Shape-controlled gold nanorods are prepared in the presence of a capping agent, cetyltrimethylammonium bromide (CTAB), which controls their morphology and dispersibility in water. To control their dispersibility between water and another organic solvent, a pH-responsive amphiphile C18AA was introduced on gold nanorods instead of CTAB. The C18AA-capped gold nanorods were dispersed in both water and chloroform. These gold nanorods were pH-responsive depending on the extent of C18AA deprotonation observed: deprotonation of the terminal amine above pH 9.5 increases the hydrophobicity of the nanorods, resulting in them being more soluble in chloroform than in water. C18AA-capped gold nanorods can transfer from the water phase to the organic phase by changing the pH from 9.0 to 12.5. The morphology of the nanorods did not change as a result of ligand-exchange, or phase transfer, due to the stabilizing effect of the C18AA capping molecule. C18AA-capped gold nanorods can also be transferred to the water phase by evaporating the chloroform.

Shape-controlled metal nanocrystals such as nanorods are attractive because of their potential novel catalytic properties. It is important to improve the stability of the shape-controlled nanocrystals to be applied as nanocatalysts. In this study, α-Al2O3-supported Au nanorods (AuNR/α-Al2O3) and silica-coated α-Al2O3-supported Au nanorods (SiO2/AuNR/α-Al2O3) were prepared as alcohol oxidation catalysts for the transformation of 1-phenylethyl alcohol to acetophenone. The formation rate of acetophenone over AuNR/α-Al2O3 is higher than that over α-Al2O3-supported spherical Au nanoparticles obtained by calcining AuNR/α-Al2O3. In addition, SiO2/AuNR/α-Al2O3 exhibits higher catalytic performance and thermal stability than those of AuNR/α-Al2O3 in alcohol oxidation.