Synthesis of mesoporous silicas in alkaline and acidic media using the systems cetyltrimethylammonium tosylate (CTAT)–Pluronic F127 triblock copolymer and CTAT–Pluronic F68 triblock copolymer as templates

Abstract

Mesoporous silica materials were synthesized in alkaline and acidic media, using cetyltrimethylammonium tosylate (CTAT), Pluronic triblock copolymers F127 and F68, and mixtures of CTAT with each copolymer in order to investigate the effects of pH, surfactant concentration, and CTAT/triblock copolymer molar ratios on the morphology and texture of the synthesized materials. The results show that the kind of mesoporous materials and their pore size can be tuned by changing not only the pH but also the proportion of components and the nature of the copolymer. In alkaline synthesis, microscopic bicontinuous materials are obtained, which are composed by nanoscopic plate-like particles having slit-shaped pores. In acidic synthesis, on the contrary, monolithic silicas are obtained. These materials are also composed by nanoscopic plate-like particles having slit-shaped pores, although in some cases, the microscopic structures are formed by fused spherical particles. The inclusion of the triblock copolymer in the template composition causes a transformation from a bimodal to a monomodal pore size distribution, leading to small and nearly round pores which are probably formed by copolymer or copolymer-CTAT mixed micelles. The differences between the systems synthesized by CTAT–Pluronic F127 and CTAT–Pluronic F68 are explained on the basis of the different interactions between each copolymer and CTAT.