Biomimetic Preparation and Morphology Control of Mesoporous Silica - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 309

silica powder or poorly ordered products are obtained, whereas higher
temperatures (> 80 C) yield silica gel. TEOS, TMOS, and TPOS are suit-

able sources of silica for the preparation of SBA-15. Hexagonal meso-
porous SBA-15 has been formed in acid media (pH < 1) with HCI, HBr,
HI, HNO 3 , H 2 PO 4 , or H 3 PO 4 acids. At pH values from 2 to 6, above the
isoelectric point of silica (pH ~ 2), no precipitation or formation of sil-
ica gel occurs. At neutral pH ~ 7, only disordered or amorphous silica is
obtained [52-55].

°

13.4.2 The Preparation and Morphologies Control of

Mesoporous Silica

In this section, we will introduce our studies about the morphology con-
trol of mesoporous silica. As shown in Figure 13.5, the schematic com-
pass displays our group's research work. The morphology of mesoporous
silica can change with the condition of reaction system, such as type of
catalysts, solvent, composition ratio, as well as certain factors. The fac-
tors could be assistant surfactant, ions and assistant silane. We found that
the type of solvent and the total volume of solvent determine the meso-
scopic order and the uniformity of the morphologies of the products. This
is because the polarity of solvent and the concentration of the surfactant
strongly infl uents the microstructure of the building blocks at the meso-
scopic scale, for example, micelles, vesicles, emulsions and so on, but also
the reaction rate of hydrolysis as well as condensation from the silicate
precursor of silane.
Three systems of solvent will be introduced. They are diluted aqueous
system, alcohol-water system, and ether-water system.

Water(NaOH)

Alcohol
-water

Ether-
water

MSRB

Figure 13.5 Left: the schematic compass. Different typical morphologies
in the solvent system. Right: TEM image of the mesoporous silica in the
different solvent system. From left to right, MCM-41 single crystal, MCM-41
submicrometer rod, mesoporous silica with worm-like pore structure prepared
via alcohol-water solvent system, mesoporous silica with hierarchical pore
structure prepared via ether-water solvent system, scale bar, 24 nm.