Gold microsheets having nano/microporous structures fabricated by ultrasonic-assisted cyclic galvanic replacement

Abstract

A novel technique for the fabrication of nano/microporous gold (Au) microsheets using an ultrasonic-assisted cyclic galvanic replacement reaction between a sacrificial silver (Ag) plate and gold ions (AuCl₄⁻) is reported. First of all, AuCl₄⁻ is reduced on the surface of sacrificial Ag via a galvanic replacement reaction. Then, the epitaxial growth of the Au film on the Ag surface is disturbed by the precipitated AgCl by-product of this galvanic replacement reaction. The co-precipitated AgCl and galvanic-generated Au nanostructures induce the formation of an interpenetrated Au/AgCl nanocomposite film on the surface of the sacrificial Ag plate. Finally, ultrasonic radiation enables auto-detachment of the galvanic-generated film along the AgCl/Ag interface. The galvanic replacement and auto-detachment processes continuously occur as a cycle until the scarified Ag is totally consumed. The coral-like Au nanostructures with nano/microporous morphologies are realized after removing AgCl by NH₃ treatment. The hierarchical nano/microporous structures have micropores and nanopores with sizes of 0.15–0.30 μm and 30–60 nm, respectively, separated by chain-like Au structures. The complex porous structures, through which liquids can easily flow, can potentially be used in applications such as high-efficiency free-standing catalysts, super capacitors, electrochemical sensors and surface-enhanced Raman scattering (SERS) substrates. A SERS application of the Au microsheets is also demonstrated.