EPR Spin Probe Investigation into the Synthesis of Mesoporous Silica from the Water/Acetonitrile/n-Dodecylamine System

Mesoporous silica prepared in the dodecylamine/acetonitrile (ACN)/water/tetraethoxysilane (TEOS) system, has led, by functionalization, to a series of catalytically active materials with well-defined narrow pore size distributions. In this contribution, we follow the mechanism of templated synthesis of mesoporous silica in the nonfunctionalized parent system, for different ACN/water proportions. Electron paramagnetic resonance (EPR) of spin probes was employed to follow structural changes in the template structure during precipitation, while X-ray diffraction (XRD) and porosimetry determinations have in parallel reported on the time evolution of the mesoporous structure. Three solvent mixtures were studied, with largely different solvent compositions, and EPR data have shown that a 0.3 M dodecylamine (DDA) solution in (i) ACN/water = 1/1 v/v was a true micellar solution, in (ii) ACN/water = 2/8 v/v was a biphasic system with a lamellar liquid crystalline phase, and in (iii) ACN/water = 8/2 was a molecular...