Influence of alkaline earth metals (M= Ca²⁺ and Sr²⁺) in the MZrO₃ system on the photochemistry of the methylene blue

Full text: Perovskites of the type ABO₃ constitute a class of mixed oxides that present diverse properties as, chemical sensors, sensors of humidity, catalysts and semiconductors [1]. In the present work, MZrO₃ M = (Ca²⁺ and Sr²⁺) perovskites were synthesized by the polymer precursors method, in order to evaluate the influence of these metals in the degradation process for the Methylene Blue (MB) dye. The materials were characterized by X-ray diffraction (XRD), Infrared (FTIR), UV-Vis and Raman spectroscopy. The heterogeneous photocatalysis tests were performed using 0,1000 g of the catalyst, in a photoreactor with UV-C type lamps, with a power of 30 W, and monitoring by the UV-vis spectrophotometer. The XRD patterns showed the crystalline phase of the materials, indicating that the orthorhombic structures, as well as the formation of carbonates. The substitution of Sr²⁺ by Ca²⁺ promoted a widening of the peaks, evidenced by the increase of FWHM values. One being that cation substitution has occurred, as well as distortion of the dodecahedron structure. In the Infrared spectra the presence of carbonates in the system was verified, CaZrO₃ having a higher amount of CaCO₃. In the polyhedral region, CaZrO₃ is the most disordered system. In the Raman spectra we observed an increase in the number of vibrational modes when the Sr²⁺ network modifier was replaced by Ca²⁺, indicating a greater degree of distortion in the structure. The semiconductors were efficient in the heterogeneous photocatalysis process of MB, having above 82 % discoloration and values higher than 62 % in the region of the aromatic rings. These results are in agreement with the results of XRD and Raman, in view of the degree of disorder of the crystalline structure. References: [1] I.L.V. ROSA, et al., Ceramics International 41., 3069-3074 (2015). (author)