Palladium nanoparticles have proven to be useful in catalyzing chemical transformations in organic and inorganic synthesis, pollutant treatment, and energy conversion. Recently, there is a growing interest to improve the catalytic property of palladium nanoparticles by introducing a second metal to form a composite nanostructure. Gold has attracted much attention as the potential second metal because of its own catalytic activity and surface plasmon resonance (SPR) in the form of nanometer-sized structures.
In this study, we coat Pd onto rod-shaped gold nanoparticles. We demonstrate that trace amount of Pd-coated gold nanorods greatly expedites the photo-reduction of resazurin to resorufin as compared to Pd spheres. The photo-reaction in the presence of hydrazine undergoes two steps: (1) a radical intermediate-generating step caused by the photon-initiated electron transfer, and (2) the deoxygenation of the radical intermediate. The presence of the Pd facilitates both the electron transfer and the deoxygenation steps. The enhanced catalytic activity of Pd-coated gold nanorods as compared to Pd nanospheres comes from gold nanorod cores acting as an antenna to receive photon energy and transfer to the reactants more efficiently due to their SPR at the photo-reaction wavelength. The existence of gold nanorod core SPR is confirmed by observing the scattering spectra of individual palladium-coated gold nanorod particles. This study demonstrated a new way to tune the catalytic property of nanoparticle catalysts.