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In the previous funding period, our research activities were focused on two areas, functional nanomaterials that exhibited novel optical properties and might be exploited as new photosensitizers for photovoltaic applications, and oxide nanostructures with unique photocatalytic characteristics.

The first area of research entailed the preparation of luminescent carbon nanoparticles from natural gas soot. The photoluminescence was found to be enhanced by more than 10 folds when the particles were subject to hydrothermal treatment between 200 and 340 ^oC for varied periods of time (up to 15 hours). This was accounted for by the removal of quinone moieties from the particle surface, which are well-known as electron acceptors. Consistent results were observed in UV-vis, NMR, and electrochemical measurements. Such a strong correlation may be exploited for controlled functionalization of carbon nanoparticles and manipulation of their optoelectronic properties. Another study was carried out with ruthenium nanoparticles functionalized with pyrene moieties that were prepared by olefin metathesis reactions of carbene-stabilized nanoparticles with vinyl derivatives of pyrene. The particle-bound pyrene moieties were found to behave equivalently to pyrene dimers with a conjugated linker by virtue of the Ru=carbene pi bonds.

In the second area of reserch, we carried out three studies. (i) SnO₂ nanoparticles were synthesized by a facile electrochemical method based on anodic oxidation of a tin metal sheet. The resulting particles, with an average diameter of around 20 nm, were then loaded with Au nanoparticles of varied sizes (15 to 35 nm in diameter). It was found that the incorporation of gold nanoparticles significantly improved the catalytic activity of SnO₂ nanoparticles towards oxygen electroreduction. (ii) TiO₂ nanotube arrays were synthesized by anodization of Ti metal sheets followed by thermal annealing at elevated temperatures from 400 °C to 600 °C. X-ray diffraction measurements showed that the as-prepared nanotubes were largely amorphous whereas thermal annealing at 470 °C led to the emergement of the brookite crystalline phase (along with the anatase phase), which became better defined at 500 °C and disappeared at higher temperatures, a phenomenon that has not been observed previously in TiO₂ nanotube arrays prepared by anodization. The impacts of the TiO₂ nanocrystalline structure on the photocatalytic activity were then examined by using the reduction of methylene blue in water as an illustrating example, and the sample thermally annealed at 500 °C was found to exhibit the highest activity. These results demonstrate the significance of nanoscale engineering in the manipulation of oxide photocatalytic performance. (iii) Au-TiO₂ snowman-like heterodimer nanoparticles were prepared by a surface sol gel process based on gold Janus nanoparticles whose surface protecting monolayers consisted of  a hemisphere of hydrophobic 1-hexanethiolates and the other of hydrophilic 2-(2-mercaptoethoxy)ethanol. Transmission electron microscopic measurements showed that the resulting TiO₂ nanoparticles (dia. 6 nm) exhibited well-defined lattice fringes that were consistent with the (101) diffraction planes of anatase TiO₂. The heterodimer nanoparticles displayed apparent photoluminescence that was ascribed to electronic transitions involving trap states of the TiO₂ particles, and the photocatalytic activity was manifested by the oxidative conversion of methanol into formaldehyde which was detected quantitatively by the Nash method.