Swollen mixed Pluronic surfactant micelles as templates for mesoporous nanotubes with diverse bridged-organosilica frameworks

Bridged-organosilica nanotubes with a variety of bridging groups (methylene, ethylene, ethenylene, phenylene and p-xylylene) were synthesized using swollen mixtures of Pluronic triblock copolymer surfactants as micellar templates. The mixtures consisted of Pluronic F127 surfactant (EO₁₀₆PO₇₀EO₁₀₆) with long poly(ethylene oxide), PEO, blocks, which help prevent the formation of consolidated structures, and another Pluronic with shorter PEO blocks and higher poly(propylene oxide) content, which promote swelling and the cylindrical micelle morphology. In the presence of toluene as a swelling agent, the use of Pluronic P123 (EO₂₀PO₇₀EO₂₀) in the mixture allowed us to readily generate organosilica nanotubes, but the products were often contaminated, sometimes substantially, with large nanospheres and other impurities. On the other hand, the use of Pluronic P104 (EO₂₇PO₆₁EO₂₇) instead of Pluronic P123 typically afforded nanotube products of significant purity. The nanotube morphology was well preserved upon the surfactant removal via extraction or calcination, even though the resulting nanotubes were often more clustered. The nanotubes exhibited high surface areas and uniform inner diameters in the range from ∼12 to 21 nm, depending on the composition and synthesis conditions. Our results indicate that the swollen mixed Pluronic surfactant templates provide an unprecedented access to mesoporous bridged-organosilica nanotubes.