Facile aqueous synthesis of hollow dual plasmonic hetero-nanostructures with tunable optical responses through nanoscale Kirkendall effects

Abstract

Herein, we report the colloidal synthesis of hollow dual-plasmonic nanoparticles (NPs) using Au@Cu₂O core-shell NPs as templates and exploiting the nanoscale Kirkendall effect. In our synthesis, we used organic compounds as a source of chalcogenide ions for an anion exchange reaction at elevated temperatures using polyvinylpyrrolidone (PVP) as a capping reagent to transform the solid Cu₂O shell into a hollow copper chalcogenide shell. The resulting structures possess different features depending on the chalcogenide precursor employed. TEM images confirm the complete transformation of Au@Cu₂O templates when 1,1-dimethyl-2-selenourea was added and the formation of hollow Au@Cu_2-x Se nanostructures. In contrast, residues of Cu₂O attached to the Au core were present when thioacetamide was used for the synthesis of Au@Cu_2-x S with all other conditions kept the same. The divergence of architectures caused distinct optical properties of Au@Cu_2-x S and Au@Cu_2-x Se NPs. This synthetic approach is an effective pathway for maneuvering the size of interior voids by varying the concentration of chalcogenide ions in the reaction mixture. The insights gained from this work will enrich the synthetic toolbox at the nanoscale and guide us on the rational design of multicomponent plasmonic nanoparticles with precisely controlled hollow interiors and sophisticated geometries, further enhancing our capabilities to fine-tune the electronic, optical, compositional, and physicochemical properties.

Fig. 1. Formation of the sacrificial hard templates. TEM images of (A) Au quasi-spherical nanoparticles and (B) Au@Cu₂O core–shell NPs. Insets: color pictures of corresponding colloidal solutions of Au quasi-spherical NPs and Au@Cu₂O core–shell NPs. Scale bars correspond to 200 nm. (C) The extinction spectra of colloidal Au and Au@Cu₂O NPs (cuvette path length is 0.5 cm).

Fig. 2. Characterization of hollow Au@Cu_2−xSe NPs. (A) UV-vis-NIR extinction spectra of aqueous solutions of hollow Au@Cu_2−xSe NPs obtained using 10, 50, 100, 150, and 200 μL of 50 mM (CH₃)₂NC(Se)NH₂ for synthesis. TEM images of hollow Au@Cu_2−xSe nanostructures obtained using (B) 10 μL, (C) 50 μL, (D) 100 μL, (E) 150 μL, and (F) 200 μL of 50 mM (CH₃)₂NC(Se)NH₂ aqueous solution. Scale bars correspond to 200 nm.

Fig. 3. Characterization of hollow Au@Cu_2−xS NPs. (A) UV-vis-NIR extinction spectra of aqueous solutions of hollow Au@Cu_2−xSe NPs obtained using 10, 50, 100, 150, and 200 μL of 50 mM CH₃C(S)NH₂ for synthesis. TEM images of hollow Au@Cu_2−xS nanostructures obtained using (B) 10 μL, (C) 50 μL, (D) 100 μL, (E) 150 μL, and (F) 200 μL of 50 mM CH₃C(S)NH₂ aqueous solution. Scale bars correspond to 200 nm.

Fig. 4. Elemental distributions of Au, Cu, and Se in hollow dual-plasmonic Au@Cu_2−xSe (left panel). Mapping images of Au, Cu, O, and S in hollow dual-plasmonic Au@Cu_2−xS (right panel). Scale bar: 200 nm.