Cage-like ordered mesoporous organosilicas with isocyanurate bridging groups: Synthesis, template removal and structural properties

Abstract

The removal of triblock copolymer template from SBA-16 cage-like ordered mesoporous organosilicas (OMOs) functionalized with bulky isocyanurate (ICS) heterocyclic bridging groups is examined. These isocyanurate-containing OMOs (ICS–OMOs) were prepared by co-condensation synthesis of tris[3-(trimethoxysilyl)propyl]isocyanurate and tetraethyl orthosilicate in the presence of poly(ethylene oxide)- block-poly(propylene oxide)- block-poly(ethylene oxide) (EO 106PO 70EO 106) triblock copolymer F127 used as a template and sodium chloride additive under low acidic conditions. Initial studies revealed that the extracted ICS–OMOs materials have a cubic structure ( Im3m symmetry), high contents of isocyanurate bridging groups (0.76 and 1.08 mmol/g) as well as pore diameters ranging from 6.6 to 7.2 nm. The effect of the heating temperature on the structural ordering, specific surface area, pore volume and cage pore diameter of the as-synthesized and extracted ICS–OMOs was investigated. In addition, the synthesis, characterization and template removal of a bifunctional cage-like periodic mesoporous organosilica (PMO) containing ethane (E) and isocyanurate bridging groups is discussed. The E–ICS–PMO samples were fabricated via one-pot synthesis using 1,2-bis(triethoxysilyl)ethane, tris[3-(trimethoxysilyl)propyl]isocyanurate and F127 block copolymer. The resulting ICS–OMOs and E–ICS–PMOs were characterized by nitrogen adsorption–desorption isotherms at −196 °C, small-angle X-ray scattering (SAXS) or low-angle powder X-ray diffraction (XRD), high-resolution thermogravimetry (TG), Fourier-transform infrared spectroscopy (FT-IR) and CHNS elemental analysis. The SAXS/XRD and nitrogen adsorption show that the use of a short extraction and temperature-controlled heating at 315 °C in flowing nitrogen is an effective way to remove the remaining polymeric template from cubic mesostructures without decomposition of isocyanurate bridging groups, as evidenced by FT-IR, TGA and CHNS analysis. Moreover, a complete thermal degradation of isocyanurate groups at 550 °C in air has led to a significant shrinkage of the mesostructure, however its ordered nature was retained.