Decolourization of an Azo Dye by Heterogeneous Photocatalysis

The decolourization of the azo dye Acid Orange 7 was investigated using a heterogeneous photocatalysis which comprised irradiating aqueous solutions of the dye with UV light at a wavelength of 254 nm in the presence of either (TiO 2 + ZnO) mixture, [ ( Ti O 2 + ZnO ) / S 2 O 8 2 − + or [(TiO 2 + ZnO)/Ag 2SO 4] at a pH of 6.1. It was observed that the dye decolourization was enhanced using UV / [ ( Ti O 2 + ZnO ) / S 2 O 8 2 − ] and UV/[(TiO 2 + ZnO)/Ag 2SO 4] catalytic systems over UV/(TiO 2 + ZnO) alone. Also, it can be seen that increasing the concentration of oxidant (Na 2S 2O 8 or Ag 2SO 4) added to (TiO 2 + ZnO) mixture led to a higher rate of dye decolourization. Electrical energy per order (EE/O) was proposed to assess the relative performance of each catalytic system used. It was found that EE/O decreases with increasing the concentration of Na 2S 2O 8 and Ag 2SO 4.