HETEROGENEOUS PHOTOCATALYZED OXIDATION OF CREOSOTE COMPONENTS - MINERALIZATION OF XYLENOLS BY ILLUMINATED TIO2 IN OXYGENATED AQUEOUS-MEDIA

Dimethylphenols (xylenols) represent an important component of the phe nolic substances in coal tar creosote, a mixture used widely as a wood preservative. The photocatalyzed degradation of ah six isomeric forms of xylenol and the mineralization of 3,4-dimethylphenol were examined in air-equilibrated and oxygenated, illuminated titania dispersions. Some of the hydroxylated intermediates were identified by high perform ance liquid chromatography (HPLC). The effects of varying the pH, conc entration of TiO2 and xylenol, temperature and light intensity on the process kinetics were also examined. Kinetic considerations emphasize the notion that the oxidative mineralization process follows natural s aturation-type kinetics for which the Langmuir-Hinshelwood model, ofte n invoked in photocatalysis, is a special case; however, it is emphasi zed that this model is not an a priori requirement in heterogeneous ph otocatalysis.