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Photocatalytic activity of KTaO3 catalyst to water splitting is much improved by organic dye-modification. In particular, cyanocobalamin (Vitamin B12) is the most effective for improving water splitting activity, and the formation rate of H2 and O2 are achieved values of 1912 and 979 μimol gcat“’h”1, respectively, under the light irradiation from Xe lamp (300W). Mechanism of photocatalytic H2O splitting into H2 and O2 on PtOx/KTa(Zr)O3 modified with various dyes were investigated. Photoluminescence (PL) spectra of KTaO3 catalysts suggested that the excitation energy transfers from KTaO3 to Cr-Tetraphenylporphyrin (Cr-TPP) and PtOx co-catalyst. Transient response of photovoltaic potential revealed that the excitation state of KTaO3 was enlarged over 500 μs by dye-modification. Photo-excited electron in KTaO3 transfers to dye, and a long charge separation state was achieved. Thus, it was suggested that the photocatalytic activity was much improved by increasing lifetime of photo-excited charges which can reach to the reaction site effectively.

Titanate layered oxide intercalated with hydrated Eu3+ was synthesized by the electrostatic self-assembly deposition (ESD) method. The emission intensity of Eu3+ decreased rapidly with time during irradiation by UV light having energy higher than the band gap energy of the host Ti1.81O4 (TiO) layer. This is presumably due to the decrease in energy transfer from the host TiO layer to Eu3+ as a result of the change in the hydration state of water molecules surrounding Eu3+, which is caused by the hole produced in the TiO valence band. When irradiation was discontinued, the emission intensity gradually recovered. The recovery time increased when the water in the interlayer is removed by heat treatment. This indicates that the state of interlayer water changes during irradiation and returns to its initial state after discontinuation of irradiation. The excitation spectra changed drastically at any given wavelength upon irradiation with UV light. A comparison of the excitation spectra before and after irradiation reveals that only the excitation peak at around the irradiation wavelength decreased upon irradiation, as in the case of spectral hole burning. The hydration state of water molecules surrounding Eu3+ presumably changes depending on the irradiation wavelength.