Kinetic study of the removal of pure and mixed TTMA+, CTMA+ and DTMA+ templates from MCM-41

Abstract

This work assessed the thermal degradation of surfactants, i.e., tetradecyltrimethylammonium bromide (TTMA+—C17H38NBr), cetyltrimethylammonium bromide (CTMA+—C19H42NBr) and trimethyloctadecylammonium bromide (DTMA+—C21H46NBr), 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 C17, C19, C21, C17C19, C19C21, C17C21 and C17C19C21. Before the kinetic study, the materials obtained by the 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 C17C19. Combining these results with XRD and BET analyses, it was observed that C17C19 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.