Síntese de compósitos a base de akaganeita com cobre e fósforo: aplicação no processo fenton

Abstract

Industrial practices lead to the generation of a vast volume of effluent that often contains problematic substances, and when improperly disposed of, can cause irreversible damage to the environment. In this context, advanced oxidation processes (AOPs), which are a set of chemical reactions capable of generating hydroxyl radicals, can be employed for treating effluents containing organic matter, aiming for complete mineralization. Among the AOPs, the Fenton reaction generates hydroxyl radicals through the reaction between ferric or ferrous species and the oxidant hydrogen peroxide, which was chosen in this study to degrade the model molecule methylene blue. The phase of akaganeite iron oxide (AK) and copper-doped akaganeite (AKCu) was used for the synthesis of iron phosphide (FeP) and iron and copper phosphide (FeCuP). These materials were applied in the heterogeneous Fenton process. The elemental composition of the materials was identified using portable X-ray fluorescence, and the morphology and distribution of elements were evaluated by scanning electron microscopy with energy-dispersive X-ray spectroscopy, revealing an irregular surface and heterogeneous particle distribution. The infrared spectrum showed characteristic bands of akaganeite iron oxide. X-ray diffraction confirmed the synthesis of the materials. The oxygen evolution test allowed the identification of catalytic activity in the materials. Through the same test in an organic medium, it became evident that the predominant degradation mechanism of methylene blue is radical-based. The degradation kinetics of methylene blue were conducted at three different temperatures. As the temperature increased, the activity of the AKCu catalyst decreased, while the akaganeite phase showed good activity in the various tests conducted. Iron and copper phosphide exhibited excellent catalytic activity, achieving 98% removal of methylene blue from the reaction medium. By determining reaction rates at different temperatures, the reaction in the presence of the FeCuP composite was found to be about 243 times faster than its precursor AKCu. The reuse of materials was evaluated over four different cycles. From the second cycle onward, the AK phase practically lost its activity, which did not happen with the other materials, which still showed reduced activity in the fourth cycle.