Preparation and characterization of (3-aminopropyl)triethoxysilane-modified mesoporous SBA-15 silica molecular sieves

Abstract

Mesoporous SBA-15 silica molecular sieves with internal channels uniformly lined with aminopropyl groups have been prepared via incipient-wetness impregnation of (3-aminopropyl)triethoxysilane in dry toluene at 100 °C, and characterized thoroughly by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), electron energy loss spectroscopy (EELS), 1H magic-angle-spinning (MAS) NMR, and 13C and 29Si MAS NMR spectroscopies with and without 1H cross-polarization (CP). The goal of this research is to characterize the pore structures of the modified materials and the chemical nature and thermal stability of incorporated organic moieties. The results reveal that the channels of the SBA-15 silica material are essentially lined with abundant silanol groups that serve as the sites for the incorporation of aminopropyl groups. The loading of the aminopropyl groups by impregnation is quantitatively controllable, and reaches a maximum molar percentage of about 13% with respect to silicons in parent silica material. The incorporated aminopropyl groups remain intact during various stages of the preparation, are thermally stable up to 550 °C, and are chemically bonded to the silicon associated with the silanol groups of the SBA-15 silica material. The modified materials still possess high BET surface areas of up to 700 m 2 g −1 and strictly defined mesoporous structure with pore dimensions less than 7 Å smaller than that of the parent SBA-15 silica of 57.4 Å, which indicate a uniform distribution of aminopropyl groups on the internal surface of the SBA-15 silica material.