Enhancement of Scattering and Near Field of TiO₂–Au Nanohybrids Using a Silver Resonator for Efficient Plasmonic Photocatalysis

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO₂ provides pure TiO₂ visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO₂ and TiO₂ layers in sequence, with Au NPs on the outer surface, Ag@SiO₂@TiO₂-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO₂ interface via SPR coupling with Au. Consequently, the activity of the TiO₂-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H₂ production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.