Unprecedentedly enhanced solar photocatalytic activity of a layered titanate simply integrated with TiO2 nanoparticles

We report a simple, low-cost methodology for unprecedentedly enhancing the photocatalytic activity of layered inorganic semiconductors. A layered titanate with a lepidocrocite-type structure scarcely showed photocatalytic activity for a test reaction, the oxidative decomposition of formic acid in water into CO2, under simulated solar light, but it showed highly enhanced photocatalytic activity upon mixing with a much smaller amount (approximately 10 wt%) of commercially available TiO2 nanoparticles (P25) in water. The photocatalytic activity of the mixture was approximately 5 times that of P25, a benchmark photocatalyst. From various analyses, the enhancement resulted from the transfer of photoexcited electrons from the layered titanate to P25 at their particle interfaces and retardation of charge recombination. When applied to a photocatalyst for H-2 production from water containing methanol under simulated solar light, the layered titanate/P25 mixture showed considerably enhanced activity and the apparent quantum yield was 23% (at 320 nm). By replacing P25 with Pt co-catalyst-loaded P25, the apparent quantum yield of the mixture increased from 23 to 73%, although an extremely small amount (below 0.06%) of Pt was used in the system.