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

The pore size of micelle-templated mesoporous silicates (MTS) is thermodyna mically controlled, while their grain size is kinetically controlled. The p ore size is affected by all parameters which modify the size of micelles; h ydrocarbons 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 h eads in the rim of the micelle. The size of MTS particles depends on the ra tio between their nucleation and growth rates. Rapid aggregation of silica and surfactant leads to the formation of small grains, while a low concentr ation of ionized silica allows the growth of large particles of MTS mesopha ses. The ionic strength and the pH affect particle size and wall thickness through their effect on the rates of hydrolysis and condensation of the sil icate species, as shown by syntheses of MCM-41 in the system cetyltrimethyl ammonium-tetraethylorthosilicate. (C) 1999 Elsevier Science B.V. All rights reserved.