Morphological stability and catalytic activity of Au nanoflowers (NFs) were improved by using γ-Al2O3 support and water extraction procedure. Formation rate of acetophenone on Au NFs/γ-Al2O3 was ten-fold higher than that on spherical Au NPs/γ-Al2O3.

The pH-responsive self-assembly of zwitterionic amphiphile C16CA was expanded to the recovery of gold (Au) nanoparticles for environmentally friendly chemistry applications. Multilayered lamellae at pH ∼ 4 were successfully incorporated into nanoparticles by dispersion. Redispersion of nanoparticles was achieved under basic conditions by the transition of self-assembly.

Shape-controlled nanocrystals, such as nanowires and nanoflowers, are attractive because of their potential novel optical and catalytic properties. However, the dispersion and morphological stabilities of shape-controlled nanocrystals are easily destroyed by changing the dispersion solvent and temperature. Methods of support and the silica coating are known to improve the dispersion and morphological stabilities of metal nanocrystals. The silica-coating method often causes morphological changes in shape-controlled nanocrystals because the silica coating is formed in mixed solutions of water and organic solvents such as ethanol, and this results in aggregation due to changes in the dispersion solvent. Furthermore, ligand exchange, designed to improve the dispersion stability in the solvent, often causes morphological changes. This article introduces a method for the preparation of highly stable silica-coated Au nanoflowers (AuNFs) supported on AlO. The method of support prevents the aggregation and precipitation of AuNFs when the solvent is changed from water to water/ethanol. Through stability improvement, silica coating of AuNFs/AlO was conducted in water/ethanol without ligand exchange that causes morphological changes. Furthermore, silica-coated AuNFs/AlO exhibit high morphological stability under high-temperature conditions compared to uncoated AuNFs/AlO. These results are very useful when preparing highly morphologically stable, silica-coated, shape-controlled nanocrystals without ligand exchange.

The pH-responsive amphiphile C16CA was used for the functionalization of gold nanorods. The pH-induced recovery–redispersion of gold nanorods using C16CA self-assembly was accomplished without affecting the catalytic activity of the nanorods.