Síntese, caracterização e estudo das propriedades fotocatalíticas de compostos de nióbio em matrizes ambientais

Abstract

One of the materials that is currently highlighted are the compounds of niobium, because they have features like acidity, oxidative and photocatalytic properties and for being one of the most abundant metals in the country, Brazil is the world's largest producer. In this scenario, the work has to evaluate the efficiency of heterogeneous photocatalysis niobium materials in the oxidation of methanol and the inactivation of Escherichia coli using immobilization systems ―coating” and suspension. Commercial niobium oxide (Nb2O5) was evaluated in suspension and immobilization in different systems (tubes and rings) for photocatalytic processes for water treatment (methanol oxidation and inactivation of Escherichia coli). From the results of the commercial Nb2O5 characterizations was observed the presence of an amorphous structure with heat thermal treatment at temperatures above 550 °C becomes crystalline phases, however, this fact produce a significant aggregation of the particles which reduced the specific area and the photocatalytic activity. The not calcined Nb2O5 material showed a higher activity, for both oxidation of methanol as for the inactivation of bacterial tests, the latter being very sensitive to the chemical composition water. Immobilization of the photocatalyst reactor walls prevents the need for removal of Nb2O5 particles after treatment, but significantly reduction its activity. In contrast, immobilization in a fixed-bed (rings) led to a moderate reduction in activity, which is counteracted by improvement in the long-term stability of the material. Niobium catalysts were synthesized using a refluxing method with and without the use of NaOH in different conditions of synthesis and characterized by different techniques in order to verify the phase formation of niobium. From the results of X-ray diffraction for the synthesized materials were recorded forming of species niobium oxide and sodium niobates depending on the adopted synthesis methodology. The catalytic activity of these materials was evaluated in the oxidation of methanol in relation to the amount of catalyst in which the activities have different behaviors have been dependent on the structure, surface and morphological parameters. Materials with sodium niobate structure have a lineal tendency of activity in relation to the mass of catalysts, while the materials niobium oxide structure have an abrupt loss of their catalytic activity at higher catalyst concentrations, indicating that the dispersion of the light is higher in these catalysts as increases the amount of particles in suspension. Among the materials synthesized and analyzed in the oxidation of methanol, which was more efficient, was the material of sodium niobate NaNbO3 to their textural properties, optical, which is a promising material for photocatalysis.