Improved catalytic activity and surface electro-kinetics of bimetallic Au–Ag core–shell nanocomposites

Abstract

This paper demonstrates the preparation of core–shell nanocomposites (NCs) of Au_core–Ag_shell (Au@Ag) and Ag_core–Au_shell (Ag@Au) for measuring their catalytic activity and electro-kinetic properties relative to their respective monometallic counterparts. A significant blue-shift (530 → 408 nm) and a red-shift (420 → 550 nm) of the surface plasmon band for Au@Ag and Ag@Au NCs, respectively, were observed due to increased size of binary composites depending on the nature of the core and shell material. The thickness of the deposited Ag shells varied from ∼3–10 nm on the Au core leading to the formation of Au@Ag NCs. On the other hand, the Ag core served as a sacrificial template, where Ag@Au NCs were converted to hollow Ag–Au alloy shells (∼15 nm) because of the galvanic reaction between them due to the difference in their redox potential. An increased zeta potential was found for resulting Au@Ag (+57.8 mV) and hollow Ag–Au alloy shell (−20.13 mV) NCs in comparison to monometallic Au (−6.13 mV) and Ag nanospheres (−5.74 mV) due to surface passivation with aqueous AgNO₃ and AuCl₄⁻ solution, respectively. These bimetallic NCs exhibited ∼2 times higher catalytic activity than the monometallic nanoparticles depending on the shell thickness and the core of the respective metals for the nitrobenzene and 1,3-dinitrobenzene reduction.