Adsorption of 17α-ethinylestradiol from aqueous solution onto a reduced graphene oxide-magnetic composite

A reduced graphene oxide (rGO) magnetic nanocomposite rGO/Fe₃O₄ was prepared and used to adsorb 17α-ethinylestradiol from aqueous solutions. The magnetic nanocomposite was characterized using X-ray powder diffraction, Raman spectroscopy, vibrating sample magnetometer measurements, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. It was shown that the Fe₃O₄ nanoparticles are uniformly deposited on the rGO sheets. Experiments were performed to elucidate the mechanism by which 17α-ethinylestradiol adsorbs onto rGO/Fe₃O₄. The kinetic adsorption data for 17α-ethinylestradiol fitted well with a pseudo-second-order model, while the equilibrium data followed Langmuir isotherms. Thermodynamic analysis indicated that the adsorption is a spontaneous and endothermic process. The effects of water chemistry (pH, coexisting ions, humic acid level, and water matrix) on 17α-ethinylestradiol adsorption were also investigated. It was found that pH and humic acid level have noticeable effects on the adsorption of 17α-ethinylestradiol, while coexisting ions and water matrix do not. Desorption experiments performed using methanol as eluent demonstrated that the adsorbent could be reused for five cycles without significant deterioration in performance. The results show that rGO/Fe₃O₄ exhibits high adsorption capacity and may be conveniently recovered, making it a promising adsorbent for 17α-ethinylestradiol removal from real-world water resources.