Avaliação do uso de diferentes surfactantes catiônicos na síntese do material mesoporoso MCM-48

Abstract

The control of the pore geometry and diameter of the mesoporous materials based on silica is necessary for the greater applicability of these materials, especially in processes dependent on the shape selectivity. In this sense, several studies have dedicated efforts to the greater control of the structure of these materials. Samples of MCM-48 molecular sieves having different pore sizes were prepared starting from a gel having the following molar composition: 1 SiO2 – 0,25 NaOH – 0,4 (CnH2n-1N(CH3)3Br – 100 H2O. The pore diameter of the samples was controlled by varying the hydrocarbon chain length of the surfactant. In this study the influence of surfactants with different hydrophobic tail lengths (alkyltrimethylammonium, CnH2n-1N(CH3)3Br , n = 17-21) on the formation and properties of mesoporous silicas was verified. The samples were characterized by X-ray diffraction (XRD), thermal analysis (TG / DTG), infrared spectroscopy (FT-IR) and adsorption and physical desorption of N2 (BET). It was observed a relation between the chain size and the pore diameter was observed and inversely proportional to the structural ordering. Furthermore, it is observed that as silicas synthesized with a mixture of the surfactants resulted in materials with a high surface area, main pore diameters and structural ordering. As analysis by N2 physisorption revealed that emerging material from specific surface areas in the range of 703 to 1069 m2 g-1 for samples synthesized by blends being a more expressive C17C19C21 (1069 m2 g-1) blend. From the XRD analysis it was observed that as mixtures of surfactants they assigned as samples a better cubic organization of the pores and a narrow distribution of comparisons as synonyms synthesized with only one of the surfactants.