Exceptional Sensitizer Dye Loading via a New Porous Titanium–Niobium Metal Oxide with Tris(2,2′-bipyridyl)ruthenium(II) in the Structure

Exceptionally high loadings of tris(2,2′-bipyridyl)ruthenium(II), abreviated as Ru(bpy)32+, were successfully incorporated into a titanium niobium mixed oxide framework. Ru(bpy)32+ loadings of 295.6 mg/g were achieved, equivalent to 518.9 μmol/g. Through an aqueous-phase mixing process, a solution of Ru(bpy)32+ was used to aggregate colloids of unilamellar anionic nanosheets, derived from the exfoliation of the layered semiconductor KTiNbO5. The aggregates formed were porous metal oxide composite materials with Ru(bpy)32+ electrostatically bound within the structure of the pore walls. The new solids were highly orange-colored due to the high internal content of Ru(bpy)32+. X-ray diffraction and chemical and theoretical analyses indicate that the ruthenium dye is incorporated as a single layer between the metal oxide sheets and that the dye loading is maximized. In well-rinsed samples, the Ru(bpy)32+ remained in the solid with only trace amounts of leaching even after 3 months in water at room temperature. The strategy demonstrated here is general enough to be applicable to other layered metal oxides. This report describes the first successful use of Ru(bpy)32+ and restacked KTiNbO5 to synthesize a stable, dye-sensitized, porous metal oxide semiconductor material. Improved sensitizer loadings correlate with light capture efficiencies, giving this new technique promise in solar energy conversion technologies.