Size Control in the Synthesis of 1–6 nm Gold Nanoparticles via Solvent-Controlled Nucleation

We report a facile synthetic route for size-controlled preparation of gold nanoparticles. Nearly monodisperse gold nanoparticles with core diameters of 1–6 nm were obtained by reducing AuP(Phenyl)₃Cl with <i>tert</i>-butylamine borane in the presence of dodecanethiol in the solvent mixture of benzene and CHCl₃. Mechanism studies have shown that the size control is achieved by the solvent-controlled nucleation in which the nuclei concentration increases with increasing the fraction of CHCl₃, leading to smaller particles. It was also found that, following the solvent-controlled nucleation, particle growth occurs via ligand replacement of PPh₃ on the nuclei by Au(I)thiolate generated by the digestive etching of small particles. This synthetic strategy was successfully demonstrated with other alkanethiols of different chain length with which size-controlled, monodisperse gold nanoparticles were prepared in remarkable yield without requiring any postsynthesis treatments

Unexpected Size Effect Observed in ZnO-Au Composite Photocatalysts

Semiconductor-metal nanocomposites prepared with well-defined gold nanoclusters, such as Au₂₅, Au₁₄₄, and Au₈₀₇, showed size-dependent photocatalytic activities for the reduction of nile blue and azobenzene. Whereas the photoreduction of nile blue was directly related with the charge separation and transfer rate from the photoexcited ZnO to gold nanoclusters, the photoreaction of azobenzene showed unexpected size effect with a clear threshold. Mechanistic investigations revealed that the photoreduction of azobenzene proceeded via a proton-coupled electron transfer process. The photocatalytic activity of the ZnO-Au nanocomposites was also dependent on the excitation intensity, demonstrating that the multielectron/multiproton process was controlled by the charge separation and transfer in the nanocomposites