Estudo do crescimento de nanocristais de TiO2

Abstract

STUDY GROWTH OF TiO2 NANOCRYSTALS In the last three decades, the development of nanotechnology has become a reality in many areas of industry and science, already reaching applications in society in sectors such as: health, information technology, transport, energy, food security and the environment. Despite all the research work already done, there are still gaps, mainly in the process of growth and morphology of nanocrystals. Such knowledge is essential for the nanostructures to present the expected gains in optical, mechanical, electrical and magnetic properties, such characteristics are directly dependent on the shape and size of the nanostructures. The processes of nucleation and crystal growth have been studied since the beginning of the 20th century, with the most accepted mechanism for explaining this phenomenon the Ostwald ripening process, where the largest particles grow at the expense of the smallest ones. However, this proposed model does not explain the growth observed in many nanocrystal syntheses. In 1998, Penn and Banfield, proposed a new growth model called oriented attachement, where growth is described as a kind of self-assembly of close crystals when the collision occurs between the faces of these crystals, being these on the same crystallographic orientation. Since then, much effort has been made to better understand the oriented attachment mechanism. In this context, the objective of this work was to study and control the growth process of nanocrystals, using TiO2 nanocrystals as a model, employing a solvent-controlled solvothermal synthesis route, using a titanium alkoxide and oleic acid as a precursor for obtaining nanocrystals. Parameters such as concentration and synthesis time were evaluated, using the techniques of characterization of transmission electron microscopy, x-ray diffraction and thermogravimetric analysis to evaluate the results. The hypothesis that led this study was to verify whether it is possible to grow nanocrystals outside the reaction medium of synthesis. In this work, the results achieved will be presented, with emphasis on the influence of morphology on the stability of TiO2 nanocrystals when exposed to radiation, the growth observed by side-by-side oriented attachment and the growth of nanocrystals after the reaction step in reaction medium different from the initial.