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

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 similar to 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 (similar to 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 similar to 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.