Hierarchical Porous Silicas for Chromatographic Applications Obtained by Pseudomorphic Synthesis

Pseudomorphic transformation of pre-shaped silica beads into MCM-41 and MCM-48 is introduced as a new versatile procedure to independently control and finely tune the textural characteristics of advanced high-performance chromatographic supports at nano- and micrometer scale. The reaction takes place in the intergranular porosity of the parent silica-gel particle which acts as a nanoreactor. Because the resulting hybrid mesophase is metastable in its synthesis medium, the kinetics of each of the elementary steps–diffusion of hydroxide and surfactant, dissolution of parent silica, self-assembly, condensation of the new silica network-must be precisely controlled. In the paper examples are given of the preparation of discrete homodisperse spherical particles of MCM-41 and MCM-48, with pore sizes in the range 4 to 9 nm, form different silica sources.