Synthesis and Characterization of Periodic Mesoporous Organosilica Materials

[摘要] Periodic mesoporous organosilica (PMO) materials (consisting of ethane groupsin the framework) and bifunctional periodic mesoporous organosilica materials(consisting of ethane groups in the framework and either glycidoxypropyl groupsor aminopropyl groups in the channels) were synthesized by the sol-gel methodunder basic conditions. Ethanesilica materials were synthesized by condensationof 1,2-bistrimethoxysilylethane (BTME) and by co-condensation of BTME withtetraethylorthosilicate (TEOS). Bifunctional periodic mesoporous organosilicamaterials were synthesized by the co-condensation of BTME with either 3-glycidoxypropyltriethoxysilane (GPTS) or 3-aminopropyltriethoxysilane (APTS).Cetyltrimethylammonium bromide was used as the structure-directing template.Cobalt ion incorporated ethanesilica and modified ethanesilica materials weresynthesized in situ by adding cobalt nitrate to the reaction mixture. Cobalt wasalso supported on ethanesilica materials and APTS-modified materials by usingthe incipient wetness impregnation method.Raman spectroscopy and diffuse reflectance infrared spectroscopy (DRIFTS)results confirmed the formation of organosilica materials and showed that thesurfactant was removed by solvent extraction. Thermogravimetric analysis(TGA) and differential thermal analysis (DTA) showed that the ethane portion ofthe materials (originating from the bridging ethane group in BTME) onlydecomposed at temperatures > 400 oC. These techniques also showed that thesurfactant is removed by solvent extraction. Cobalt ion incorporation wasconfirmed by Raman spectroscopy and UV-vis diffuse reflectance spectroscopy.Powder powder X-ray diffraction (XRD) and nitrogen adsorption data indicatedthat the mesophase and textural properties of the materials are dependent on thereaction conditions (i.e. ageing duration, ageing temperature, amount of silicaprecursor(s), amount of water and amount of base (NH4OH)). The periodicity ofthe materials was indicated by the presence of low angle diffraction peaks in powder X-ray diffraction patterns. Cubic and hexagonal mesophases wereidentified using powder X-ray diffraction. When solvent extraction is prolonged,the BET surface area and the pore volume increase, while the average porediameter decreases. Materials with more dominant XRD structural features andlarger d values, higher surface areas, lower pore volumes and average porediameters are obtained when low ageing temperatures are used.For samples prepared from a mixture of BTME and TEOS at a given temperature,the surface area was found to increase with increasing amount of TEOS added.This trend was observed for materials with and without cobalt. Type IVisotherms, typical of mesoporous materials, were obtained for ethanesilica andmodified ethanesilica materials prepared without cobalt.For cobalt incorporated periodic mesoporous ethanesilica materials, the XRDlattice parameter (d100) increased whereas surface area and pore volume decreasedwith increasing cobalt loading.Nitrogen gas adsorption on samples with varying ratios of BTME:GPTS orBTME:APTS revealed that increasing the amount of GPTS or APTS affects poresize, surface area and pore volume as well as shapes of the isotherms andhysteresis loops. The hysteresis loops of the Type IV isotherms obtained forGPTS-modified ethane silica materials (without cobalt) change from Type H3 toType H4. There is a tendency for pore sizes to change from mesopore tomicropore when the amount of GPTS is increased. Isotherms of cobaltincorporated GPTS-modified ethane silica materials changed from Type IV toType I. The surface area, pore volume and pore diameter decreased withincreasing loading of GPTS or APTS as well as after cobalt incorporation.

[发布机构] University of the Witwatersrand