Control of morphology in synthesizing mesoporous silica*

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