(Au@Ag)@Au double shell nanoparticles loaded on rutile TiO2 for photocatalytic decomposition of 2-propanol under visible light irradiation

• (Au@Ag)@Au nanoparticles were synthesized for utilization as photosensitizers of TiO2.
• (Au@Ag)@Au/TiO2 can oxidize 2-propanol into acetone and CO2 under visible light irradiation.
• Photocatalytic reaction process of (Au@Ag)@Au/TiO2 is proposed.

We synthesized (core@shell)@shell ((Au@Ag)@Au) nanoparticles (NPs) by a multistep citrate reduction method for utilization as photosensitizers of TiO2. The (Au@Ag)@Au NPs exhibited strong photoabsorption in visible light response due to LSPR excitation of the Ag shell, and its LSPR characteristics were stable under visible light irradiation for a long time because oxidation of the Ag shell was prevented by the outermost Au shell. Furthermore, we successfully loaded (Au@Ag)@Au NPs on rutile TiO2 by an impregnation method. (Au@Ag)@Au/TiO2 could oxidize 2-propanol into acetone and CO2 under visible light irradiation (λ > 440 nm), and its acetone evolution rate was approximately 15-times higher than that of Au/TiO2. From a comparison of action spectra for acetone evolution and the Kubelka–Munk function, it was confirmed that photocatalytic activity of (Au@Ag)@Au/TiO2 was induced by photoabsorption based on LSPR excitation of the Ag shell. In addition, photoelectrochemical measurements revealed electron injection from LSPR-excited (Au@Ag)@Au NPs into TiO2 under visible light irradiation. We proposed the photocatalytic reaction process of (Au@Ag)@Au/TiO2 in conjunction with optical, structural and photoelectrochemical properties.

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