Pulsed laser-induced oxidation of phenol in acid aqueous TiO2 sols

Abstract

Transient formation in aqueous acid unprotected TiO₂ sols containing phenol has been studied by timeresolved 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 (HCl or HClO₄). Phenoxyl radical formation is demonstrated, the major part of which involves Cl^˙–₂ radical anions as intermediates which oxidize phenol. The formation of Cl^˙–₂, in turn, occurs by valence-band hole oxidation of Cl^–, which is either introduced into the solution as HCl 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^–.