Charge carriers injection in tandem semiconductors for dyes mineralization

Four mono-component and three tandem structures were prepared by robotic spray pyrolysis deposition using different precursor compositions and deposition temperatures. The structures of the electronic bands and the light generation/injection of the charge carriers trough the tandem layers (CuxS, CuO, SnO2, ZnO, TiO2) were studied using electrical (J-V, photocurrent) and optical (UV-vis transmittance) measurements. The crystalline structures and crystallite sizes were evaluated by X-ray diffraction and the morphologies were studied via atomic force microscopy. The wettability properties and the surface energy were calculated based on contact angle measurements using two liquids with different polarities (glycerol and ethylene glycol). The photocatalytic investigations show that the sample containing TiO2_CuO-CuxS_SnO2 has the highest photo-mineralization efficiency (78% removal of total organic carbon). It was found that copper sulfide compounds increase the photosensitivity properties of the tandem structure especially in vis region of the spectra. The efficiency and kinetics data of the photocatalytic processes were in agreement with the electronic bands alignment, which shows that tandem structures with suitable band energy values and at least one active interface allow high charge carrier mobility and the generation of oxidative species during photocatalysis. (C) 2014 Elsevier B.V. All rights reserved.