Synthesis And Characterization Of The Spherical Organic-inorganic Porous Silica Bonded By Octadecyl

Monodispersed organic-inorganic hybrid silica spheres with a particle size larger than 2μm have attracted considerable attention due to their potential applications as stationary phase of liquid chromatography(LC). In the present paper, ethane-bridged organic-inorganic silica spheres were synthesized via the surfactant(dodecyltrimethylammonium bromide, DTAB)-mediated assembly of 1,2-bis(triethoxysilyl)ethane(BTESE) in a modified st?ber process under various conditions. Then the dispersity of the organic-inorganic silica spheres was controlled by ultrasonic treatment, mechanical shearing and vacuum freeze drying. Finally octadecyl group(C18) was used to modify the organic-inorganic silica spheres by the co-hydrolysis and condensation of BTESE and octadecyltriethoxysilane(ODTES) under basic condition and the post-grafting method. The morphology, pore structure and the modification result of the organic-inorganic hybrid silica materials were characterized by means of scanning electron microscopy(SEM), nitrogen adsorption, Fourier translation infrared spectroscopy(FT-IR), elemental analysis and solid state nuclear magnetic resonance(NMR), respectively.The results show the morphology of silica particles varies from irregular shape to uniform sphere depending on the amount of water in the mixture. Larger silica spheres are obtained under lower surfactant concentration, higher ammonia concentration and lower synthesis temperature. The optimal molar ratio for silica spheres synthesis is 1BTESE:x DTAB:10NH3: 300H2 O, where x ranges from 0.2 to 0.6.The silica spheres are well dispersed after ultrasonic treatment for 5min, mechanical shearing with a velocity of 5k r.p.m. for 5min, and freeze drying successively.Octadecyl groups are possible to be bonded on the organic-inorganic hybrid silica spheres by both co-hydrolysis and condensation method and post-grafting method. For the co-hydrolysis and condensation method, the molar ratio of ODTES /BTESE should be no higher than 0.1 in order to retain the morphology of the silica spheres. For the post-grafting method, the hydroxylation of silica spheres is necessarily required by gentlely stirring the silica spheres in hydrochloric acid solution after sonicating for 6h before C18 bonding. The amount of C18 in the functionalized silica materials increases rather slightly with increasing ODTES concentration used for modification. The pore structure and morphology of silica materials remain almost intact after the C18 bonding.