Utilização de nanopartículas magnéticas de óxido de ferro e seus derivados na adsorção dos corantes Rodamina 6G e Rodamina B

Abstract

Synthetic dyes Rhodamine 6G and Rhodamine B are used in industries of various branches, such as textiles, manufacturing dyes for printers and lasers, among others. When residues contaminated by these dyes are improperly disposed of in the environment, they cause contamination of water bodies. In order to minimize environmental damage, several types of effluent decontamination processes have been studied. The adsorption method has stood out in the treatment of these effluents, due to its ease of operation, low cost and high efficiency. In this work, two types of nanoparticles (NPs) were synthesized and characterized, one by co-precipitation, Fe3O4, and the other by the solvothermal technique, CoFe2O4, to be applied as adsorbents for the dyes Rhodamines 6G and B. The synthesized Fe3O4 and CoFe2O4 NPs were characterized by the pH of the zero charge point (pHPCZ) obtaining pHs of 6.46 and 7.16, respectively. The cubic phases of magnetite and cobalt ferrite were indexed by X-ray diffraction, with mean crystallite sizes around 46.3 and 20.8 nm, respectively. Scanning electron microscopy showed spherical morphologies for both NPs, with diameters around 51.0 ± 5.0 nm for Fe3O4 NPs and 57.0 ± 4.7 nm for CoFe2O4 NPs. The dyes were characterized by spectroscopy in the visible region and their stability analyzed as a function of the pH of the medium. The maximum absorption wavelengths for Rhodamine 6G and B were 526 nm and 554 nm, respectively. Both rhodamines were stable when the pHs of the media were changed, with no changes in absorption wavelengths being observed in the visible spectrum. The adsorption tests of Rhodamines by NPs were evaluated by analyzing the initial pH of the solution, the adsorbent-adsorbate contact time, the dye concentration and the system temperature. The highest adsorption capacity occurred at pH 4.0 and the adsorption equilibrium at the contact time close to 30 min, where the Pseudo Second Order model with 99% adjustment was the one that best described the adsorption kinetics of the systems. The adsorption isotherms, at temperatures of 301, 311 and 321 K, satisfactorily fit the Temkin model. The maximum adsorption capacity occurred in both dyes at a temperature of 321 K for Rhodamine 6G-NPs of Fe3O4 (279.51 mg.g-1), while for NPs of CoFe2O4 it presented 281.78 mg.g-1 of maximum adsorption capacity. For the dye Rhodamine B, when adsorbed on Fe3O4, the adsorptive capacity was 276.64 mg.g-1 and adsorbed on CoFe2O4 was 269.08 mg.g-1. The study carried out shows that the synthesized NPs are efficient in the adsorption of Rhodamines in aqueous medium and can be removed from the medium through the application of an external magnetic field. The systems studied proved to be promising for the treatment of effluents.