Hydrothermally Stable Periodic Mesoporous Ethane-Silica and Bimodal Mesoporous Nanostructures

Abstract

We report the hydrothermally stable organized periodic mesoporous organosilicas (PMOs) and bimodal mesoporous structures by using mixed templates of oligomeric alkyl-ethylene oxide and ionic surfactants under basic conditions. Oligomeric alkyl-ethylene oxide surfactant [(Polyoxyethylene (2) cetyl ether, structure is C16H33(OCH2CH2)nOH, n-2, hereafter known as B52) and ionic surfactant (cethyltrimethylammonium bromide (CTAB)) templating systems form mixed micelles that self-assemble into well-ordered hexagonal and bimodal mesostructures. The X-ray diffraction (XRD), transmission electron microscopy (TEM), BET, NMR and hydrothermal study have been used to investigate the effects of B52 on the formation of various PMOs. It is found that surface structural properties of mesostructures largely depend on the concentration of the B52 in the surfactant solution. The addition of B52 in the surfactant solution is not only improves mesostructural ordering and also enables to produces mesostructures with tuned surface structural properties. The final PMO structure shows good hydrothermal stability and can withstand for 72 h in boiling water, due to the hydrophobic pore wall chemistry in ethane-bridged PMO framework (triple bond Si-CH2-CH2-Si triple bond) and relatively more condensed framework such T3 supported by NMR spectrum. So, the lacking affinity for water through the favorable hydrophobic framework chemistry enhances the hydrothermal stability.