Silica-based nanospheres, nanowires, nanosubstrates, nanotubes, and nanofiber arrays

Silica-based nanospheres, nanosphere wire-like agglomerates, nanotubes, and nanofiber arrays, bi- and coaxial SiC/SiO2 nanowires, and silica nanosubstrates have been generated and their structural, mechanical, and catalytic properties examined. Nearly monodisperse SiO2 nanospheres of diameter less than or equal to30 nm have been synthesized in gram quantities and used to sequester active copper sites for the selective catalytic conversion of ethanol to acetaldehyde in a process that is at least three times more efficient than that which uses fumed silica produced from the flame hydrolysis of silicon tetrachloride. A Ni(III) solution has been reduced in an electroless process on the surface of the nanospheres, producing a ferromagnetic crystalline nickel coating of variable thickness. Partially agglomerated SiO2 nanospheres of diameter similar to45 nm have been used as nanosubstrates for SnOx crystallites of diameter 3-6 nm. The agglomeration of smaller nanospheres (dless than or equal to10 nm) to wire-like configurations has suggested the means to grow silica nanotubes and to produce unique silica nanofiber arrays. Generated silica nanotubes may fill an existing need for the catalytic conversion of high molecular weight hydrocarbons (MWsimilar to1000). Both coaxial and side-by-side biaxially structured silicon carbide-silica nanowires have now also been generated from C/Si/SiO2 mixtures. The structure of these nanowires, their cross-sectional shape, and their structural transformation between a biaxial and coaxial configuration have been studied. The Young's modulus of the biaxially structured nanowires has been measured to be 50-100 GPa, depending on the size of the nanowires.