Hollow A1203 nanospheres with well-defined structure and shape were successfully prepared via flame spray pyrolysis （FSP） in the presence of a surfactant as droplet stabilizer. The morphology and structure of the nanospheres were systematically characterized by transmission electron microscopy, scanning electron microscopy, and N2 sorption. A solution of hydrated aluminum nitrate, polyethylene glycol （PEG） and absolute ethanol was sprayed into a flame to transform droplets into particles after evaporation and surface nucleation, forming hollow AI203 nanospheres from aluminum nitrate decomposition. The surfactant was found effective in producing smaller droplets because of decreased surface tension and viscosity, while the combination of oxygen atoms on PEG chains and aluminum ions in solution reduced interfacial turbulence, leading to increased stability of the droplets.
For better performance of dye sensitized solar cells （DSSCs）, a bilayer structured electrode was constructed by employing a mesoporous anatase TiO2 overlayer above a commercial P25 TiO2 nanoparticles underlayer. The mesoporous anatase TiO2, prepared through a facile surfactant-assisted sol-gel process, possessed large pore size and well inter-connected network structure, both beneficial for dye adsorption and electron transfer. The dye adsorption capability of the mesoporous TiO2 was nearly twice that of the P25 counterpart. In the electrode, the mesoporous TiO2 film enhanced both dye adsorption and lightharvest, to increase photocurrent （Jsc） from 12.32 to 14.78 mA/cm^2. Compared to the single P25 TiO2 film, the synergy of the mesoporous TiO2 and the P25 TiO2 nanoparticle films in the electrode resulted in a 24% improvement in light-to-electricity conversion efficiency （η）. This bilayered electrode provides an alternative approach for further developing a photovoltaic device with better cell performance.
Jun JiangJian ZhangFeng GuWei ShaoChunzhong LiMengkai Lu
The flame technology has been employed broadly for large-scale manufacture of carbon blacks, fumed silica, pigmentary titania, and also ceramic commodities such as SiO2, Ti02, and A1203. A deeper understanding of the process also made it possible for production of novel nanomaterials with high functionality--various novel nanomaterials such as nanorods, nanowires, nanotubes, nanocoils, and nanocomposites with core/shell, hollow and ball-in-shell structures, have been synthesized recently via gas combustion technology, while the mechanisms of the material formation were investigated based on the nucleation-growth and chemical engineering principles. Studies of the fluid flow and mass mixing, supported by principles of chemical reaction engineering, could provide knowledge for better understanding of the process, and thus make rational manipulation of the products possible.
