The simultaneous photocatalytic reduction of Cr(VI) and Ni(II) ions in aqueous media was studied using extremely low dosages of commercial TiO2 nanoparticles. A direct imposed irradiation photo reactor, equipped with ultrasonic source was used. The effects of temperature within the conventional range of (20 to 40) °C, solution pH within 4.5-8.5, ratio of Cr(VI)/Ni(II) within 0.5- 1.5, were studied. The results show that both ions reduction was enhanced, compared with the corresponding individual ions and that Cr(VI) and Ni(II) were reduced to Cr(III) and Ni0, respectively. Furthermore, the effect of hole scavengers was studied. The average photo-reduction of both ions increases with the scavengers in the order of ethylene glycol > formic acid > citric acid. Under the best found conditions of [TiO2] = 40 mg/L, pH = 7.5, T= 35 °C, presence of ethylene glycol and during 110 min, about 61% average reduction (50% Cr(VI) and 72% Ni(II)) was achieved for the ratio of Cr(VI)/Ni(II) = 0.5. In kinetic investigations, the rate of reduction was expressed with respect to the individual ions reduction branches.
