A Plasmonic Photocatalyst Consisting of Silver Nanoparticles Embedded in Titanium Dioxide

Abstract

Titanium dioxide (TiO2) displays photocatalytic behavior under near-ultraviolet (UV) illumination. In another scientific field, it is well understood that the excitation of localized plasmon polaritons on the surface of silver (Ag) nanoparticles (NPs) causes a tremendous increase of the near-field amplitude at well-defined wavelengths in the near UV. The exact resonance wavelength depends on the shape and the dielectric environment of the NPs. We expected that the photocatalytic behavior of TiO2 would be greatly boosted if it gets assisted by the enhanced near-field amplitudes of localized surface plasmon (LSP). Here we show that this is true indeed. We named this new phenomenon "plasmonic photocatalysis". The key to enable plasmonic photocatalysis is to deposit TiO2 on a NP comprising an Ag core covered with a silica (SiO2) shell to prevent oxidation of Ag by direct contact with TiO2. The most appropriate diameter for Ag NPs and thickness for the SiO2 shell giving rise to LSP in the near UV were estimated from Mie scattering theory. Upon implementing a device that took these design considerations into account, the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst, monitored by decomposition of methylene blue, was enhanced by a factor of 7. The enhancement of the photocatalytic activity increases with a decreased thickness of the SiO2 shell. The plasmonic photocatalysis will be of use as a high performance photocatalyst in nearly all current applications but will be of particular importance for applications in locations of minimal light exposure.

Near‐Infrared‐Plasmonic Energy Upconversion in a Nonmetallic Heterostructure for Efficient H2 Evolution from Ammonia Borane

“…This H 2 evolution amount is about 3.5 times higher than the H 2 evolution of pure W 18 O 49 NWs and even 35 times higher than the H 2 evolution of single BH 3 NH 3 hydrolysis. Meanwhile, the apparent quantum efficiency is comparable to the corresponding values obtained in other visible‐light photocatalysts 40, 41, 42. This implies that the upconversion NPs play a central role on the enhanced catalytic activity of the H 2 evolution.…”

Recent Progress in Energy‐Driven Water Splitting

“…Ag@SiO 2 ), demonstrating the enhanced photocatalytic activity of TiO 2 under near‐ultraviolet light irradiation. The photocatalytic activity was enhanced with a decreased thickness of silica shell because the near field enhancement of Ag nanoparticles was strongest in close proximity to their surface 42. Kumar et al also investigated the proximity effects of near field enhancement by fine‐tuning silica thickness to separate Ag nanoparticles from TiO 2 thin films.…”

Plasmon‐Mediated Solar Energy Conversion via Photocatalysis in Noble Metal/Semiconductor Composites

“…For LSPRs, plasmon resonance wavelengths in the visible and infrared (IR) regions enable the improved utilization of the solar spectrum 19. The enhanced local electric fields caused by plasmon effects raise the possibility of electron‐hole pair generation 20. Furthermore, the increased current density can lead to heat generation which may contribute to faster photochemical reactions 21…”