Hybrids of a Ruthenium(II) Polypyridyl Complex and a Metal Oxide Nanosheet for Dye-Sensitized Hydrogen Evolution with Visible Light: Effects of the Energy Structure on Photocatalytic Activity

Hybrid materials consisting of a ruthenium­(II) polypyridyl complex and a Dion–Jacobson type perovskite oxide nanosheet were studied as photocatalysts for dye-sensitized H₂ evolution under visible light with respect to the energy structure of the hybrids. Three Ru­(II) complexes, Ru^II{(4,4′-X₂-bpy)₂(4,4′-(CH₂PO₃H₂)₂-bpy)} (X = H, CH₃, CF₃; bpy = 2,2′-bipyridine), were used as redox photosensitizers. HCa_2–<i>x</i>Sr_<i>x</i>Nb₃O₁₀ (0 ≤ <i>x</i> ≤ 2) and HCa₂Nb_3–<i>y</i>Ta_<i>y</i>O₁₀ (0 ≤ <i>y</i> ≤ 1.5) nanosheet aggregates, having a tunable conduction band potential (<i>E</i>_CB), were employed as the building block. Nanosheets that possess more negative <i>E</i>_CB value were found to be preferable for the dye-sensitized H₂ evolution, unless electron injection from the excited-state sensitizer to the conduction band of a nanosheet is hindered. Among the combinations tested, the highest activity was obtained when an HCa₂Nb₃O₁₀ nanosheet was sensitized by Ru^II{(4,4′-(CH₃)₂-bpy)₂(4,4′-(CH₂PO₃H₂)₂-bpy)}, exhibiting a maximum apparent quantum yield of ca. 10% at 460 nm and a turnover number of ca. 3800 (for 20 h). This study highlighted that it is possible to maximize the performance of dye-sensitized H₂ evolution on a sensitizer/semiconductor hybrid by refining the <i>E</i>_CB value of a semiconductor and the oxidation potential of the excited state of a photosensitizer