Influence of azo dye additives on structural ordering of mesoporous silicas

Abstract

Organosilica materials with mesoporous structure were prepared by hydrothermal sol–gel condensation of tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane in the presence of cetyltrimethylammonium and decyltrimethylammonium bromide as pore-generating agents. The effect of azo dyes, alizarin yellow, and methyl red as cosurfactants and their alkoxysilane derivatives as structure-forming silanes on mesostructure and morphology of resulting silicas was studied. The mesoporous structure of synthesized materials was characterized by low-temperature adsorption–desorption of nitrogen, X-ray diffraction analysis, and transmission electron microscopy. It was confirmed that the pore size, specific surface area, and hexagonal arrangement of mesopores in synthesized silica nanoparticles were strongly affected by the azo dye additives. Solubilization of azo dyes by liquid crystal phase of long-chain alkyltrimethylammonium salts and cooperative organization of dye-containing silanes with surfactants, involving penetration of aromatic groups of silanes into micelles, causes formation of more uniform mesoporous structure. As it was elucidated from the analysis of low-temperature adsorption–desorption of nitrogen, introduction of azo dye additives in sol–gel process results in noticeable increase of surface area, narrowing of pore size distribution and pore diameter. In accordance with the results of X-ray powder diffraction analysis, formation of silica materials which are characterized by the more distinct long-range ordering of porous structure takes place. The presence of azo dye compounds in sol–gel reaction mixture does not influence the morphology of resulting aminopropyl silica nanoparticles in noticeable extent, but causes formation of highly ordered arrays of cylindrical mesopores.