Photocatalytic oxidation of As(III) to As(V) in aqueous solutions: A low cost pre-oxidative treatment for total removal of arsenic from water

Nonionic nature of As(III) in aqueous solutions, pH less than nine makes it a difficult form of arsenic which cannot be efficiently removed from drinking water by conventional ion exchange and adsorption chromatographic techniques. In the presence of TiO2 photocatalyst and UV radiation, nonionic H3AsO3 can be readily oxidizied to the anionic form of As(V) with no formation of metallic arsenic. The rate of oxidation is found to be less pH dependent. The suggested mechanism for the holes and electrons consuming steps are: H3AsO3 + 2h(+) + 4OH(-) --> HAsO42- + 3H(2)O and 2H(+) + 2O(2) + 2e(-) --> H2O + 3/2O(2) respectively.