Síntese e propriedades de sílicas híbridas contendo surfactantes catiônicos
Abstract
The control of pore geometry and pore diameter of silica mesoporous materials is
necessary for application of these materials, mainly in industrial process that depends on the shape selectivity. This way, considerable efforts have been devoted to control pore structure of these materials. In this study it has been found the influence of cetyltrialkylammonium and
alkyltripropylammonium (CnPr3Br, n = 14-22) surfactants in the formation and properties of
mesoporous silicas and subsequently microporous silicas. Regarding the mesoporous silicas synthesized through cetyltrialkylammonium surfactants, it was observed that the silicas pore size increased and the structural ordering decreased as the head group of surfactants increased. In contrast, the increase of lkyltripropylammonium tail resulted in silicas with larger porous diameter and structural ordering. The mesoporous silica with the largest pore
diameter (3,60 nm), synthesized with C22Pr3Br surfactant exhibited narrow pore-diameter
distribution and a hexagonal organization characteristic of MCM-41 silica. The performance of alkyltripropylammonium surfactant as zeolitic structure directing agents was also investigated. The results showed the formation of a physical mixture between MFI and magadiite structures under different hydrothermal treatment temperatures. Only after addition of tetrapropylammonium cations to reaction mixture containing alkyltripropylammonium cations it was possible to obtain pure MFI structure. However, the presence of alkyltripropylammonium cations had strong influence on the crystals growth and
consequently in the form of zeolite crystals obtained.