Formation Mechanism of Spherical Mesoporous Silica Prepared Using Dodecylamine.

Abstract

Formation mechanism of spherical mesoporous silica particles prepared using dodecylamine (DDA) as a template was investigated by measuring surface tension, conductivity, pH and concentration of silicic acid in the mixed solutions. Porous structure of spherical mesoporous silica was found for irregular structure by means of X-ray diffraction and scanning electron microscopy. The fomation of DDA micell in DDA-H2O-C2H5OH system was confirmed by the presence of inflection points for tension and conductivity curves at about 0.5 mmol/l of DDA concentration. When tetraethyl orthsilicate was added in the solution, the conductivity raised suddenly, stayed the same for a few minutes, and decreased steadily while the concentration of silicic acid decreased largely. In addition, the value of pH shifted from about 11 to 9.8 at the same time. From these results, the formation mechanism of spherical mesoporous silica is considered to be as follows; 1st step: cationization(DDAH+) of DDA; 2nd step: formation of DDA H+ micell; 3rd step: hydrolysis of TEOS and polymerization of silicic acid; 4th step: complexation of DDAH+ and polysilicic acid; 5th step: nucleation and growth of the mesoporous silica; and 6th step: reconfiguration and growth of the mesoporous silica particles.