No abstract

Resumo Nas últimas décadas, pesquisas estão sendo desenvolvidas para obtenção de materiais eficientes e economicamente viáveis para aplicação em diversos setores da indústria. Os materiais mesoporosos da família MCM-41 estão entre os candidatos eficazes pela facilidade de síntese e estrutura que favorece uma gama de aplicações. O objetivo desse trabalho foi apresentar uma abordagem rítica das características e propriedades dos materiais mesoporosos do tipo MCM-41, enfocando nos aspectos estruturais. Além isso, foram discutidas as vantagens e desvantagens do uso de sílica comerciais e alternativas. As fontes de sílica comerciais analisadas foram sílica gel e TEOS; já as fontes de sílica alternativas foram cinza da casca de arroz, quartzo e pó de vidro. Os materiais analisados foram sintetizados pelo método hidrotérmico e caracterizados por DRX, FTIR, BET e TG. Os resultados apresentados comprovam a eficiência das fontes de sílica alternativas na síntese do MCM-41, pois os materiais apresentaram propriedades texturais dentro dos padrões exigidos. Dessa forma, eles estão aptos a serem testados na indústria em substituição aos MCM-41 sintetizados com fonte de sílica comercial.

Thermogravimetry analysis was used to study the thermal decomposition of Ti-MCM-41 to determine the best calcination conditions. Ti-MCM-41 molecular sieve was synthesized using a hydrothermal route in which Ti ions were incorporated into the pore channels of MCM-41 starting from a hydrogel method according to the following molar composition: 1.00 CTMABr:4.00 SiO 2 :X TiO 2 :1.00 Na 2 O:200.00 H 2 O. Physicochemical properties of samples were investigated using XRD, FTIR, and N 2 adsorptiondesorption to confirm the incorporation of TiO 2 nanoparticles inside of MCM-41 mesoporous without destroying its structure. The high temperatures facilitate the rapid removal of the surfactant; however, it caused destruction of the MCM-41 structure by breaking the bonds of the silica tetrahedral structure. The procedures to obtain the apparent activation energies of CTMABr decomposition were based on the kinetic model proposed by Flynn-Wall using thermal analysis of data performed with heating rates 5, 10, and 20 °C min -1 .

This work assessed the thermal degradation of surfactants, i.e., tetradecyltrimethylammonium bromide (TTMA ? -C 17 H 38 NBr), cetyltrimethylammonium bromide (CTMA ? -C 19 H 42 NBr) and trimethyloctadecylammonium bromide (DTMA ? -C 21 H 46 NBr), used to obtain MCM-41-type mesoporous materials using Flynn-Wall kinetic model. The cationic surfactants and their mixture at ratios of 1:1 and 1:1:1 resulting materials were labeled C hydrothermal method were characterized by physical, chemical and microstructural analyses such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric and nitrogen adsorption-desorption plots (BET). The mesoporous materials showed a well-defined hexagonal arrangement from the calcination process and significant structural differences. The kinetic model was used to determine the apparent activation energy for the removal of pure surfactant and associated with pores of the MCM-41-type molecular sieve. From the kinetic study results, a decrease in activation energy was observed when using the mixture of surfactants, especially C 17 C 19 . Combining these results with XRD and BET analyses, it was observed that C 17 C 19 showed the largest surface area and pore volume along with hexagonal arrangement. The mixture of cationic surfactants of hydrophobic chains of different sizes used in the preparation of MCM-41 reduced the activation energy and surfactant removal.