Synthesis and Characterization of Ir and Rh Complexes Supported on Layered K4Nb6O17 as a Heterogeneous Photocatalyst for Visible-Light-Induced Hydrogen Evolution

Abstract Immobilization of photosensitizer cyclometalated iridium(III) ([Ir(ppy)2(bpy)]+) and proton reduction catalyst tris(2,2′-bipyridyl)rhodium(III) ([Rh(bpy)3]3+) complexes onto layered niobate (K4Nb6O17) has been achieved with the aim of developing a photocatalyst for H2 production under visible light irradiation. Ir LIII-edge and Rh K-edge X-ray absorption fine structure measurements suggest that the Ir and Rh complexes are easily immobilized with little effect on the surrounding ligand structure. The photoluminescence emission of the immobilized Ir complex near 550 nm decreases with increasing amounts of adjacent Rh complex, suggesting direct electron transfer from Ir to Rh. The Ir–Rh/K4Nb6O17 acts as a heterogeneous photocatalyst enabling both visible light sensitization and H2 production from an aqueous solution without an electron relay reagent. Leaching and agglomeration of the active metal complexes are not observed after catalytic reactions, and the recovered photocatalyst can be repeatedly recycled without deterioration in its catalytic activity. Moreover, use of exfoliated K4Nb6O17 nanosheets is proven to significantly enhance photocatalytic activity.