Macroporous SiO2 Monoliths Prepared via Sol-Gel Process Accompanied by Phase Separation

Macroporous SiO2 monoliths were prepared via a sol-gel process accompanied by phase separation using a tetramethoxysilane (TMOS) precursor, 0.01 mol.L-1 HCl catalyst, propylene oxide (PO) gelation agent, and poly(ethylene oxide) (PEO, viscosity-averaged molecular weight (M-v): 10000) phase separation inducer. Monoliths were characterized by differential thermal analysis/thermogravimetry (DTA/TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen adsorption/desorption analysis (BET). The mechanism of the epoxide-mediated sol-gel reaction and PEO induced phase separation was discussed. The addition of PEO induced phase separation, and monolithic SiO2 with a cocontinuous macroporous skeletal structure was obtained at PEO/TMOS molar ratio of 0.0018. Monoliths had a narrow pore size distribution of 1-3 mu m, surface area as high as 719 m(2).g(-1) and pore volume of 0.48 m(3).g(-1). This sol-gel transition is mediated by PO because of its strong nucleophilic properties and irreversible ring-opening reaction. Simultaneous phase separation is induced by PEO adsorbed on the SiO2 oligomers.