SPIN TRAP STUDY OF HYDROXYL RADICALS FORMED IN THE PHOTOCATALYTIC SYSTEM TIO2-WATER-P-CRESOL-OXYGEN

The formation of hydroxyl radicals in the photocatalytic system TiO2-water-p-cresol-oxygen employing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap was investigated at various initial concentrations of p-cresol. The reciprocal values of the relative concentrations of the DMPO adduct with hydroxyl radicals (DMPO-OH.) exhibited a linear dependence upon the initial concentrations of p-cresol. The data obtained are well described by the Langmuir-Hinshelwood kinetic model. The adsorption isotherms, separately determined for DMPO and p-cresol on TiO2, indicated that the adsorption of DMPO is three times higher than that of p-cresol. The adsorption measured at constant p-cresol concentrations and variable DMPO concentrations confirms a competitive adsorption and implies that both species adsorb on the same TiO2 SiteS. (C) 1994 Academic Press, Inc.