Effect of pH in hydrothermal treatment of as-synthesized MCM-41 on wetting stability of resulting materials in aqueous solution

Effect of pH in aqueous media used in the hydrothermal treatment of as-synthesized MCM-41 on the structure and the wetting stability of the resulting materials was studied using XRD, TG-DTA and N(2) adsorption. The long-range structural order and the wetting stability of the mesoporous MCM-41 were improved through hydrothermal treatment of as-synthesized sample at around pH 7 without salt addition. The pH adjustment of aqueous media toward neutral is thought to shift the polymerization equilibrium of silica species around external surface of the micelles to a higher degree of condensation, and to reduce the electrostatic repulsion between the silicate-micelle composites. This leads to the further formation of Si-O-Si network within the silica walls of the mesoporous materials, resulting in the enhancement of the structural stability of MCM-41 samples.