Expanding mesoporosity of triblock-copolymer-templated silica under weak synthesis acidity

With initial aging at low temperature for enough time, silicas with large mesoporosity were synthesized using triblock copolymer as template agent under weak acidities. SBA-15 with periodic mesostructure and short mesochannels could be synthesized at pH 2.5–3.0 within weak acidity range, and the surface areas, pore diameters and pore volumes reached up to ca. 1000 m2/g, 8.8 nm and 2.0 cm3/g, respectively, which were significantly higher than those of the conventional SBA-15 synthesized under strong acidities. Mesoporous silica with wormhole structure and abundant textural porosity was formed at pH ∼ 3.5. The increased hydrophobic volume of the copolymer micelles at elevated pH values was responsible for the enlargement of mesoporosity in the products. The materials synthesized under weak acidities showed lower hexagonal ordering in comparison to the general SBA-15 synthesized under strong acidities because the decreased hydronium ion concentration induced relatively weaker assembly forces during the synthesis. Nonetheless, the short mesochannels and large pore diameter in the products might be beneficial to some applications in which fast diffusion of molecules is required.

The protonation degree of the PEO chains decreases with lowering the synthesis acidities, leading to large hydrophobic volume of the template phases and large pore of the final products.Figure optionsDownload as PowerPoint slide