Removal of 17α-ethinylestradiol (EE2) from aqueous solutions by peanut shells (Arachis hypogaea): adsorption kinetic, isothermal, and thermodynamic studies

Abstract

This study evaluated the potential of using raw peanut shells as an adsorbent to remove the hormone 17α-ethylestradiol (EE2) from water. High-performance liquid chromatography with fluorescence detection was used in the determination of EE2. Kinetics data were tested with the pseudo-first-order, pseudo-second-order, and Elovich models, whereas isothermal data were tested with the Langmuir, Freundlich, and Sips models, and the parameters (ΔG°, ΔH° and ΔS°) were evaluated. A maximum removal rate of approximately 90% was observed in a solution with an initial EE2 concentration of 263.2 μg L−1, under the best experimental conditions (stirring speed = 500 rpm, pH = 6, and adsorbent mass = 2 g in 24 h), and showed an adsorption capacity of 17.3 μg g−1 at 306 K. The pseudo-first-order model adjusted better to the data in the studied temperature range, presenting a potential barrier of 16.69 kJ mol−1 (Ea) for adsorption kinetics. The Freundlich model and Sips model adjusted better to the data in the studied temperature range. The negative value of ΔG° (−15.87 kJ mol−1 at 306 K) confirmed the viability and spontaneity of the adsorption process. The positive value of ΔH° (168.9 kJ mol−1) characterized the chemical nature of the adsorption process.