A. S. Maia

New methodology for a faster synthesis of SrSnO3 by the modified Pechini method

SrSnO3, a perovskite-type complex oxide, was synthesized by the modified Pechini method using two different precursors, tin chloride and metallic tin. The first one is already traditional in the literature and it claims about 30 days, only for the cleaning of tin citrate aiming at the elimination of the chloride. The second route was developed by our research group and saves time, taking 6 h to complete the synthesis of the resin. The results show that SrSnO3 obtained from the metallic tin show a higher short range order, leading to a band gap value higher than those reported in the literature, besides a meaningful reduction in the formation of SrCO3, as compared to the one obtained from tin chloride.

Effect of the composition on the thermal behaviour of the SrSn1-xTixO3 precursor prepared by the polymeric precursor method

Strontium stannate titanate Sr(Sn, Ti)O3 is a solid solution between strontium stannate (SrSnO3) and strontium titanate (SrTiO3). In the present study, it was synthesized at low temperature by the polymeric precursor method, derived from the Pechini process. The powders were calcined in oxygen atmosphere in order to eliminate organic matter and to decrease the amount of SrCO3 formed during the synthesis. The powders were annealed at different temperatures to crystallize the samples into perovskites-type structures. All the compositions were studied by thermogravimetry (TG) and differential thermal analysis (DTA), infrared spectroscopy (IR) and X-ray diffraction (XRD). The lattice former, Ti4+ and Sn4+, had a meaningful influence in the mass loss, without changing the profile of the TG curves. On the other hand, DTA curves were strongly modified with the Ti4+:Sn4+ proportion in the system indicating that intermediate compounds may be formed during the synthesis being eliminated at different temperature ranges, while SrCO3 elimination occurs at higher temperature as shown by XRD and IR spectra.

Synthesis of potassium niobates by the microwave-assisted solvothermal method

Potassium niobates have been synthesized by different methods, but few papers use the microwave-assisted solvothermal method, with possibility of a deeper evaluation in this area. In this work, the synthesis of KNbO3, KNb3O8 and K4Nb6O17 was performed by calcinations of precursors obtained by the microwave-assisted solvothermal method. This study evaluates the influence of various synthesis parameters such as reaction time, pH of the reaction medium, K+ concentration in the precursor solution. The results show the formation of different niobates, KNbO3, KNb3O8, K4Nb6O17, depending on the short and long-range order of the precursor used in the post annealing process.

Alkaline earth stannates applied in photocatalysis: prospection and review of literature

The ABO3 mixed oxide class known for its perovskite-like structure has aroused great scientific and technological interest in recent decades, due to its optical, magnetic and conductive properties. The objective of this work was to search the articles and patent databases for papers that relate the activity of the alkaline earth metal stannates BaSnO3, CaSnO3 and SrSnO3 as photocatalysts for environmental application. The databases researched were the Web of Science, Scopus and Scielo for articles and USPTO, EPO and INPI for patent banks. From the exclusion criteria, 21 review articles presented different experimental parameters and conditions. Due to the excellent photocatalytic performance, the stannates presented as promising candidates in the heterogeneous photocatalysis. A description of the main papers published in literature is provided for an overview of the literature data about these materials.

Iron-doped alfa-alumina applied in the degradation of phenol solutions

Neste trabalho buscou-se avaliar a atividade catalitica de alumina dopada com ferro na degradacao do fenol, pelo processo Fenton heterogeneo, que foi quantificado por dois metodos diferentes, Folin-Ciocalteu e cromatografia liquida de alta eficiencia. A alumina foi caracterizada por difracao de raios-X, espectroscopia de infravermelho, fluorescencia de raios-X e area superficial pelo metodo de BET. Apos os testes cataliticos, foi observado que houve degradacao de 94% do fenol com duas horas de reacao, chegando ao maximo de 99,2% com quatro horas. Esta alumina foi reutilizada por tres vezes para o mesmo processo catalitico, mantendo o percentual de degradacao apos quatro horas de reacao. A estabilidade quimica do material foi avaliada e observou-se que nao ha lixiviacao do ferro.