Multiplasmon modes for enhancing the photocatalytic activity of Au/Ag/Cu₂O core-shell nanorods

One of the critical challenges for semiconductor photocatalysis is the high efficiency utilization of solar energy. For plasmonic metal-semiconductor photocatalysts, the photocatalytic activity over an extended wavelength range for a photoresponsive semiconductor could be significantly improved either via the direct electron transfer (DET) or via the plasmon-induced resonant energy transfer (PIRET). Still, the narrow spectral overlap of plasmon and the semiconductor band edge is a key factor in restricting the development of PIRET. Herein, we have introduced a simple and versatile strategy to realize a broad spectral overlap by creating multipolar plasmon resonances near the semiconductor band edge. Cu₂O coated Au/Ag nanorods (NRs) were prepared using a facile wet chemistry method. Transverse plasmon modes of Au/Ag/Cu₂O NRs can split into dipole and octupole plasmon modes. The core aspect ratio and shell thickness could be used to regulate these two modes for extending the spectral overlap of plasmon resonance and the Cu₂O band edge. Au/Ag/Cu₂O NRs were found to display enhanced visible light photocatalytic activity compared to spherical Au/Ag/Cu₂O nanoparticles. The enhancement mechanism was ascribed to both dipole and octupole plasmon modes boosting electron-hole separation in Cu₂O via PIRET as confirmed by transient absorption measurements.