Plasmon-Induced Photocatalysis Based on Pt–Au Coupling with Enhanced Oxidation Abilities

Pt has been used as a cocatalyst for semiconductor photocatalysis because of its high catalytic activity. Although Pt catalysts are highly active for both oxidation and reduction reactions, photocatalysts have exploited the activity of Pt almost exclusively for reduction reactions. In the case of Au nanoparticles combined with a semiconductor, oxidation reactions take place at the Au surface due to plasmon-induced charge separation (PICS). If Au nanoparticles are replaced with Pt nanoparticles, oxidation reactions may occur at the Pt surface. However, Pt is much less plasmonic in comparison with Au, in the visible wavelength range. In order to make Pt nanoparticles resonant with visible light, here we coupled small Pt nanospheres (PtNSs) with large Au nanocubes (AuNCs) electromagnetically on TiO2, so that a coupling resonance mode arose at ∼600 nm. The bimetallic coupling allowed the PtNS and the AuNC to serve as a charge separation and catalytic reaction unit and a light-harvesting antenna unit, respectively. Light collected by the AuNC is transferred to the PtNS, where hot electron–hole pairs are generated. The electrons are injected into TiO2, and the holes drive the oxidation reactions at the Pt surface. We performed oxidation of water at the PtNSs. As a result of coupling, the external quantum efficiency of PICS was enhanced by a factor of 28 because of the amplified interparticle electric field and intensified light absorption in the PtNS.