Synthesis of Single-Crystal-Like, Hierarchically Nanoporous Silica and Periodic Mesoporous Organosilica, Using Polyelectrolyte–Surfactant Mesomorphous Complexes as a Template

Single-crystal-like, hierarchically nanoporous silica SBA-1 particles were successfully fabricated by employing organic mesomorphous complexes of polyelectrolyte (poly(acrylic acid) (PAA)) and cationic surfactant (hexadecylpyridinium chloride (CPC)) as templates. By adjusting the amount of PAA in the synthesis, a series of silica particles with well-defined morphologies and well-ordered cubic Pm 3̅ n mesostructure were obtained. Both the mesostructure and well-defined morphology of the silica particles inherited those of the corresponding PAA/CPC mesomorphous complexes. The materials possess bimodal nanopores corresponding to the mesopore size of SBA-1 templated by surfactant micelles and secondary interstitial nanopores templated by phase-separated PAA with different domain sizes, respectively. Notably, the presence of a large amount of foamlike secondary nanopores did not disturb the single-crystal characteristic of the SBA-1 particles. By means of pore-expanding with 1,3,5-trimethylbenzene, the mesopore size of the SBA-1 could be easily tuned from 3.0 nm to 5.0 nm, and the secondary nanopore were enlarged to several hundreds of nanometers, while the morphology of the particles was not changed. Besides, using bridged organosilane as a precursor, a series of hierarchically nanoporous periodic mesoporous organosilicas (H-PMO) with well-defined morphology were fabricated. Because of the hierarchically nanoporous structure and inherent hydrophobic bridged-ethylene group, the H-PMO exhibited rapid adsorption rate and high adsorption capacity in enzyme and protein immobilization.