Promoting Plasmonic Photocatalysis with Ligand-Induced Charge Separation

Plasmonic nanoparticles have been demonstrated to enhance photocatalysis due to strong photon absorption and efficient hot-carrier generation. The intraband Landau damping creates hot electrons and warm holes by exciting surface plasmon resonances, while the d-sp interband transition yields hot d-band holes and warm electrons. However, plasmonic photocatalysts suffer a short lifetime of plasmon-generated hot carriers that decays through internal relaxation pathways before being harnessed for chemical reactions. Here, we demonstrate an enhancement of the photocatalytic reduction reaction of gold ions on gold nanorods coated with Polyvinylpyrrolidone (PVP). The catalytic activities of the reaction are quantified by in-situ monitoring the spectral evolution of single nanorods using dark-field spectro-microscopy. We observed an increased reduction rate by a factor of five with the excitation of d-sp interband transition compared to the dark condition and a negligible increase in reduction rate when excited with the intraband transition. Additionally, the hole scavenger only plays a minor role in the photocatalytic reduction reaction with the interband transition. We attribute the enhanced photocatalysis to an efficient charge separation at the gold-PVP interface where a photogenerated d-band hole at gold transfers to the HOMO of PVP, leading to the prolonged lifetime of the warm electrons that subsequently reduce gold ions to gold atoms. These results provide new insight into the design of plasmonic photocatalysts with capping ligands.