Adsorção da Losartana Potássica (contaminante emergente) pelo Hidróxido Duplo Lamelar em Águas Contaminadas

Abstract

In recent years, several studies on the removal of emerging pharmaceutical contaminants in contaminated water have addressed the adsorption method, as it is an operationally simpler and less costly method. In this context, this study aimed to remove the drug losartan from the synthesis by the co-precipitation method at constant pH of different LDHs, such as: [Mg-Al-NO3], [Ni-Al-NO3] and [ Co-Al-NO3] and the respective structural and morphological characterizations: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Spectroscopy in the Infrared Region with Fourier Transform (IR-TF), Specific Surface Area by the method (BET) and Thermogravimetric Analysis (ATG). LDHs XRDs [Mg-Al-NO3] and [Ni-Al-NO3] showed defined diffraction peaks, which were indexed to hexagonal structure, rhombohedral symmetry, space group R(-3)m (JCPDS 14-191). The morphological characterization of LDH [Mg-Al-NO3] showed particles with irregular sizes in the shape of hexagons, and in LDH [Ni-Al-NO3] crystalline aggregates and particles with rounded edges, both similar to the results obtained in the literature. Spectra (IR-TF) of all LDH s confirmed the presence of the NO3- anion, water molecules between the coverslips and metals present referring to Mg-O, Ni-O, Co-O or Al-O bonds. By the BET method, the isotherm profiles of both LDHs were similar to the V type, characteristic of mesoporous materials. Among the LDHs investigated, [Mg-Al-NO3] (synthesized with water) was the one that presented the highest thermal stability, highest interlamellar spacing, lowest cost of reagents and lowest toxicity, so it was selected as an adsorbent in the adsorption tests of the pharmaceutical pollutant. LDH [Mg-Al-NO3] showed a zero charge point at pHpcz 7. The adsorption tests were carried out in batches from solutions containing the drug losartan potassium (LP) at pH 5.5 and under agitation. The adsorption kinetics was studied at room temperature (298 K) and the thermodynamic analysis investigated the following temperatures: 298, 308, 318 and 328 K. Based on the kinetic adsorption data, adjustments were made to the linear mathematical models of pseudofirst order and pseudosecond order. For the study of isotherms adjustments to the mathematical models proposed by Langmuir and Freundlich were used. The adsorption kinetics experimental data for LP better fit the pseudosecond order model, suggesting that the adsorption rate was dependent on the initial drug concentration and suggesting a chemisorption. The adsorption process showed a better fit to the Freundlich isotherm model describing a physical interaction between adsorbent and adsorbate. Values of (1/n) in the range between 0 to 1 and (n) greater than 1 suggest that LP adsorption on LDH is favorable and are present in energetically heterogeneous binding sites. Equilibrium time was reached in about 40 min with removal efficiency (51.55%) and adsorptive capacity of 6.19 mg g-1. The thermodynamic parameters demonstrate that the adsorption was spontaneous, exothermic and with a lower degree of freedom between the molecules adsorbed on the LDH surface. The LP adsorption process by LDH showed q max (19.53 mg g-1 at 298 K). Therefore, LDH [Mg-Al-NO3] is a promising material as an adsorbent in the removal of LP in contaminated water, thus allowing a significant reduction of its pollution in several aquatic environments.