Mesoporous silica molecular sieves prepared by ionic and neutral surfactant templating : A comparison of physical properties

A series of mesoporous MCM-41 and HMS silica molecular sieves have been prepared by electrostatic and neutral assembly pathways, respectively, and their properties have been compared by a variety of physical techniques. Direct S+I- charge matching between cationic quaternary ammonium ion surfactants (S+) and the anionic silicate precursors (I-) affords long-range hexagonal structures under hydrothermal synthesis conditions (100 °C), but the long-range order is greatly reduced when the synthesis is conducted at ambient temperature. Conversely, owing to weaker assembly forces, counterion-mediated S+X-I+ and neutral S0I0 pathways (where X- is halide and S0 is a primary amine) provide calcined products with the best long-range order when the syntheses are conducted at ambient temperature. In general, MCM-41 silicas formed by electrostatic S+I- or S+X-I+ assembly exhibit greater long-range order than the HMS analogues prepared by the S0I0 assembly. However, the framework-confined pore structures, though depend...