One-electron oxidation pathways during beta-cyclodextrin-modified TiO2 photocatalytic reactions.

The photocatalytic one-electron oxidation reactions of aromatic sulfides using the carboxymethyl-beta-cyclodextrin (CM-beta-CD)-modified TiO(2) nanoparticles (TiO(2)/CM-beta-CD) were investigated by using nano- and femtosecond transient absorption spectroscopies. The one-electron oxidation processes of the substrate (S) by the valence band hole (h(VB) (+)) at the TiO(2) 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 TiO(2)/CM-beta-CD is significantly enhanced relative to bare TiO(2). 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.