Textural control of micelle-templated mesoporous silicates: the effects of co-surfactants and alkalinity

The pore size of micelle-templated mesoporous silicates (MTS) is thermodynamically controlled, while their grain size is kinetically controlled. The pore size is affected by all parameters which modify the size of micelles; hydrocarbons can be used as swelling agents and co-surfactants as shrinking agents. In a typical example, alcohol co-surfactants decrease the pore size of amine-templated silica (HMS) by increasing the distance between polar heads in the rim of the micelle. The size of MTS particles depends on the ratio between their nucleation and growth rates. Rapid aggregation of silica and surfactant leads to the formation of small grains, while a low concentration of ionized silica allows the growth of large particles of MTS mesophases. The ionic strength and the pH affect particle size and wall thickness through their effect on the rates of hydrolysis and condensation of the silicate species, as shown by syntheses of MCM-41 in the system cetyltrimethylammonium-tetraethylorthosilicate. (C) 1999 Elsevier Science B.V. All rights reserved.