Synthesis And Study On The Formation Mechanism Of Hollow Silica Microspheres And Core-Shell Structures

In this dissertation, solution-based routes have been developed to realize the chemical synthesis of silica microspherical nanomaterials and composite namo-materials. The synthesis of low-dimensional nanostructures with controlled size and morphology was probed under mild conditions. Highly symmetric structures/ amorphous microspherical composite namomaterials and core-shell coating nanostructures were synthesized through sol-gel and simple hydrothermal procedure, and the growth mechanisms have been proposed. The main obtained results can be summarized as follows.1. High yield synthesis of hollow silica spheres with controllable size and wall thickness can be realized by a modified Stober method under control of poly-electrolyte (i.e., PAA, PAA-Na, PMA-Na), using tetraethoxysilane (TEOS) as the silica source in ethanol solution of ammonia. The polyelectrolyte could be removed by centrifugal washing with doubled deioned water. The inner diameter (20-400 nm) and wall thickness (in the span of tens of nanometers) can be adjustable by altering the concentration of polyelectrolyte, ammonia and/or TEOS.2. Well-defined concaved cuboctahedrons of CuS crystals were prepared in our group, and each caved cuboctahedron of the CuS is apparently "caved" with highly symmetric 14 cavities and is constructed by four identical hexagonal flakes while sharing the 24 edges in a dymaxion way. Inspired from the high symmetric quality of this structure, M. C. Escher, a graphic artist from Holand, took this symmetry element as an element in his wood engraving Stars in 1948. Also, enlightened from this wood engraving works, the cavities of the unique concaved cuboctahedrons were filled with silica spheres at microcosmic scopes (30 nm, 130 nm, 730 nm in diameter) using 3-aminopropyltrimethoxysilane (APS) as a linker, which provided hydrogen bonding and metal-ligand bonding interaction with the facets of CuS crystals and covalent bonding of its functional silane groups onto the surface of hydrophilic silica spheres. The suitable proportion of the amount of silica spheres and CuS crystals and amount of APS determined the perfection of the CuS crystals/silica composite. The successful loading silica spheres onto the polar facets of unique CuS cuboctahedron crystals enriched the concept of "organization of microcrystals".3. Carbon and carbon-based materials have potential applications in electrochemistry, sorbent, catalyst carrier, etc. The present results demonstrated that the PVP can effectively restain the usual homogeneous nucleation of carbon spheres from the bulk solution through hydrothermal routes, and the carbonized materials coated on the outer surface of 100 nm-in-diameter silica microspheres. The carbon layer is 25-50 nm in thickness and can be controllable. It is interesting that the thin interspace between the carbon and silica layer, which provided an alterable media for storing some metal nanoparticles, oxide nanoparticles, semiconductor quantum dots and biomaterials or disposing certain reactions. Another siliea layer was obtained by the modified Stober method. The carbon and silica could be removed by calcination and etched away by ammonia, respectively. The carbon layer showed an outstanding reactivity to in situ reduce noble-metal irons to nanoparticles spontaneously without using any other reducing agent.