The Aldehyde-modified Stober Method To Synthesis Of Mesoporous Silica Nanoparticles

Monodisperse non-porous silica spheres were first synthesized in1968by the classical Stober method, which is a facile and effective approach based on the hydrolysis and condensation of tetraalkyl silicates in a water-alcohol-ammonia system. Since first reported by the Mobil Corporation in1992, mesoporous silica materials have maintained the interest of the material science community. The Unger’s group modified this method by adding a cationic surfactant to the reaction to prepare micrometer-sized mesoporous silica spheres. Mesoporous silica nanoparticles (MSNs) have become an important class of nanomaterials and have been used in chromatography, drug delivery, enzyme immobilization and gene transfection carriers. The particle size and pore structure of MSNs are critical for many applications.Herein, the purpose of our study was to develop the aldehyde-modified Stober method for the preparation of MSNs. The preparation procedure is facile and stable via the self-assembly process of TEOS with the surfactant template in aldehyde/water solutions at room temperature. Cetyltrimethylammonium bromide (CTAB) was used as the template of mesopores, aqueous ammonia (NH4OH) as basic catalyst and tetraethyl orthosilicate (TEOS) as silica source. The particle size and pore structure of MSNs can be tuned by changing the synthesis conditions. Based on the above investigations, we got the following conclusions.(1) Size-controlled micro/mesoporous silica nanoparticles (MMSNs) were successfully prepared by the acetaldehyde-modified Stober method. The average particle size can be controlled from40nm to800nm by simply adjusting the ratio of acetaldehyde to water, the initial pH value and the molar amount of acetaldehyde. The particle size also can be increased by increasing the synthesis temperature. When the synthesis temperature is as high as100℃, the nanoparticles aggregated together and capsule-like particles were obtained. The MMSNs exhibited worm-like mesopores of2nm and micropores of0.6nm.(2) Novel hierarchical spherical mesoporous silica nanoparticles (HMSNs) were produced by using propionaldehyde and butyraldehyde. The HMSNs with mesopores of2.3nm have the radially cone-like pore structure. The particle size and the hierarchical pore structure of HMSNs depend on the alkyl chain of aldehyde.(3) An effective one-pot hydrothermal synthesis method was developed to produce MSNs in a TEOS-CTAB-NH4OH-Water-Formaldehyde systems, the particle size of the MSNs with mesopores of2.3nm was about30nm. A nanoporous carbon framework was obtained when precursor was carbonized in N? followed by a HF leaching of the silica. The pore size of the carbon was about31nm. The mechanism for the synthesis process was described.