Visible light degradation of Orange II using xCuyOz/TiO2 heterojunctions

Cu2O/TiO2, Cu/Cu2O/TiO2 and Cu/Cu2O/CuO/TiO2 heterojunctions were prepared and studied for their potential application as photocatalysts able to induce high performance under visible light. Orange II was used as a representative dye molecule. The effect of the amount and composition of the photosensitizers toward the activation of TiO2 was studied. In each case, the global mechanism of Inter Particle Electrons Injection (IPEI) was discussed. The highest photocatalytic activity was observed for the system Cu/Cu2O/CuO (MB2 catalyst) under visible light (t(1/2) = 24 min, k = 159.7 x 10(-3) min(-1)) and for the heterojunction cascade Cu/Cu2O/CuO/TiO2 (MB2 (50%)/TiO2) under UV-vis light (t(1/2) = 4 min, k = 1342 x 10(-3) min(-1)). In the last case, the high performance was attributed firstly to the electromotive forces developed under this configuration in which CuO energy bands mediate the electrons transfer from Cu2O to TiO2. The formation of monobloc sensitizers also accounts for the decrease of the probability of the charges lost. It was demonstrated that Cu2O/CuO governs the capability of the heterojunction cascade and Cu does not play a significant role regardless of the heterojunction cascade efficiency. The electrical energy consumption per order of magnitude for photocatalytic degradation of Orange II was investigated for some representative catalytic systems. Visible/MB2 and UV/vis MB2 (50%)/TiO2 exhibited respectively 0.340 and 0.05 kWh m(-3) demonstrating the high efficiency of the systems. (C) 2009 Elsevier B.V. All rights reserved.