Estudo das modificações em HDL-MgFe e produzidos por diferentes rotas sintéticas : análise da capacidade de adsorção

Abstract

Double Lamellar Hydroxides (LDHs) are commonly applied as adsorbents to remove contaminants in aqueous matrices. However, chemical methods for synthesizing LDHs can promote variations in their structure. This work investigated how the surface area, basal spacing and crystallinity, important parameters for the adsorption dynamics, are modified using different synthetic routes to produce LDH-MgFe. Thus, the synthesis by coprecipitation at variable pH (CV) and at constant pH (CC), hydrothermal synthesis (HC), drip hydrothermal (HCG), coprecipitation followed by hydrothermal (CCH), ultrasonic vibration (UHC) and microwave radiation (MHC) were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform infrared spectroscopy (FTIR), N2 adsorption- desorption, Zeta Potential, Point of Zero Charge (PZC). The adsorption capacity was quantitatively measured by the results of removal of the following adsorbates: Nitrate, Rifampicin and 17-α-methyltestosterone. The effect of pH, adsorbent dose, kinetics, and adsorption equilibrium were investigated based on the best results of characterization and Life Cycle Analysis (LCA), later the thermodynamics of the process was analyzed. Thus, the physical structure and typical bands of LDHs were formed in all methods. Hydrothermal treatment increased crystallinity and basal spacing. The surface area varied from 49.5 to 84.0 m2 g -1, the isotherms classified the materials in mesopores. 17-α-methyltestosterone showed low selectivity, however, the affinity for Nitrate and Rifampicin increased significantly in CC (69.77, 67.78%), UHC (76.63, 82.71%) and MHC (74.57, 82.50%), respectively. The simplified LCA showed that the use of the CC method presented the lowest environmental impacts for acidification, climate change, eutrophication, and human toxicity. The pseudo-second order model was the one that best explained the adsorption kinetics for the CC, HC and UHC methods. The Langmuir model best fitted the adsorption curves for CC, HC and UHC. The thermodynamic data indicate exothermic and spontaneous process for CC and HC and, in UHC, as endothermic reaction. The spectra IR, before and after adsorption, suggested that the nitrate was adsorbed by electrostatic interactions in both methods, as well as by anion exchange interactions of the hydroxyl groups in HC and UHC. Therefore, the materials produced demonstrate applicability as adsorbents for the removal of pollutants in an aqueous matrix, allowing the targeting of specific compounds to be captured, depending on the synthetic route chosen.