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 (TiO2 + ZnO) mixture, [(TiO2 + ZnO)/ S2O82-) or [(TiO2 + ZnO)/Ag2SO4] at a pH of 6.1. It was observed that the dye decolourization was enhanced using UV/[(TiO2 + ZnO)/S2O82-] and UV/[(TiO2 + ZnO)/Ag2SO4] catalytic systems over UV/(TiO2 + ZnO) alone. Also, it can be seen that increasing the concentration of oxidant (Na2S2O8 or Ag2SO4) added to (TiO2 + 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 Na2S2O8 and Ag2SO4.