Navegando por Autor "Araújo, Maria Helena"
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Item Magnetic composites based on metallic nickel and molybdenum carbide : a potential material for pollutants removal.(2012) Mambrini, Raquel Vieira; Fonseca, Thales L.; Dias, Anderson; Oliveira, Luiz Carlos Alves de; Araújo, Maria Helena; Moura, Flávia Cristina CamiloNew magnetic composites based on metallic nickel and molybdenum carbide, Ni/Mo2C, have been produced via catalytic chemical vapor deposition from ethanol. Scanning electron microscopy, thermal analysis, Raman spectroscopy and X-ray diffraction studies suggest that the CVD process occurs in a single step. This process involves the reduction of NiMo oxides at different temperatures (700, 800 and 900 ◦C) with catalytic deposition of carbon from ethanol producing molybdenum carbide on Ni surface. In the absence of molybdenum the formation of Ni/C was observed. The magnetic molybdenum carbide was successfully used as pollutants removal by adsorption of sulfur and nitrogen compounds from liquid fuels and model dyes such as methylene blue and indigo carmine. The dibenzothiofene adsorption process over Ni/Mo2C reached approximately 20 mg g−1, notably higher than other materials described in the literature and also removed almost all methylene blue dye. The great advantage of these carbide composites is that they may be easily recovered magnetically and reused.Item New heterogeneous catalyst for the esterification of fatty acid produced by surface aromatization/sulfonation of oilseed cake.(2015) Santos, Eleonice Moreira; Teixeira, Ana Paula de Carvalho; Silva, Flávia Gontijo da; Cibaka, Thérèse Ebambi; Araújo, Maria Helena; Oliveira, Willian Xerxes Coelho; Medeiros, Felipe; Brasil, Alex Nogueira; Oliveira, Leandro Soares de; Lago, Rochel MonteroIn this work, an efficient heterogeneous acid catalyst for the esterification of oleic acid was prepared directly from oilseed cake by a simple sulfonation with concentrated H2SO4. Characterization by SEM/EDS, IR, Raman, TG, TG/MS, potentiometric titration showed that treatment with H2SO4 for 1, 2 and 4 h at 120 _C partially dehydrates the cake to form a carbon/cellulose composite which is sulfonated to produce strong ASO3H acidic sites. These surface sites were active for the esterification of oleic acid with yields ca. 84%, 88% and 94% in the presence of 5, 10 and 20 wt% catalyst, respectively. These results are comparable to 98% yield obtained with 1 wt% H2SO4 and higher than 75% observed for a high surface area (880 m2 g_1) sulfonated activated carbon with similar number of ASO3H active groups. These results are discussed in terms of two effects: (i) the number of sulfonic surface acidic groups and (ii) the presence of a hydrophilic cellulosic fraction in the catalyst that adsorbs/traps water formed in the reaction shifting the esterification equilibrium and improving the yield.Item Physico-chemical, cooking and texture characteristics of polished and whole rice grain of different varieties marketed in Brazil.(2020) Silva, Amanda Souza da; Anselmo, Kerolaine Lijanda; Silva, Géssica Regiane; Lima, Clara Mariana Gonçalves; Araújo, Maria Helena; Benfica, Tatiana Aparecida Ribeiro dos Santos; Silva, Washington Azevêdo da; Santos, Eleonice Moreira; Trombete, Felipe MachadoThe diversity of whole rice grains with black and red pericarp has been valued in Brazil due to its different characteristics of color, texture, and also due to the association with health benefits. This work aimed to evaluate the physicochemical, cooking, and textural characteristics of different samples of polished and whole rice grains from different varieties marketed in Brazil. An exploratory and random sampling was carried out, aiming to obtain the largest number of brands, being collected 28 samples, and divided into 6 groups: polished white rice, white polished parboiled rice, whole white rice, whole red rice, whole black rice, and whole wild rice. Moisture content, crude protein, ash, mineral content, hardness, and adhesiveness were analyzed. The cooking quality was evaluated through the determination of cooking time, swelling ratio, and volume expansion ratio. A strong correlation between the protein content and the hardness value of cooked grains was observed. The polished samples showed the lowest ash and mineral values and the shortest cooking time. A strong correlation was also observed for the volume expansion ratio and hardness of cooked samples. The data obtained contribute to a better understanding of the quality of the rice marketed in Brazil and demonstrate a considerable variation among samples in terms of physicochemical, cooking, and texture properties.