Ag@Pt Core–Shell\nNanoparticles for Plasmonic\nCatalysis

Abstract

Bimetallic nanocatalysts (NCs) composed of two metal\nelements are\na promising way to achieve high catalytic performance based on so-called\nsynergistic effects. In this context, we have designed bimetallic\ncore–shell nanoparticles (NPs) combining a plasmonic metal\nAg as a core and a catalytic metal Pt as a shell. Ag@Pt core–shell\nNPs were synthesized via a seed-mediated growth process allowing fine\ncontrol of the Ag core size and Pt shell thickness. In the first step,\nAg seeds (8–13 nm) with a narrow size distribution (<10%)\nwere synthesized via chemical reduction by tuning the reaction time,\nheating ramp, and temperature. In the second step, we tuned the Pt\nshell thickness (from 1 to 6 atomic layers) by adjusting the ratio\nof the Pt precursor to silver seed concentrations. The Pt shell covered\nall of the particles, mostly heterogeneously. The robustness and versatility\nof the synthesis method were tested and successfully applied to different\nsystems (Ag/Au core and Pd/Pt shell). Subsequently, we studied the\nimpact of size and shell thickness on Ag@Pt optical properties by\nultraviolet-visible absorption spectroscopy (UV–visible) and\nby discrete dipole approximation (DDA) calculations. Finally, Ag@Pt\ncore–shell NPs were demonstrated to be more catalytically active\nthan Ag and Pt NPs of similar sizes through a model reaction of reduction\nof 4-nitrophenol (4-NP) in 4-aminophenol (4-AP) in the presence of\nNaBH₄. These results highlight the synergistic catalytic\neffect of Ag and Pt species, which may be due to the electronic structure\nof Ag@Pt core–shell NPs, but may also arise from the localized\nsurface plasmon resonance (LSPR) excitation of the Ag core. This shows\nthe potential of these particles for applications in plasmonic catalysis