Synthesis of Discrete Micrometer-Sized Spherical Particles of MCM-48

The direct synthesis of a mesostructured silica with a tridimensional mesopore network with micrometer-sized and -shaped particles control is reported for the first time. Micrometer-sized beads of the cubic silica mesostructure MCM-48 have been obtained through a MCM-41 pseudomorphic synthesis procedure using preformed porous silica particles as silica source combined with a MCM-41/-48 phase transition. The low degree of polymerization of the MCM-41 formed in high alkaline conditions allows the further MCM-41/-48 phase transition. The kinetics of MCM-48 formation depends on the surface area of the parent silica, indicating that the dissolution of the silica in a confined environment is the rate-determining step of the process. The reaction time required to produce MCM-48 decreases from 7 to 2 h when the surface area of the parent silica increases from 160 to 740 m 2 /g. The MCM-48 mesostructure is metastable toward a lamellar mesostructure at longer synthesis times (>20 h). The domain of existence of the different mesostructures as a function of synthesis time and surface area of the parent silica sources has been established. The aggregation state of the MCM-48 particles can be controlled by adjusting the dilution and the alkalinity of the synthesis medium.