Banca de DEFESA: ADRIANA PAULA BATISTA DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : ADRIANA PAULA BATISTA DOS SANTOS
DATA : 27/02/2018
HORA: 09:00
LOCAL: Sala de reunião do NUP-ER
TÍTULO:

Alkaline hydrothermal synthesis of La(OH)₃ nanotubes and CeO₂ nanotubes and study of the influence of the synthesis parameters about its physicochemical properties

PALAVRAS-CHAVES:

Nanotubes, Nanostructures, Morphology, La(OH)₃ and CeO₂

PÁGINAS: 135
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Cinética Química e Catálise
RESUMO:

Nanotubes 1D consisting of La(OH)₃ and CeO₂ obtained by hydrothermal synthesis, has attracted much interest recently, due to their detachable physical-chemical characteristics and potential applications. Due to its tubular structure with three different contact surface (inner, outer surface and tube ends), high surface area, low density and good load transfer ability. The hydrothermal method has been widely used to obtain this type of nanostructures, since it is a simple technique in which the properties of the products obtained depend on the formation mechanism and the hydrothermal conditions used. Thus, La(OH)₃ and CeO₂ nanotubes were synthesized using alkaline hydrothermal synthesis, free from templates. The effect of the synthesis conditions used, as NaOH concentration in the reaction medium, temperature and time of synthesis, as well as the calcination conditions were discussed on the formation of the nanotubular morphology and its properties, in the two types of nanotubes. This route to obtain nanostructures, besides the lower cost, and to treat in a more environmentally correct way, allows a greater degree of control over the size and properties of the obtained nanotubes. The results of this study were divided into three chapters, in which chapter 1, through patent of invention, presents the results obtained for the synthesis of La(OH)₃ nanotubes, with the influence of the synthesis conditions on the obtained morphology. The main results for this type of material showed that in all the synthesis conditions used, high yield of the nanotubular morphology were obtained, in which the materials in all cases were composed of La(OH)₃, organized in hexagonal form, which differed in the size of their external diameters. It was also observed that the higher the temperatures, the synthesis time and the NaOH concentration, the higher the diffraction peak intensities, indicating a larger structural organization, when these parameters were increased. The chapter 2, show an article that exposes the influence of calcination on the physicochemical properties of nanotubes of La(OH)₃. The results showed that the calcination temperature influences the organization, composition, and texture properties of the nanotubes obtained. The hydrated material consisting of La(OH)₃ with hexagonal structure was obtained after the hydrothermal synthesis and was maintained after the calcination process at 750 ° C. However, the nanotubular morphology was destroyed after this process. Calcination at 450 ° C generated a La₂O₂CO₃ composite material with a mixture of symmetries (hexagonal and tetragonal), in which the nanotubular morphology was preserved. The calcined nanostructures presented specific surface areas of 45 and 25 m².g^-1, when calcined at 450 and 750 °C, respectively. Thus, nanotubes consisting of La(OH)₃ can be obtained by alkaline hydrothermal synthesis, without templates, which can have their composition and properties altered, through the calcination process, according to their catalytic application. Chapter 3 presents the influence of the synthesis parameters (NaOH concentration on the reaction medium and temperature and time of synthesis) and of calcination process on its physicochemical properties of CeO₂ nanotubes. Hydrated nanotubes consisting of CeO₂ with cubic fluorite structure were obtained in all cases, in which hydration, size of nanostructures, and oxygen vacancies varied according to the synthesis condition used, providing materials with different catalytic activities. The mechanism of formation of CeO₂ nanotubes was discussed. However, the results of these three chapters show for the first time the dominance over the formation, composition and size of the nanotubular morphologies of La(OH)₃ and CeO₂ obtained by this route, through the control of these synthesis parameters and the calcination process. This is of fundamental importance in order to obtain nanotubes with characteristics according to future applications in catalysis, sensors and electronic devices.

MEMBROS DA BANCA:
Presidente - 350509 - ANTONIO SOUZA DE ARAUJO
Externo à Instituição - GERALDO EDUARDO DA LUZ JUNIOR - UESPI
Externo à Instituição - LUIZ DI SOUZA - UERN
Interno - 1308577 - SIBELE BERENICE CASTELLA PERGHER
Interno - 2087667 - TIAGO PINHEIRO BRAGA