Charge-Transfer Mechanism in Pt/KTa(Zr)O-3 Photocatalysts Modified with Porphyrinoids for Water Splitting

The mechanism of photocatalytic splitting of H2O into H-2 and O-2 on Pt/KTa(Zr)O-3 modified with various porphyrinoids was investigated. The photocatalytic activity of KTaO3 catalysts is improved by dye modification. Cyanocobalamin (vitamin B I,) is the most effective for improving water-splitting activity, and the formation rates of H-2 and O-2 achieved values of 575 and 280 mu mol g(cat)(-1) h(-1), respectively. X-ray photoelectron spectroscopy spectra of KTa(Zr)O-3 photocatalysts showed that Pt loaded onto dye-modified KTaO3 was slightly oxidized and had low catalytic activity for the H, oxidation reaction. Photoluminescence (PL) spectra of KTAO(3) catalysts suggested that excitation energy was transferred between KTaO3, tetraphenylporphyrinatochromium (III) (Cr-TPP), and the Pt cocatalyst. The wavelength dependence of the activity of dye-modified KTa(Zr)O-3 photocatalysts indicated that excitation of both KTa(Zr)O-3 and the dye was essential for achieving increased photocatalytic activity. This result suggests that two-step excitation occurred in the dye-modified KTa(Zr)O-3 photocatalysts. Because the lifetime of the charge-separated state increased, this study reveals that modification with porphyrinoids is effective for increasing water-splitting activity.