Evolution from hollow nanospheres to highly ordered FDU-12 induced by inorganic salts under weak acidic conditions

Sulfates have big influence on the structure and morphology of the mesoporous silicas synthesized under weak acidic conditions. The evolution from silica hollow nanospheres to doughnut-like nanoparticles, and to FDU-12 type mesoporous silicas with Fm  3¯m symmetry can be induced by CuSO4 during the condensation of TMOS around Pluronic F127 surfactant in weak acidic solution (pH = 3.25). It is noteworthy that doughnut-like nanoparticles can be obtained in the presence of lower amounts of CuSO4. Similar to CuSO4, other divalent sulfates, such as ZnSO4, NiSO4, and MgSO4 can also induce the formation of Fm  3¯m mesostructure. However, the presence of K2SO4 and Na2SO4 specially results in the formation of hollow nanospheres. Plausible mechanisms for the formation of FDU-12 and hollow nanospheres were also proposed.