Síntese e modulação de propriedades texturais de nanocompósitos sílica/pentóxido de nióbio

Abstract

Porous materials have a great impact on contemporary society. Especially after the development of porosity tailoring routes by research groups at company Mobil in the 90s, (development of silica MCM family), advances in the development of new pore architectures have been intensified. The interest is due to the fact that a wide variety of chemical and physical processes start or re highly dependent on the interface properties between two coexisting phases in the same environment and, therefore, are intensified when the surface areas and porosity of the materials that participate in the process are increased. In this work a new method was developed for the production of the silica / niobium pentoxide nanocomposite, without the long precursor adsorption step, by the direct addition of a niobium pentoxide precursor (ammoniacal niobate oxalate) before gelation by sol-gel processing, and its subsequent decomposition inside the silica matrix with temperature variation. The textural properties of the nanocomposite were studied at temperatures of 500, 700, 900 and 1100 ºC, revealing that the presence of the niobium pentoxide precursor changes the pore morphology of the silica matrix. It was also possible to demonstrate that the addition of polyethylene glycol 10000, before gelation, is able to alter even more significantly the porous structure of the nanocomposite, including by spinodal decomposition, leading to an interconnected network of macropores inside the composite monoliths. The gas adsorption studies revealed specific surface areas of up to 785 m² g-1, but they also revealed the importance of more cautious studies in relation to gas adsorption, given that the BET theory has limitations, often neglected during calculations. The materials produced in a monolithic shape, with macropores, present themselves as candidates for use as columns in continuous flow devices (such as chromatographic columns or flow reactors) due to the macroporous network that facilitates mass transports through their bodies and their retention capacity as demonstrated by the adsorption of the antibiotic doxycycline and the dye methylene blue.