PULSED LASER-INDUCED OXIDATION OF PHENOL IN ACID AQUEOUS TIO2 SOLS

Transient formation in aqueous acid unprotected TiO2 sols containing phenol has been studied by time-resolved absorption spectroscopy upon irradiation with 10 ns laser pulses at 355 nm. Four types of sol were studied, differing in the starting compound used for colloid preparation [TiCl4 or titanium(IV) tetraisopropylate] and in the acid used for pH adjustment (HCI or HCIO4). Phenoxyl radical formation is demonstrated, the major part of which involves Cl2.- radical anions as intermediates which oxidize phenol. The formation of Cl2.-, in turn, occurs by valence-band hole oxidation of Cl-, which is either introduced into the solution as HCI to adjust the pH or is present on the particle surface if TiCl4 is used as starting compound. Laser pulse energy-dependent measurements of transient formation were performed to determine oxidation quantum yields and concentrations of surface-adsorbed Cl-.