Roles of trifluoroacetic acid, acetic acid and their salts in the synthesis of helical mesoporous materials

Abstract

Helical mesoporous materials have attracted much attention due to their potential applications in catalysis and chiral recognition. In this paper, we have systematically studied the influence of trifluoroacetic acid, acetic acid and their salts on the synthesis of helical mesoporous materials in the presence of a cationic surfactant cetyltrimethylammonium bromide (CTAB) as a template. Results show that helical mesostructures can be successfully synthesized when CF3COO- anions were used as additives with an additive/CATB molar ratio (R) range of 0.1-0.375 for the CF3COOH/CTAB templating system and a relatively wider R range of 0.1-0.5 for the CF3COONa/CTAB templating system, which can be attributed to the influence of pH caused by the acid- or salt-form of additives. The pitch sizes of the helical mesostructures can be finely controlled by varying the additive/CTAB ratio. The results indicate that in order to synthesize helical mesostructures in a broad range of additive/CTAB ratios, the perfluorinated salt with a short fluorocarbon chain should be used. Our synthesis strategy can be used for the fabrication of helical mesostructured porous materials with adjustable pore and helical pitch sizes, which are important in their potential applications.