Enhanced Adsorptive Removal of β-Estradiol from Aqueous and Wastewater Samples by Magnetic Nano-Akaganeite: Adsorption Isotherms, Kinetics, and Mechanism

A surfactant-free method was used to synthesize iron oxyhydroxide (akaganeite, &beta:-FeOOH) nanorods and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM). The synthesized nanoadsorbent was applied for the adsorptive removal of &beta:-estradiol from aqueous solutions. The parameters affecting the adsorption were optimized using a multivariate approach based on the Box&ndash:Behnken design with the desirability function. Under the optimum conditions, the equilibrium data were investigated using two and three parameter isotherms, such as the Langmuir, Freundlich, Dubinin&ndash:Radushkevich, Redlich&ndash:Peterson, and Sips models. The adsorption data were described as Langmuir and Sips isotherm models and the maximum adsorption capacities in Langmuir and Sips of the &beta:-FeOOH nanorods were 97.0 and 103 mg g&minus:1, respectively. The adjusted non-linear adsorption capacities were 102 and 104 mg g&minus:1 for Langmuir and Sips, respectively. The kinetics data were analyzed by five different kinetic models, such as the pseudo-first order, pseudo-second order, intraparticle, as well as Boyd and Elovich models. The method was applied for the removal &beta:-estradiol in spiked recoveries of wastewater, river, and tap water samples, and the removal efficiency ranged from 93&ndash:100%. The adsorbent could be reused up to six times after regeneration with acetonitrile without an obvious loss in the removal efficiency (%RE = 95.4 &plusmn: 1.9%). Based on the results obtained, it was concluded that the &beta:-FeOOH nanorods proved to be suitable for the efficient removal of &beta:-estradiol from environmental matrices.