Aqueous Phase Synthesis of Au–Ag Core–Shell Nanocrystals with Tunable Shapes and Their Optical and Catalytic Properties

Abstract

In this study, rhombic dodecahedral gold nanocrystals were used as cores for the generation of Au-Ag core-shell nanocrystals with cubic, truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures. Gold nanocrystals were added to an aqueous mixture of cetyltrimethylammonium chloride (CTAC) surfactant, AgNO3, ascorbic acid, and NaOH to form the core-shell nanocrystals. The nanocrystals are highly uniform in size and shape, and can readily self-assemble into ordered packing structures on substrates. Results from observation of solution color changes and variation in the reaction temperature suggest octahedra are produced at a higher growth rate, while slower growth favors cube formation. The major localized surface plasmon resonance (LSPR) band positions for these nanocrystals are red-shifted compared to those for pristine silver particles with similar dimensions due to the LSPR effect from the gold cores. By increasing the concentrations of reagents, Au-Ag core-shell cubes and octahedra with tunable sizes were obtained. Au-Ag cubes with body diagonals of 130, 144, and 161 nm and octahedra with body diagonals of 113, 126, and 143 nm have been prepared, allowing the investigation of size effect on their optical properties. Au-Ag octahedra with thinner Ag shells (12-16.5 nm) exhibit a blue-shifted major LSPR band relative to the LSPR band at 538 nm for the gold cores. For Au-Ag octahedra and cubes with thicker shells (22.5-37 nm), the major LSPR band is progressively red-shifted from that of the gold cores with increasing shell thickness and particle size. The Au-Ag octahedra show higher catalytic activity than cubes toward reduction of 2-amino-5-nitrophenol by NaBH4 at 30 °C, but both particle shapes display significantly enhanced catalytic efficiency at 40 °C.

Comparison of 20 nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages

“…[67][68][69] The current works shows that Ag grown on an Au seed crystal can impact particle structure, especially for shell thicknesses of size comparable or smaller than the core. However, other effects of a seed crystal or core on particle stability need to be considered.…”

Core-Size-Dependent Catalytic Properties of Bimetallic Au/Ag Core–Shell Nanoparticles

“…The catalytic properties can be tuned by tuning the size and shape of the nanoparticles. 21 Recently, Xia et al 22 have reported the comparative catalytic activity of the Au nanoparticles, nanoboxes, and nanocages by reduction of nitrophenols. Again, the catalytic property can be tuned with changing the nanoparticle composition from single component to bimetallic.…”

“…Among the different morphologies, the core−shell type nanoparticles are most interesting as the core diameter and the shell thickness might play important role on the catalytic activity. Recently, Tsao et al 21 have demonstrated the shape dependent catalytic activity of the Au−Ag core−shell nanocrystals. Thus, the catalytic and other physiochemical activities of the core−shell materials can be tuned by changing the size of the core in core−shell structures.…”

Semiconductor and Metallic Core–Shell Nanostructures: Synthesis and Applications in Solar Cells and Catalysis

“…They found that Au/Ag core-shell octahedra were more catalytically active than cubes toward the reduction of 2-amino-5-nitrophenol at 30 8C. [150] Oxygen reduction reaction (ORR)…”