The enhancement of the photocatalytic properties of SmFe0.7Co0.3O3 thin films by synergistic effect of Sr doping and H2O2 as co-catalyst

In this paper we have made a comparative study of the photocatalytic properties of SmFe0.7Co0.3O3 and Sm0.7Sr0.3Fe0.7Co0.3O3 thin films for rhodamine B degradation, in the absence and in the presence of hydrogen peroxide as co-catalyst, by using low power UV deuterium lamp and materials consumption. The rhodamine B photodegradation was investigated for three concentrations: 2, 3, 4 mg.L-1. Orthorhombic films have been studied by X-ray diffraction, X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and Diffuse Reflectance Spectrophotometry. The presence of Sr atoms in SmFe0.7Co0.3O3 matrix induces: (1) the increase of oxygen vacancies number, (2) the reduction of Fe4+ to Fe3+ and Fe2+ with the decrease of Co2+ concentration and (3) the increase of porosity, all having as effects the increased photocatalytic efficiency of the Sr doped film. In the presence of co-catalyst, the degradation efficiency reached 100% after 120 min for the doped film, and 150 min for undoped one, while, in its absence, the highest values were obtained for the doped film (60-80% after 45 h). We determined that, in the absence of the co-catalyst, the dominant mechanisms are likely pseudo-first order in the first 4 h, and pseudo-half order in 4-45 h interval. For the photosystems that contain the co-catalyst, the mechanism is pseudo-first order, the apparent rate constants being higher for the doped sample, for all photoreaction systems. No structural changes are observed after the photocatalytic cycles, and their photocatalytic performance remains practical unchanged, indicating a good stability of the investigated films.