Impact of Photosensitizing Multilayered Structureon Ruthenium(II)-Dye-SensitizedTiO2-Nanoparticle Photocatalysts

摘要

To improve the efficiency of photoinduced charge separation on the surface of dye-sensitized TiO2 nanoparticles, we synthesized the Ru(II)-photosensitizer-immobilized, Pt-cocatalyst-loaded TiO2 nanoparticles >RuCP^>2@Pt–TiO2, >RuCP^>2–Zr–>RuP^>6@Pt–TiO2, and >RuCP^>2–Zr–>RuP^>4–Zr–>RuP^>6@Pt–TiO2 (>RuCP^>2 = [Ru(bpy)2(mpbpy)]^2–, >RuP^>4 = [Ru(bpy)(pbpy)2]^6–, >RuP^>6 = [Ru(pbpy)3]^10–, H4mpbpy = 2,2′-bipyridine-4,4′-bis(methanephosphonic acid), and H4pbpy = 2,2′-bipyridine-4,4′-bis(phosphonic acid)) using phosphonate linkers with bridging Zr⁴⁺ ions. X-ray fluorescence and ultraviolet–visible absorption spectra revealed that a layered molecular structure composed of Ru(II) photosensitizers and Zr⁴⁺ ions (i.e., >RuCP^>2–Zr–>RuP^>6 and >RuCP^>2–Zr–>RuP^>4–Zr–>RuP^>6) was successfully formed on the surface of Pt–TiO2 nanoparticles, which increased the surface coverage from 0.113 nmol/cm² for singly layered >RuCP^>2@Pt–TiO2 to 0.330 nmol/cm² for triply layered >RuCP^>2–Zr–>RuP^>4–Zr–>RuP^>6@Pt–TiO2. The photocatalytic H2 evolution activity of the doubly layered >RuCP^>2–Zr–>RuP^>6@Pt–TiO2 was three times higher than that of the singly layered >RuCP^>2@Pt–TiO2, whereas the activity of triply layered >RuCP^>2–Zr–>RuP^>4–Zr–>RuP^>6@Pt–TiO₂ was less than half of that for >RuCP^>2@Pt–TiO₂. The photosensitizing efficiencies of these Ru(II)-photosensitizer-immobilized nanoparticles for the O₂ evolution reaction catalyzed by the Co(II)-containing Prussian blue analogue [Co^II(H₂O)₂]_1.31[{Co^III(CN)₆}_0.63{Pt^II(CN)₄}_0.37]decreased as the number of Ru(II)-photosensitizing layers increased.Thus, crucial aspects of the energy- and electron-transfer mechanismfor the photocatalytic H₂ and O₂ evolution reactionsinvolve not only the Ru(II)-complex-TiO₂ interface butalso the multilayered structure of the Ru(II)-photosensitizers onthe Pt–TiO₂ surface.