Photocatalytic conversion of hexavalent chromium with low dosages of titania nanoparticles: RSM modeling, employing a new method in kinetic Study and energy consumption

Photocatalytic reduction of hexavalent chromium Cr(VI) ions in aqueous media was performed with remarkably low dosages of commercial TiO2 nanoparticles. A direct imposed irradiation photo reactor, equipped with ultrasonic source was used. Four influencing parameters, including temperature within the conventional range of (15 to 45) °C, were considered. Design of experiments, modeling and process optimization were performed using central composite design (CCD) of response surface methodology. Accordingly, a reduced quadratic expression was developed to predict the reduction efficiency, and analysis of variance showed the model well consistency with experimental data. At the found optimized conditions of [TiO2]= 33.1 mg/L, pH= 2.50, T= 36 °C and t= 120 min, about 81% efficiency was achieved for reduction of 5 mg/L of initial Cr(VI). The process was revealed proceeding through parallel branches of photolysis and the photocatalysis simultaneously. In kinetic investigations, the effect of catalyst particles’ turbidity was taken into account and the rate of reduction of the Cr(VI), under mild conditions, was expressed as the sum of the rates of individual photolysis and photocatalysis process branches. Pseudo first order reactions are proceeding. Furthermore electrical energy consumption was evaluated for overall process.

Keywords:

Photocatalytic reduction , Hexavalent chromium , Modeling , Kinetic , Energy consumption