Enhancement of Photocatalytic Activity for Hydrogen Production by Surface Modification of Pt-TiO2 Nanoparticles with a Double Layer of Photosensitizers

To investigate the effect of the surface structure of dye-sensitized photocatalyst nanoparticles, we prepared three types of Ru-II-photosensitizer (PS)-double-layered Pt-cocatalyst-loaded TiO2 nanoparticles with different surface structures, Zr-RuCP6-Zr-RuP6@N wt %Pt-TiO2, RuCP6-Zr-RuP6@N wt %Pt-TiO2, and RuCP2-Zr-RuP6@N wt %Pt-TiO2 (N=0.2, 1, and 5), and evaluated their photocatalytic H-2 evolution activity in the presence of redox-reversible iodide as the electron donor. Although the driving force of the electron injection from I- to the photo-oxidized Ru-III PS is comparable, the activity increased in the following order: RuCP2-Zr-RuP6@1 wt %Pt-TiO2 < RuCP6-Zr-RuP6@1 wt %Pt-TiO2 < Zr-RuCP6-Zr-RuP6@1 wt %Pt-TiO2. The apparent quantum yield of Zr-RuCP6-Zr-RuP6@1 wt %Pt-TiO2 in the first hour reached 1 %. Zeta-potential measurements suggest that the surface Zr4+-phosphate groups attracted I- anions to the nanoparticle-solution interface. Our results indicate that the surface modification of dye-sensitized photocatalysts is a promising approach to enhance photocatalytic activity with various redox mediators.