Formation Mechanism for Monodispersed Mesoporous Silica Spheres and Its Application to the Synthesis of Core/Shell Particles

Abstract

A formation mechanism for monodispersed mesoporous silica spheres was investigated from the viewpoint of both particle growth and the progress of the condensation of the silica precursor. The particle growth of monodispersed mesoporous silica spheres was studied by TEM observation. The development of the mesopores was examined by in situ X-ray diffraction measurements. The condensation reaction of the silica precursor was analyzed by silicic acid titration and pH-conductivity measurements during the synthesis. It was found that small particles emerged suddenly after the commencement of the synthesis, and then the residual silica precursors reacted preferentially with the surface silanols on these existing particles. This led to the formation of monodispersed mesoporous silica spheres. Conversely, new small particles emerge throughout the synthesis in the case of a heterogeneous system. To confirm the preferential reaction of the silica precursors with the surface silanols, expansion of the existing particles was carried out by adding more silica precursor after the completion of the synthesis. It was found that the sizes of the particles were enlarged by the successive addition of more of the silica precursor. Surprisingly, the radial alignment of the hexagonal mesopores was still retained in the expanded particles. In addition, by the addition of a different silica precursor to the initial one, highly monodispersed core/shell mesoporous silica spheres possessing a hydrophilic core and a hydrophobic shell were successfully obtained for the first time.

Preparation and CO2 adsorption properties of aminopropyl-functionalized mesoporous silica microspheres

“…In particular, the spherical adsorbents have advantages including fluidity improvement of the fluid bed, lower pressure drops, and avoiding damage to the reactor at exchange, unlike the conventional adsorbents used, which have edges. Mesoporous spherical silicas have been prepared by the analogous Stöber method [9,[13][14][15][16][17][18][19][20]. Zhang et al prepared mesoporous spherical silica, with a unique starburst pore structure, using cetyltrimethylammonium bromide as the template and NaOH as a catalyst for the hydrolysis and condensation of TEOS [19].…”

Colloidal Mesoporous Silica Nanoparticles

“…However, the details of the formation mechanism have not yet been clarified. 70 Furthermore, Trofimova et al also prepared monodispersed MSNs with large size through one-pot process with short reaction time. 50 On the other hand, the seedgrowth method is also known to be an effective method to obtain monodispersed MSNs.…”

Synthesis of Core-shell Structured Porous Materials and Applications as Catalysts and Precursors for Hollow Porous Materials

“…Core-shell structured dual-mesoporous silica spheres with larger mesopores in the core were formed 44) . Preparation of novel mono-dispersed silica spheres with mesopores in the radial orientation was reported 47) , and growth of the spheres could be obtained with mercaptopropyl-modified silica to form a core-shell structure 45) . Mesoporous silica spheres were also synthesized with sulfonic acid-functionalized core and shell grafted with propyl groups by overgrowth 46) .…”

“…Such silica spheres showed high catalytic performance in the condensation of 2-methylfuran with acetone 46) . In accordance with Yano's method 45) , we prepared mesoporous silica spheres with hydrophilic pure silica core and hydrophobic silica shell grafted with propyl groups by particle growth to apply fabrication of hollow mesoporous silica spheres.…”