Preparação de heteroestruturas formadas por hidróxidos duplos lamelares recobertos com sílica mesoporosa
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Data
2019
Autores
Bianconi, Lister Pronestino [UNIFESP]
Orientadores
Bizeto, Marcos Augusto [UNIFESP]
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Sólidos inorgânicos porosos são materiais que apresentam grande área superficial e são
normalmente utilizados em aplicações envolvidas com separação, adsorção, catálise e liberação
modificada de substâncias, que são processos que se beneficiam de tal propriedade. Os
hidróxidos duplos lamelares (HDL) e as sílicas mesoporosas (SM) são exemplos de sólidos
inorgânicos porosos que despertam muito interesse científico e tecnológico, não só pela grande
área superficial que possuem, mas devido as suas propriedades estruturais, texturais e químicas.
Neste estudo, os HDL do tipo hidrotalcita [Mg4Al2(OH)12]CO3·xH2O e
[Zn4Al2(OH)12]CO3·xH2O foram combinados à SM visando produzir heteroestruturas
compostas de um núcleo de HDL envolto por uma camada externa de SM. Diferentes condições
sintéticas foram testadas visando produzir um recobrimento de sílica uniforme e com
porosidade ordenada, mas utilizando quantidades menores de direcionador estrutural usado para
formação dos poros na sílica em relação aos métodos reportados na literatura, além do uso do
HDL com Zn na composição, ainda não reportado na literatura. A difratometria de raios X e a
espectroscopia vibracional confirmaram a presença das fases de sílica e HDL. A distribuição e
o arranjo entre essas fases foram determinados por microscopias eletrônicas de varredura e
transmissão. A microscopia de varredura mostrou uma grande influência da razão molar entre
os reagentes e dos reagentes utilizados na etapa do recobrimento no hábito da partícula
resultante. A microscopia de transmissão indicou que o recobrimento das partículas de HDL foi
efetivo quando usado menores concentrações de direcionador estrutural e sem etanol como
cosolvente, aparentemente, uniforme e sem a formação de fases segregadas. Entretanto, o
processo de calcinação para remoção do molde levou à desestruturação do HDL, fato que não
ocorreu quando o molde foi removido por extração. A reconstrução parcial do arranjo lamelar
do HDL na heteroestrutura calcinada foi conseguida através do efeito memória, que algumas
das fases HDL apresentam. A calcinação também afetou a porosidade das heteroestruturas, que
somadas ao efeito de reconstrução parcial da fase de HDL observado, podem indicar a
ocorrência de uma possível reação entre a sílica e o HDL, formando uma outra fase não porosa,
fato que ainda precisa ser investigado em estudos futuros. Os resultados mais importantes deste
estudo foram: o desenvolvimento de um procedimento sintético que utilizou menor
concentração do direcionador estrutural, que possibilitou a remoção posterior por extração de
forma mais eficiente; a confecção de heteroestruturas inéditas com o HDL Zn2Al-CO3; a
avaliação do efeito memória para reconstrução da estrutura lamelar do HDL na heteroestrutura
após o processo de calcinação para remoção do direcionador estrutural usado na formação do
recobrimento de sílica.
Inorganic porous solids are materials with large surface area, commonly used in applications such as separation, adsorption, catalysis and modified release of substances, which are processes benefited from such property. Layered double hydroxides (LDH) and mesoporous silica (MS) are examples of inorganic solids that have such characteristics and are currently of great scientific and technological interest not only for their large surface area but also for their structural, textural and chemical properties. In this study, the hydrotalcite-like LDH [Mg4Al2(OH)12]CO3•xH2O and [Zn4Al2(OH)12]CO3•xH+O were combined to MS to produce heterostructures composed of an LDH core surrounded by an MS shell (MII 2Al-CO3@mSiO2). Different synthetic conditions were tested in order to obtain a uniform and ordered porous silica coating but using smaller amounts of structural directing agent compared to the methods reported in the literature, besides the use of the Zn2Al-CO3 LDH not yet already reported in the literature. X-ray diffraction and vibrational spectroscopy confirmed the presence of silica and LDH phases in the produced heterostructures. The distribution and arrangement between these phases were determined by scanning and transmission electron microscopy. Scanning microscopy showed a great influence of molar composition among the reagents used in the coating step in the habit of the resulting particle. Transmission microscopy indicated that the LDH particle coating was effective and apparently uniform without the formation of segregated phases. However, the calcination process for template removal led to the destruction of the LDH, which did not occur when the template was removed by extraction. Partial reconstruction of the lamellar arrangement of LDH after calcination was achieved through the memory effect. Calcination also affected the porosity of the heterostructures, which in addition to the partial reconstruction effect of the observed LDH phase, could indicate the occurrence of a possible reaction between silica and LDH, forming another non-porous phase, a fact that has must be investigated in future studies. The most important results of this study were: the development of a synthetic procedure that used a lower concentration of the structural directing agent; the production of heterostructures containing Zn2Al-CO3 as the core; the evaluation of the memory effect to reconstruction the LDH core after calcination to remove the template.
Inorganic porous solids are materials with large surface area, commonly used in applications such as separation, adsorption, catalysis and modified release of substances, which are processes benefited from such property. Layered double hydroxides (LDH) and mesoporous silica (MS) are examples of inorganic solids that have such characteristics and are currently of great scientific and technological interest not only for their large surface area but also for their structural, textural and chemical properties. In this study, the hydrotalcite-like LDH [Mg4Al2(OH)12]CO3•xH2O and [Zn4Al2(OH)12]CO3•xH+O were combined to MS to produce heterostructures composed of an LDH core surrounded by an MS shell (MII 2Al-CO3@mSiO2). Different synthetic conditions were tested in order to obtain a uniform and ordered porous silica coating but using smaller amounts of structural directing agent compared to the methods reported in the literature, besides the use of the Zn2Al-CO3 LDH not yet already reported in the literature. X-ray diffraction and vibrational spectroscopy confirmed the presence of silica and LDH phases in the produced heterostructures. The distribution and arrangement between these phases were determined by scanning and transmission electron microscopy. Scanning microscopy showed a great influence of molar composition among the reagents used in the coating step in the habit of the resulting particle. Transmission microscopy indicated that the LDH particle coating was effective and apparently uniform without the formation of segregated phases. However, the calcination process for template removal led to the destruction of the LDH, which did not occur when the template was removed by extraction. Partial reconstruction of the lamellar arrangement of LDH after calcination was achieved through the memory effect. Calcination also affected the porosity of the heterostructures, which in addition to the partial reconstruction effect of the observed LDH phase, could indicate the occurrence of a possible reaction between silica and LDH, forming another non-porous phase, a fact that has must be investigated in future studies. The most important results of this study were: the development of a synthetic procedure that used a lower concentration of the structural directing agent; the production of heterostructures containing Zn2Al-CO3 as the core; the evaluation of the memory effect to reconstruction the LDH core after calcination to remove the template.