Role of inorganic salts in the formation of ordered periodic mesoporous organosilicas (PMOs) without extra acids

The promoting effects of several inorganic salt pairs as NaCl/M(O)Clx (M = Zr4+, Sn4+, Fe3+, Cr3+, Al3+) on the assembly of periodic mesoporous ethanesilicas templated by copolymer surfactant (EO20PO70EO20, P123) were studied under the conditions where no additional acid was added. The structural properties were thoroughly characterized by small angle X-ray scattering (SAXS), nitrogen sorption isotherms, transmission electron microscopy (TEM), scanning electron microscopy (SEM), 13C and 29Si CP MAS NMR, and thermogravimetric analysis (TGA). It was observed that while keeping the NaCl/Si ratio constant highly ordered SBA-15-like ethanesilicas can be easily prepared in the presence of inorganic salt pairs within a wide synthesis range except for the NaCl/AlCl3 combination. A plausible assembly mechanism based on the favorable effects of both NaCl and MClx inorganic salts is discussed, that is, the “salting out” effect and self-generated acidity from both inorganic salts, respectively, are important for the formation of ordered large-pore ethanesilicas under the present synthesis conditions.