Functionalization of Plasmonic Photocatalysts by the Introduction of Core–Shell Structure

Abstract

This chapter introduces two examples of functionalization of gold (Au) plasmonic photocatalysts by the introduction of core–shell structure, i.e., control of surface plasmon resonance (SPR) and drastic improvement of the catalytic performance. Au particles supported on tin(IV) oxide were modified with copper (Cu) and silver (Ag) by the multi-step photodeposition method. Absorption at around λ = 550 nm attributed to SPR of Au gradually shifted to longer wavelengths by modification with Cu and finally reached λ = 620 nm. On the other hand, the absorption shifted to a shorter wavelength with an increase in the amount of Ag and reached λ = 450 nm. The Au@Ag/SnO₂, Au@Cu/SnO_2, and Au/SnO₂ samples mineralized formic acid in water under irradiation of visible light and the reaction rates over these samples changed depending on the wavelength of light. These photocatalysts can also be used for selective oxidation of alcohols to corresponding carbonyl compounds in aqueous solutions. By using a two-step photodeposition method, Au@Pd/TiO₂ samples were successfully prepared and Au@Pd/TiO₂ with a shell thickness of 1.0 nm quantitatively converted chlorobenzene and 2-propanol to benzene and acetone under irradiation of visible light. Thickness control of the Pd shell was very important for both a satisfactory co-catalyst effect and absorption due to the SPR of Au nanoparticles.