Light induced elimination of mono-and polychlorinated phenols from aqueous solutions by PW12O403-. The case of 2.4.6-trichlorophenol

Light induced catalytic decomposition of several mono-, di-, and trichlorophenols and phenol in the presence of PW12O403- in aqueous solutions (pH 1) leads to mineralization of substrates. The method is an example of Advanced Oxidation Processes (AOP) that cause mineralization of organic pollutants through the generation of very active, mainly OH, radicals. Generally, chlorination of phenolic ring enhances the decomposition, whereas the effect of chlorine substituents in the ortho position is less pronounced. However, the rates of decomposition of chlorinated phenols are very much the same. Dioxygen's main function seems to be the regeneration of the catalyst, with limited participation in the initial stages of the photoreactions. A detailed study of 2,4,6-trichlorophenol (2,4,6-TCP) photodecomposition showed that key reactions involved were hydroxylation, substitution of chlorine by OH radicals mainly in the ortho and para positions, and breaking of the aromatic ring. Ring-opened products detected were maleic, oxalic, acetic, and formic acids. Acetic acid has been so far a common intermediate iri the photodecomposition of aromatic compounds with this method. The ultimate products were CO2, H2O, and Cl-.