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Eletrofiação de nanofibras de KBiFe2O5 com potencial aplicação em células solares
(Universidade Federal de São Carlos, 2020-07-15) Melo, Guilherme Henrique França; Bretas, Rosario Elida Suman; https://lattes.cnpq.br/2805349172281345; https://lattes.cnpq.br/4572506926485001
Today, ferroelectric semiconductors with perovskite type structure are widely studied due to the possibility of obtaining voltages higher than their band gap and to their contribution to the charge carriers’ separation due to the intrinsic polarization of these materials. Ferroelectric oxides usually have high Eg (2.70 - 4.00 eV), which allows only harnessing 8-20 % of the solar spectrum. However, the development of new ferroelectric semiconductors like KBiFe2O5 (KBFO) (Eg = 1.60 eV), has encouraged the application of these materials in solar cells. Routes of chemical synthesis, with reduced times and temperatures are essential, however, for the future application of these oxides in solar cells. KBFO was discovered in 2013 as an alternative to BiFeO3 (BFO) (Eg = 2.70 eV); however, until now, this material has only been synthesized at temperatures equal or higher than 650 °C, which difficult its application in photovoltaic devices. Besides, due to the high resistivity of the KBFO, recombination of the charge carriers is facilitated, thus decreasing its potential; this problem can be diminished, however, by reducing the thickness of the sample. In this work, the KBFO phase was obtained through two routes with a polymer as an additive (PVP), sol-gel synthesis and electrospinning, using five different heat treatments. The formation of the phase was confirmed by X-Ray Diffraction, the presence of the phase was confirmed for synthesis temperatures above 550 ° C and the non-formation for the temperature of 500 ° C; the morphology of the samples was analyzed using Scanning Electron Microscopy, proving the nanometric dimension in the samples obtained through the electrospinning process; the band gap value was obtained through absorption spectroscopy in the Ultraviolet-Visible region (UV-Vis), presenting a band gap close to 1.75 eV. The work presented two unprecedented results: obtaining the KBFO phase at temperatures below 650 ° C (without the use of high pressures) and obtaining nanofibers from this phase.
Efeitos do treinamento físico na adiposidade visceral, tecido adiposo marrom e parâmetros metabólicos de ratos Wistar alimentados com dieta hiperlipídica
(Universidade Federal de São Carlos, 2020-07-15) Alves, João Manoel; Duarte, Ana Cláudia Garcia de Oliveira; https://lattes.cnpq.br/1996950253264696; https://lattes.cnpq.br/5967275591258470
Obesity is a multifactorial disease that produces various metabolic disorders through the local and systemic inflammatory response occasioned by the pathological remodeling of visceral white adipose tissue (WAT). Furthermore, the activation of inflammatory pathways and the constant obesogenic state caused by the consumption of high-fat diet changes the morphology and function of the brown adipose tissue (BAT), a notable metabolic sink that oxidizes different energetic substrates in the form of heat and contributes to the regulation of the body mass and energy homeostasis. Notwithstanding, physical training is a non-pharmacological tool capable of decreasing the negative consequences of obesity and maintaining the metabolic flexibility of different peripheral tissues through decreasing visceral adiposity. Therefore, the purpose of this study was to investigate the effects of physical training on BAT mass, visceral adiposity and on metabolic parameters of Wistar rats fed a high-fat diet. First, male adult Wistar rats were separated within a control group fed a standard diet (CTR) and obese fed a high-fat diet (OB). After 12 weeks of obesity induction, the animals were subdivided into four groups: sedentary control group (CTR-SED), trained control group (CTR-TR), sedentary obese (OB-SED) and trained obese (OB-TR). The animals of the trained groups (CTR-TR and OB-TR) were submitted to physical training by swimming modality for eight weeks, in which each session of physical exercise was composed of 60 minutes of duration, frequency of 3 times a week, and intensity equivalent between 3 to 5% of the animal's body mass. The morphology of the epididymal fat (visceral WAT) was verified through histological analysis; visceral adiposity by weighing the deposits of epididymal, retroperitoneal and mesenteric WAT; the mass of the interscapular BAT was measured by weighing on an analytical balance and the glycogen and lipid content in the liver and soleus muscle were obtained using previously established methods in the literature. In the results, we observed that obesity (OB-SED) increased body mass, visceral adiposity, promoted adipocyte hypertrophy, deposition of ectopic lipids in the liver, reduced hepatic glycogen content and increased BAT relative mass. Physical training attenuated body mass increase, intraperitoneal adiposity, and adipocyte hypertrophy; however, was not efficient in reducing liver lipid content and increasing glycogen stores. Besides, physical training independent of the energy diet increased the relative mass of BAT, reduced the overlap of visceral fat on brown fat, and showed a negative correlation with the content of liver lipids. In summary, we conclude that physical training reduces weight gain and intraperitoneal adiposity in obese animals; however, these effects are not accompanied by changes in the metabolic flexibility of peripheral tissues in using fatty acids and glucose during cell activity. Furthermore, physical training and a high-fat diet are effective in increasing the mass of BAT, however, we do not know if this morphometric modification caused a thermogenic signature (expression of uncoupling protein 1 - UCP1) or whitening of brown adipocytes. Thus, further studies are needed to verify the biochemical and morphological adaptations of WAT and BAT in obese animals submitted to physical training.
Preparo de amostras refratárias aplicando procedimentos de digestão assistidos por radiação micro-ondas e análise elementar usando ICP OES
(Universidade Federal de São Carlos, 2020-07-15) Mello, Matheus Lima de; Nóbrega, Joaquim de Araújo; https://lattes.cnpq.br/8833989058164529; https://lattes.cnpq.br/9911429694446183
In this study microwave-assisted preparation procedures for decomposition of several inorganic samples and further analysis by inductively coupled plasma optical emission spectrometry (ICP OES) were developed. In order to obtain reference values, a digestion procedure using heating block with an acid mixture of concentrated HF and HNO3 was applied to achieve total digestion of the samples. This procedure was adopted for establishing reference values. In order to evaluate the feasibility of application of mild sample preparation procedures, 14, 7.0, 4.0 and 2.0 mol L-1 HNO3 and 30 % v v-1 H2O2 were utilized for digestion of inorganic samples in a single reaction chamber microwave oven. Total digestion of calcite, rock phosphate, Rh and Ru catalysts was achieved without needing of HF. Quantitative recoveries were obtained for most evaluated elements despite incomplete digestions, however, for few samples calculated recoveries were not quantitative. In order to evaluate the feasibility of HNO3 recovery from sample digests, two sub-boiling distillation experiments were proposed and involved the mixture of sample digests with technical grade HNO3 and the distillation of pre-evaporated sample digest solution. It was demonstrated that most contaminants were quantitatively removed and the recovered nitric acid provided accurate results when applied for digestion of two certified reference materials.