Morphology and shape control of porous silica nanostructures with dual-templating approaches

There has been great interest in the synthesis of porous silica nanostructures because of their potential applications in catalysis, adsorption, molecular separation, and biomedical engineering. In this paper, we report the synthesis of porous silica nanostructures with varied morphologies and shapes from two-phase systems by using lithocholic acid (LCA) and cetyltrimethylammmonium bromide (CATB) or LCA and Pluronic F127 in the lower ammonia aqueous phase as dual directing agents and tetraethylsiloxane (TEOS) in the upper oil phase as a silica precursor. Porous silica spheres are formed by using LCA/CTAB as a dual directing agent, while silica fibers with pits are synthesized by using LCA/F127 as a dual directing agent. The straight-to-helical shape transition of silica fibers with pits can be achieved by increasing the ammonia concentration in the low aqueous phase.