Plasmonic Antenna–Reactor Photocatalysts Based on Anisotropic Gold–Rhodium Superstructures for Biological Cofactor Regeneration

Abstract

The creation of antenna−reactor systems with a precise arrangement of reactor sites around an anisotropic plasmonic nanomaterial is essential to achieving a perfect balance between the charge generation, separation, and extraction processes in plasmonic photocatalysis. Here, we propose the formation and photocatalytic properties of gold−rhodium superstructures (AuNR-Rh SSs), wherein site-selective epitaxial growth of ordered rhodium islands is achieved on plasmonic gold nanorods (AuNR). Iodide ions play a crucial role in spatially controlling the nucleation and growth of reactor sites (Rh islands). The rational design of AuNR-Rh SSs led to the formation of uniform and spatially separated Rh islands with high-index facets on the surface of AuNR, ensuring efficient light excitation and hot charge carrier separation, as well as enhanced reactant adsorption and activation. These antenna−reactor superstructures are further used for plasmon-driven photoregeneration of biological nicotinamide cofactors (NADH and NADPH). A suitable functionalization of AuNR-Rh SSs with negatively charged surface ligands helped the electrostatic channeling of electron mediators toward the photocatalyst surface, thereby increasing the charge transfer and utilization processes. Both the antenna−reactor effect and favorable catalyst−reactant interaction collectively boost the photocatalytic activity of AuNR-Rh SSs in regenerating the enzymatically active 1,4-NAD(P)H cofactors in ∼40% yield. A series of control experiments prove the role of each component, the precise arrangement of active sites, and appropriate surface functionalization in dictating the photocatalytic activity of anisotropic AuNR-Rh SSs antenna−reactor construct. Our work shows the need for a uniform but spatially separated deposition of reactor sites on the surface of an anisotropic nanoparticle to achieve the desired photocatalytic output from the corresponding antenna−reactor system. The anisotropic Au−Rh based antenna−reactor systems reported here could find applications in other plasmon-driven chemical transformations as well.