Abstract
Natural bentonite is an adsorbent that can be easily modified as a low-cost material effective for the removal of persistent pharmaceutical micropollutants from water bodies. In this study, the modification of untreated bentonite by sodium is addressed to obtain Na-bent, which was further modified with L-Tryptophan (L-Trp) as well as with FeCl2.4H2O to produce Trp-Na-bent and Fe-Na-bent, respectively. The nonmodified and modified bentonite samples were tested for the adsorption of the pharmaceutical micropollutant 17α-ethinylestradiol (EE2) present in water bodies, a synthetic estrogen with very high toxicity. The structure of bentonite, before and after modification, was characterized using Fourier transform infrared, X-ray diffraction, Brunauer-Emmett-Teller, and thermal analysis (thermogravimetric analysis and differential scanning calorimetry) techniques. The influence of various experimental parameters on the adsorbent/adsorbate interaction was investigated. Equilibrium and kinetic studies of EE2 micropollutant adsorption were performed varying the initial adsorbate concentration, mass of bentonite, and contact time. The maximum adsorption for an initial concentration of 10 mg/L of EE2 was 4.20 mg/g, reaching the equilibrium after 2 h. The equilibrium data were fitted with Langmuir, Freundlich, and Dual-mode model equations. Adsorption kinetic data were analyzed using the pseudo-first order, pseudo-second order, and intraparticle diffusion models. The pseudo-second order model was the one that better described the kinetic data. The highest value of the equilibrium rate constant was obtained for Trp-Na-bent, followed by Fe-Na-bent. The results obtained show that the Trp-Na-bent complex exhibits a promising performance for the adsorption of EE2.
Get full access to this article
View all access options for this article.
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
