Synthesis of novel sepiolite–iron oxide–manganese dioxide nanocomposite and application for lead(II) removal from aqueous solutions

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Abstract
In this study, the sepiolite–iron oxide–manganese dioxide (Sep–Fe3O4–MnO2) nanocomposite was synthesized and applied as a magnetically separable adsorbent for removal of Pb(II) ions from water in a batch system. The effects of initial Pb(II) concentration, adsorbent dosage, contact time, pH value, and temperature were investigated to optimize the conditions for maximum adsorption. The equilibrium adsorption data were analyzed with the Langmuir, Freundlich, and Temkin models. The adsorption process closely agreed with the Langmuir adsorption isotherm, and the monolayer saturation adsorption value was achieved as 131.58 mg g−1. The adsorption kinetics follow the pseudo-second-order (PSO) model that illustrated the rate controlling step might be chemisorption. Thermodynamic investigations for the removal process were conducted by determining the values of ∆G°, ∆H°, and ∆S°. The adsorption behavior of Pb(II) on the Sep–Fe3O4–MnO2 was a spontaneous and endothermic process. Several consecutive adsorption–desorption cycles confirmed that the proposed Sep–Fe3O4–MnO2 nanocomposite could be reused after successive lead removal. Furthermore, the practical application of the adsorbent was successfully realized by the treatment of real Pb-contaminated water samples.

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