Synthesis of Ag–Au and Ag–Pd alloy triangular hollow nanoframes by galvanic replacement reactions without and with post-treatment using NaCl in an aqueous solution

Abstract

Ag–Au and Ag–Pd alloy triangular hollow nanoframes were prepared using galvanic replacement (GR) reactions of Ag nanoprisms with HAuCl₄ and Na₂PdCl₄ in an aqueous solution. Their growth mechanisms were studied by observing transmission electron microscopic (TEM) and TEM-energy dispersed X-ray spectroscopic (EDS), XRD, and ultraviolet (UV)-visible (Vis)-near infrared (NIR) extinction spectral data. Results show that Ag–Au alloy triangular frames start with formation of a truncated prism, followed by expansion of a hollow structure to the interior of the prism, reformation of the triangular shape, and finally formation of a triangular frame at ambient temperature within a few minutes. On the other hand, triangular Ag–Pd alloy plates are slowly formed by the addition of Na₂PdCl₄ and heating at 100 °C for 30–120 min. Results show that post-treatment using saturated NaCl solution is effective for the transformation of Ag–Pd alloy nanoplates to Ag–Pd nanoframes. The difference in the formation of nanoframes is explained by the difference in the dealloying rates between Ag–Au alloys by AuCl₄⁻ and Ag–Pd alloys by Pd²⁺. XRD data suggested that hexagonally closed packed (hcp) layers are involved as major components of the triangular Ag–Au and Ag–Pd alloy nanoframes.