Efficient Extraction of Energetic Charge Carriers from an Engineered Plasmonic Nanocomposite to Perform Cascade Reactions

The realization of plasmon-generated hot charge carriers presents tremendous opportunities for light-harvesting in the field of photocatalysis. However, extracting the energetic charge carriers while competing with their recombination tendency is still a major bottleneck for efficient plasmonic photocatalysis. Therefore, strategic changes in the design principles of hybrid plasmonic nanocomposites to generate highly localized charge carriers at the catalytic site are imperative for hot electrons (holes) transfer to short-lived reaction intermediates. Here, we engineered Au-Pt core-shell nanostructures with only a few monolayers of epitaxially grown Pt onto Au nanocubes. The finite element method (FEM) simulations for optical properties of Au-Pt system support the design and hypothesis of selective funneling of plasmonic energy/charge carriers from Au core to Pt shell and their potential extraction for activating chemical bonds on Au-Pt nanocubes (Au-Pt NCs) surface. Further, investigating Au-Pt NCs as plasmonic catalysts, we show direct, visual evidence of plasmon-assisted cascade reduction of nonfluorescent resazurin (Rz) dye to nonfluorescent dihydroresorufin (DHRf) via a highly fluorescent resorufin (Rf) intermediate form. In the excitation wavelength-dependent study, the maximum apparent quantum efficiency of 48% (Rz to Rf conversion) and 8.4% (Rf to DHRf conversion) at 561 nm laser excitation demonstrates the plasmon assisted charge carrier driven cascade reduction on Au-Pt NCs surface. Control experiments carried out with only Au nanocubes (Au NCs) or Pt seed nanoparticles under the same reaction conditions show no significant cascade reduction of Rz, highlighting the synergistic effect of the plasmonic core and ultrathin catalytic shell.