Systematic investigation of the synthesis parameters driving the preparation of mesoporous materials using a nonionic fluorinated surfactant

In this study, we have investigated the influence of different synthesis parameters such as the pH of the micellar solution, the surfactant/silica precursor molar ratio and the hydrothermal conditions on the properties of mesostructured silica prepared from a nonionic fluorinated surfactant based-system. The recovered materials have been characterized by SAXS measurements, nitrogen adsorption–desorption analysis and scanning electron microscopy. Results clearly evidence that the pH of the micellar solution does not affect significantly the channel array. Nevertheless, a better pore ordering is obtained in very acidic conditions. Another parameter that affects the structure of the recovered material is the surfactant/silica molar ratio. Indeed, the mesopore ordering is detected only for ratios located in the range between 0.4 and 2.5. The optimal ratio has been found equal to 0.5. The last parameters that have been optimized are the hydrothermal temperature and duration. Higher the hydrothermal treatment temperature is lower the time required to obtain a hexagonal mesopore ordering is. The increase of both the duration and the temperature leads to an increase of the pore diameter of the recovered materials due to a thinning of the silica pore walls. A change of the conformation of the hydrophilic surfactant chains is considered to explain the variation of the mesopore diameter.A comparison of the characteristics of the materials obtained with both hydrogenated and fluorinated surfactants is also reported.

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► Influence of synthesis parameters on the properties of mesostructured silica.
► pH of the micellar solution does not affect significantly the mesopore ordering.
► Optimal surfactant/silica ratio is equal to 0.5.
► Higher temperature is lower the time required to obtain a hexagonal structure is.
► Increase of the hydrothermal temperature leads to an increase of the pore diameter.