Síntese do compósito magnético Fe3O4/HDL-MgAl e seus materiais precursores para remoção adsortiva de verde malaquita em meio aquoso

Abstract

The removal of emerging pollutants (EPs) in wastewater, groundwater and surface water, combined with the growing demand for higher levels of supply, has led the scientific community to seek new materials and more efficient methodologies for the treatment of water containing PEs. Several methodologies have been shown to be promising, including adsorption - a technology used efficiently to remove these pollutants. Many studies have sought to develop new adsorbent materials capable of being regenerated and reused during several cycles. In this sense, the Double Lamellar Hydroxides (LDHs) already have a well-established role in studies aimed at removing pollutants via adsorption. On the other hand, its association with other materials, in the formation of composite, has aimed to reduce some disadvantages of this material, for example, the final process of adsorbent/solution separation. Within this context, this project aims to synthesize a composite based on a Double Lamellar Hydroxide (LDH) and Fe3O4 (Fe3O4/LDH-MgAl), to act in the adsorption in aqueous medium of malachite green dye (MG). In the adsorption/desorption of N2 by the BET method, an increase in the surface area was observed, in addition to a decrease in the volume and pore size of Fe3O4/LDH-MgAl, compared to its precursors, Fe3O4 and LDH-MgAl. In Energy Dispersive Spectroscopy (EDS), the elemental composition of the Fe3O4/LDH-MgAl composite was evidenced, as well as the elemental constituents of its precursors. Through Fourier Transform Infrared Spectroscopy (FTIR), characteristic regions of OH, MgO, Fe-O bonds and Fe3O4, LDH-MgAl and Fe3O4/LDH-MgAl, reported in the literature, were observed. For Raman spectroscopy, Fe3O4 did not show enough polarizability to generate a signal, different from what was observed in LDH-MgAl and Fe3O4/LDH-MgAl, where they presented similar signals to each other. In X-Ray Diffraction, the characteristic peaks of LDH-MgAl were not observed in the Fe3O4/LDH-MgAl composite, thus indicating a coating of LDH-MgAl by Fe3O4. The pH values of the Zero Charge Point (pHzcp) of Fe3O4, LDH-MgAl and Fe3O4/LDH-MgAl were 6.67; 8.80 and 7.09, respectively, eliciting the presence of a slight alteration in the pHzcp of the composite, also indicating the presence of LDH-MgAl in small amounts. In the adsorptive process, malachite green was used as a pollutant, reaching equilibrium adsorbed amounts (qe) of 198.94 and 172.13 mg g-1 for LDH-MgAl and Fe3O4/LDH-MgAl, respectively. Furthermore, for the three materials, the pseudo-first order model, in the kinetic study, was the one that best fit the experimental data. Furthermore, through the adsorption isotherm data, a better fit to the Sips model was observed, compared to the other models used in this study. Although LDH-MgAl and the composite (Fe3O4/LDH-MgAl) have shown excellent efficiency for removing the pollutant, the difference was in the operational process, since for Fe3O4/LDH-MgAl the recovery of the adsorbent after the process, was facilitated via the application of a magnetic field.