Efeito do íon isomórfico (Cu2+) e da adição de agente precipitante na atividade de um óxi-hidróxido de ferro

Abstract

Feroxyhyte is a little explored phase of iron oxides of the chemical formula δ-FeOOH, so that its study can be of great value to evaluate the properties of this material. It has been used as an adsorbent and catalyst in Fenton reactions, for the removal of potentially toxic organic compounds. Modifications in these materials, whether with the insertion of a second element (Cu2+) in the structure, even changes in synthesis parameters, are carried out in order to increase the activity. Thus, the objective of this work has been to study the influence of copper insertion and the manner of adding (controlled and uncontrolled) of the precipitating agent during the synthesis, on the properties of feroxyhyte when removing the dyes of Methylene Blue (MB) and Reactive Black (RB) via adsorption and heterogeneous Fenton. The synthesized materials have been characterised by Scanning Electron Microscopy (SEM) that allowed to analyze their morphology, observing that the crystals cluster in the form of sheets; Nitrogen Physisorption Isotherms, making it possible to measure the specific surface area, verifying that the materials presented larger values than other iron oxide phases, reaching 157 m2 g-1, also, it has been examined that the doping and the controlled addition of the precipitating agent, evidence to a reduction in the magnitude of this property; Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR),to identify the functional groups in the oxide, confirming the presence of O-H groups characteristic of the oxyhydroxide; Elementary analysis by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), being possible to quantify iron and copper, proving that the addition of the doping element followed the theoretical values of 10%; Zero Charge Potential (ZCP), in which it have been able to determine the pH value at which the oxides have zero surface charge, and the values obtained 6.80-7.26 and Thermal Analysis, such as Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA), that indicated good stability of the iron oxides obtained, mainly, of the dopeds.The removal of MB dye (50 mg L-1) have been despicable with adsorption and with low degradation rates in the Fenton process, however, when adding hydroquinone (HQ), as an organic additive, to the reaction, the removal reached 98 %, achieving 72 % mineralization, in 90 minutes, when using the material with the best performance. In the case of RB (50 mg L-1), adsorption exhibited satisfactory removal, and when combined with Fenton, total dye removal have been achieved in less time. The materials that showed the best results were evaluated in 7 reuse tests, with no significant loss of catalytic activity. The copper-modified oxides showed the best results for the removal of dyes in all reactions and, according to the synthesis method, the one performed without controlling the addition of base proved to be comparable to the controlled and even superior, in some cases. Thus, it was possible to obtain a material with satisfactory performance in a shorter period of time.