Contribution to water purification using polyoxometalates. Aromatic derivatives, chloroacetic acids

Abstract

Polyoxometalates appear to be effective photocatalysts for a variety of organic pollutants, leading to their decomposition to CO 2 and H 2O and Cl − in case of chlorinated hydrocarbons. Various aromatic derivatives and chlorinated acetic acids, undergo mineralization upon photolysis with near visible and UV light, in presence of W 10O 4− 32, PW 12O 3− 40, and SiW 12O 4− 40. These catalysts are, at least, as effective as TiO 2. The main oxidant appears to be OH radicals formed by the reaction of the excited polyoxometalates with H 2O. At the initial stages of photoreaction, dioxygen has a profound effect (up to eighteen times faster) on the photodegradation of chloroacetic acid, whereas, it has minor effect on chlorophenols. On the contrary, at the final stages of photodegradation of chlorophenols, the rates were an order of magnitude faster in presence than in absence of dioxygen. Substitution of WO moiety of SiW 12O 4− 40 for transition metals, namely, [H 2OMn IISiW 11O 39] 6− and [H 2OCu IISiW 11O 39] 6− reduced, by about an order of magnitude, the effectiveness of the catalyst.