Direct observation of the cascade hole transfer giving free radical cations of trans-stilbenes during TiO2 photocatalytic reactions

One-electron oxidation of 4-phenylbenzoic acid (PBA) by the photo-generated holes and cascade hole transfer from surface-bound radical cation of PBA to free trans-stilbenes (St) at the surface of TiO2 powder slurried in CH3CN has been investigated by time-resolved diffuse reflectance spectroscopy. Formation of radical cations of St (St+) was clearly observed, suggesting that St+ were generated by the cascade hole transfer from the radical cation of PBA adsorbed on the TiO2 surface to free St at the TiO2 surface. The hole transfer kinetics at the TiO2 surface and in the bulk CH3CN solution were also discussed in terms of Marcus theory.