Dictating Nanoparticle Architecture with Reaction Stoichiometry Using Galvanic Replacement

Galvanic replacement (GR) provides a simple and versatile route to engineer interesting multimetallic nanostructures, with examples such as nanoboxes, nanocages, nanoshells, nanorings, and heterodimers reported. In GR a solution containing cations of a more noble element is added to a dispersion of NPs of a less noble metal. The less noble metal NPs serve as sacrificial templates, from which some portion of the metal is oxidized and transferred into solution concurrently with the reduction and deposition of the more noble metal. The replacement of bimetallic templates by a more noble metal is less studied and can generate trimetallic nanostructures with different architectures. Here, the specific nanostructure depends on the reduction potentials of the participating metals, the stoichiometry of the GR reaction, and the reaction temperature. Interestingly, titrating NP templates with different cationic species of the same metal can lead to nanostructures with different morphologies and compositions. Herein, architecturally complex PdCu-Au NPs were synthesized through GR between PdCu NPs and AuCl₂^- (Au¹⁺) and AuCl₄^- (Au³⁺), allowing for the role of reaction stoichiometry on NP architecture to be systematically studied. Interestingly, PdCu-Au heterostructures with multiple Au domains formed in the case of GR with AuCl₂^- while only single Au domains (PdCu-Au Janus particles) were observed in the case of AuCl₄^-. Moreover, with an increase in AuCl₂^-volume, the Au domain adopts a boat-like shape with PdCu positioned within the concavity (confirmed by tomographic reconstruction). These different NP architectures and their connection to reaction stoichiometry are consistent with Stranski–Krastanov (SK) growth, providing general guidelines on how the conditions of GR processes can be used to achieve multimetallic nanostructures with different defined architectures. Broadly, the stoichiometry of a GR reaction provides a synthetic lever to generate different architecturally complex NPs, with potential utility in chemical sensing, as theranostics, and in catalysis.