Study of the photo-electrochemical activity of cobalt- and nickel-doped TiO2 photo-anodes for the treatment of a dye-contaminated aqueous solution

Abstract

The photo-electrochemical activity of Co- and Ni-doped TiO2 electrodes was studied using an aqueous solution containing an organic dye (Orange II) as a model polluted effluent. The results showed not only that both dopant species increased the activity of the photo-anode toward the dye color degradation but also that a specific proportion of the dopant materials maximized this effect. Interestingly, the best performance in the photo-electrochemical dye degradation process for the two doped materials was obtained using a 20 wt% doping synthetic proportion; achieving in both cases close to 90 % color removal during the first 10 min of reaction time. Employing the Langmuir–Hinshelwood formalism, the dopant effect was measured in terms of an increase in the kinetic rate coefficient and a coupled decrease in the dye adsorption equilibrium constant. In this way, while the surface rate constant (k c) for the doped materials were found to be 3.3 (Co) and 2.7 (Ni) times higher than that of the un-doped TiO2, the L–H adsorption constant were calculated as 0.083, 0.021, and 0.036 (mgL−1)−1 for the TiO2, Co- and Ni-doped materials, respectively. The results from additional experiments that followed the temporal evolution of the concentration of electro-generated H2O2 suggested a Fenton-like effect with regard to the anode performance caused by the doping species in the semiconductor anode.