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Sol-gel synthesis and properties of lithium and cerium codoped perovskite

Variety of potential applications in electronics, ceramics, superconductors and catalysis made perovskites an important group of ceramic materials. Perovskites possess a structural formula of ABO3, where A is alkaline earth or rare earth metal having large ionic radius and coordination 12 and B is a hexacoordinated first row transition metal with smaller radius. CaTiO3, by which the whole group was named for, is one of the most important perovskites, particularly due to the use in catalysis. Since it has a large band gap value (~3.5 eV), CaTiO3 is not useful for photocatalytic degradation under solar irradiation. However, the A and B cations can be substituted with foreign cations without altering the crystal structure, thus altering various perovskite properties, including enhancement of the photocatalytic efficiency. Various synthesis methods have been used to prepare perovskite, one of the methods particularly convenient for the preparation of doped crystal phases is the sol-gel process. Thus, the aim of this work was the sol-gel synthesis of lithium and cerium codoped CaTiO3 and characterization of the obtained gel, as well ceramics obtained thereof by thermal treatment. Five samples of codoped perovskite, Ca1-xLixCexTiO3, where x=0, 0.01, 0.02, 0.03 and 0.04 were prepared. The characterization methods used were powder X–ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), differential thermal and thermo-gravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Photocatalytic activity of CaTiO3 was evaluated through investigation of methylene blue photocatalytic degradation. It was determined that the prepared samples are consisted of calcium nitrate and titanium chelate. Thermal treatment yields first with the liberation of solvent and water, followed with the decomposition of chelate and finally decomposition of nitrate and crystallization of perovskite. In concordance with the established thermal evolution path, all samples were subjected to thermal treatment at 500 °C for 2 hours. Secondary phases such as lime and anatase were detected in all samples thermally treated at at 500 °C for 2 hours, except sample with x=0.04, where, beside perovskite, Ca2Ti2O6 appeared. SEM analysis showed that the thermally treated samples are consisted of agglomerates of irregular morphology and that the primary particles size diminishes with the increase of the dopants concentration. The sample with x=0.04 showed an increased photocatalytic activity.

perovskite ; codoping ; sol-gel synthesis ; photocatalysis

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