Ag@Pt Core-Shell Nanoparticles for Plasmonic Catalysis

Bimetallic nanocatalysts (NCs) composed of two metal elements are a promising way to achieve high catalytic performance based on so-called synergistic effects. In this context, we have designed bimetallic core-shell nanoparticles (NPs) combining a plasmonic metal Ag as a core and a catalytic metal Pt as a shell. Ag@Pt core-shell NPs were synthesized via a seedmediated growth process allowing fine control of the Ag core size and Pt shell thickness. In the first step, Ag seeds (8-13 nm) with a narrow size distribution (<10%) were synthesized via chemical reduction by tuning the reaction time, heating ramp, and temperature. In the second step, we tuned the Pt shell thickness (from 1 to 6 atomic layers) by adjusting the ratio of the Pt precursor to silver seed concentrations. The Pt shell covered all of the particles, mostly heterogeneously. The robustness and versatility of the synthesis method were tested and successfully applied to different systems (Ag/Au core and Pd/Pt shell). Subsequently, we studied the impact of size and shell thickness on Ag@Pt optical properties by ultraviolet-visible absorption spectroscopy (UV-visible) and by discrete dipole approximation (DDA) calculations. Finally, Ag@Pt core-shell NPs were demonstrated to be more catalytically active than Ag and Pt NPs of similar sizes through a model reaction of reduction of 4-nitrophenol (4-NP) in 4-aminophenol (4-AP) in the presence of NaBH4. These results highlight the synergistic catalytic effect of Ag and Pt species, which may be due to the electronic structure of Ag@Pt core-shell NPs, but may also arise from the localized surface plasmon resonance (LSPR) excitation of the Ag core. This shows the potential of these particles for applications in plasmonic catalysis