Herein, we present a ternary hybrid system formed by loading both a dye and a catalyst on n-type semiconductor nanoparticles, in which the TiO2 semiconductor should function as an efficient electron acceptor against the photoexcited dye (push-pull organic dye), as a pool capable of storing multiple electrons, and as a path for transporting electrons to the catalyst (Re(bpy)(CO)3Cl anchored on TiO2 nanoparticles). Given that the three different components have different excited states and conduction bands, which determine the position of the photoexcited electrons, an appropriate alignment of energy levels is essential for efficient electron flow from the sensitizer to the catalytic site. To meet this requirement, the flat-band potential of TiO2, which has a sizable energy barrier (between the energies of the sensitizer and TiO2 semiconductor) in a non-aqueous environment, was lowered to a suitable position for efficient electron flow through the use of additives (H2O, Li+, Na+, and TEOA). When this lowering of the energy barrier was accomplished, dramatic enhancement was achieved in the CO2 reduction catalytic reaction, indicating efficient electron flow from the sensitizer to the reduction catalytic site in our triad system. It is also observed that immobilization of Re(bpy)(CO)3Cl on TiO2 nanoparticles effectively improves the low reliability of homogeneous catalysis, yielding consistent photocatalytic behavior. In addition, screening light-harvesting materials and n-type semiconductors including TiO2 nanocystals to optimize CO2 reduction as well as introduction of new types of photocatalysts will be discussed.

Improving the efficiency and stability of photochemical CO2 reduction mediated by dye-sensitized ternary system (dye/TiO2/Re(I))

251st National Meeting (2016)

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