Dual-Plasmonic\nGold@Copper Sulfide Core–Shell\nNanoparticles: Phase-Selective Synthesis and Multimodal Photothermal\nand Photocatalytic Behaviors

Abstract

Although\nthe intriguing plasmonic properties of noble metal nanoparticles\noriginate from the collective oscillations of free electrons in the\nconduction band, nanoparticles of doped semiconductors may also exhibit\nmetal-like, plasmonic features that are dictated by the resonantly\nexcited free hole oscillations in the valence band. Here, we combine\nAu, a representative free electron metal, with copper sulfides, a\nclass of plasmonic <i>p</i>-type semiconductors, in a core–shell\nnanoparticle geometry to construct dual-plasmonic hetero-nanostructures\ndisplaying unique multiplex optical characteristics dominated by plasmonic\nhole oscillations in the semiconductor shells, plasmonic electron\noscillations in the metallic cores, and interband electronic transitions\nfrom the valence to conduction bands. Through deliberately designed\ncolloidal synthesis, we are able to selectively grow nanoshells comprising\ncopper sulfides of specifically targeted crystalline phases and Cu/S\nstoichiometries, such as covellite (CuS), digenite (Cu_1.8S), and nonstoichiometric Cu_2–<i>x</i>S, on the surfaces of Au nanoparticle cores. Our synthetic approach\nenables us not only to finely control the core and shell dimensions\nbut also to systematically adjust the free hole concentrations in\nthe semiconductor shells, which forms the keystone for the fine tuning\nof multiple optical resonance modes supported by these hybrid hetero-nanostructures.\nThe dual-plasmonic Au@copper sulfide core–shell nanoparticles\nexhibit unique multimodal photothermal and photocatalytic behaviors\nupon selective photoexcitations of different optical transitions at\ntheir characteristic resonant frequencies, allowing us to quantitatively\nevaluate and rigorously compare the intrinsic photothermal and photocatalytic\nefficacies of multiple types of hot charge carriers, all photoexcited\nin the same hybrid nanoparticles but with distinct photophysical origins,\nexcited-state lifetimes, energy distributions, and transfer pathways.