One-electron oxidation pathways during β-cyclodextrin-modified TiO2 photocatalytic reactions

The photocatalytic one-electron oxidation reactions of aromatic sulfides using the carboxymethyl-beta-cyclodextrin (CM-beta-CD)-modified TiO2 nanoparticles (TiO2/CM-beta-CD) were investigated by using nano- and femto-second transient absorption spectroscopies. The one-electron oxidation processes of the substrate (S) by the valence band hole (h(VB)(+)) at the TiO2 surface and the trapped hole at the adsorption site of the CM-beta-CD (h(CD)(+)) were examined. The transient absorption spectra and time traces observed for the charge carriers and the radical cation of S (S.+) revealed that the one electron oxidation reaction of S during the nano- and femtosecond laser flash photolyses of TiO2/CM-beta-CD is significantly enhanced relative to bare TiO2. The kinetics of the decay and the dimerization processes between S(.+)s are discussed on the basis of the results obtained by the pulse radiolysis technique.