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

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.