Estruturas core@shell NiFe2O4@TiO2-Fe aplicadas na degradação fotocatalítica de glifosato em meio aquoso

Abstract

Glyphosate is currently considered the main agricultural input sold in Brazil and worldwide. Despite being considered low toxic, the intensive use of glyphosate and glyphosate-based herbicides can compromise the soil and aquatic environment, modifying the integrity of existing ecosystems. Thus, methodologies capable of degrading this compound have been developed over the last few decades. Effective and relatively low-cost technologies are the Advanced Oxidative Processes (AOPs), among which heterogeneous photocatalysis stands out. Titanium dioxide (TiO2) is the most used semiconductor in the field of photocatalysis. However, TiO2 requires the use of UV radiation, which makes its use in processes that occur under visible radiation unfeasible. Furthermore, TiO2 is not easily removed from the aqueous medium at the end of the reactions, which implies a low reuse rate. In order to improve the photocatalytic properties of TiO2, it is possible to associate this semiconductor with other materials that reduce the band gap energy of the photocatalyst and facilitate its removal from the reaction medium. In this sense, this work aimed at the synthesis and characterization of nanoparticles with core@shell structure, where the core is formed by nickel ferrite (NiFe2O4) and the shell by TiO2 doped with different iron contents, forming NiFe2O4@TiO2-Fe structures to evaluate the influence of Fe content on the photocatalytic degradation of glyphosate (Roundup®) in an aqueous solution. The photocatalysts were prepared by the adapted Pechini method and calcined at 700 ºC. Through X-ray diffraction analysis and Rietveld refinement, NiFe2O4, NiO, α-Fe2O3 and the polymorphs of TiO2, anatase and rutile were identified. It was also observed that the doping of TiO2 with Fe and its association with NiFe2O4 favored the formation of the rutile polymorph. Through the data obtained by scanning electron microscopy (SEM-EDS) analysis, it was verified that the coating of ferrite by TiO2 did not occur homogeneously. At the photocatalytic tests of decontamination of glyphosate in aqueous medium under visible radiation, the photocatalyst that showed the best performance was the NiFe2O4@TiO2 sample. However, tests with H2O2 were necessary to obtain satisfactory results in the conversion rate of glyphosate to phosphate. H2O2 played a very important role in the photocatalytic degradation of glyphosate and, according to the obtained results, the association of the photocatalyst with H2O2 and visible radiation was the system that provided the best results in the degradation reaction of the glyphosate herbicide. Finally, it was found that the photocatalyst showed a reduction in adsorptive and photocatalytic capacity over 4 sequential tests.