Dye Mixing Effects on Photocatalytic Water Splitting Activity on Dye-Modified $KTaO3$ Catalyst

Dye mixing effects on water splitting activity of $KTaO3$ photocatalyst modified by various porphyrinoids was investigated. Photocatalytic activity of dye-modified $KTaO3$ catalyst is greatly improved by mixing various porphyrinoids, in which transition metals such as Cr, Fe, and Co are used as central metal. Pentametylene bis[4-(10, 15, 20-triphenyl porphine-5-yl) benzoate]-dizinc(II) (Zn-TPP dimer) showed positive effect on photocatalytic activity, and $H2$ and $O2$ formation rates are $365μmolg−cat.−1h−1$ and $152μmolg−cat.−1h−1$⁠, respectively. On the other hand, the combination of chloroprotoporphyrinato iron (III) (chlorohemin) with Cr-phthalocyanine (CrPc) is the most effective for increasing water splitting activity, and the formation rates of $H2$ and $O2$ are $2.12mmolg−cat.−1h−1$ and $1.11mmolg−cat.−1h−1$⁠, respectively. Energy conversion efficiency of this photocatalyst is estimated to be approximately 0.05%. From X-ray photoelectron spectroscopy measurement and cyclic voltammetry of organic dyes, it is suggested that the electronic state of the dye mixture is modified compared with that of a single dye. Energy transfer between mixing dyes is observed in the fluorescence spectra of dye-modified $KTaO3$ photocatalysts. Recombination of photoexited charge in $KTaO3$ is clearly suppressed by dye mixing, thus improvement of photocatalytic activity is attributed to the lengthening of excitation lifetime. This study reveals that mixing porphyrinoid dyes is an effective method for increasing water splitting activity of dye-modified $KTaO3$ photocatalysts.