Materiais híbridos aplicados na química Fenton

Abstract

The scarcity of water resources in line with environmental pollution today are topics of constant discussion. The search for catalytically active materials that aim to remove organic contaminants from wastewater has been the subject of several researches. In this sense, iron oxides are undoubtedly the most studied, since, these oxides represent a family of materials with remarkable diversity of properties and very interesting chemistry. Among iron oxides, magnetite (Fe3O4) is highly important, due to its differentiated structure and magnetism. In addition, its structure allows both structural and superficial modifications that greatly assist in its catalytic potential. With this, this work aimed at the synthesis of magnetite nanoparticles modified isomorphically by cobalt and supported in graphite, with application in the heterogeneous Fenton chemistry, aiming at the removal of two model compounds, methylene blue (MB) and remazol black (RB) . The materials were synthesized using the inverse coprecipitation method, where isomorphic iron substitutions were made using 5 mol% and 10 mol% of cobalt and surface modification with 10 mol% of graphite (Fe3O4, Fe2,85Co0,15O4, Fe2,7Co0,3O4, GF-Fe3O4, GF-Fe2,85Co0,15O4, GF-Fe2,7Co0,3O4). All materials were characterized by infrared spectroscopy (FTIR-ATR). However, due to the work difficulties faced due to the COVID-19 pandemic, only Fe3O4 and Fe2.85Co0.15O4 materials were characterized by scanning electron microscopy with mapping by energy dispersive spectroscopy (EDS-SEM), differential scanning calorimetry ( DSC) and X-ray diffractometry (XRD). Likewise, catalytic tests for hydrogen peroxide (H2O2) decomposition, adsorption and degradation using heterogeneous Fenton (catalyst/H2O2/CH2O2), were also performed only for these materials. The FTIR-ATR results indicated bands characteristic of the formation of magnetite and for materials containing graphite, some bands can be attributed to carbon. The analysis by EDS-SEM showed great superficial agglomeration, and the semi-quantitative analysis of the cobalt doping metal was not possible to be performed, due to the proximity between the X-ray emission energies of iron and cobalt. The DSC analysis showed endothermic and exothermic events characteristic of magnetite, water evaporation and phase transitions. The XRD indicated agreement with the standard magnetite chart, an evidence of the purity of the oxide obtained. And no changes in the diffraction peaks were observed for the doped material, which results from the low percentage of cobalt used. The crystallite size was calculated using the Debye-Scherrer equation, which revealed crystallites in the order of nanometers. In the H2O2 catalytic decomposition test, the evidence shows that the vacancy mechanism must govern the reaction. Furthermore, the leaching test indicates that the catalytic reaction is heterogeneous. For the degradation, the results were more promising for the dye RB (anionic), obtaining a degradation of 91% and 28% in 30 minutes (Fe3O4, Fe2,85Co0,15O4) for this dye and 0% and 46% in 120 minutes (Fe3O4, Fe2,85Co0,15O4) for MB (cationic). This is an indication that the material developed has a greater affinity for anionic dyes, which probably must be due to the vacancy mechanism. The adsorption tests showed low adsorption, indicating that the materials are not able to adsorb the dyes. Through all the results obtained, it is possible to conclude that although the characterizations do not leave clear evidence that the material has actually been doped, the catalytic tests may be an indication of this, due to the improvements obtained in its catalytic activity. In order to complement the research, the second chapter presents a schedule of future work and a review manuscript