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 H 2 evolution under visible light with respect to the energy structure of the hybrids. Three Ru(II) complexes, Ru II {(4,4′-X 2 -bpy) 2 (4,4′-(CH 2 PO 3 H 2 ) 2 -bpy)} (X = H, CH 3, CF 3; bpy = 2,2′-bipyridine), were used as redox photosensitizers. HCa 2– x Sr x Nb 3 O 10 (0 ≤ x ≤ 2) and HCa 2 Nb 3– y Ta y O 10 (0 ≤ y ≤ 1.5) nanosheet aggregates, having a tunable conduction band potential ( E CB ), were employed as the building block. Nanosheets that possess more negative E CB value were found to be preferable for the dye-sensitized H 2 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 HCa 2 Nb 3 O 10 nanosheet was sensitized by Ru II {(4,4′-(CH 3 ) 2 -bpy) 2 (4,4′-(CH 2 PO 3 H 2 ) 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 H 2 evolution on a sensitizer/semiconductor hybrid by refining the E CB value of a semiconductor and the oxidation potential of the excited state of a photosensitizer.