Interband\nand Intraband Hot Carrier-Driven Photocatalysis\non Plasmonic Bimetallic Nanoparticles: A Case Study of Au–Cu\nAlloy Nanoparticles

Photoexcited nonthermal electrons and holes in metallic\nnanoparticles,\nknown as hot carriers, can be judiciously harnessed to drive interesting\nphotocatalytic molecule-transforming processes on nanoparticle surfaces.\nInterband hot carriers are generated upon direct photoexcitation of\nelectronic transitions between different electronic bands, whereas\nintraband hot carriers are derived from nonradiative decay of plasmonic\nelectron oscillations. Due to their fundamentally distinct photogeneration\nmechanisms, these two types of hot carriers differ strikingly from\neach other in terms of energy distribution profiles, lifetimes, diffusion\nlengths, and relaxation dynamics, thereby exhibiting remarkably different\nphotocatalytic behaviors. The spectral overlap between plasmon resonances\nand interband transitions has been identified as a key factor that\nmodulates the interband damping of plasmon resonances, which regulates\nthe relative populations, energy distributions, and photocatalytic\nefficacies of intraband and interband hot carriers in light-illuminated\nmetallic nanoparticles. As exemplified by the Au–Cu alloy nanoparticles\ninvestigated in this work, both the resonant frequencies of plasmons\nand the energy threshold for the <i>d</i>-to-<i>sp</i> interband transitions can be systematically tuned in bimetallic\nalloy nanoparticles by varying the compositional stoichiometries and\nparticle sizes. Choosing photocatalytic degradation of Rhodamine B\nas a model reaction, we elaborate on how the variation of the particle\nsizes and compositional stoichiometries profoundly influences the\nphotocatalytic efficacies of interband and intraband hot carriers\nin Au–Cu alloy nanoparticles under different photoexcitation\nconditions.