Control of morphology in synthesizing mesoporous silica

Mesoporous silica can be synthesized by either the alkaline route or the ac idic route, both using surfactants as templates. Morphological transformati ons of mesoporous silica can produce various hierarchical orders. Different morphologies are produced under different synthetic conditions. In the alk aline route, the surfactant/silicate liquid crystal system undergoes phase transformation to form vesicles and further transforms to the hexagonal pha se. The results are tubule-within-tubule and hollow pillar-within-sphere st ructures depending on cosurfactant/surfactant composition. Using nitric aci d in the acidic route, one can obtain hierarchical ropes or gyroids dependi ng on stirring conditions. Ammonia hydrothermal treatment can induce furthe r morphological transformation to nanotubes of mesoporous silica.