RESUMO
Nanocrystalline titania (TiO2) is one of the most investigated crystalline nanostructured systems in the field of materials science. The technological applications of this material are related to its optoelectronic and photocatalytic properties, which in turn are strongly dependent on the crystal phase (i.e., anatase, brookite, and rutile), particle size, and surface structure. However, systematic comparative studies of all its crystal phases are scarce in literature due to difficulties in providing a controlled synthesis, which is primarily important in obtaining the brookite phase. In this report, the synthesis of TiO2 nanoparticles in the anatase, brookite, and rutile structures was explored, using amorphous TiO2 as a common precursor under microwave-assisted hydrothermal conditions. The influence of parameters such as temperature, acidity, and precursor concentration on phase crystallization were investigated. The TiO2 materials (amorphous and crystalline phases as well as commercial Degussa P25) were systematically characterized using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible reflectance spectroscopy, and dynamic and electrophoretic light scattering. The bactericidal activity and photocatalytic antibacterial effectiveness of each material were evaluated through the determination of the minimum inhibitory and bactericidal concentrations, and via the mortality kinetic method under ultraviolet (UV) illumination under similar conditions with two bacterial groups of unique cellular structures: Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The results are discussed with particular emphasis on the relationship between the synthesis parameters (acidity, precursor concentration, temperature and reaction time) and the bactericidal properties.
Assuntos
Micro-Ondas , Staphylococcus aureus , Catálise , Escherichia coli , TitânioRESUMO
Foram utilizadas 22 novilhas, 11 da raça Holandesas e 11 da Guzerá, com peso vivo (PV) inicial de 189kg. Após o abate inicial de seis animais de cada raça, outros dois grupos, cinco animais de cada raça, passaram a receber dieta à base de feno de Tifton 85 (Cynodon spp.), milho, farelo de soja e mistura mineral, para ganho diário de 1kg de peso vivo (PV). O abate final ocorreu após ganho de peso de 100kg. Durante os dois abates, todos os tecidos foram pesados e amostrados, retirando-se como amostra representativa da carcaça entre a nona e a décima primeira costela para determinação dos conteúdos corporais de Ca, P, Mg, Na e K. Determinaram-se a composição corporal e as exigências nutricionais desses minerais para ganho de 1kg de PV. Houve decréscimo na concentração dos cinco macrominerais no peso de corpo vazio e no peso ganho com a elevação do PV. Não houve diferença entre as raças quanto às exigências nutricionais dos macrominerais. As exigências dietéticas totais de Ca, P, Mg, Na e K para animais de 200kg de PV foram de 11,57; 5,97; 0,36; 1,30 e 0,86g/dia, respectivamente.
Twenty-two heifers, 11 Holstein and 11 Guzera, with initial live weight (LW) of 189kg were used in this study. Six animals of each breed were slaughtered (treatment R), and two groups of five animals of each breed were fed ad libitum diet of Tifton 85 (Cynodon spp.) hay, ground corn, soybean meal and mixture minerals, for a daily gain of 1kg. The animals were slaughtered after reaching weight gain of 100kg. All tissues were weighted and representative samples were taken from the ninth to eleventh rib, and analyzed for body contents of Ca, P, Mg, Na and K. The body composition and the mineral requirements for a 1kg LW daily weight gain were determined. Decreases in the concentration of macrominerals in the empty body weight and in carcass weight gain were related to LW increased. No differences among breeds for macrominerals were observed. The Ca, P, Mg, Na and K dietary requirements for animals of 200kg of LW were 11.57; 5.97; 0.36; 1.30 and 0.86g/day, respectively.
