Large-Pore Ethylene-Bridged Periodic Mesoporous Organosilicas with Face-Centered Cubic Structure

Abstract

Listen

Translate article

Low-temperature (∼15 °C) Pluronic-F127-templated synthesis of periodic mesoporous organosilicas (PMOs) with ethylene (−CH2−CH2−) framework groups and a face-centered cubic structure of spherical mesopores (Fm3m symmetry) was greatly enhanced through the use of judiciously chosen swelling agents and the optimization of synthesis conditions. The resulting materials were characterized by using small-angle X-ray scattering (SAXS), nitrogen adsorption, transmission electron microscopy (TEM), and thermogravimetry. While it was confirmed that 1,3,5-trimethylbenzene is a facile swelling agent for F127-templated ethylene-bridged PMOs with cubic Fm3m structure and our optimization of the synthesis afforded hitherto unreported unit-cell size and pore size, it was also shown that swelling agents predicted to have a higher extent of solubilization in Pluronics provide vast new opportunities. In particular, xylene was found to afford highly ordered PMOs with large unit-cell size and pore diameter, and a wide range of moderately or weakly ordered organosilicas with very large unit-cell parameters (up to ∼50 nm) and pore diameters (up to ∼18 nm). In the case of xylene, the pore size and unit-cell size were tunable by adjusting the amount of inorganic salt (KCl) in the synthesis mixture. The use of toluene allowed us to obtain unprecedented well-ordered PMOs with large unit-cell size (∼42 nm), very large mesopores (nominal diameter 16−17 nm; capillary condensation pressure up to ∼0.87 p/p0), and enhanced primary mesopore volume, and also afforded large-pore (nominal diameter ∼15 nm) PMO in the absence of an inorganic salt. The use of benzene also afforded large-pore PMO under salt-free conditions. Ethylene-bridged PMO was successfully converted to closed-pore ordered mesoporous silica at a temperature as low as 400 °C. The identification of new swelling agents for large-pore ethylene-bridged PMO with spherical mesopores is likely to be extendable on PMOs of other framework compositions and on other related materials.