Photocatalytic degradation of textile dye X3B by heteropolyoxometalate acids

Reactive brilliant red X3B, one recalcitrant textile dye, was decolorized in water by (Photo)-Fenton reactions and TiO2 photocatalysis [Chemosphere 43 (2001) 1103]. Complementary to this study, the present work has shown the effectiveness of several Keggin-type heteropolyoxomatalates (POM) as a photocatalyst for X3B degradation in water at pH 1.0 under UV light (λgreater-or-equal, slanted320 nm) irradiation. Among four POMs, the relative activity was observed to be H3PW12O40 much greater-than H4SiW12O40 > H4GeW12O40 > H3PMo12O40. The reaction was dependent of pH, light intensity and the catalyst loading, but not obviously of the molecular oxygen dissolved in water. Compared to the photocatalyst of TiO2 (Degussa p25), H3PW12O40 was less efficient for the dye bleaching and mineralization. The mechanism study reveals that hydroxyl radicals are involved in the degradation of X3B (and Rhodamine B) by POM photocatalysis.