Galvanically Replaced Hollow Au–Ag Nanospheres: Study of Their Surface Plasmon Resonance

Abstract

We synthesized hollow Au-Ag nanospheres (NSs) by employing a galvanic replacement reaction between HAuCl4 and Ag NSs. Uniform Ag NSs with controllable sizes were synthesized as sacrificial templates by a seed-mediated strategy. The atomic ratio of Au to Ag in Au-Ag NSs was tunable by controlling the reagent concentration. UV-vis extinction spectra acquired from well-dispersed colloidal NS solutions were used to investigate the optical properties of the solutions. In addition to a common dipole mode exhibited on most transition metal nanoparticles, we observed a quadrupole plasmon resonance mode when the diameters of the Ag and Au-Ag NSs were larger than 100 nm. The quadrupole and dipole peaks both shifted to longer wavelengths with increased Au content in Au-Ag NSs. The experimental observation of optical properties of hollow Au-Ag NSs was compared with the theoretical simulation using DDA calculation, showing a good agreement.

Effect of Ag Templates on the Formation of Au-Ag Hollow/Core-Shell Nanostructures

“…The literature claims that the 0-D Au-Ag nanostructure formed through galvanic replacement between Ag atom and Au ions are mostly core-shell NPs or hollow spheres [6,19,[22][23][24][25][26][27][28][29][30]. In order to clarify this issue, the 0-D hollow structures synthesized in this study were examined by HAADF-STEM images from different (Fig.…”

“…The concentration of the Au precursors plays an important role in the replacement reaction of Ag by Au, and the structure, morphology, as well as the composition, can thus be controlled. The excessive galvanic reaction between Au and Ag might give rise to the formation of hollow structures [6,[24][25][26][27][28][29][30], e.g., AuAg hollow particles and tubes. As also tabulated in Table 1, the characteristics of Ag templates, e.g., the existence of planar defects (twins in this case), size, and specific surface area of templates, may also affect the morphology of the AuAg nanostructures.…”

Synthesis of Au/Ag nanoframes from Ag nanoplates by galvanic replacement reaction and its optical properties

“…35 nm. In addition, pre-oxidation of AgNP was helpful to shorten the reaction time (less than 5 min), compared to the reported method [3,4]. During GRR to oxidize AgNP using HAuCl 4 , the Ag (111) facets are converted to very thin layers of gold, and finally, via Ostwald ripening, these thin gold layers dissolved and re-grew on the ring-like structure (Au/AgNF).…”

“…Metallic hollow nanostructures, prepared using a galvanic replacement reaction (GRR), give rise to hot-spots in electromagnetic fields, because they exhibit plasmon field coupling between their interior and exterior surface fields [3]. Bimetallic hollow nanoparticles, which have unusual observation of the quadrupole and/or dipole plasmon resonance, could also be synthesized by GRR [4][5][6]. In a typical procedure for creating Au/Ag nanoparticles, silver nanoparticles were used as sacrificial templates to react with an aqueous chloroauric acid (HAuCl 4 ) solution, resulting in the formation of Au/Ag nanoframe with hollow interior.…”

“…Hollow Au/Ag nanoparticles with spherical [4], cubic [5], and triangular [8] shape were prepared by epitaxial edge-gold-coating to increase chemical stability and the plamonic particle-cavity formation to enhance the optical sensitivity.…”