Navegando por Palavras-chave "Seleção de fases cristalinas"

Agora exibindo 1 - 1 de 1
  • Imagem de Miniatura
    Item
    Acesso aberto (Open Access)
    Nanocompósitos TiO2:SBA-15 e suas potenciais aplicações em fotocatálise e fotoproteção
    (Universidade Federal de São Paulo, 2015-08-10) Jardim, Alice Antunes Muscas Leandro Ferreira [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Nanomaterials have been prominent in the research and development area. In particular, titanium dioxide (TiO2) has been extensively studied due to its interesting properties such as stability under severe conditions, low cost, absorbance in the ultraviolet region and high photocatalytic activity, being especially interesting as photocatalyst and photoprotector. The use of SBA-15 type ordered mesoporous silica to prepare TiO2:SBA-15 nanocomposites is advantageous since the final material has large surface area and, consequently, better performance in photocatalysis. For use in cosmetics, SBA-15 is recommended because it has micrometric particle size, less likely to penetrate the skin. This work aimed to study the influence of the synthesis parameters on the structural, textural and morphological properties of TiO2:SBA-15 nanocomposites and to establish the best synthesis conditions for application in photocatalysis and photoprotection. The studied parameters were: titanium dioxide molar ratio (10, 20 and 30% relative to silica amount), calcination temperature (540, 700 and 800 °C), synthesis route (standard or hydrothermal treatment (HT)), and presence of ionic liquid, IL, (CMIBF4, CMITf2N and CMIBr), acetylacetone and isopropyl alcohol. The nanocomposites were characterized by wide and small angle X ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption isotherms (NAI) and scanning electron microscopy (SEM). XRD measurements showed that the 20% TiO2 molar ratio resulted in more intense rutile phase peaks, whilst the ratio of 10% favored anatase phase. 10% and 20% ratios produced samples that retained the structure of SBA-15. Regarding the calcination temperature, it was observed that higher temperatures led to more intense rutile peaks, however, the crystallite size increased. FTIR spectra showed that titanium dioxide interacts weakly with SBA-15. Regarding IL presence, the molar ratio of 0.032LI:1TiO2 yielded structured materials. CMIBr has little influence on TiO2 crystalline phase selection, while CMITf2N favors rutile phase formation (for the 0.32:1 ratio) and CMIBF4 favors anatase. In the absence of alcohol, CMIBF4 (0.032:1) led to a nanocomposite with 100% anatase phase, suitable for application in photocatalysis. It was verified that both acetylacetone and HT synthesis route favor rutile phase, and the combined effect of the two resulted in a nanocomposite that would be interesting for application as photoprotector, with 90% rutile phase and small crystallite size incorporated into micrometric size silica. It was possible to visualize tubes with particle size of about 1 micrometer as expected for SBA-15, as well as the nanometric particles of titanium dioxide dispersed throughout the silica using SEM images. The exception was the sample prepared with CMITf2N in absence of alcohol, which exhibited SBA-15 particle size of about 0.1 micrometer, demonstrating the great influence of this IL in the silica's morphology.