Polyoxometallate photocatalysis for decontaminating the aquatic environment from organic and inorganic pollutants

Abstract

Polyoxometallates (POMs), i.e. metal oxide clusters of mainly tungsten, are effective homogeneous photocatalysts for the mineralization of organic pollutants. ·OH radicals formed by the reaction of the photo-excited POMs with H₂O appear to play a key role in the process. POMs are similar to TiO₂. In this article, the photocatalytic activity of POMs has been presented on several diversified organic pollutants of interest such as phenol, chlorophenols, chloroacetic acids, and pesticides to determine the feasibility of decontamination of aqueous solutions from these pollutants. The results show that aqueous solutions containing the target pollutants, upon photolysis in the presence of POMs, undergo effective degradation to CO₂, H₂O, and the corresponding inorganic anions. The intermediates identified give rise to complicated degradation mechanisms prior to mineralization. In addition, photolysis of an aqueous solution of metal ions in the presence of POMs and organic substrate leads to the oxidative degradation of the organic and the simultaneous reduction–precipitation of metals in elemental state. This process has been successful in the removal–recovery of a great variety of metal ions including either toxic metallic compounds (chromium and mercury) or valuable metals (such as copper, silver, gold, palladium, and platinum). Finally, the two pathways were combined into a simple one-pot process for the decontamination of aquatic environment from both organic pollutants and metal cations.