PHOTOCATALYZED TRANSFORMATION OF CHLOROAROMATIC DERIVATIVES ON ZINC-OXIDE .4. 2,4-DICHLOROPHENOL

The irradiation of aqueous solutions of 2,4-dichlorophenol (2,4-DCP) in the presence of ZnO (2 g.l-1) leads to the formation of several products which were analysed by HPLC and GC-MS coupling. The main initial reaction is a hydroxylation in ortho or para position with respect to phenol function. In position 2 and 4, this hydroxylation implies a dechlorination. The main identified photoproducts were chlorohydroquinone and 3,5-dichlorocatechol, but the formations of 4-chlorocatechol and chlorohydroxybiphenyls were also observed. The formation of hydrogen peroxide was a linear function of the irradiation time up to conversion extents higher than 30%, whereas the conversion of 2,4-DCP decreased with increasing irradiation time. From the inhibiting effect of EtOH on the transformation of 2,4-DCP, it can be concluded that about 70% of the conversion involves hydroxyl radicals and about 30% can be attributed to positive holes formed on ZnO.