Preparation of spherical large-particle MCM-41 with a broad particle-size distribution by a modified pseudomorphic transformation

Large-particle MCM-41 with spherical morphology and broad particle-size distribution was synthesized using a modified pseudomorphic transformation. The MCM-41 sample exhibited well-defined mesophase porosity characterized by X-ray diffraction (XRD), nitrogen physisorption, and transmission electron microscopy (TEM). Broad particle-size distribution of parent silica presented a great challenge during the synthesis because small particles may suffer grain fragmentation, whereas large ones were unchanged. In order to maintain the spherical shape of the parent silica particles with broad particle-size distribution, over-hydrolysis of silica source had to be avoided with optimized preparation time, moderately basic synthesis condition, and introducing an appropriate amount of 3-(2-aminoethyl aminopropyl) trimethoxysilane (ATMS). The ATMS had significant effect on preserving the morphology of the parent silica particles characterized by field emission scanning electron microscopy (FESEM) and particle-size analyzer, the optimal molar ratio ATMS/SiO₂ = 0.1 was required in this study for obtaining the perfectly spherical shape and well-ordered mesostructure. Solid state ²⁹Si NMR confirmed that the incorporation of ATMS did not affect the silanol group condensation during synthesis.