PHOTOCATALYTIC DEGRADATION OF 4-CHLOROPHENOL IN TIO2 AQUEOUS SUSPENSIONS

Photocatalytic degradation of 4-chlorophenol in TiO2 aqueous suspensions produces 4-chlorocatechol, an ortho hydroxylated product, as the main intermediate. This result disagrees with data reported by other researchers, who proposed the formation of a para-hydroxylated product, hydroquinone, as the major intermediate. Results also indicated that further oxidation of 4-chlorocatechol yields hydroxyhydroquinone, which can readily be oxidised and mineralized to carbon dioxide. Complete dechlorination and mineralization of 4-chlorophenol can be achieved. In contrast, direct photolysis of 4-chlorophenol produces hydroquinone and p-bensoquinone as the main reaction products. The photocatalytic oxidation reaction, initially mediated by TiO2, is generated by an electrophilic reaction of the hydroxyl radical attacking the benzene ring.