Promoting reactivity of photoexcited hot electrons in small-sized plasmonic metal nanoparticles that are supported on dielectric nanospheres.

Plasmonic metal nanoparticles (NPs) represent a promising class of photocatalysts to drive chemical transformations by the photoexcited hot electrons in the NPs. In this work, the dependence of photon-to-chemical conversion efficiency on the size of plasmonic silver nanoparticles (Ag NPs) has been comprehensively studied with the use of the photocatalytic degradation of methylene blue as a probe reaction. Comparison of Ag NPs with two different sizes (6 nm and 13 nm in diameter) highlights that the smaller sized Ag NPs favor the photocatalytic activity by positively translating the high efficiency of hot electron generation to the hot-electron-driven chemical reaction on the surface of the Ag NPs. Loading the small Ag NPs to the dielectric silica nanospheres (SiO NSs, average diameter of 400 nm) with high surface coverage increases the light absorption power in the Ag NPs due to the surface light scattering resonances of the SiO NSs and interparticle plasmon coupling of the adjacent Ag NPs. The enhanced light absorption can also be rendered to the improved photocatalytic activity. This design principle of plasmonic photocatalysts provides a promise of utilizing solar energy to drive desirable chemical reactions with high photon-to-chemical conversion efficiency.