Esferas de sílica mesoporosa com estrutura análoga à família M41S: influência das condições de síntese às propriedades –

Abstract

Mesoporous silica is widely studied as adsorvent or catalyst support. For a lot of these applications the morphology control of the adsorvent or support is of great importance, especially if the preparation of hierarchically structured pore systems is desired. The present work was carried the preparation of mesoporous silica spheres prepared by a modified Stöber synthesis, which is widely known for the synthesis of non-porous silica spheres. In order to identify the influence of the different factors on the final properties of the mesoporos silica the different synthesis parameters such as ethanol-, water-, ammonia concentration, surfactant/silica ratio, reaction time and temperature were varied and the obtained solids widely characterised by X-ray diffraction, physisorption of nitrogen and granulometry which determine the size of the synthesised silica microspheres. The obtained results reveal that the ethanol concentration, the reaction time and temperature and the surfactant/silica ratio are the principal influences on the structure of the mesopore arrangement. High temperature or prolonged reaction time results in disordered mesopre systems, while the structure type (hexagonal or cubic arrangement) is strongly influenced by the ethanol content and the surfactant/silica ratio in the reaction mixture. The water concentration is the most important factor on the sphere size, which increases with increasing water concentration. On the other hand the ammonia concentration does not influence significantly the properties of the mesoporous silica spheres.