Photocatalytic degradation of phenol and p-cresol by polyoxotungstates. Mechanistic implications

Phenol and p-cresol undergo complete mineralization in aqueous solution upon photolysis with near visible and UV light, in the presence of polyoxometallates (POM) W10O324-, PW12O403- and SiW12O404-. The main oxidant appears to be the OH radicals produced by reaction of the excited POM with H2O. Carbon dioxide is produced after an induction period, indicating that the degradation process involves several intermediates prior to and after the opening of the ring. Hydroxylation products from the attack of OH radicals on the aromatic ring, as well as on the methyl group of p-cresol, have been detected. Dimerization products have also been detected in the mineralization process of p-cresol and are attributed to the relatively long lifetime of the intermediate p-hydroxybenzyl radical. Copyright (C) 1996 Elsevier Science Ltd