Short-time formation of well-ordered cubic mesoporous MCM-48 molecular sieve with the aid of fluoride ions

摘要

The crystallization time for cubic Ia3d mesoporous MCM-48 molecular sieve was first reduced by combining slight increase of reaction temperature with addition of tiny fluoride ions to the synthesis system. The reaction time reduces with the increasing F~-/Si ratio, but the high ratio of 0.4 will only lead to a disordered structure with poor crystallinity. The pore ordering is also considerably improved with the aid of fluoride ions even the reaction time is much shorter than those without any fluorides. The time-reduction action of fluoride ions on the synthesis of MCM-48 is attributed to the accelerated hydrolysis speed of silica source and condensation degree of silicates by fluoride ions.