Synthesis and structure of cage-like mesoporous silica using different precursors

In this work the synthesis of cubic, FDU-1 type, ordered mesoporous silica (OMS) was developed from two types of silicon source, tetraethyl orthosilicate (TEOS) and a less expensive compound, sodium silicate (Na2Si3O7), in the presence of a new triblock copolymer template Vorasurf 504 (EO38BO46EO38). For both silicon precursors the synthesis temperature was evaluated. For TEOS the effect of polymer dissolution in methanol and the acid solution (HCl and HBr) on the material structure was analyzed. For Na2Si3O7 the influence of the polymer mass and the hydrothermal treatment time were the explored experimental parameters. The samples were examined by Small Angle X-ray Scattering (SAXS) and Nitrogen Sorption. For both precursors the decrease on the synthesis temperature from ambient, −25 °C, to −15 °C improved the ordered porous structure. For TEOS, the SAXS results showed that there is an optimum amount of hydrophobic methanol that contributed to dissolve the polymer but did not provoke structural disorder. The less electronegative Br− ions, when compared to Cl−, induced a more ordered porous structure, higher surface areas and larger lattice parameters. For Na2Si3O7 the increase on the hydrothermal treatment time as well as the use of an optimized amount of polymer promoted a better ordered porous structure.

Research highlights
► FDU-1 mesoporous silica was made with TEOS, Na2Si3O7 and a new template Vorasurf 504.
► The synthesis temperature of 15 °C improved the ordered porous structure.
► HBr solution induced ordered pores, larger surface area and lattice parameter.