CONTRIBUTION TO WATER-PURIFICATION USING POLYOXOMETALATES - AROMATIC DERIVATIVES, CHLOROACETIC ACIDS

Polyoxometalates appear to be effective photocatalysts for a variety o f organic pollutants, leading to their decomposition to CO2 and H2O an d Cl- in case of chlorinated hydrocarbons. Various aromatic derivative s and chlorinated acetic acids, undergo mineralization upon photolysis with near visible and UV light, in presence of W10O324-, PW12O403-, a nd SiW12O404-. These catalysts are, at least, as effective as TiO2. Th e main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometalates with H2O. At the initial stages of photoreac tion, dioxygen has a profound effect (up to eighteen times faster) on the photodegradation of chloroacetic acid, whereas, it has minor effec t on chlorophenols. On the contrary, at the final stages of photodegra dation of chlorophenols, the rates were an order of magnitude faster i n presence than in absence of dioxygen. Substitution of W-O moiety of SiW12O404- for transition metals, namely, [(H2OMnSiW11O39)-Si-II](6-) and [(H2OCuSiW11O39)-Si-II](6-) reduced, by about an order of magnitud e, the effectiveness of the catalyst.