell particles, construting hybrid nanocomposites. The resultant particles display strong blue-light emissions. The experiments also found that the matrix of the core-shell particles not only provides a novel structure (e.g. ordered mesoporous shells), but also improves the luminescence quantum yield of the small organic molecules, and enhances the thermal stability of the organic molecules, thereby expanding the potential applications of organic molecules.2) The covalent grafting technique has been applied to demonstrate an innovative preparation of Eu3+/Tb3+co-doped complexes covalently incorporated into solid silica core/ordered mesoporous silica shell nanoparticles, achieving novel architectures and strong red emissions. The photoluminescence spectra show the intensities for Eu3+characterized red-light emission are effectively tunneled by the Eu3+/Tb3+mole ratios. When the Eu3+/Tb3+mole ratio is only2:1, the red light emission intensity reaches a maximum, suggesting at this time Tb3+most effectively sensitizes the Eu+emission. With high-brightness red-light emissions, ordered mesoporous channels, large specific surface area, thermal stability, and biocompatibility, the Eu3+/Tb3+complexes convalently encapsultated mesoporous core-shell silica nanoparticles are expected to promise potential applications in the biomedicine.3. the preparation and luminescence properties of hollow mesoporous silica-based microspheres1) A conbined template technique with calcining process has been applied to successfully prepare hollow silica microspheres with a mesoporous shell. The luminescence properties are investigated in details and we found that the microspheres possess blue-light emissions. C-impurities, which are induced by calcining process, and oxygen-related defects, which exist in the nanostructured silica, are proposed to be attributed to the blue emissions.2) A conbined layer-by-layer assembly technique with calcining process has been applied to demonstrate an innovative synthetic procedure for hollow SiO2/Sn2SiO4/ZnO and SiO2/Zn2SiO4:Mn/ZnO composite microspheres with mesoporous shells, using tetraethyl orthosilicate (TEOS) and3-aminopropyltriethoxysilane (APTES) as common Si sources, zinc acetate and manganese acetate as Zn and Mn sources, respectively. The mesoporous SiO2/Zn2SiO4/ZnO hollow microspheres have low density, large specific surface area, plenty of porosities and negatively charged surfaces, exhibiting a strong removal capacity for Pb2+, Cd2+, Fe3+. The results show that the products are expected to display enormous potential applications in water treatment. The mesoporous SiO2Zn2SiO4:Mn/ZnO hollow composite microspheres not only have the above advantages, but also show a strong Mn2+characterized green-light emission, which can be used as excellent green phosphors. With double characteristics of a unique morphology and strong emissions, the application for the the mesoporous SiO2/Zn2SiO4:Mn/ZnO hollow composite can be extended to the biomedicine.(e.g. the tracer drug delivery).