Nb2O5 aplicado em processos fotocatalíticos de degradação da Rodamina B: influência da composição, estrutura e método de síntese

Abstract

Heterogeneous photocatalysis is a method capable of degrading organic pollutants found in effluents. Among the semiconductors capable of being used, niobium pentoxide (Nb2O5) has interesting optical and electrical properties, in addition to being thermodynamically stable, enabling its use in photocatalysis processes. Nb2O5 can be obtained by different synthesis methods, and combustion, sol-gel, polymeric precursors (PP) and microwave-assisted hydrothermal (HAM) were evaluated in this work. The temperature used to obtain the material, as well as the heat treatment applied, influences the crystalline phase, since low temperatures, such as sol-gel synthesis and HAM, can obtain amorphous Nb2O5 or with low crystallinity. The more crystalline the Nb2O5 phase is, the worse the photoactivity since it decreases the surface area and the number of active sites. In addition to temperature, the synthesis method also influences photocatalysis, where considering the same crystalline phase (orthorhombic), there was a better performance for the combustion method, since it has a greater number of pores, as well as smaller particles. When comparing the use of different precursors in HAM synthesis for low crystallinity samples, it was found that this variable also influences the photocatalytic response, showing a difference of approximately 6% in the photocatalytic efficiency between the ammoniacal oxalate niobium oxalate precursor and the pentachloride of niobium. Even though this difference was small, a 24 factorial design was carried out to assess whether the change in certain variables influences the photocatalytic response. All variables (precursor, amount of catalyst, dye concentration and process time) influence the process, some positive and others negative, but the concentration of Rhodamine B (RhB) dye and the process time are the ones that most influenced the process. Additionally, modifications such as the insertion of iron ions in the structure of Nb2O5 and the heterostructure with TiO2, both by HAM synthesis, were evaluated, showing that the modifications improved the photocatalytic performance, indicating that they can decrease the rapid recombination of electrons that may occur in pure Nb2O5.