Influência dos parâmetros de síntese nas propriedades estruturais e morfológicas de nanotubos a base de La e Ce obtidos por via hidrotérmica alcalina sem templates
Recently, one-dimensional nanotubes consisting of La(OH)3 and CeO2 obtained by alkaline hydrothermal synthesis have attracted much interest in researches, due to their detachable physical-chemical characteristics and potential applications. The hydrothermal method has been widely used to obtain t...
Na minha lista:
| Autor principal: | |
|---|---|
| Outros Autores: | |
| Formato: | doctoralThesis |
| Idioma: | por |
| Publicado em: |
Brasil
|
| Assuntos: | |
| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/25605 |
| Tags: |
Adicionar Tag
Sem tags, seja o primeiro a adicionar uma tag!
|
| Resumo: | Recently, one-dimensional nanotubes consisting of La(OH)3 and CeO2 obtained
by alkaline hydrothermal synthesis have attracted much interest in researches, due to
their detachable physical-chemical characteristics and potential applications. The
hydrothermal method has been widely used to obtain this type of nanostructures, since it
is a simple, low cost technique in which the properties of the products obtained depend
on the formation mechanism and the hydrothermal conditions used. The present work
aims the synthesis of La(OH)3 and CeO2 nanotubes through the template-free
hydrothermal route and evaluate the influence of the synthesis parameters, (such as
NaOH concentration, temperature and synthesis time) and calcination temperature on
the physical and chemical properties of the obtained nanostructures. The results of this
research were divided into five chapters. The Chapter 1 presents the theoretical basis,
addressing relevant issues on the subject. The Chapter 2 shows the materials and
methods used. The Chapter 3 presents an article whose title is the "Influence of
calcination on the physical-chemical properties of nanotubes of La(OH)3". The results
showed that the calcination temperature influence in the organization, composition and
texture properties of the obtained nanotubes. The hydrated material consisting of
La(OH)3 with hexagonal structure was obtained after the hydrothermal synthesis and
was maintained after the calcination at 750 °C. However, the nanotubular morphology
was collapsed after this process. The calcination at 450 °C generated the La2O2CO3
composite material with a mixture of symmetries (hexagonal and tetragonal), in which
the nanotubular morphology was preserved. Thus, nanotubes consisting of La(OH)3 can
be obtained by the alkaline hydrothermal synthesis without templates, which have their
composition and properties altered, through of the calcination temperature, according
with the desired catalytic application. The Chapter 4 presents the results of the influence
of alkaline concentration and hydrothermal synthesis on the morphological and
structural properties of La(OH)3 nanotubes. Nanotubes composed of La(OH)3 organized
in a hexagonal structure were obtained in all the synthesis conditions performed, in
NaOH concentrations of 5; 10 and 20 mol L
-1
and synthesis temperatures of 100; 125
and 150 °C. The nanostructures differed in their crystallinity, sizes and the mechanism
involved in their formation were proposed as being the dissolution/recrystallization. The
Chapter 5 presents an article that shows the influence of the synthesis parameters (such as NaOH concentration, temperature and synthesis time, and calcination temperature)
on the morphological, structural and optical properties of cerium oxide nanotubes.
Hydrated nanotubes consisting of CeO2 with a cubic fluorite structure were obtained in
some cases. The morphology, hydration, size of nanostructures and oxygen vacancies
varied according to the synthesis condition used, providing materials with different
properties for catalysis. The mechanism involved in the formation of CeO2
nanostructures was proposed and discussed. Thus, all the results obtained in this
research show for the first time the domain in the formation, composition and size of the
nanotubular morphologies of the La(OH)3 and CeO2 obtained by the template-free
hydrothermal route, through the control of the synthesis parameters and the calcination
temperature. This domain is of fundamental importance in order to obtain nanotubes
with characteristics suitable for specific applications in catalysis, sensors, and electronic
devices as well as in the biomedical area. |
|---|