Polymorph control of calcium carbonate on the surface of mesoporous silica

The influence of mesoporous silica on the polymorph selectivity in CaCO ₃ has been investigated. Vaterite is selectively formed from an aqueous solution containing CaCl ₂ and Na ₂CO ₃ by precipitation under the presence of KIT-6-type mesoporous silica. Crystallization time of vaterite from amorphous calcium carbonate (ACC) is much longer on the addition of KIT-6 than that reported previously, indicating the remarkable stabilization of ACC on the surface of mesoporous silica. Other types of silica affect the polymorph selectivity; the addition of amorphous silica gel or assembled silica nanoparticles 12 nm in particle size induced the formation of vaterite as a main phase whereas the presence of assembled silica nanoparticles 30 nm in particle size resulted in the formation of calcite as a main phase with a minor component of vaterite. Therefore, the porous nature of the surfaces of silica greatly influences the polymorph, and a sort of "surface confinement" should play a major role in the selectivity of polymorph.