Collect. Czech. Chem. Commun. 2001, 66, 555-566

The Influence of pH on the Structure of Templated Mesoporous Silicas Prepared from Sodium Metasilicate

Patricia J. Kooymana, Markéta Slabováb, Vladimír Bosáčekb, Jiří Čejkab, Jiří Rathouskýb,* and Arnošt Zukalb

a National Centre for High Resolution Electron Microscopy, Delft University of Technology, Delft, The Netherlands
b J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic


A recently developed homogeneous precipitation method was used for the investigation of the influence of pH on the structure of mesoporous silicas prepared from sodium metasilicate in the presence of a quaternary alkyl ammonium surfactant as a structure directing agent. The rate of pH decrease affects the assembly of mesoscopically ordered composites and, consequently, the porous structure of mesoporous silicas prepared from them by calcination. Pure MCM-41 molecular sieve was prepared by controlling the pH decrease of the reaction mixture so as to achieve the final pH 7.8. The as-made material prepared at higher pH (final value 10.1) is characterized by a lower degree of silica polycondensation. Due to the shrinkage of this material during calcination, a less well-ordered silica with extraordinary large surface area was prepared. A large decrease in pH (final value 5.2) led to non-organized polycondensation of silica species besides the organized assembly of the ordered material, which resulted in the formation of silica with a bimodal mesoporous structure.

Keywords: Mesoporous silicas; Silicates; Molecular sieves; Homogeneous precipitation; MCM-41; 29Si MAS NMR spectroscopy; Powder X-ray diffraction.

References: 23 live references.